diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraEnumerator.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraEnumerator.java
index a693db63092..e6a4be488d0 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraEnumerator.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraEnumerator.java
@@ -61,7 +61,7 @@ class CassandraEnumerator implements Enumerator<Object> {
    *
    * @return A new row from the results
    */
-  public Object current() {
+  @Override public Object current() {
     if (fieldTypes.size() == 1) {
       // If we just have one field, produce it directly
       return currentRowField(0);
@@ -123,7 +123,7 @@ private Object convertToEnumeratorObject(Object obj) {
     return obj;
   }
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     if (iterator.hasNext()) {
       current = iterator.next();
       return true;
@@ -132,11 +132,11 @@ public boolean moveNext() {
     }
   }
 
-  public void reset() {
+  @Override public void reset() {
     throw new UnsupportedOperationException();
   }
 
-  public void close() {
+  @Override public void close() {
     // Nothing to do here
   }
 }
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraFilter.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraFilter.java
index 46e56756a71..c6781904237 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraFilter.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraFilter.java
@@ -90,13 +90,13 @@ public CassandraFilter(
     return super.computeSelfCost(planner, mq).multiplyBy(0.1);
   }
 
-  public CassandraFilter copy(RelTraitSet traitSet, RelNode input,
+  @Override public CassandraFilter copy(RelTraitSet traitSet, RelNode input,
       RexNode condition) {
     return new CassandraFilter(getCluster(), traitSet, input, condition,
         partitionKeys, clusteringKeys, implicitFieldCollations);
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
     implementor.add(null, Collections.singletonList(match));
   }
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraLimit.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraLimit.java
index 7627acb6ded..be6f42c30d0 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraLimit.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraLimit.java
@@ -54,7 +54,7 @@ public CassandraLimit(RelOptCluster cluster, RelTraitSet traitSet,
     return new CassandraLimit(getCluster(), traitSet, sole(newInputs), offset, fetch);
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
     if (offset != null) {
       implementor.offset = RexLiteral.intValue(offset);
@@ -64,7 +64,7 @@ public void implement(Implementor implementor) {
     }
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     super.explainTerms(pw);
     pw.itemIf("offset", offset, offset != null);
     pw.itemIf("fetch", fetch, fetch != null);
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraProject.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraProject.java
index ca2367fb8e8..5c2424ebc20 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraProject.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraProject.java
@@ -57,7 +57,7 @@ public CassandraProject(RelOptCluster cluster, RelTraitSet traitSet,
     return super.computeSelfCost(planner, mq).multiplyBy(0.1);
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
     final CassandraRules.RexToCassandraTranslator translator =
         new CassandraRules.RexToCassandraTranslator(
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSchemaFactory.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSchemaFactory.java
index db64ac286a0..bed42e09371 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSchemaFactory.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSchemaFactory.java
@@ -30,7 +30,7 @@ public class CassandraSchemaFactory implements SchemaFactory {
   public CassandraSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     Map map = (Map) operand;
     String host = (String) map.get("host");
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSort.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSort.java
index b8a70e0728b..384e066ffeb 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSort.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraSort.java
@@ -59,7 +59,7 @@ public CassandraSort(RelOptCluster cluster, RelTraitSet traitSet,
     return new CassandraSort(getCluster(), traitSet, input, collation);
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
 
     List<RelFieldCollation> sortCollations = collation.getFieldCollations();
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTable.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTable.java
index ed652847836..cf60fcbbeaf 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTable.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTable.java
@@ -70,11 +70,11 @@ public CassandraTable(CassandraSchema schema, String columnFamily) {
     this(schema, columnFamily, false);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "CassandraTable {" + columnFamily + "}";
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     if (protoRowType == null) {
       protoRowType = schema.getRelDataType(columnFamily, view);
     }
@@ -191,7 +191,7 @@ public Enumerable<Object> query(final Session session, List<Map.Entry<String, Cl
     final String query = queryBuilder.toString();
 
     return new AbstractEnumerable<Object>() {
-      public Enumerator<Object> enumerator() {
+      @Override public Enumerator<Object> enumerator() {
         final ResultSet results = session.execute(query);
         // Skip results until we get to the right offset
         int skip = 0;
@@ -204,12 +204,12 @@ public Enumerator<Object> enumerator() {
     };
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new CassandraQueryable<>(queryProvider, schema, this, tableName);
   }
 
-  public RelNode toRel(
+  @Override public RelNode toRel(
       RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     final RelOptCluster cluster = context.getCluster();
@@ -227,7 +227,7 @@ public CassandraQueryable(QueryProvider queryProvider, SchemaPlus schema,
       super(queryProvider, schema, table, tableName);
     }
 
-    public Enumerator<T> enumerator() {
+    @Override public Enumerator<T> enumerator() {
       //noinspection unchecked
       final Enumerable<T> enumerable =
           (Enumerable<T>) getTable().query(getSession());
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTableScan.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTableScan.java
index d9a7936e66a..a2520693437 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTableScan.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraTableScan.java
@@ -71,7 +71,7 @@ protected CassandraTableScan(RelOptCluster cluster, RelTraitSet traitSet,
     }
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.cassandraTable = cassandraTable;
     implementor.table = table;
   }
diff --git a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraToEnumerableConverter.java b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraToEnumerableConverter.java
index 111d48ece9f..c26bf81eeca 100644
--- a/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraToEnumerableConverter.java
+++ b/cassandra/src/main/java/org/apache/calcite/adapter/cassandra/CassandraToEnumerableConverter.java
@@ -68,7 +68,7 @@ protected CassandraToEnumerableConverter(
     return super.computeSelfCost(planner, mq).multiplyBy(.1);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     // Generates a call to "query" with the appropriate fields and predicates
     final BlockBuilder list = new BlockBuilder();
     final CassandraRel.Implementor cassandraImplementor = new CassandraRel.Implementor();
diff --git a/core/src/main/java/org/apache/calcite/adapter/clone/ArrayTable.java b/core/src/main/java/org/apache/calcite/adapter/clone/ArrayTable.java
index bc4560ed2b0..db045dbf632 100644
--- a/core/src/main/java/org/apache/calcite/adapter/clone/ArrayTable.java
+++ b/core/src/main/java/org/apache/calcite/adapter/clone/ArrayTable.java
@@ -67,11 +67,11 @@ class ArrayTable extends AbstractQueryableTable implements ScannableTable {
     this.supplier = supplier;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return protoRowType.apply(typeFactory);
   }
 
-  public Statistic getStatistic() {
+  @Override public Statistic getStatistic() {
     final List<ImmutableBitSet> keys = new ArrayList<>();
     final Content content = supplier.get();
     for (Ord<Column> ord : Ord.zip(content.columns)) {
@@ -82,21 +82,21 @@ public Statistic getStatistic() {
     return Statistics.of(content.size, keys, content.collations);
   }
 
-  public Enumerable<Object[]> scan(DataContext root) {
+  @Override public Enumerable<Object[]> scan(DataContext root) {
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         final Content content = supplier.get();
         return content.arrayEnumerator();
       }
     };
   }
 
-  public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new AbstractTableQueryable<T>(queryProvider, schema, this,
         tableName) {
       @SuppressWarnings("unchecked")
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         final Content content = supplier.get();
         return content.enumerator();
       }
@@ -225,11 +225,11 @@ public static List asList(final Representation representation,
       // Cache size. It might be expensive to compute.
       final int size = representation.size(dataSet);
       return new AbstractList() {
-        public Object get(int index) {
+        @Override public Object get(int index) {
           return representation.getObject(dataSet, index);
         }
 
-        public int size() {
+        @Override public int size() {
           return size;
         }
       };
@@ -269,21 +269,21 @@ public static class ObjectArray implements Representation {
       this.ordinal = ordinal;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "ObjectArray(ordinal=" + ordinal + ")";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.OBJECT_ARRAY;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       // We assume the values have been canonized.
       final List<Comparable> list = permuteList(valueSet.values, sources);
       return list.toArray(new Comparable[0]);
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       Comparable[] list = (Comparable[]) dataSet;
       final int size = list.length;
       final Comparable[] comparables = new Comparable[size];
@@ -293,19 +293,19 @@ public Object permute(Object dataSet, int[] sources) {
       return comparables;
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       return ((Comparable[]) dataSet)[ordinal];
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       return ((Number) getObject(dataSet, ordinal)).intValue();
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       return ((Comparable[]) dataSet).length;
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       return Arrays.toString((Comparable[]) dataSet);
     }
   }
@@ -323,40 +323,40 @@ public static class PrimitiveArray implements Representation {
       this.p = p;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "PrimitiveArray(ordinal=" + ordinal
           + ", primitive=" + primitive
           + ", p=" + p
           + ")";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.PRIMITIVE_ARRAY;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       //noinspection unchecked
       return primitive.toArray2(
           permuteList((List) valueSet.values, sources));
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       return primitive.permute(dataSet, sources);
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       return p.arrayItem(dataSet, ordinal);
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       return Array.getInt(dataSet, ordinal);
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       return Array.getLength(dataSet);
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       return p.arrayToString(dataSet);
     }
   }
@@ -367,35 +367,35 @@ public static class PrimitiveDictionary implements Representation {
     PrimitiveDictionary() {
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "PrimitiveDictionary()";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.PRIMITIVE_DICTIONARY;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       throw new UnsupportedOperationException(); // TODO:
     }
   }
@@ -413,17 +413,17 @@ public static class ObjectDictionary implements Representation {
       this.representation = representation;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "ObjectDictionary(ordinal=" + ordinal
           + ", representation=" + representation
           + ")";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.OBJECT_DICTIONARY;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       final int n = valueSet.map.keySet().size();
       int extra = valueSet.containsNull ? 1 : 0;
       Comparable[] codeValues =
@@ -446,29 +446,29 @@ public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       return Pair.of(codes, codeValues);
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       final Pair<Object, Comparable[]> pair = toPair(dataSet);
       Object codes = pair.left;
       Comparable[] codeValues = pair.right;
       return Pair.of(representation.permute(codes, sources), codeValues);
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       final Pair<Object, Comparable[]> pair = toPair(dataSet);
       int code = representation.getInt(pair.left, ordinal);
       return pair.right[code];
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       return ((Number) getObject(dataSet, ordinal)).intValue();
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       final Pair<Object, Comparable[]> pair = toPair(dataSet);
       return representation.size(pair.left);
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       return Column.asList(this, dataSet).toString();
     }
   }
@@ -482,31 +482,31 @@ public static class StringDictionary implements Representation {
       return "StringDictionary()";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.STRING_DICTIONARY;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       return Column.asList(this, dataSet).toString();
     }
   }
@@ -516,35 +516,35 @@ public static class ByteStringDictionary implements Representation {
     ByteStringDictionary() {
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "ByteStringDictionary()";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.BYTE_STRING_DICTIONARY;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       throw new UnsupportedOperationException(); // TODO:
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       return Column.asList(this, dataSet).toString();
     }
   }
@@ -557,39 +557,39 @@ public static class Constant implements Representation {
       this.ordinal = ordinal;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "Constant(ordinal=" + ordinal + ")";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.CONSTANT;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       final int size = valueSet.values.size();
       return Pair.of(size == 0 ? null : valueSet.values.get(0), size);
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       return dataSet;
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       Pair<Object, Integer> pair = toPair(dataSet);
       return pair.left;
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       Pair<Object, Integer> pair = toPair(dataSet);
       return ((Number) pair.left).intValue();
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       Pair<Object, Integer> pair = toPair(dataSet);
       return pair.right;
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       Pair<Object, Integer> pair = toPair(dataSet);
       return Collections.nCopies(pair.right, pair.left).toString();
     }
@@ -622,11 +622,11 @@ public static class BitSlicedPrimitiveArray implements Representation {
           + ", signed=" + signed + ")";
     }
 
-    public RepresentationType getType() {
+    @Override public RepresentationType getType() {
       return RepresentationType.BIT_SLICED_PRIMITIVE_ARRAY;
     }
 
-    public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
+    @Override public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       final int chunksPerWord = 64 / bitCount;
       final List<Comparable> valueList =
           permuteList(valueSet.values, sources);
@@ -677,7 +677,7 @@ public Object freeze(ColumnLoader.ValueSet valueSet, int[] sources) {
       return longs;
     }
 
-    public Object permute(Object dataSet, int[] sources) {
+    @Override public Object permute(Object dataSet, int[] sources) {
       final long[] longs0 = (long[]) dataSet;
       int n = sources.length;
       final long[] longs = new long[longs0.length];
@@ -689,7 +689,7 @@ public Object permute(Object dataSet, int[] sources) {
       return longs;
     }
 
-    public Object getObject(Object dataSet, int ordinal) {
+    @Override public Object getObject(Object dataSet, int ordinal) {
       final long[] longs = (long[]) dataSet;
       final int chunksPerWord = 64 / bitCount;
       final int word = ordinal / chunksPerWord;
@@ -721,7 +721,7 @@ public Object getObject(Object dataSet, int ordinal) {
       }
     }
 
-    public int getInt(Object dataSet, int ordinal) {
+    @Override public int getInt(Object dataSet, int ordinal) {
       final long[] longs = (long[]) dataSet;
       final int chunksPerWord = 64 / bitCount;
       final int word = ordinal / chunksPerWord;
@@ -771,13 +771,13 @@ public static void orLong(
       values[word] |= value << shift;
     }
 
-    public int size(Object dataSet) {
+    @Override public int size(Object dataSet) {
       final long[] longs = (long[]) dataSet;
       final int chunksPerWord = 64 / bitCount;
       return longs.length * chunksPerWord; // may be slightly too high
     }
 
-    public String toString(Object dataSet) {
+    @Override public String toString(Object dataSet) {
       return Column.asList(this, dataSet).toString();
     }
   }
@@ -788,11 +788,11 @@ private static <E> List<E> permuteList(
       return list;
     }
     return new AbstractList<E>() {
-      public E get(int index) {
+      @Override public E get(int index) {
         return list.get(sources[index]);
       }
 
-      public int size() {
+      @Override public int size() {
         return list.size();
       }
     };
@@ -846,19 +846,19 @@ private static class ObjectEnumerator implements Enumerator<Object> {
         this.representation = column.representation;
       }
 
-      public Object current() {
+      @Override public Object current() {
         return representation.getObject(dataSet, i);
       }
 
-      public boolean moveNext() {
+      @Override public boolean moveNext() {
         return ++i < rowCount;
       }
 
-      public void reset() {
+      @Override public void reset() {
         i = -1;
       }
 
-      public void close() {
+      @Override public void close() {
       }
     }
 
@@ -874,7 +874,7 @@ private static class ArrayEnumerator implements Enumerator<Object[]> {
         this.columns = columns;
       }
 
-      public Object[] current() {
+      @Override public Object[] current() {
         Object[] objects = new Object[columns.size()];
         for (int j = 0; j < objects.length; j++) {
           final Column pair = columns.get(j);
@@ -883,15 +883,15 @@ public Object[] current() {
         return objects;
       }
 
-      public boolean moveNext() {
+      @Override public boolean moveNext() {
         return ++i < rowCount;
       }
 
-      public void reset() {
+      @Override public void reset() {
         i = -1;
       }
 
-      public void close() {
+      @Override public void close() {
       }
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/adapter/clone/CloneSchema.java b/core/src/main/java/org/apache/calcite/adapter/clone/CloneSchema.java
index 3f1f7eedcd6..2b82d387b12 100644
--- a/core/src/main/java/org/apache/calcite/adapter/clone/CloneSchema.java
+++ b/core/src/main/java/org/apache/calcite/adapter/clone/CloneSchema.java
@@ -152,7 +152,7 @@ public static <T> Table createCloneTable(final JavaTypeFactory typeFactory,
    * }</pre></blockquote>
    */
   public static class Factory implements SchemaFactory {
-    public Schema create(
+    @Override public Schema create(
         SchemaPlus parentSchema,
         String name,
         Map<String, Object> operand) {
diff --git a/core/src/main/java/org/apache/calcite/adapter/clone/ColumnLoader.java b/core/src/main/java/org/apache/calcite/adapter/clone/ColumnLoader.java
index 3128b0d584c..1b89c46b398 100644
--- a/core/src/main/java/org/apache/calcite/adapter/clone/ColumnLoader.java
+++ b/core/src/main/java/org/apache/calcite/adapter/clone/ColumnLoader.java
@@ -151,12 +151,12 @@ private void load(final RelDataType elementType,
         new AbstractList<Type>() {
           final List<RelDataTypeField> fields =
               elementType.getFieldList();
-          public Type get(int index) {
+          @Override public Type get(int index) {
             return typeFactory.getJavaClass(
                 fields.get(index).getType());
           }
 
-          public int size() {
+          @Override public int size() {
             return fields.size();
           }
         };
@@ -169,11 +169,11 @@ public int size() {
               : new AbstractList<Object>() {
                 final int slice = pair.i;
 
-                public Object get(int index) {
+                @Override public Object get(int index) {
                   return ((Object[]) list.get(index))[slice];
                 }
 
-                public int size() {
+                @Override public int size() {
                   return list.size();
                 }
               };
@@ -444,7 +444,7 @@ private static class Kev implements Comparable<Kev> {
       this.key = key;
     }
 
-    public int compareTo(Kev o) {
+    @Override public int compareTo(Kev o) {
       //noinspection unchecked
       return key.compareTo(o.key);
     }
diff --git a/core/src/main/java/org/apache/calcite/adapter/clone/ListTable.java b/core/src/main/java/org/apache/calcite/adapter/clone/ListTable.java
index 8c6184636bc..b522df04998 100644
--- a/core/src/main/java/org/apache/calcite/adapter/clone/ListTable.java
+++ b/core/src/main/java/org/apache/calcite/adapter/clone/ListTable.java
@@ -58,35 +58,35 @@ class ListTable extends AbstractQueryableTable {
     this.list = list;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return protoRowType.apply(typeFactory);
   }
 
-  public Statistic getStatistic() {
+  @Override public Statistic getStatistic() {
     return Statistics.of(list.size(), ImmutableList.of());
   }
 
-  public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new AbstractQueryable<T>() {
-      public Type getElementType() {
+      @Override public Type getElementType() {
         return elementType;
       }
 
-      public Expression getExpression() {
+      @Override public Expression getExpression() {
         return expression;
       }
 
-      public QueryProvider getProvider() {
+      @Override public QueryProvider getProvider() {
         return queryProvider;
       }
 
-      public Iterator<T> iterator() {
+      @Override public Iterator<T> iterator() {
         //noinspection unchecked
         return list.iterator();
       }
 
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         //noinspection unchecked
         return Linq4j.enumerator(list);
       }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumUtils.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumUtils.java
index d5e9a411283..0537aa4f942 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumUtils.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumUtils.java
@@ -111,10 +111,10 @@ static List<Type> fieldTypes(
       final JavaTypeFactory typeFactory,
       final List<? extends RelDataType> inputTypes) {
     return new AbstractList<Type>() {
-      public Type get(int index) {
+      @Override public Type get(int index) {
         return EnumUtils.javaClass(typeFactory, inputTypes.get(index));
       }
-      public int size() {
+      @Override public int size() {
         return inputTypes.size();
       }
     };
@@ -126,13 +126,13 @@ static List<RelDataType> fieldRowTypes(
       final List<Integer> argList) {
     final List<RelDataTypeField> inputFields = inputRowType.getFieldList();
     return new AbstractList<RelDataType>() {
-      public RelDataType get(int index) {
+      @Override public RelDataType get(int index) {
         final int arg = argList.get(index);
         return arg < inputFields.size()
             ? inputFields.get(arg).getType()
             : extraInputs.get(arg - inputFields.size()).getType();
       }
-      public int size() {
+      @Override public int size() {
         return argList.size();
       }
     };
@@ -1020,7 +1020,7 @@ private static class HopEnumerator implements Enumerator<Object[]> {
       list = new ArrayDeque<>();
     }
 
-    public Object[] current() {
+    @Override public Object[] current() {
       if (list.size() > 0) {
         return takeOne();
       } else {
@@ -1038,16 +1038,16 @@ public Object[] current() {
       }
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       return list.size() > 0 || inputEnumerator.moveNext();
     }
 
-    public void reset() {
+    @Override public void reset() {
       inputEnumerator.reset();
       list.clear();
     }
 
-    public void close() {
+    @Override public void close() {
     }
 
     private Object[] takeOne() {
@@ -1080,19 +1080,19 @@ public static <TSource, TResult> Enumerable<TResult> tumbling(
         return new Enumerator<TResult>() {
           Enumerator<TSource> inputs = inputEnumerable.enumerator();
 
-          public TResult current() {
+          @Override public TResult current() {
             return outSelector.apply(inputs.current());
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             return inputs.moveNext();
           }
 
-          public void reset() {
+          @Override public void reset() {
             inputs.reset();
           }
 
-          public void close() {
+          @Override public void close() {
           }
         };
       }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregate.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregate.java
index 03f3192b3c3..8a4d4992106 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregate.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregate.java
@@ -90,7 +90,7 @@ public EnumerableAggregate(RelOptCluster cluster, RelTraitSet traitSet,
     }
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final JavaTypeFactory typeFactory = implementor.getTypeFactory();
     final BlockBuilder builder = new BlockBuilder();
     final EnumerableRel child = (EnumerableRel) getInput();
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregateBase.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregateBase.java
index ffb26d4b37a..da6741128ea 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregateBase.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableAggregateBase.java
@@ -188,43 +188,43 @@ protected class AggContextImpl implements AggContext {
       this.typeFactory = typeFactory;
     }
 
-    public SqlAggFunction aggregation() {
+    @Override public SqlAggFunction aggregation() {
       return agg.call.getAggregation();
     }
 
-    public RelDataType returnRelType() {
+    @Override public RelDataType returnRelType() {
       return agg.call.type;
     }
 
-    public Type returnType() {
+    @Override public Type returnType() {
       return EnumUtils.javaClass(typeFactory, returnRelType());
     }
 
-    public List<? extends RelDataType> parameterRelTypes() {
+    @Override public List<? extends RelDataType> parameterRelTypes() {
       return EnumUtils.fieldRowTypes(getInput().getRowType(), null,
           agg.call.getArgList());
     }
 
-    public List<? extends Type> parameterTypes() {
+    @Override public List<? extends Type> parameterTypes() {
       return EnumUtils.fieldTypes(
           typeFactory,
           parameterRelTypes());
     }
 
-    public List<ImmutableBitSet> groupSets() {
+    @Override public List<ImmutableBitSet> groupSets() {
       return groupSets;
     }
 
-    public List<Integer> keyOrdinals() {
+    @Override public List<Integer> keyOrdinals() {
       return groupSet.asList();
     }
 
-    public List<? extends RelDataType> keyRelTypes() {
+    @Override public List<? extends RelDataType> keyRelTypes() {
       return EnumUtils.fieldRowTypes(getInput().getRowType(), null,
           groupSet.asList());
     }
 
-    public List<? extends Type> keyTypes() {
+    @Override public List<? extends Type> keyTypes() {
       return EnumUtils.fieldTypes(typeFactory, keyRelTypes());
     }
   }
@@ -253,7 +253,7 @@ protected void createAccumulatorAdders(
 
       AggAddContext addContext =
           new AggAddContextImpl(builder2, accumulator) {
-            public List<RexNode> rexArguments() {
+            @Override public List<RexNode> rexArguments() {
               List<RelDataTypeField> inputTypes =
                   inputPhysType.getRowType().getFieldList();
               List<RexNode> args = new ArrayList<>();
@@ -263,14 +263,14 @@ public List<RexNode> rexArguments() {
               return args;
             }
 
-            public RexNode rexFilterArgument() {
+            @Override public RexNode rexFilterArgument() {
               return agg.call.filterArg < 0
                   ? null
                   : RexInputRef.of(agg.call.filterArg,
                       inputPhysType.getRowType());
             }
 
-            public RexToLixTranslator rowTranslator() {
+            @Override public RexToLixTranslator rowTranslator() {
               return RexToLixTranslator.forAggregation(typeFactory,
                   currentBlock(),
                   new RexToLixTranslator.InputGetterImpl(
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableBindable.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableBindable.java
index fc2223ff0ab..9ee7ec81aad 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableBindable.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableBindable.java
@@ -55,11 +55,11 @@ protected EnumerableBindable(RelOptCluster cluster, RelNode input) {
     return new EnumerableBindable(getCluster(), sole(inputs));
   }
 
-  public Class<Object[]> getElementType() {
+  @Override public Class<Object[]> getElementType() {
     return Object[].class;
   }
 
-  public Enumerable<Object[]> bind(DataContext dataContext) {
+  @Override public Enumerable<Object[]> bind(DataContext dataContext) {
     final ImmutableMap<String, Object> map = ImmutableMap.of();
     final Bindable bindable = EnumerableInterpretable.toBindable(map, null,
         (EnumerableRel) getInput(), EnumerableRel.Prefer.ARRAY);
@@ -67,7 +67,7 @@ public Enumerable<Object[]> bind(DataContext dataContext) {
     return arrayBindable.bind(dataContext);
   }
 
-  public Node implement(final InterpreterImplementor implementor) {
+  @Override public Node implement(final InterpreterImplementor implementor) {
     return () -> {
       final Sink sink =
           implementor.relSinks.get(EnumerableBindable.this).get(0);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCalc.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCalc.java
index a09d9fa3e90..fbf0b0a054b 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCalc.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCalc.java
@@ -108,7 +108,7 @@ public static EnumerableCalc create(final RelNode input,
     return new EnumerableCalc(getCluster(), traitSet, child, program);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final JavaTypeFactory typeFactory = implementor.getTypeFactory();
     final BlockBuilder builder = new BlockBuilder();
     final EnumerableRel child = (EnumerableRel) getInput();
@@ -284,7 +284,7 @@ public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
         input.getRowType(), input.getCluster().getTypeFactory(), traitSet);
   }
 
-  public RexProgram getProgram() {
+  @Override public RexProgram getProgram() {
     return program;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCollect.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCollect.java
index 625748dd4cf..ff7bf0539fa 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCollect.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCollect.java
@@ -40,7 +40,7 @@ public EnumerableCollect(RelOptCluster cluster, RelTraitSet traitSet,
     return new EnumerableCollect(getCluster(), traitSet, newInput, fieldName);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final EnumerableRel child = (EnumerableRel) getInput();
     // REVIEW zabetak January 7, 2019: Even if we ask the implementor to provide a result
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableConvention.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableConvention.java
index 6acc25da01f..3cbffaf0c1e 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableConvention.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableConvention.java
@@ -43,11 +43,11 @@ public enum EnumerableConvention implements Convention {
     return getName();
   }
 
-  public Class getInterface() {
+  @Override public Class getInterface() {
     return EnumerableRel.class;
   }
 
-  public String getName() {
+  @Override public String getName() {
     return "ENUMERABLE";
   }
 
@@ -67,26 +67,26 @@ public String getName() {
     return rel;
   }
 
-  public RelTraitDef getTraitDef() {
+  @Override public RelTraitDef getTraitDef() {
     return ConventionTraitDef.INSTANCE;
   }
 
-  public boolean satisfies(RelTrait trait) {
+  @Override public boolean satisfies(RelTrait trait) {
     return this == trait;
   }
 
-  public void register(RelOptPlanner planner) {}
+  @Override public void register(RelOptPlanner planner) {}
 
-  public boolean canConvertConvention(Convention toConvention) {
+  @Override public boolean canConvertConvention(Convention toConvention) {
     return false;
   }
 
-  public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
+  @Override public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
       RelTraitSet toTraits) {
     return true;
   }
 
-  public RelFactories.Struct getRelFactories() {
+  @Override public RelFactories.Struct getRelFactories() {
     return RelFactories.Struct.fromContext(
             Contexts.of(
                 EnumerableRelFactories.ENUMERABLE_TABLE_SCAN_FACTORY,
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCorrelate.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCorrelate.java
index 86bc0420733..666d84417b0 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCorrelate.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCorrelate.java
@@ -104,7 +104,7 @@ public static EnumerableCorrelate create(
     return DeriveMode.LEFT_FIRST;
   }
 
-  public Result implement(EnumerableRelImplementor implementor,
+  @Override public Result implement(EnumerableRelImplementor implementor,
       Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final Result leftResult =
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableFilter.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableFilter.java
index 5af195c826f..4a2075ca81c 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableFilter.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableFilter.java
@@ -66,12 +66,12 @@ public static EnumerableFilter create(final RelNode input,
     return new EnumerableFilter(cluster, traitSet, input, condition);
   }
 
-  public EnumerableFilter copy(RelTraitSet traitSet, RelNode input,
+  @Override public EnumerableFilter copy(RelTraitSet traitSet, RelNode input,
       RexNode condition) {
     return new EnumerableFilter(getCluster(), traitSet, input, condition);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     // EnumerableCalc is always better
     throw new UnsupportedOperationException();
   }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpretable.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpretable.java
index ee74a5302f0..44c992e5720 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpretable.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpretable.java
@@ -79,7 +79,7 @@ protected EnumerableInterpretable(RelOptCluster cluster, RelNode input) {
     return new EnumerableInterpretable(getCluster(), sole(inputs));
   }
 
-  public Node implement(final InterpreterImplementor implementor) {
+  @Override public Node implement(final InterpreterImplementor implementor) {
     final Bindable bindable = toBindable(implementor.internalParameters,
             implementor.spark, (EnumerableRel) getInput(),
         EnumerableRel.Prefer.ARRAY);
@@ -181,29 +181,29 @@ static ArrayBindable box(final Bindable bindable) {
       return (ArrayBindable) bindable;
     }
     return new ArrayBindable() {
-      public Class<Object[]> getElementType() {
+      @Override public Class<Object[]> getElementType() {
         return Object[].class;
       }
 
-      public Enumerable<Object[]> bind(DataContext dataContext) {
+      @Override public Enumerable<Object[]> bind(DataContext dataContext) {
         final Enumerable<?> enumerable = bindable.bind(dataContext);
         return new AbstractEnumerable<Object[]>() {
-          public Enumerator<Object[]> enumerator() {
+          @Override public Enumerator<Object[]> enumerator() {
             final Enumerator<?> enumerator = enumerable.enumerator();
             return new Enumerator<Object[]>() {
-              public Object[] current() {
+              @Override public Object[] current() {
                 return new Object[] {enumerator.current()};
               }
 
-              public boolean moveNext() {
+              @Override public boolean moveNext() {
                 return enumerator.moveNext();
               }
 
-              public void reset() {
+              @Override public void reset() {
                 enumerator.reset();
               }
 
-              public void close() {
+              @Override public void close() {
                 enumerator.close();
               }
             };
@@ -226,7 +226,7 @@ private static class EnumerableNode implements Node {
       this.sink = compiler.sink(rel);
     }
 
-    public void run() throws InterruptedException {
+    @Override public void run() throws InterruptedException {
       final Enumerator<Object[]> enumerator = enumerable.enumerator();
       while (enumerator.moveNext()) {
         Object[] values = enumerator.current();
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpreter.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpreter.java
index 4e8f63336d3..7ad2465b453 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpreter.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableInterpreter.java
@@ -83,7 +83,7 @@ public static EnumerableInterpreter create(RelNode input, double factor) {
         factor);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final JavaTypeFactory typeFactory = implementor.getTypeFactory();
     final BlockBuilder builder = new BlockBuilder();
     final PhysType physType =
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableIntersect.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableIntersect.java
index a18c5c4a1a8..ab95359709e 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableIntersect.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableIntersect.java
@@ -36,12 +36,12 @@ public EnumerableIntersect(RelOptCluster cluster, RelTraitSet traitSet,
     super(cluster, traitSet, inputs, all);
   }
 
-  public EnumerableIntersect copy(RelTraitSet traitSet, List<RelNode> inputs,
+  @Override public EnumerableIntersect copy(RelTraitSet traitSet, List<RelNode> inputs,
       boolean all) {
     return new EnumerableIntersect(getCluster(), traitSet, inputs, all);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     Expression intersectExp = null;
     for (Ord<RelNode> ord : Ord.zip(inputs)) {
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableLimit.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableLimit.java
index b7eae2023a8..fb0836eb237 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableLimit.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableLimit.java
@@ -90,7 +90,7 @@ public static EnumerableLimit create(final RelNode input, RexNode offset,
         .itemIf("fetch", fetch, fetch != null);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final EnumerableRel child = (EnumerableRel) getInput();
     final Result result = implementor.visitChild(this, 0, child, pref);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMatch.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMatch.java
index 85bfaedbfe3..bb0d09539ea 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMatch.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMatch.java
@@ -102,7 +102,7 @@ public static EnumerableMatch create(RelNode input, RelDataType rowType,
         subsets, allRows, partitionKeys, orderKeys, interval);
   }
 
-  public EnumerableRel.Result implement(EnumerableRelImplementor implementor,
+  @Override public EnumerableRel.Result implement(EnumerableRelImplementor implementor,
       EnumerableRel.Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final EnumerableRel input = (EnumerableRel) getInput();
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMergeJoin.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMergeJoin.java
index 8a16be08019..10c253b1a38 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMergeJoin.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMergeJoin.java
@@ -393,7 +393,7 @@ public static EnumerableMergeJoin create(RelNode left, RelNode right,
     return planner.getCostFactory().makeCost(d, 0, 0);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     BlockBuilder builder = new BlockBuilder();
     final Result leftResult =
         implementor.visitChild(this, 0, (EnumerableRel) left, pref);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMinus.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMinus.java
index 1bbda3f66e9..656c9a43715 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMinus.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMinus.java
@@ -36,12 +36,12 @@ public EnumerableMinus(RelOptCluster cluster, RelTraitSet traitSet,
     super(cluster, traitSet, inputs, all);
   }
 
-  public EnumerableMinus copy(RelTraitSet traitSet, List<RelNode> inputs,
+  @Override public EnumerableMinus copy(RelTraitSet traitSet, List<RelNode> inputs,
       boolean all) {
     return new EnumerableMinus(getCluster(), traitSet, inputs, all);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     Expression minusExp = null;
     for (Ord<RelNode> ord : Ord.zip(inputs)) {
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableNestedLoopJoin.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableNestedLoopJoin.java
index 1561d8fb2f4..fce87e51e0e 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableNestedLoopJoin.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableNestedLoopJoin.java
@@ -148,7 +148,7 @@ public static EnumerableNestedLoopJoin create(
     return DeriveMode.LEFT_FIRST;
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final Result leftResult =
         implementor.visitChild(this, 0, (EnumerableRel) left, pref);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableProject.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableProject.java
index 7c62e2f3a88..4c718833dd3 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableProject.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableProject.java
@@ -78,13 +78,13 @@ public static EnumerableProject create(final RelNode input,
     return new EnumerableProject(cluster, traitSet, input, projects, rowType);
   }
 
-  public EnumerableProject copy(RelTraitSet traitSet, RelNode input,
+  @Override public EnumerableProject copy(RelTraitSet traitSet, RelNode input,
       List<RexNode> projects, RelDataType rowType) {
     return new EnumerableProject(getCluster(), traitSet, input,
         projects, rowType);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     // EnumerableCalcRel is always better
     throw new UnsupportedOperationException();
   }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelFactories.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelFactories.java
index ab9cdd08c84..8dcff99be32 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelFactories.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelFactories.java
@@ -53,7 +53,7 @@ public class EnumerableRelFactories {
    */
   private static class TableScanFactoryImpl
       implements org.apache.calcite.rel.core.RelFactories.TableScanFactory {
-    public RelNode createScan(RelOptTable.ToRelContext toRelContext, RelOptTable table) {
+    @Override public RelNode createScan(RelOptTable.ToRelContext toRelContext, RelOptTable table) {
       return EnumerableTableScan.create(toRelContext.getCluster(), table);
     }
   }
@@ -64,7 +64,7 @@ public RelNode createScan(RelOptTable.ToRelContext toRelContext, RelOptTable tab
    */
   private static class ProjectFactoryImpl
       implements org.apache.calcite.rel.core.RelFactories.ProjectFactory {
-    public RelNode createProject(RelNode input, List<RelHint> hints,
+    @Override public RelNode createProject(RelNode input, List<RelHint> hints,
                           List<? extends RexNode> childExprs, List<String> fieldNames) {
       final RelDataType rowType =
           RexUtil.createStructType(input.getCluster().getTypeFactory(), childExprs,
@@ -79,7 +79,7 @@ public RelNode createProject(RelNode input, List<RelHint> hints,
    */
   private static class FilterFactoryImpl
       implements org.apache.calcite.rel.core.RelFactories.FilterFactory {
-    public RelNode createFilter(RelNode input, RexNode condition,
+    @Override public RelNode createFilter(RelNode input, RexNode condition,
                          Set<CorrelationId> variablesSet) {
       return EnumerableFilter.create(input, condition);
     }
@@ -91,7 +91,7 @@ public RelNode createFilter(RelNode input, RexNode condition,
    */
   private static class SortFactoryImpl
       implements org.apache.calcite.rel.core.RelFactories.SortFactory {
-    public RelNode createSort(RelNode input, RelCollation collation,
+    @Override public RelNode createSort(RelNode input, RelCollation collation,
                               RexNode offset, RexNode fetch) {
       return EnumerableSort.create(input, collation, offset, fetch);
     }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelImplementor.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelImplementor.java
index eafd642a216..0a6a02c4145 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelImplementor.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRelImplementor.java
@@ -472,7 +472,7 @@ public EnumerableRel.Result result(PhysType physType, BlockStatement block) {
         block, physType, ((PhysTypeImpl) physType).format);
   }
 
-  public SqlConformance getConformance() {
+  @Override public SqlConformance getConformance() {
     return (SqlConformance) map.getOrDefault("_conformance",
         SqlConformanceEnum.DEFAULT);
   }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSort.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSort.java
index 568a4ee6f28..559e1c89a25 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSort.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSort.java
@@ -68,7 +68,7 @@ public static EnumerableSort create(RelNode child, RelCollation collation,
         offset, fetch);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final EnumerableRel child = (EnumerableRel) getInput();
     final Result result = implementor.visitChild(this, 0, child, pref);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortRule.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortRule.java
index 84ef93c8eec..a449c8bec7a 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortRule.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortRule.java
@@ -39,7 +39,7 @@ protected EnumerableSortRule(Config config) {
     super(config);
   }
 
-  public RelNode convert(RelNode rel) {
+  @Override public RelNode convert(RelNode rel) {
     final Sort sort = (Sort) rel;
     if (sort.offset != null || sort.fetch != null) {
       return null;
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregate.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregate.java
index 1bb5fd31a28..77041dfccbe 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregate.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregate.java
@@ -100,7 +100,7 @@ public EnumerableSortedAggregate(
     return null;
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     if (!Aggregate.isSimple(this)) {
       throw Util.needToImplement("EnumerableSortedAggregate");
     }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregateRule.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregateRule.java
index 06577c2a18a..cfc3660af43 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregateRule.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregateRule.java
@@ -44,7 +44,7 @@ protected EnumerableSortedAggregateRule(Config config) {
     super(config);
   }
 
-  public RelNode convert(RelNode rel) {
+  @Override public RelNode convert(RelNode rel) {
     final LogicalAggregate agg = (LogicalAggregate) rel;
     if (!Aggregate.isSimple(agg)) {
       return null;
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableFunctionScan.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableFunctionScan.java
index bd3c7ff5d4c..7e2b507a328 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableFunctionScan.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableFunctionScan.java
@@ -65,7 +65,7 @@ public EnumerableTableFunctionScan(RelOptCluster cluster,
         elementType, rowType, rexCall, columnMappings);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     if (isImplementorDefined((RexCall) getCall())) {
       return tvfImplementorBasedImplement(implementor, pref);
     } else {
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableModify.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableModify.java
index f49ba7cc1b0..b40c809f679 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableModify.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableModify.java
@@ -70,7 +70,7 @@ public EnumerableTableModify(RelOptCluster cluster, RelTraitSet traits,
         isFlattened());
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final Result result = implementor.visitChild(
         this, 0, (EnumerableRel) getInput(), pref);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableScan.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableScan.java
index 13814639e89..1fbee99d429 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableScan.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableTableScan.java
@@ -317,7 +317,7 @@ private boolean hasCollectionField(RelDataType rowType) {
     return new EnumerableTableScan(getCluster(), traitSet, table, elementType);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     // Note that representation is ARRAY. This assumes that the table
     // returns a Object[] for each record. Actually a Table<T> can
     // return any type T. And, if it is a JdbcTable, we'd like to be
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUncollect.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUncollect.java
index 0f7d709c507..18add9cc4eb 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUncollect.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUncollect.java
@@ -76,7 +76,7 @@ public static EnumerableUncollect create(RelTraitSet traitSet, RelNode input,
         withOrdinality);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     final EnumerableRel child = (EnumerableRel) getInput();
     final Result result = implementor.visitChild(this, 0, child, pref);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUnion.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUnion.java
index be1f4d3d21d..701cbd2a051 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUnion.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableUnion.java
@@ -36,12 +36,12 @@ public EnumerableUnion(RelOptCluster cluster, RelTraitSet traitSet,
     super(cluster, traitSet, inputs, all);
   }
 
-  public EnumerableUnion copy(RelTraitSet traitSet, List<RelNode> inputs,
+  @Override public EnumerableUnion copy(RelTraitSet traitSet, List<RelNode> inputs,
       boolean all) {
     return new EnumerableUnion(getCluster(), traitSet, inputs, all);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder builder = new BlockBuilder();
     Expression unionExp = null;
     for (Ord<RelNode> ord : Ord.zip(inputs)) {
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableValues.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableValues.java
index 8c6fa5cae51..4a624a8a4da 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableValues.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableValues.java
@@ -107,7 +107,7 @@ public static EnumerableValues create(RelOptCluster cluster,
     return DeriveMode.PROHIBITED;
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
 /*
           return Linq4j.asEnumerable(
               new Object[][] {
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableWindow.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableWindow.java
index 0e8cc219aac..900349ff30a 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableWindow.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableWindow.java
@@ -78,7 +78,7 @@ public class EnumerableWindow extends Window implements EnumerableRel {
         constants, rowType, groups);
   }
 
-  public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
+  @Override public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
     return super.computeSelfCost(planner, mq)
         .multiplyBy(EnumerableConvention.COST_MULTIPLIER);
   }
@@ -102,7 +102,7 @@ private WindowRelInputGetter(Expression row,
       this.constants = constants;
     }
 
-    public Expression field(BlockBuilder list, int index, Type storageType) {
+    @Override public Expression field(BlockBuilder list, int index, Type storageType) {
       if (index < actualInputFieldCount) {
         Expression current = list.append("current", row);
         return rowPhysType.fieldReference(current, index, storageType);
@@ -159,7 +159,7 @@ private void sampleOfTheGeneratedWindowedAggregate() {
     // source = Linq4j.asEnumerable(list);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final JavaTypeFactory typeFactory = implementor.getTypeFactory();
     final EnumerableRel child = (EnumerableRel) getInput();
     final BlockBuilder builder = new BlockBuilder();
@@ -533,7 +533,7 @@ public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
       final DeclarationStatement jDecl,
       final PhysType inputPhysType) {
     return block -> new WinAggFrameResultContext() {
-      public RexToLixTranslator rowTranslator(Expression rowIndex) {
+      @Override public RexToLixTranslator rowTranslator(Expression rowIndex) {
         Expression row =
             getRow(rowIndex);
         final RexToLixTranslator.InputGetter inputGetter =
@@ -545,7 +545,7 @@ public RexToLixTranslator rowTranslator(Expression rowIndex) {
             block, inputGetter, conformance);
       }
 
-      public Expression computeIndex(Expression offset,
+      @Override public Expression computeIndex(Expression offset,
           WinAggImplementor.SeekType seekType) {
         Expression index;
         if (seekType == WinAggImplementor.SeekType.AGG_INDEX) {
@@ -583,15 +583,15 @@ private Expression checkBounds(Expression rowIndex,
         return res;
       }
 
-      public Expression rowInFrame(Expression rowIndex) {
+      @Override public Expression rowInFrame(Expression rowIndex) {
         return checkBounds(rowIndex, startX, endX);
       }
 
-      public Expression rowInPartition(Expression rowIndex) {
+      @Override public Expression rowInPartition(Expression rowIndex) {
         return checkBounds(rowIndex, minX, maxX);
       }
 
-      public Expression compareRows(Expression a, Expression b) {
+      @Override public Expression compareRows(Expression a, Expression b) {
         return Expressions.call(comparator_,
             BuiltInMethod.COMPARATOR_COMPARE.method,
             getRow(a), getRow(b));
@@ -605,27 +605,27 @@ public Expression getRow(Expression rowIndex) {
                 inputPhysType.getJavaRowType()));
       }
 
-      public Expression index() {
+      @Override public Expression index() {
         return i_;
       }
 
-      public Expression startIndex() {
+      @Override public Expression startIndex() {
         return startX;
       }
 
-      public Expression endIndex() {
+      @Override public Expression endIndex() {
         return endX;
       }
 
-      public Expression hasRows() {
+      @Override public Expression hasRows() {
         return hasRows;
       }
 
-      public Expression getFrameRowCount() {
+      @Override public Expression getFrameRowCount() {
         return frameRowCount;
       }
 
-      public Expression getPartitionRowCount() {
+      @Override public Expression getPartitionRowCount() {
         return partitionRowCount;
       }
     };
@@ -762,41 +762,41 @@ private void declareAndResetState(final JavaTypeFactory typeFactory,
     for (final AggImpState agg : aggs) {
       agg.context =
           new WinAggContext() {
-            public SqlAggFunction aggregation() {
+            @Override public SqlAggFunction aggregation() {
               return agg.call.getAggregation();
             }
 
-            public RelDataType returnRelType() {
+            @Override public RelDataType returnRelType() {
               return agg.call.type;
             }
 
-            public Type returnType() {
+            @Override public Type returnType() {
               return EnumUtils.javaClass(typeFactory, returnRelType());
             }
 
-            public List<? extends Type> parameterTypes() {
+            @Override public List<? extends Type> parameterTypes() {
               return EnumUtils.fieldTypes(typeFactory,
                   parameterRelTypes());
             }
 
-            public List<? extends RelDataType> parameterRelTypes() {
+            @Override public List<? extends RelDataType> parameterRelTypes() {
               return EnumUtils.fieldRowTypes(result.physType.getRowType(),
                   constants, agg.call.getArgList());
             }
 
-            public List<ImmutableBitSet> groupSets() {
+            @Override public List<ImmutableBitSet> groupSets() {
               throw new UnsupportedOperationException();
             }
 
-            public List<Integer> keyOrdinals() {
+            @Override public List<Integer> keyOrdinals() {
               throw new UnsupportedOperationException();
             }
 
-            public List<? extends RelDataType> keyRelTypes() {
+            @Override public List<? extends RelDataType> keyRelTypes() {
               throw new UnsupportedOperationException();
             }
 
-            public List<? extends Type> keyTypes() {
+            @Override public List<? extends Type> keyTypes() {
               throw new UnsupportedOperationException();
             }
           };
@@ -849,15 +849,15 @@ private void implementAdd(List<AggImpState> aggs,
     for (final AggImpState agg : aggs) {
       final WinAggAddContext addContext =
           new WinAggAddContextImpl(builder7, agg.state, frame) {
-            public Expression currentPosition() {
+            @Override public Expression currentPosition() {
               return jDecl.parameter;
             }
 
-            public List<RexNode> rexArguments() {
+            @Override public List<RexNode> rexArguments() {
               return rexArguments.apply(agg);
             }
 
-            public RexNode rexFilterArgument() {
+            @Override public RexNode rexFilterArgument() {
               return null; // REVIEW
             }
           };
@@ -885,7 +885,7 @@ private boolean implementResult(List<AggImpState> aggs,
       nonEmpty = true;
       Expression res = agg.implementor.implementResult(agg.context,
           new WinAggResultContextImpl(builder, agg.state, frame) {
-            public List<RexNode> rexArguments() {
+            @Override public List<RexNode> rexArguments() {
               return rexArguments.apply(agg);
             }
           });
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/JavaRowFormat.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/JavaRowFormat.java
index eb3192340c1..cebe0a6228e 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/JavaRowFormat.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/JavaRowFormat.java
@@ -37,7 +37,7 @@
  */
 public enum JavaRowFormat {
   CUSTOM {
-    Type javaRowClass(
+    @Override Type javaRowClass(
         JavaTypeFactory typeFactory,
         RelDataType type) {
       assert type.getFieldCount() > 1;
@@ -49,7 +49,7 @@ Type javaRowClass(
       return typeFactory.getJavaClass(type.getFieldList().get(index).getType());
     }
 
-    public Expression record(
+    @Override public Expression record(
         Type javaRowClass, List<Expression> expressions) {
       switch (expressions.size()) {
       case 0:
@@ -60,7 +60,7 @@ public Expression record(
       }
     }
 
-    public MemberExpression field(Expression expression, int field,
+    @Override public MemberExpression field(Expression expression, int field,
         Type fromType, Type fieldType) {
       final Type type = expression.getType();
       if (type instanceof Types.RecordType) {
@@ -76,7 +76,7 @@ public MemberExpression field(Expression expression, int field,
   },
 
   SCALAR {
-    Type javaRowClass(
+    @Override Type javaRowClass(
         JavaTypeFactory typeFactory,
         RelDataType type) {
       assert type.getFieldCount() == 1;
@@ -89,12 +89,12 @@ Type javaRowClass(
       return javaRowClass(typeFactory, type);
     }
 
-    public Expression record(Type javaRowClass, List<Expression> expressions) {
+    @Override public Expression record(Type javaRowClass, List<Expression> expressions) {
       assert expressions.size() == 1;
       return expressions.get(0);
     }
 
-    public Expression field(Expression expression, int field, Type fromType,
+    @Override public Expression field(Expression expression, int field, Type fromType,
         Type fieldType) {
       assert field == 0;
       return expression;
@@ -105,7 +105,7 @@ public Expression field(Expression expression, int field, Type fromType,
    * (empty list is a good singleton) but sometimes also for records with 2 or
    * more fields that you need to be comparable, say as a key in a lookup. */
   LIST {
-    Type javaRowClass(
+    @Override Type javaRowClass(
         JavaTypeFactory typeFactory,
         RelDataType type) {
       return FlatLists.ComparableList.class;
@@ -116,7 +116,7 @@ Type javaRowClass(
       return Object.class;
     }
 
-    public Expression record(
+    @Override public Expression record(
         Type javaRowClass, List<Expression> expressions) {
       switch (expressions.size()) {
       case 0:
@@ -177,7 +177,7 @@ public Expression record(
       }
     }
 
-    public Expression field(Expression expression, int field, Type fromType,
+    @Override public Expression field(Expression expression, int field, Type fromType,
         Type fieldType) {
       final MethodCallExpression e = Expressions.call(expression,
           BuiltInMethod.LIST_GET.method, Expressions.constant(field));
@@ -206,7 +206,7 @@ public Expression field(Expression expression, int field, Type fromType,
       return Expressions.call(BuiltInMethod.ROW_AS_COPY.method, expressions);
     }
 
-    public Expression field(Expression expression, int field, Type fromType,
+    @Override public Expression field(Expression expression, int field, Type fromType,
         Type fieldType) {
       final Expression e = Expressions.call(expression,
           BuiltInMethod.ROW_VALUE.method, Expressions.constant(field));
@@ -218,7 +218,7 @@ public Expression field(Expression expression, int field, Type fromType,
   },
 
   ARRAY {
-    Type javaRowClass(
+    @Override Type javaRowClass(
         JavaTypeFactory typeFactory,
         RelDataType type) {
       return Object[].class;
@@ -229,7 +229,7 @@ Type javaRowClass(
       return Object.class;
     }
 
-    public Expression record(Type javaRowClass, List<Expression> expressions) {
+    @Override public Expression record(Type javaRowClass, List<Expression> expressions) {
       return Expressions.newArrayInit(Object.class, expressions);
     }
 
@@ -237,7 +237,7 @@ public Expression record(Type javaRowClass, List<Expression> expressions) {
       return Expressions.call(BuiltInMethod.ARRAY_COMPARER.method);
     }
 
-    public Expression field(Expression expression, int field, Type fromType,
+    @Override public Expression field(Expression expression, int field, Type fromType,
         Type fieldType) {
       final IndexExpression e = Expressions.arrayIndex(expression,
           Expressions.constant(field));
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/LazyAggregateLambdaFactory.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/LazyAggregateLambdaFactory.java
index b83423bd6ae..7ecc880cee7 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/LazyAggregateLambdaFactory.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/LazyAggregateLambdaFactory.java
@@ -48,11 +48,11 @@ public LazyAggregateLambdaFactory(
     this.accumulators = accumulators;
   }
 
-  public Function0<LazySource<TSource>> accumulatorInitializer() {
+  @Override public Function0<LazySource<TSource>> accumulatorInitializer() {
     return LazySource::new;
   }
 
-  public Function2<LazySource<TSource>,
+  @Override public Function2<LazySource<TSource>,
       TSource, LazySource<TSource>> accumulatorAdder() {
     return (lazySource, source) -> {
       lazySource.add(source);
@@ -60,7 +60,7 @@ TSource, LazySource<TSource>> accumulatorAdder() {
     };
   }
 
-  public Function1<LazySource<TSource>, TResult> singleGroupResultSelector(
+  @Override public Function1<LazySource<TSource>, TResult> singleGroupResultSelector(
       Function1<TOrigAccumulate, TResult> resultSelector) {
     return lazySource -> {
       final TOrigAccumulate accumulator = accumulatorInitializer.apply();
@@ -71,7 +71,7 @@ public Function1<LazySource<TSource>, TResult> singleGroupResultSelector(
     };
   }
 
-  public Function2<TKey, LazySource<TSource>, TResult> resultSelector(
+  @Override public Function2<TKey, LazySource<TSource>, TResult> resultSelector(
       Function2<TKey, TOrigAccumulate, TResult> resultSelector) {
     return (groupByKey, lazySource) -> {
       final TOrigAccumulate accumulator = accumulatorInitializer.apply();
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/NestedBlockBuilderImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/NestedBlockBuilderImpl.java
index abc186ea265..036943c5f81 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/NestedBlockBuilderImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/NestedBlockBuilderImpl.java
@@ -43,7 +43,7 @@ public NestedBlockBuilderImpl(BlockBuilder block) {
    * @return new code block that can optimize expressions and reuse already
    * calculated values from the parent blocks.
    */
-  public final BlockBuilder nestBlock() {
+  @Override public final BlockBuilder nestBlock() {
     BlockBuilder block = new BlockBuilder(true, currentBlock());
     nestBlock(block);
     return block;
@@ -55,14 +55,14 @@ public final BlockBuilder nestBlock() {
    * @param block new code block
    * @see #exitBlock()
    */
-  public final void nestBlock(BlockBuilder block) {
+  @Override public final void nestBlock(BlockBuilder block) {
     blocks.add(block);
   }
 
   /**
    * Returns the current code block.
    */
-  public final BlockBuilder currentBlock() {
+  @Override public final BlockBuilder currentBlock() {
     return blocks.get(blocks.size() - 1);
   }
 
@@ -70,7 +70,7 @@ public final BlockBuilder currentBlock() {
    * Leaves the current code block.
    * @see #nestBlock()
    */
-  public final void exitBlock() {
+  @Override public final void exitBlock() {
     blocks.remove(blocks.size() - 1);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/PhysTypeImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/PhysTypeImpl.java
index d6f23b3562f..47f6c4649b3 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/PhysTypeImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/PhysTypeImpl.java
@@ -109,15 +109,15 @@ static PhysType of(
         JavaRowFormat.CUSTOM);
   }
 
-  public JavaRowFormat getFormat() {
+  @Override public JavaRowFormat getFormat() {
     return format;
   }
 
-  public PhysType project(List<Integer> integers, JavaRowFormat format) {
+  @Override public PhysType project(List<Integer> integers, JavaRowFormat format) {
     return project(integers, false, format);
   }
 
-  public PhysType project(List<Integer> integers, boolean indicator,
+  @Override public PhysType project(List<Integer> integers, boolean indicator,
       JavaRowFormat format) {
     final RelDataTypeFactory.Builder builder = typeFactory.builder();
     for (int index : integers) {
@@ -136,13 +136,13 @@ public PhysType project(List<Integer> integers, boolean indicator,
     return of(typeFactory, projectedRowType, format.optimize(projectedRowType));
   }
 
-  public Expression generateSelector(
+  @Override public Expression generateSelector(
       ParameterExpression parameter,
       List<Integer> fields) {
     return generateSelector(parameter, fields, format);
   }
 
-  public Expression generateSelector(
+  @Override public Expression generateSelector(
       ParameterExpression parameter,
       List<Integer> fields,
       JavaRowFormat targetFormat) {
@@ -166,7 +166,7 @@ public Expression generateSelector(
     }
   }
 
-  public Expression generateSelector(final ParameterExpression parameter,
+  @Override public Expression generateSelector(final ParameterExpression parameter,
       final List<Integer> fields, List<Integer> usedFields,
       JavaRowFormat targetFormat) {
     final PhysType targetPhysType =
@@ -191,7 +191,7 @@ public Expression generateSelector(final ParameterExpression parameter,
         targetPhysType.record(expressions), parameter);
   }
 
-  public Pair<Type, List<Expression>> selector(
+  @Override public Pair<Type, List<Expression>> selector(
       ParameterExpression parameter,
       List<Integer> fields,
       JavaRowFormat targetFormat) {
@@ -215,7 +215,7 @@ public Pair<Type, List<Expression>> selector(
     }
   }
 
-  public List<Expression> accessors(Expression v1, List<Integer> argList) {
+  @Override public List<Expression> accessors(Expression v1, List<Integer> argList) {
     final List<Expression> expressions = new ArrayList<>();
     for (int field : argList) {
       expressions.add(
@@ -226,7 +226,7 @@ public List<Expression> accessors(Expression v1, List<Integer> argList) {
     return expressions;
   }
 
-  public PhysType makeNullable(boolean nullable) {
+  @Override public PhysType makeNullable(boolean nullable) {
     if (!nullable) {
       return this;
     }
@@ -236,11 +236,11 @@ public PhysType makeNullable(boolean nullable) {
   }
 
   @SuppressWarnings("deprecation")
-  public Expression convertTo(Expression exp, PhysType targetPhysType) {
+  @Override public Expression convertTo(Expression exp, PhysType targetPhysType) {
     return convertTo(exp, targetPhysType.getFormat());
   }
 
-  public Expression convertTo(Expression exp, JavaRowFormat targetFormat) {
+  @Override public Expression convertTo(Expression exp, JavaRowFormat targetFormat) {
     if (format == targetFormat) {
       return exp;
     }
@@ -256,7 +256,7 @@ public Expression convertTo(Expression exp, JavaRowFormat targetFormat) {
     return Expressions.call(exp, BuiltInMethod.SELECT.method, selector);
   }
 
-  public Pair<Expression, Expression> generateCollationKey(
+  @Override public Pair<Expression, Expression> generateCollationKey(
       final List<RelFieldCollation> collations) {
     final Expression selector;
     if (collations.size() == 1) {
@@ -388,7 +388,7 @@ public Pair<Expression, Expression> generateCollationKey(
             memberDeclarations));
   }
 
-  public Expression generateComparator(RelCollation collation) {
+  @Override public Expression generateComparator(RelCollation collation) {
     // int c;
     // c = Utilities.compare(v0, v1);
     // if (c != 0) return c; // or -c if descending
@@ -490,29 +490,29 @@ public Expression generateComparator(RelCollation collation) {
         memberDeclarations);
   }
 
-  public RelDataType getRowType() {
+  @Override public RelDataType getRowType() {
     return rowType;
   }
 
-  public Expression record(List<Expression> expressions) {
+  @Override public Expression record(List<Expression> expressions) {
     return format.record(javaRowClass, expressions);
   }
 
-  public Type getJavaRowType() {
+  @Override public Type getJavaRowType() {
     return javaRowClass;
   }
 
-  public Type getJavaFieldType(int index) {
+  @Override public Type getJavaFieldType(int index) {
     return format.javaFieldClass(typeFactory, rowType, index);
   }
 
-  public PhysType component(int fieldOrdinal) {
+  @Override public PhysType component(int fieldOrdinal) {
     final RelDataTypeField field = rowType.getFieldList().get(fieldOrdinal);
     return PhysTypeImpl.of(typeFactory,
         toStruct(field.getType().getComponentType()), format, false);
   }
 
-  public PhysType field(int ordinal) {
+  @Override public PhysType field(int ordinal) {
     final RelDataTypeField field = rowType.getFieldList().get(ordinal);
     final RelDataType type = field.getType();
     return PhysTypeImpl.of(typeFactory, toStruct(type), format, false);
@@ -527,32 +527,32 @@ private RelDataType toStruct(RelDataType type) {
         .build();
   }
 
-  public Expression comparer() {
+  @Override public Expression comparer() {
     return format.comparer();
   }
 
   private List<Expression> fieldReferences(
       final Expression parameter, final List<Integer> fields) {
     return new AbstractList<Expression>() {
-      public Expression get(int index) {
+      @Override public Expression get(int index) {
         return fieldReference(parameter, fields.get(index));
       }
 
-      public int size() {
+      @Override public int size() {
         return fields.size();
       }
     };
   }
 
-  public Class fieldClass(int field) {
+  @Override public Class fieldClass(int field) {
     return fieldClasses.get(field);
   }
 
-  public boolean fieldNullable(int field) {
+  @Override public boolean fieldNullable(int field) {
     return rowType.getFieldList().get(field).getType().isNullable();
   }
 
-  public Expression generateAccessor(
+  @Override public Expression generateAccessor(
       List<Integer> fields) {
     ParameterExpression v1 =
         Expressions.parameter(javaRowClass, "v1");
@@ -653,12 +653,12 @@ public Expression generateAccessor(
     }
   }
 
-  public Expression fieldReference(
+  @Override public Expression fieldReference(
       Expression expression, int field) {
     return fieldReference(expression, field, null);
   }
 
-  public Expression fieldReference(
+  @Override public Expression fieldReference(
       Expression expression, int field, Type storageType) {
     Type fieldType;
     if (storageType == null) {
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/ReflectiveCallNotNullImplementor.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/ReflectiveCallNotNullImplementor.java
index 1a97467e7dd..21fb69be9e7 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/ReflectiveCallNotNullImplementor.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/ReflectiveCallNotNullImplementor.java
@@ -44,7 +44,7 @@ public ReflectiveCallNotNullImplementor(Method method) {
     this.method = method;
   }
 
-  public Expression implement(RexToLixTranslator translator,
+  @Override public Expression implement(RexToLixTranslator translator,
       RexCall call, List<Expression> translatedOperands) {
     translatedOperands =
         EnumUtils.fromInternal(method.getParameterTypes(), translatedOperands);
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java
index 176ed1abc34..6203bdb010e 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java
@@ -1085,11 +1085,11 @@ static class MinMaxImplementor extends StrictAggImplementor {
 
   /** Implementor for the {@code SINGLE_VALUE} aggregate function. */
   static class SingleValueImplementor implements AggImplementor {
-    public List<Type> getStateType(AggContext info) {
+    @Override public List<Type> getStateType(AggContext info) {
       return Arrays.asList(boolean.class, info.returnType());
     }
 
-    public void implementReset(AggContext info, AggResetContext reset) {
+    @Override public void implementReset(AggContext info, AggResetContext reset) {
       List<Expression> acc = reset.accumulator();
       reset.currentBlock().add(
           Expressions.statement(
@@ -1100,7 +1100,7 @@ public void implementReset(AggContext info, AggResetContext reset) {
                   getDefaultValue(acc.get(1).getType()))));
     }
 
-    public void implementAdd(AggContext info, AggAddContext add) {
+    @Override public void implementAdd(AggContext info, AggAddContext add) {
       List<Expression> acc = add.accumulator();
       Expression flag = acc.get(0);
       add.currentBlock().add(
@@ -1117,7 +1117,7 @@ public void implementAdd(AggContext info, AggAddContext add) {
               Expressions.assign(acc.get(1), add.arguments().get(0))));
     }
 
-    public Expression implementResult(AggContext info,
+    @Override public Expression implementResult(AggContext info,
         AggResultContext result) {
       return EnumUtils.convert(result.accumulator().get(1),
           info.returnType());
@@ -1278,17 +1278,17 @@ static class BitOpImplementor extends StrictAggImplementor {
 
   /** Implementor for the {@code GROUPING} aggregate function. */
   static class GroupingImplementor implements AggImplementor {
-    public List<Type> getStateType(AggContext info) {
+    @Override public List<Type> getStateType(AggContext info) {
       return ImmutableList.of();
     }
 
-    public void implementReset(AggContext info, AggResetContext reset) {
+    @Override public void implementReset(AggContext info, AggResetContext reset) {
     }
 
-    public void implementAdd(AggContext info, AggAddContext add) {
+    @Override public void implementAdd(AggContext info, AggAddContext add) {
     }
 
-    public Expression implementResult(AggContext info,
+    @Override public Expression implementResult(AggContext info,
         AggResultContext result) {
       final List<Integer> keys;
       switch (info.aggregation().kind) {
@@ -1452,23 +1452,23 @@ protected FirstLastValueImplementor(SeekType seekType) {
       this.seekType = seekType;
     }
 
-    public List<Type> getStateType(AggContext info) {
+    @Override public List<Type> getStateType(AggContext info) {
       return Collections.emptyList();
     }
 
-    public void implementReset(AggContext info, AggResetContext reset) {
+    @Override public void implementReset(AggContext info, AggResetContext reset) {
       // no op
     }
 
-    public void implementAdd(AggContext info, AggAddContext add) {
+    @Override public void implementAdd(AggContext info, AggAddContext add) {
       // no op
     }
 
-    public boolean needCacheWhenFrameIntact() {
+    @Override public boolean needCacheWhenFrameIntact() {
       return true;
     }
 
-    public Expression implementResult(AggContext info,
+    @Override public Expression implementResult(AggContext info,
         AggResultContext result) {
       WinAggResultContext winResult = (WinAggResultContext) result;
 
@@ -1497,23 +1497,23 @@ protected LastValueImplementor() {
   /** Implementor for the {@code NTH_VALUE}
    * windowed aggregate function. */
   static class NthValueImplementor implements WinAggImplementor {
-    public List<Type> getStateType(AggContext info) {
+    @Override public List<Type> getStateType(AggContext info) {
       return Collections.emptyList();
     }
 
-    public void implementReset(AggContext info, AggResetContext reset) {
+    @Override public void implementReset(AggContext info, AggResetContext reset) {
       // no op
     }
 
-    public void implementAdd(AggContext info, AggAddContext add) {
+    @Override public void implementAdd(AggContext info, AggAddContext add) {
       // no op
     }
 
-    public boolean needCacheWhenFrameIntact() {
+    @Override public boolean needCacheWhenFrameIntact() {
       return true;
     }
 
-    public Expression implementResult(AggContext info,
+    @Override public Expression implementResult(AggContext info,
         AggResultContext result) {
       WinAggResultContext winResult = (WinAggResultContext) result;
 
@@ -1559,23 +1559,23 @@ protected LeadLagImplementor(boolean isLead) {
       this.isLead = isLead;
     }
 
-    public List<Type> getStateType(AggContext info) {
+    @Override public List<Type> getStateType(AggContext info) {
       return Collections.emptyList();
     }
 
-    public void implementReset(AggContext info, AggResetContext reset) {
+    @Override public void implementReset(AggContext info, AggResetContext reset) {
       // no op
     }
 
-    public void implementAdd(AggContext info, AggAddContext add) {
+    @Override public void implementAdd(AggContext info, AggAddContext add) {
       // no op
     }
 
-    public boolean needCacheWhenFrameIntact() {
+    @Override public boolean needCacheWhenFrameIntact() {
       return false;
     }
 
-    public Expression implementResult(AggContext info,
+    @Override public Expression implementResult(AggContext info,
         AggResultContext result) {
       WinAggResultContext winResult = (WinAggResultContext) result;
 
@@ -1637,23 +1637,23 @@ protected LagImplementor() {
 
   /** Implementor for the {@code NTILE} windowed aggregate function. */
   static class NtileImplementor implements WinAggImplementor {
-    public List<Type> getStateType(AggContext info) {
+    @Override public List<Type> getStateType(AggContext info) {
       return Collections.emptyList();
     }
 
-    public void implementReset(AggContext info, AggResetContext reset) {
+    @Override public void implementReset(AggContext info, AggResetContext reset) {
       // no op
     }
 
-    public void implementAdd(AggContext info, AggAddContext add) {
+    @Override public void implementAdd(AggContext info, AggAddContext add) {
       // no op
     }
 
-    public boolean needCacheWhenFrameIntact() {
+    @Override public boolean needCacheWhenFrameIntact() {
       return false;
     }
 
-    public Expression implementResult(AggContext info,
+    @Override public Expression implementResult(AggContext info,
         AggResultContext result) {
       WinAggResultContext winResult = (WinAggResultContext) result;
 
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/RexToLixTranslator.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/RexToLixTranslator.java
index d7ecad3baa9..0a908f457a0 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/RexToLixTranslator.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/RexToLixTranslator.java
@@ -1389,7 +1389,7 @@ public InputGetterImpl(List<Pair<Expression, PhysType>> inputs) {
       this.inputs = inputs;
     }
 
-    public Expression field(BlockBuilder list, int index, Type storageType) {
+    @Override public Expression field(BlockBuilder list, int index, Type storageType) {
       int offset = 0;
       for (Pair<Expression, PhysType> input : inputs) {
         final PhysType physType = input.right;
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictAggImplementor.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictAggImplementor.java
index f5db70854b5..3b77c3c50f8 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictAggImplementor.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictAggImplementor.java
@@ -55,7 +55,7 @@ protected final void accAdvance(AggAddContext add, Expression acc,
             Expressions.assign(acc, EnumUtils.convert(next, acc.type))));
   }
 
-  public final List<Type> getStateType(AggContext info) {
+  @Override public final List<Type> getStateType(AggContext info) {
     List<Type> subState = getNotNullState(info);
     stateSize = subState.size();
     needTrackEmptySet = nonDefaultOnEmptySet(info);
@@ -87,7 +87,7 @@ public List<Type> getNotNullState(AggContext info) {
     return Collections.singletonList(type);
   }
 
-  public final void implementReset(AggContext info, AggResetContext reset) {
+  @Override public final void implementReset(AggContext info, AggResetContext reset) {
     if (trackNullsPerRow) {
       List<Expression> acc = reset.accumulator();
       Expression flag = acc.get(acc.size() - 1);
@@ -113,7 +113,7 @@ protected void implementNotNullReset(AggContext info,
     }
   }
 
-  public final void implementAdd(AggContext info, final AggAddContext add) {
+  @Override public final void implementAdd(AggContext info, final AggAddContext add) {
     final List<RexNode> args = add.rexArguments();
     final RexToLixTranslator translator = add.rowTranslator();
     final List<Expression> conditions = new ArrayList<>();
@@ -155,7 +155,7 @@ public final void implementAdd(AggContext info, final AggAddContext add) {
   protected abstract void implementNotNullAdd(AggContext info,
       AggAddContext add);
 
-  public final Expression implementResult(AggContext info,
+  @Override public final Expression implementResult(AggContext info,
       final AggResultContext result) {
     if (!needTrackEmptySet) {
       return EnumUtils.convert(
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictWinAggImplementor.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictWinAggImplementor.java
index ecc1c2a6a18..cd27b9da2db 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictWinAggImplementor.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/StrictWinAggImplementor.java
@@ -74,7 +74,7 @@ protected Expression implementNotNullResult(WinAggContext info,
         (WinAggResultContext) result);
   }
 
-  public boolean needCacheWhenFrameIntact() {
+  @Override public boolean needCacheWhenFrameIntact() {
     return true;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggAddContextImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggAddContextImpl.java
index 8e53369fd4a..fb70c133706 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggAddContextImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggAddContextImpl.java
@@ -32,7 +32,7 @@ public AggAddContextImpl(BlockBuilder block, List<Expression> accumulator) {
     super(block, null, accumulator, null, null);
   }
 
-  public final List<Expression> arguments() {
+  @Override public final List<Expression> arguments() {
     return rowTranslator().translateList(rexArguments());
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResetContextImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResetContextImpl.java
index 51e6f6124cb..28d56c8fda4 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResetContextImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResetContextImpl.java
@@ -44,7 +44,7 @@ public AggResetContextImpl(BlockBuilder block, List<Expression> accumulator) {
     this.accumulator = accumulator;
   }
 
-  public List<Expression> accumulator() {
+  @Override public List<Expression> accumulator() {
     return accumulator;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResultContextImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResultContextImpl.java
index ecf03b75fdc..c146706f6fa 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResultContextImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/AggResultContextImpl.java
@@ -53,11 +53,11 @@ public AggResultContextImpl(BlockBuilder block, AggregateCall call,
     this.keyPhysType = keyPhysType;
   }
 
-  public Expression key() {
+  @Override public Expression key() {
     return key;
   }
 
-  public Expression keyField(int i) {
+  @Override public Expression keyField(int i) {
     return keyPhysType.fieldReference(key, i);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggAddContextImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggAddContextImpl.java
index aa8d7e3612a..05a624aa329 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggAddContextImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggAddContextImpl.java
@@ -45,13 +45,13 @@ public WinAggAddContextImpl(BlockBuilder block, List<Expression> accumulator,
     this(block, accumulator, (Function<BlockBuilder, WinAggFrameResultContext>) frame::apply);
   }
 
-  public final RexToLixTranslator rowTranslator() {
+  @Override public final RexToLixTranslator rowTranslator() {
     return rowTranslator(
         computeIndex(Expressions.constant(0),
             WinAggImplementor.SeekType.AGG_INDEX));
   }
 
-  public final List<Expression> arguments() {
+  @Override public final List<Expression> arguments() {
     return rowTranslator().translateList(rexArguments());
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResetContextImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResetContextImpl.java
index 7478f4e8df5..f1e83cda163 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResetContextImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResetContextImpl.java
@@ -61,27 +61,27 @@ public WinAggResetContextImpl(BlockBuilder block,
     this.hasRows = hasRows;
   }
 
-  public Expression index() {
+  @Override public Expression index() {
     return index;
   }
 
-  public Expression startIndex() {
+  @Override public Expression startIndex() {
     return startIndex;
   }
 
-  public Expression endIndex() {
+  @Override public Expression endIndex() {
     return endIndex;
   }
 
-  public Expression hasRows() {
+  @Override public Expression hasRows() {
     return hasRows;
   }
 
-  public Expression getFrameRowCount() {
+  @Override public Expression getFrameRowCount() {
     return frameRowCount;
   }
 
-  public Expression getPartitionRowCount() {
+  @Override public Expression getPartitionRowCount() {
     return partitionRowCount;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResultContextImpl.java b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResultContextImpl.java
index 1f0b2180bf0..6e466416353 100644
--- a/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResultContextImpl.java
+++ b/core/src/main/java/org/apache/calcite/adapter/enumerable/impl/WinAggResultContextImpl.java
@@ -62,52 +62,52 @@ private WinAggFrameResultContext getFrame() {
     return frame.apply(currentBlock());
   }
 
-  public final List<Expression> arguments(Expression rowIndex) {
+  @Override public final List<Expression> arguments(Expression rowIndex) {
     return rowTranslator(rowIndex).translateList(rexArguments());
   }
 
-  public Expression computeIndex(Expression offset,
+  @Override public Expression computeIndex(Expression offset,
       WinAggImplementor.SeekType seekType) {
     return getFrame().computeIndex(offset, seekType);
   }
 
-  public Expression rowInFrame(Expression rowIndex) {
+  @Override public Expression rowInFrame(Expression rowIndex) {
     return getFrame().rowInFrame(rowIndex);
   }
 
-  public Expression rowInPartition(Expression rowIndex) {
+  @Override public Expression rowInPartition(Expression rowIndex) {
     return getFrame().rowInPartition(rowIndex);
   }
 
-  public RexToLixTranslator rowTranslator(Expression rowIndex) {
+  @Override public RexToLixTranslator rowTranslator(Expression rowIndex) {
     return getFrame().rowTranslator(rowIndex);
   }
 
-  public Expression compareRows(Expression a, Expression b) {
+  @Override public Expression compareRows(Expression a, Expression b) {
     return getFrame().compareRows(a, b);
   }
 
-  public Expression index() {
+  @Override public Expression index() {
     return getFrame().index();
   }
 
-  public Expression startIndex() {
+  @Override public Expression startIndex() {
     return getFrame().startIndex();
   }
 
-  public Expression endIndex() {
+  @Override public Expression endIndex() {
     return getFrame().endIndex();
   }
 
-  public Expression hasRows() {
+  @Override public Expression hasRows() {
     return getFrame().hasRows();
   }
 
-  public Expression getFrameRowCount() {
+  @Override public Expression getFrameRowCount() {
     return getFrame().getFrameRowCount();
   }
 
-  public Expression getPartitionRowCount() {
+  @Override public Expression getPartitionRowCount() {
     return getFrame().getPartitionRowCount();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/java/AbstractQueryableTable.java b/core/src/main/java/org/apache/calcite/adapter/java/AbstractQueryableTable.java
index deaf4027d51..4edcc184925 100644
--- a/core/src/main/java/org/apache/calcite/adapter/java/AbstractQueryableTable.java
+++ b/core/src/main/java/org/apache/calcite/adapter/java/AbstractQueryableTable.java
@@ -36,11 +36,11 @@ protected AbstractQueryableTable(Type elementType) {
     this.elementType = elementType;
   }
 
-  public Type getElementType() {
+  @Override public Type getElementType() {
     return elementType;
   }
 
-  public Expression getExpression(SchemaPlus schema, String tableName,
+  @Override public Expression getExpression(SchemaPlus schema, String tableName,
       Class clazz) {
     return Schemas.tableExpression(schema, elementType, tableName, clazz);
   }
diff --git a/core/src/main/java/org/apache/calcite/adapter/java/ReflectiveSchema.java b/core/src/main/java/org/apache/calcite/adapter/java/ReflectiveSchema.java
index c8e6cbfc819..7aa306a41d5 100644
--- a/core/src/main/java/org/apache/calcite/adapter/java/ReflectiveSchema.java
+++ b/core/src/main/java/org/apache/calcite/adapter/java/ReflectiveSchema.java
@@ -241,15 +241,15 @@ private static class ReflectiveTable
       this.enumerable = enumerable;
     }
 
-    public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+    @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
       return ((JavaTypeFactory) typeFactory).createType(elementType);
     }
 
-    public Statistic getStatistic() {
+    @Override public Statistic getStatistic() {
       return Statistics.UNKNOWN;
     }
 
-    public Enumerable<Object[]> scan(DataContext root) {
+    @Override public Enumerable<Object[]> scan(DataContext root) {
       if (elementType == Object[].class) {
         //noinspection unchecked
         return enumerable;
@@ -259,12 +259,12 @@ public Enumerable<Object[]> scan(DataContext root) {
       }
     }
 
-    public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+    @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
         SchemaPlus schema, String tableName) {
       return new AbstractTableQueryable<T>(queryProvider, schema, this,
           tableName) {
         @SuppressWarnings("unchecked")
-        public Enumerator<T> enumerator() {
+        @Override public Enumerator<T> enumerator() {
           return (Enumerator<T>) enumerable.enumerator();
         }
       };
@@ -301,7 +301,7 @@ public Enumerator<T> enumerator() {
    * }</pre></blockquote>
    */
   public static class Factory implements SchemaFactory {
-    public Schema create(SchemaPlus parentSchema, String name,
+    @Override public Schema create(SchemaPlus parentSchema, String name,
         Map<String, Object> operand) {
       Class<?> clazz;
       Object target;
@@ -350,11 +350,11 @@ private static class MethodTableMacro extends ReflectiveFunctionBase
           + "expanded";
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "Member {method=" + method + "}";
     }
 
-    public TranslatableTable apply(final List<Object> arguments) {
+    @Override public TranslatableTable apply(final List<Object> arguments) {
       try {
         final Object o = method.invoke(schema.getTarget(), arguments.toArray());
         return (TranslatableTable) o;
@@ -382,7 +382,7 @@ private static class FieldTable<T> extends ReflectiveTable {
       this.statistic = statistic;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "Relation {field=" + field.getName() + "}";
     }
 
@@ -406,7 +406,7 @@ private static class FieldSelector implements Function1<Object, Object[]> {
       this.fields = elementType.getFields();
     }
 
-    public Object[] apply(Object o) {
+    @Override public Object[] apply(Object o) {
       try {
         final Object[] objects = new Object[fields.length];
         for (int i = 0; i < fields.length; i++) {
diff --git a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcQueryProvider.java b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcQueryProvider.java
index b516d8d3983..f58e25015e3 100644
--- a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcQueryProvider.java
+++ b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcQueryProvider.java
@@ -30,7 +30,7 @@ public final class JdbcQueryProvider extends QueryProviderImpl {
   private JdbcQueryProvider() {
   }
 
-  public <T> Enumerator<T> executeQuery(Queryable<T> queryable) {
+  @Override public <T> Enumerator<T> executeQuery(Queryable<T> queryable) {
     return null;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcRules.java b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcRules.java
index 5a46990bc87..23fcd43272a 100644
--- a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcRules.java
+++ b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcRules.java
@@ -409,7 +409,7 @@ protected JdbcJoin(
       return Math.max(leftRowCount, rightRowCount);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -432,7 +432,7 @@ protected JdbcCalcRule(Config config) {
       super(config);
     }
 
-    public RelNode convert(RelNode rel) {
+    @Override public RelNode convert(RelNode rel) {
       final Calc calc = (Calc) rel;
 
       // If there's a multiset, let FarragoMultisetSplitter work on it
@@ -470,7 +470,7 @@ public JdbcCalc(RelOptCluster cluster, RelTraitSet traitSet, RelNode input,
       Util.discard(flags);
     }
 
-    public RelWriter explainTerms(RelWriter pw) {
+    @Override public RelWriter explainTerms(RelWriter pw) {
       return program.explainCalc(super.explainTerms(pw));
     }
 
@@ -478,7 +478,7 @@ public RelWriter explainTerms(RelWriter pw) {
       return RelMdUtil.estimateFilteredRows(getInput(), program, mq);
     }
 
-    public RelOptCost computeSelfCost(RelOptPlanner planner,
+    @Override public RelOptCost computeSelfCost(RelOptPlanner planner,
         RelMetadataQuery mq) {
       double dRows = mq.getRowCount(this);
       double dCpu = mq.getRowCount(getInput())
@@ -487,11 +487,11 @@ public RelOptCost computeSelfCost(RelOptPlanner planner,
       return planner.getCostFactory().makeCost(dRows, dCpu, dIo);
     }
 
-    public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
+    @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
       return new JdbcCalc(getCluster(), traitSet, sole(inputs), program);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -576,7 +576,7 @@ public JdbcProject(RelOptCluster cluster, RelTraitSet traitSet,
           .multiplyBy(JdbcConvention.COST_MULTIPLIER);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -630,12 +630,12 @@ public JdbcFilter(
       assert getConvention() instanceof JdbcConvention;
     }
 
-    public JdbcFilter copy(RelTraitSet traitSet, RelNode input,
+    @Override public JdbcFilter copy(RelTraitSet traitSet, RelNode input,
         RexNode condition) {
       return new JdbcFilter(getCluster(), traitSet, input, condition);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -729,7 +729,7 @@ public JdbcAggregate(RelOptCluster cluster, RelTraitSet traitSet,
       }
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -807,7 +807,7 @@ public JdbcSort(
       return super.computeSelfCost(planner, mq).multiplyBy(0.9);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -849,7 +849,7 @@ public JdbcUnion(
       super(cluster, traitSet, inputs, all);
     }
 
-    public JdbcUnion copy(
+    @Override public JdbcUnion copy(
         RelTraitSet traitSet, List<RelNode> inputs, boolean all) {
       return new JdbcUnion(getCluster(), traitSet, inputs, all);
     }
@@ -859,7 +859,7 @@ public JdbcUnion copy(
       return super.computeSelfCost(planner, mq).multiplyBy(.1);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -908,12 +908,12 @@ public JdbcIntersect(
       assert !all;
     }
 
-    public JdbcIntersect copy(
+    @Override public JdbcIntersect copy(
         RelTraitSet traitSet, List<RelNode> inputs, boolean all) {
       return new JdbcIntersect(getCluster(), traitSet, inputs, all);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -956,12 +956,12 @@ public JdbcMinus(RelOptCluster cluster, RelTraitSet traitSet,
       assert !all;
     }
 
-    public JdbcMinus copy(RelTraitSet traitSet, List<RelNode> inputs,
+    @Override public JdbcMinus copy(RelTraitSet traitSet, List<RelNode> inputs,
         boolean all) {
       return new JdbcMinus(getCluster(), traitSet, inputs, all);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -1044,7 +1044,7 @@ public JdbcTableModify(RelOptCluster cluster,
           getSourceExpressionList(), isFlattened());
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
@@ -1083,7 +1083,7 @@ public static class JdbcValues extends Values implements JdbcRel {
       return new JdbcValues(getCluster(), rowType, tuples, traitSet);
     }
 
-    public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+    @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
       return implementor.implement(this);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcSchema.java b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcSchema.java
index 90ce7226598..03dbc770b19 100644
--- a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcSchema.java
+++ b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcSchema.java
@@ -208,11 +208,11 @@ public static DataSource dataSource(String url, String driverClassName,
         password);
   }
 
-  public boolean isMutable() {
+  @Override public boolean isMutable() {
     return false;
   }
 
-  public Schema snapshot(SchemaVersion version) {
+  @Override public Schema snapshot(SchemaVersion version) {
     return new JdbcSchema(dataSource, dialect, convention, catalog, schema,
         tableMap);
   }
@@ -222,7 +222,7 @@ public DataSource getDataSource() {
     return dataSource;
   }
 
-  public Expression getExpression(SchemaPlus parentSchema, String name) {
+  @Override public Expression getExpression(SchemaPlus parentSchema, String name) {
     return Schemas.subSchemaExpression(parentSchema, name, JdbcSchema.class);
   }
 
@@ -231,11 +231,11 @@ protected Multimap<String, Function> getFunctions() {
     return ImmutableMultimap.of();
   }
 
-  public final Collection<Function> getFunctions(String name) {
+  @Override public final Collection<Function> getFunctions(String name) {
     return getFunctions().get(name); // never null
   }
 
-  public final Set<String> getFunctionNames() {
+  @Override public final Set<String> getFunctionNames() {
     return getFunctions().keySet();
   }
 
@@ -341,7 +341,7 @@ private Pair<String, String> getCatalogSchema(Connection connection)
     return Pair.of(catalog, schema);
   }
 
-  public Table getTable(String name) {
+  @Override public Table getTable(String name) {
     return getTableMap(false).get(name);
   }
 
@@ -470,7 +470,7 @@ private RelDataType parseTypeString(RelDataTypeFactory typeFactory,
     }
   }
 
-  public Set<String> getTableNames() {
+  @Override public Set<String> getTableNames() {
     // This method is called during a cache refresh. We can take it as a signal
     // that we need to re-build our own cache.
     return getTableMap(!snapshot).keySet();
@@ -489,12 +489,12 @@ protected Map<String, RelProtoDataType> getTypes() {
     return getTypes().keySet();
   }
 
-  public Schema getSubSchema(String name) {
+  @Override public Schema getSubSchema(String name) {
     // JDBC does not support sub-schemas.
     return null;
   }
 
-  public Set<String> getSubSchemaNames() {
+  @Override public Set<String> getSubSchemaNames() {
     return ImmutableSet.of();
   }
 
@@ -553,7 +553,7 @@ public static class Factory implements SchemaFactory {
 
     private Factory() {}
 
-    public Schema create(
+    @Override public Schema create(
         SchemaPlus parentSchema,
         String name,
         Map<String, Object> operand) {
diff --git a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTable.java b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTable.java
index 7e85d5b943b..71d58c52962 100644
--- a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTable.java
+++ b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTable.java
@@ -90,7 +90,7 @@ public class JdbcTable extends AbstractQueryableTable
     this.jdbcTableType = Objects.requireNonNull(jdbcTableType);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "JdbcTable {" + jdbcTableName + "}";
   }
 
@@ -108,7 +108,7 @@ public String toString() {
     }
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     if (protoRowType == null) {
       try {
         protoRowType =
@@ -165,18 +165,18 @@ public SqlIdentifier tableName() {
     return new SqlIdentifier(names, SqlParserPos.ZERO);
   }
 
-  public RelNode toRel(RelOptTable.ToRelContext context,
+  @Override public RelNode toRel(RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     return new JdbcTableScan(context.getCluster(), relOptTable, this,
         jdbcSchema.convention);
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new JdbcTableQueryable<>(queryProvider, schema, tableName);
   }
 
-  public Enumerable<Object[]> scan(DataContext root) {
+  @Override public Enumerable<Object[]> scan(DataContext root) {
     final JavaTypeFactory typeFactory = root.getTypeFactory();
     final SqlString sql = generateSql();
     return ResultSetEnumerable.of(jdbcSchema.getDataSource(), sql.getSql(),
@@ -212,7 +212,7 @@ private class JdbcTableQueryable<T> extends AbstractTableQueryable<T> {
       return "JdbcTableQueryable {table: " + tableName + "}";
     }
 
-    public Enumerator<T> enumerator() {
+    @Override public Enumerator<T> enumerator() {
       final JavaTypeFactory typeFactory =
           ((CalciteConnection) queryProvider).getTypeFactory();
       final SqlString sql = generateSql();
diff --git a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTableScan.java b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTableScan.java
index a138089b5f7..25d8a145bca 100644
--- a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTableScan.java
+++ b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcTableScan.java
@@ -48,7 +48,7 @@ protected JdbcTableScan(
         getCluster(), table, jdbcTable, (JdbcConvention) getConvention());
   }
 
-  public JdbcImplementor.Result implement(JdbcImplementor implementor) {
+  @Override public JdbcImplementor.Result implement(JdbcImplementor implementor) {
     return implementor.result(jdbcTable.tableName(),
         ImmutableList.of(JdbcImplementor.Clause.FROM), this, null);
   }
diff --git a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcToEnumerableConverter.java b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcToEnumerableConverter.java
index e9eb6a6dc14..d2750a2b243 100644
--- a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcToEnumerableConverter.java
+++ b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcToEnumerableConverter.java
@@ -82,7 +82,7 @@ protected JdbcToEnumerableConverter(
     return super.computeSelfCost(planner, mq).multiplyBy(.1);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     // Generate:
     //   ResultSetEnumerable.of(schema.getDataSource(), "select ...")
     final BlockBuilder builder0 = new BlockBuilder(false);
diff --git a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcUtils.java b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcUtils.java
index b104b73179f..15630cd90ee 100644
--- a/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcUtils.java
+++ b/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcUtils.java
@@ -125,7 +125,7 @@ public static Function1<ResultSet, Function0<Object[]>> factory(
       };
     }
 
-    public Object[] apply() {
+    @Override public Object[] apply() {
       try {
         final Object[] values = new Object[columnCount];
         for (int i = 0; i < columnCount; i++) {
diff --git a/core/src/main/java/org/apache/calcite/config/CalciteConnectionConfigImpl.java b/core/src/main/java/org/apache/calcite/config/CalciteConnectionConfigImpl.java
index 93f6ea319fa..d7dc2f84d76 100644
--- a/core/src/main/java/org/apache/calcite/config/CalciteConnectionConfigImpl.java
+++ b/core/src/main/java/org/apache/calcite/config/CalciteConnectionConfigImpl.java
@@ -65,17 +65,17 @@ public boolean isSet(CalciteConnectionProperty property) {
     return properties.containsKey(property.camelName());
   }
 
-  public boolean approximateDistinctCount() {
+  @Override public boolean approximateDistinctCount() {
     return CalciteConnectionProperty.APPROXIMATE_DISTINCT_COUNT.wrap(properties)
         .getBoolean();
   }
 
-  public boolean approximateTopN() {
+  @Override public boolean approximateTopN() {
     return CalciteConnectionProperty.APPROXIMATE_TOP_N.wrap(properties)
         .getBoolean();
   }
 
-  public boolean approximateDecimal() {
+  @Override public boolean approximateDecimal() {
     return CalciteConnectionProperty.APPROXIMATE_DECIMAL.wrap(properties)
         .getBoolean();
   }
@@ -84,26 +84,26 @@ public boolean approximateDecimal() {
     return CalciteConnectionProperty.NULL_EQUAL_TO_EMPTY.wrap(properties).getBoolean();
   }
 
-  public boolean autoTemp() {
+  @Override public boolean autoTemp() {
     return CalciteConnectionProperty.AUTO_TEMP.wrap(properties).getBoolean();
   }
 
-  public boolean materializationsEnabled() {
+  @Override public boolean materializationsEnabled() {
     return CalciteConnectionProperty.MATERIALIZATIONS_ENABLED.wrap(properties)
         .getBoolean();
   }
 
-  public boolean createMaterializations() {
+  @Override public boolean createMaterializations() {
     return CalciteConnectionProperty.CREATE_MATERIALIZATIONS.wrap(properties)
         .getBoolean();
   }
 
-  public NullCollation defaultNullCollation() {
+  @Override public NullCollation defaultNullCollation() {
     return CalciteConnectionProperty.DEFAULT_NULL_COLLATION.wrap(properties)
         .getEnum(NullCollation.class, NullCollation.HIGH);
   }
 
-  public <T> T fun(Class<T> operatorTableClass, T defaultOperatorTable) {
+  @Override public <T> T fun(Class<T> operatorTableClass, T defaultOperatorTable) {
     final String fun =
         CalciteConnectionProperty.FUN.wrap(properties).getString();
     if (fun == null || fun.equals("") || fun.equals("standard")) {
@@ -116,66 +116,66 @@ public <T> T fun(Class<T> operatorTableClass, T defaultOperatorTable) {
     return operatorTableClass.cast(operatorTable);
   }
 
-  public String model() {
+  @Override public String model() {
     return CalciteConnectionProperty.MODEL.wrap(properties).getString();
   }
 
-  public Lex lex() {
+  @Override public Lex lex() {
     return CalciteConnectionProperty.LEX.wrap(properties).getEnum(Lex.class);
   }
 
-  public Quoting quoting() {
+  @Override public Quoting quoting() {
     return CalciteConnectionProperty.QUOTING.wrap(properties)
         .getEnum(Quoting.class, lex().quoting);
   }
 
-  public Casing unquotedCasing() {
+  @Override public Casing unquotedCasing() {
     return CalciteConnectionProperty.UNQUOTED_CASING.wrap(properties)
         .getEnum(Casing.class, lex().unquotedCasing);
   }
 
-  public Casing quotedCasing() {
+  @Override public Casing quotedCasing() {
     return CalciteConnectionProperty.QUOTED_CASING.wrap(properties)
         .getEnum(Casing.class, lex().quotedCasing);
   }
 
-  public boolean caseSensitive() {
+  @Override public boolean caseSensitive() {
     return CalciteConnectionProperty.CASE_SENSITIVE.wrap(properties)
         .getBoolean(lex().caseSensitive);
   }
 
-  public <T> T parserFactory(Class<T> parserFactoryClass,
+  @Override public <T> T parserFactory(Class<T> parserFactoryClass,
       T defaultParserFactory) {
     return CalciteConnectionProperty.PARSER_FACTORY.wrap(properties)
         .getPlugin(parserFactoryClass, defaultParserFactory);
   }
 
-  public <T> T schemaFactory(Class<T> schemaFactoryClass,
+  @Override public <T> T schemaFactory(Class<T> schemaFactoryClass,
       T defaultSchemaFactory) {
     return CalciteConnectionProperty.SCHEMA_FACTORY.wrap(properties)
         .getPlugin(schemaFactoryClass, defaultSchemaFactory);
   }
 
-  public JsonSchema.Type schemaType() {
+  @Override public JsonSchema.Type schemaType() {
     return CalciteConnectionProperty.SCHEMA_TYPE.wrap(properties)
         .getEnum(JsonSchema.Type.class);
   }
 
-  public boolean spark() {
+  @Override public boolean spark() {
     return CalciteConnectionProperty.SPARK.wrap(properties).getBoolean();
   }
 
-  public boolean forceDecorrelate() {
+  @Override public boolean forceDecorrelate() {
     return CalciteConnectionProperty.FORCE_DECORRELATE.wrap(properties)
         .getBoolean();
   }
 
-  public <T> T typeSystem(Class<T> typeSystemClass, T defaultTypeSystem) {
+  @Override public <T> T typeSystem(Class<T> typeSystemClass, T defaultTypeSystem) {
     return CalciteConnectionProperty.TYPE_SYSTEM.wrap(properties)
         .getPlugin(typeSystemClass, defaultTypeSystem);
   }
 
-  public SqlConformance conformance() {
+  @Override public SqlConformance conformance() {
     return CalciteConnectionProperty.CONFORMANCE.wrap(properties)
         .getEnum(SqlConformanceEnum.class);
   }
@@ -185,22 +185,22 @@ public SqlConformance conformance() {
             .getString();
   }
 
-  public String locale() {
+  @Override public String locale() {
     return CalciteConnectionProperty.LOCALE.wrap(properties)
         .getString();
   }
 
-  public boolean typeCoercion() {
+  @Override public boolean typeCoercion() {
     return CalciteConnectionProperty.TYPE_COERCION.wrap(properties)
         .getBoolean();
   }
 
-  public boolean lenientOperatorLookup() {
+  @Override public boolean lenientOperatorLookup() {
     return CalciteConnectionProperty.LENIENT_OPERATOR_LOOKUP.wrap(properties)
         .getBoolean();
   }
 
-  public boolean topDownOpt() {
+  @Override public boolean topDownOpt() {
     return CalciteConnectionProperty.TOPDOWN_OPT.wrap(properties).getBoolean();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/config/CalciteConnectionProperty.java b/core/src/main/java/org/apache/calcite/config/CalciteConnectionProperty.java
index adb9833c7f0..6f2cc17ea32 100644
--- a/core/src/main/java/org/apache/calcite/config/CalciteConnectionProperty.java
+++ b/core/src/main/java/org/apache/calcite/config/CalciteConnectionProperty.java
@@ -200,27 +200,27 @@ public enum CalciteConnectionProperty implements ConnectionProperty {
     }
   }
 
-  public String camelName() {
+  @Override public String camelName() {
     return camelName;
   }
 
-  public Object defaultValue() {
+  @Override public Object defaultValue() {
     return defaultValue;
   }
 
-  public Type type() {
+  @Override public Type type() {
     return type;
   }
 
-  public Class valueClass() {
+  @Override public Class valueClass() {
     return valueClass;
   }
 
-  public boolean required() {
+  @Override public boolean required() {
     return required;
   }
 
-  public PropEnv wrap(Properties properties) {
+  @Override public PropEnv wrap(Properties properties) {
     return new PropEnv(parse(properties, NAME_TO_PROPS), this);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/AggregateNode.java b/core/src/main/java/org/apache/calcite/interpreter/AggregateNode.java
index 9936c151a28..1f1e042374e 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/AggregateNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/AggregateNode.java
@@ -90,7 +90,7 @@ public AggregateNode(Compiler compiler, Aggregate rel) {
     accumulatorFactories = builder.build();
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     Row r;
     while ((r = source.receive()) != null) {
       for (Grouping group : groups) {
@@ -219,7 +219,7 @@ private AccumulatorFactory getAccumulator(final AggregateCall call,
 
       AggAddContext addContext =
           new AggAddContextImpl(builder2, accumulator) {
-            public List<RexNode> rexArguments() {
+            @Override public List<RexNode> rexArguments() {
               List<RexNode> args = new ArrayList<>();
               for (int index : agg.call.getArgList()) {
                 args.add(RexInputRef.of(index, inputPhysType.getRowType()));
@@ -227,14 +227,14 @@ public List<RexNode> rexArguments() {
               return args;
             }
 
-            public RexNode rexFilterArgument() {
+            @Override public RexNode rexFilterArgument() {
               return agg.call.filterArg < 0
                   ? null
                   : RexInputRef.of(agg.call.filterArg,
                       inputPhysType.getRowType());
             }
 
-            public RexToLixTranslator rowTranslator() {
+            @Override public RexToLixTranslator rowTranslator() {
               final SqlConformance conformance =
                   SqlConformanceEnum.DEFAULT; // TODO: get this from implementor
               return RexToLixTranslator.forAggregation(typeFactory,
@@ -269,7 +269,7 @@ private static class CountAccumulator implements Accumulator {
       cnt = 0;
     }
 
-    public void send(Row row) {
+    @Override public void send(Row row) {
       boolean notNull = true;
       for (Integer i : call.getArgList()) {
         if (row.getObject(i) == null) {
@@ -282,7 +282,7 @@ public void send(Row row) {
       }
     }
 
-    public Object end() {
+    @Override public Object end() {
       return cnt;
     }
   }
@@ -315,7 +315,7 @@ private ScalarAccumulatorDef(Scalar initScalar, Scalar addScalar,
       this.endContext.values = new Object[accumulatorLength];
     }
 
-    public Accumulator get() {
+    @Override public Accumulator get() {
       return new ScalarAccumulator(this, new Object[accumulatorLength]);
     }
   }
@@ -330,7 +330,7 @@ private ScalarAccumulator(ScalarAccumulatorDef def, Object[] values) {
       this.values = values;
     }
 
-    public void send(Row row) {
+    @Override public void send(Row row) {
       System.arraycopy(row.getValues(), 0, def.sendContext.values, 0,
           def.rowLength);
       System.arraycopy(values, 0, def.sendContext.values, def.rowLength,
@@ -338,7 +338,7 @@ public void send(Row row) {
       def.addScalar.execute(def.sendContext, values);
     }
 
-    public Object end() {
+    @Override public Object end() {
       System.arraycopy(values, 0, def.endContext.values, 0, values.length);
       return def.endScalar.execute(def.endContext);
     }
@@ -686,7 +686,7 @@ private static class UdaAccumulatorFactory implements AccumulatorFactory {
       this.nullIfEmpty = nullIfEmpty;
     }
 
-    public Accumulator get() {
+    @Override public Accumulator get() {
       return new UdaAccumulator(this);
     }
   }
@@ -707,7 +707,7 @@ private static class UdaAccumulator implements Accumulator {
       this.empty = true;
     }
 
-    public void send(Row row) {
+    @Override public void send(Row row) {
       final Object[] args = {value, row.getValues()[factory.argOrdinal]};
       for (int i = 1; i < args.length; i++) {
         if (args[i] == null) {
@@ -722,7 +722,7 @@ public void send(Row row) {
       empty = false;
     }
 
-    public Object end() {
+    @Override public Object end() {
       if (factory.nullIfEmpty && empty) {
         return null;
       }
@@ -746,13 +746,13 @@ private static class FilterAccumulator implements Accumulator {
       this.filterArg = filterArg;
     }
 
-    public void send(Row row) {
+    @Override public void send(Row row) {
       if (row.getValues()[filterArg] == Boolean.TRUE) {
         accumulator.send(row);
       }
     }
 
-    public Object end() {
+    @Override public Object end() {
       return accumulator.end();
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/BindableConvention.java b/core/src/main/java/org/apache/calcite/interpreter/BindableConvention.java
index 31a4cba1963..1c66e4de36a 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/BindableConvention.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/BindableConvention.java
@@ -44,11 +44,11 @@ public enum BindableConvention implements Convention {
     return getName();
   }
 
-  public Class getInterface() {
+  @Override public Class getInterface() {
     return BindableRel.class;
   }
 
-  public String getName() {
+  @Override public String getName() {
     return "BINDABLE";
   }
 
@@ -56,21 +56,21 @@ public String getName() {
     return null;
   }
 
-  public RelTraitDef getTraitDef() {
+  @Override public RelTraitDef getTraitDef() {
     return ConventionTraitDef.INSTANCE;
   }
 
-  public boolean satisfies(RelTrait trait) {
+  @Override public boolean satisfies(RelTrait trait) {
     return this == trait;
   }
 
-  public void register(RelOptPlanner planner) {}
+  @Override public void register(RelOptPlanner planner) {}
 
-  public boolean canConvertConvention(Convention toConvention) {
+  @Override public boolean canConvertConvention(Convention toConvention) {
     return false;
   }
 
-  public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
+  @Override public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
       RelTraitSet toTraits) {
     return false;
   }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/Bindables.java b/core/src/main/java/org/apache/calcite/interpreter/Bindables.java
index d75de31da75..20e7921783d 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/Bindables.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/Bindables.java
@@ -251,7 +251,7 @@ public static BindableTableScan create(RelOptCluster cluster,
       return builder.build();
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
@@ -288,11 +288,11 @@ public static boolean canHandle(RelOptTable table) {
           || table.unwrap(ProjectableFilterableTable.class) != null;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       throw new UnsupportedOperationException(); // TODO:
     }
   }
@@ -344,20 +344,20 @@ public static BindableFilter create(final RelNode input,
       return new BindableFilter(cluster, traitSet, input, condition);
     }
 
-    public BindableFilter copy(RelTraitSet traitSet, RelNode input,
+    @Override public BindableFilter copy(RelTraitSet traitSet, RelNode input,
         RexNode condition) {
       return new BindableFilter(getCluster(), traitSet, input, condition);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new FilterNode(implementor.compiler, this);
     }
   }
@@ -402,21 +402,21 @@ public BindableProject(RelOptCluster cluster, RelTraitSet traitSet,
       assert getConvention() instanceof BindableConvention;
     }
 
-    public BindableProject copy(RelTraitSet traitSet, RelNode input,
+    @Override public BindableProject copy(RelTraitSet traitSet, RelNode input,
         List<RexNode> projects, RelDataType rowType) {
       return new BindableProject(getCluster(), traitSet, input,
           projects, rowType);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new ProjectNode(implementor.compiler, this);
     }
   }
@@ -466,15 +466,15 @@ public BindableSort(RelOptCluster cluster, RelTraitSet traitSet,
           offset, fetch);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new SortNode(implementor.compiler, this);
     }
   }
@@ -531,22 +531,22 @@ protected BindableJoin(RelOptCluster cluster, RelTraitSet traitSet,
           CorrelationId.setOf(variablesStopped), joinType);
     }
 
-    public BindableJoin copy(RelTraitSet traitSet, RexNode conditionExpr,
+    @Override public BindableJoin copy(RelTraitSet traitSet, RexNode conditionExpr,
         RelNode left, RelNode right, JoinRelType joinType,
         boolean semiJoinDone) {
       return new BindableJoin(getCluster(), traitSet, left, right,
           conditionExpr, variablesSet, joinType);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new JoinNode(implementor.compiler, this);
     }
   }
@@ -594,20 +594,20 @@ public BindableUnion(RelOptCluster cluster, RelTraitSet traitSet,
       super(cluster, traitSet, inputs, all);
     }
 
-    public BindableUnion copy(RelTraitSet traitSet, List<RelNode> inputs,
+    @Override public BindableUnion copy(RelTraitSet traitSet, List<RelNode> inputs,
         boolean all) {
       return new BindableUnion(getCluster(), traitSet, inputs, all);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new SetOpNode(implementor.compiler, this);
     }
   }
@@ -620,19 +620,20 @@ public BindableIntersect(RelOptCluster cluster, RelTraitSet traitSet,
       super(cluster, traitSet, inputs, all);
     }
 
-    public BindableIntersect copy(RelTraitSet traitSet, List<RelNode> inputs, boolean all) {
+    @Override public BindableIntersect copy(RelTraitSet traitSet, List<RelNode> inputs,
+        boolean all) {
       return new BindableIntersect(getCluster(), traitSet, inputs, all);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new SetOpNode(implementor.compiler, this);
     }
   }
@@ -645,19 +646,19 @@ public BindableMinus(RelOptCluster cluster, RelTraitSet traitSet,
       super(cluster, traitSet, inputs, all);
     }
 
-    public BindableMinus copy(RelTraitSet traitSet, List<RelNode> inputs, boolean all) {
+    @Override public BindableMinus copy(RelTraitSet traitSet, List<RelNode> inputs, boolean all) {
       return new BindableMinus(getCluster(), traitSet, inputs, all);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new SetOpNode(implementor.compiler, this);
     }
   }
@@ -675,15 +676,15 @@ public static class BindableValues extends Values implements BindableRel {
       return new BindableValues(getCluster(), rowType, tuples, traitSet);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new ValuesNode(implementor.compiler, this);
     }
   }
@@ -762,15 +763,15 @@ public BindableAggregate(RelOptCluster cluster, RelTraitSet traitSet,
       }
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new AggregateNode(implementor.compiler, this);
     }
   }
@@ -825,15 +826,15 @@ public static class BindableWindow extends Window implements BindableRel {
           .multiplyBy(BindableConvention.COST_MULTIPLIER);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new WindowNode(implementor.compiler, this);
     }
   }
@@ -889,15 +890,15 @@ public static class BindableMatch extends Match implements BindableRel {
           subsets, allRows, partitionKeys, orderKeys, interval);
     }
 
-    public Class<Object[]> getElementType() {
+    @Override public Class<Object[]> getElementType() {
       return Object[].class;
     }
 
-    public Enumerable<Object[]> bind(DataContext dataContext) {
+    @Override public Enumerable<Object[]> bind(DataContext dataContext) {
       return help(dataContext, this);
     }
 
-    public Node implement(InterpreterImplementor implementor) {
+    @Override public Node implement(InterpreterImplementor implementor) {
       return new MatchNode(implementor.compiler, this);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/FilterNode.java b/core/src/main/java/org/apache/calcite/interpreter/FilterNode.java
index c60ebf41ac8..4cd95890760 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/FilterNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/FilterNode.java
@@ -36,7 +36,7 @@ public FilterNode(Compiler compiler, Filter rel) {
     this.context = compiler.createContext();
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     Row row;
     while ((row = source.receive()) != null) {
       context.values = row.getValues();
diff --git a/core/src/main/java/org/apache/calcite/interpreter/InterpretableConvention.java b/core/src/main/java/org/apache/calcite/interpreter/InterpretableConvention.java
index e6169261f4c..17446c53d7e 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/InterpretableConvention.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/InterpretableConvention.java
@@ -37,29 +37,29 @@ public enum InterpretableConvention implements Convention {
     return getName();
   }
 
-  public Class getInterface() {
+  @Override public Class getInterface() {
     return EnumerableRel.class;
   }
 
-  public String getName() {
+  @Override public String getName() {
     return "INTERPRETABLE";
   }
 
-  public RelTraitDef getTraitDef() {
+  @Override public RelTraitDef getTraitDef() {
     return ConventionTraitDef.INSTANCE;
   }
 
-  public boolean satisfies(RelTrait trait) {
+  @Override public boolean satisfies(RelTrait trait) {
     return this == trait;
   }
 
-  public void register(RelOptPlanner planner) {}
+  @Override public void register(RelOptPlanner planner) {}
 
-  public boolean canConvertConvention(Convention toConvention) {
+  @Override public boolean canConvertConvention(Convention toConvention) {
     return false;
   }
 
-  public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
+  @Override public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
       RelTraitSet toTraits) {
     return false;
   }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/InterpretableConverter.java b/core/src/main/java/org/apache/calcite/interpreter/InterpretableConverter.java
index e5d1356942a..a7c84ba427e 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/InterpretableConverter.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/InterpretableConverter.java
@@ -43,11 +43,11 @@ protected InterpretableConverter(RelOptCluster cluster, RelTraitSet traits,
     return new InterpretableConverter(getCluster(), traitSet, sole(inputs));
   }
 
-  public Class<Object[]> getElementType() {
+  @Override public Class<Object[]> getElementType() {
     return Object[].class;
   }
 
-  public Enumerable<Object[]> bind(DataContext dataContext) {
+  @Override public Enumerable<Object[]> bind(DataContext dataContext) {
     return new Interpreter(dataContext, getInput());
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/Interpreter.java b/core/src/main/java/org/apache/calcite/interpreter/Interpreter.java
index d482e6afe29..ce34edbf68b 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/Interpreter.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/Interpreter.java
@@ -103,7 +103,7 @@ private RelNode optimize(RelNode rootRel) {
     return rootRel;
   }
 
-  public Enumerator<Object[]> enumerator() {
+  @Override public Enumerator<Object[]> enumerator() {
     start();
     final NodeInfo nodeInfo = nodes.get(rootRel);
     final Enumerator<Row> rows;
@@ -116,7 +116,7 @@ public Enumerator<Object[]> enumerator() {
     }
 
     return new TransformedEnumerator<Row, Object[]>(rows) {
-      protected Object[] transform(Row row) {
+      @Override protected Object[] transform(Row row) {
         return row.getValues();
       }
     };
@@ -134,12 +134,12 @@ private void start() {
     }
   }
 
-  public void close() {
+  @Override public void close() {
   }
 
   /** Not used. */
   private class FooCompiler implements ScalarCompiler {
-    public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
+    @Override public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
       final RexNode node = nodes.get(0);
       if (node instanceof RexCall) {
         final RexCall call = (RexCall) node;
@@ -147,11 +147,11 @@ public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
         return new Scalar() {
           final Object[] args = new Object[call.getOperands().size()];
 
-          public void execute(final Context context, Object[] results) {
+          @Override public void execute(final Context context, Object[] results) {
             results[0] = execute(context);
           }
 
-          public Object execute(Context context) {
+          @Override public Object execute(Context context) {
             Comparable o0;
             Comparable o1;
             switch (call.getKind()) {
@@ -227,11 +227,11 @@ public Object execute(Context context) {
         };
       }
       return new Scalar() {
-        public void execute(Context context, Object[] results) {
+        @Override public void execute(Context context, Object[] results) {
           results[0] = execute(context);
         }
 
-        public Object execute(Context context) {
+        @Override public Object execute(Context context) {
           switch (node.getKind()) {
           case LITERAL:
             return ((RexLiteral) node).getValueAs(Comparable.class);
@@ -291,11 +291,11 @@ private ListSink(ArrayDeque<Row> list) {
       this.list = list;
     }
 
-    public void send(Row row) throws InterruptedException {
+    @Override public void send(Row row) throws InterruptedException {
       list.add(row);
     }
 
-    public void end() throws InterruptedException {
+    @Override public void end() throws InterruptedException {
     }
 
     @SuppressWarnings("deprecation")
@@ -319,7 +319,7 @@ private static class ListSource implements Source {
       this.list = list;
     }
 
-    public Row receive() {
+    @Override public Row receive() {
       try {
         if (iterator == null) {
           iterator = list.iterator();
@@ -344,13 +344,13 @@ private DuplicatingSink(List<ArrayDeque<Row>> queues) {
       this.queues = ImmutableList.copyOf(queues);
     }
 
-    public void send(Row row) throws InterruptedException {
+    @Override public void send(Row row) throws InterruptedException {
       for (ArrayDeque<Row> queue : queues) {
         queue.add(row);
       }
     }
 
-    public void end() throws InterruptedException {
+    @Override public void end() throws InterruptedException {
     }
 
     @SuppressWarnings("deprecation")
@@ -479,7 +479,7 @@ Pair<RelNode, Map<RelNode, NodeInfo>> visitRoot(RelNode p) {
     public void rewrite(RelNode r) {
     }
 
-    public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
+    @Override public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
       if (inputRowType == null) {
         inputRowType = interpreter.dataContext.getTypeFactory().builder()
             .build();
@@ -487,7 +487,7 @@ public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
       return scalarCompiler.compile(nodes, inputRowType);
     }
 
-    public RelDataType combinedRowType(List<RelNode> inputs) {
+    @Override public RelDataType combinedRowType(List<RelNode> inputs) {
       final RelDataTypeFactory.Builder builder =
           interpreter.dataContext.getTypeFactory().builder();
       for (RelNode input : inputs) {
@@ -496,7 +496,7 @@ public RelDataType combinedRowType(List<RelNode> inputs) {
       return builder.build();
     }
 
-    public Source source(RelNode rel, int ordinal) {
+    @Override public Source source(RelNode rel, int ordinal) {
       final RelNode input = getInput(rel, ordinal);
       final Edge edge = new Edge(rel, ordinal);
       final Collection<Edge> edges = outEdges.get(input);
@@ -524,7 +524,7 @@ private RelNode getInput(RelNode rel, int ordinal) {
       return rel.getInput(ordinal);
     }
 
-    public Sink sink(RelNode rel) {
+    @Override public Sink sink(RelNode rel) {
       final Collection<Edge> edges = outEdges.get(rel);
       final Collection<Edge> edges2 = edges.isEmpty()
           ? ImmutableList.of(new Edge(null, 0))
@@ -555,16 +555,16 @@ public Sink sink(RelNode rel) {
       }
     }
 
-    public void enumerable(RelNode rel, Enumerable<Row> rowEnumerable) {
+    @Override public void enumerable(RelNode rel, Enumerable<Row> rowEnumerable) {
       NodeInfo nodeInfo = new NodeInfo(rel, rowEnumerable);
       nodes.put(rel, nodeInfo);
     }
 
-    public Context createContext() {
+    @Override public Context createContext() {
       return new Context(getDataContext());
     }
 
-    public DataContext getDataContext() {
+    @Override public DataContext getDataContext() {
       return interpreter.dataContext;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/Interpreters.java b/core/src/main/java/org/apache/calcite/interpreter/Interpreters.java
index 255c0687918..2ae81a3ca66 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/Interpreters.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/Interpreters.java
@@ -36,11 +36,11 @@ public static ArrayBindable bindable(final RelNode rel) {
       return (ArrayBindable) rel;
     }
     return new ArrayBindable() {
-      public Enumerable<Object[]> bind(DataContext dataContext) {
+      @Override public Enumerable<Object[]> bind(DataContext dataContext) {
         return new Interpreter(dataContext, rel);
       }
 
-      public Class<Object[]> getElementType() {
+      @Override public Class<Object[]> getElementType() {
         return Object[].class;
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/interpreter/JaninoRexCompiler.java b/core/src/main/java/org/apache/calcite/interpreter/JaninoRexCompiler.java
index da95be4efd2..a259683ce46 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/JaninoRexCompiler.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/JaninoRexCompiler.java
@@ -65,7 +65,7 @@ public JaninoRexCompiler(RexBuilder rexBuilder) {
     this.rexBuilder = rexBuilder;
   }
 
-  public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
+  @Override public Scalar compile(List<RexNode> nodes, RelDataType inputRowType) {
     final RexProgramBuilder programBuilder =
         new RexProgramBuilder(inputRowType, rexBuilder);
     for (RexNode node : nodes) {
diff --git a/core/src/main/java/org/apache/calcite/interpreter/JoinNode.java b/core/src/main/java/org/apache/calcite/interpreter/JoinNode.java
index e7cfdeaddd6..2df06c45b65 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/JoinNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/JoinNode.java
@@ -49,7 +49,7 @@ public JoinNode(Compiler compiler, Join rel) {
 
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
 
     final int fieldCount = rel.getLeft().getRowType().getFieldCount()
         + rel.getRight().getRowType().getFieldCount();
diff --git a/core/src/main/java/org/apache/calcite/interpreter/MatchNode.java b/core/src/main/java/org/apache/calcite/interpreter/MatchNode.java
index 0f98a524964..f330a86038b 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/MatchNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/MatchNode.java
@@ -27,7 +27,7 @@ public class MatchNode extends AbstractSingleNode<Match> {
     super(compiler, rel);
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     Row row;
     while ((row = source.receive()) != null) {
       sink.send(row);
diff --git a/core/src/main/java/org/apache/calcite/interpreter/ProjectNode.java b/core/src/main/java/org/apache/calcite/interpreter/ProjectNode.java
index 8a61f446cfb..dda0d9fe270 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/ProjectNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/ProjectNode.java
@@ -35,7 +35,7 @@ public ProjectNode(Compiler compiler, Project rel) {
     this.context = compiler.createContext();
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     Row row;
     while ((row = source.receive()) != null) {
       context.values = row.getValues();
diff --git a/core/src/main/java/org/apache/calcite/interpreter/SortNode.java b/core/src/main/java/org/apache/calcite/interpreter/SortNode.java
index ae71482a04f..9c4dc3e4f00 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/SortNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/SortNode.java
@@ -36,7 +36,7 @@ public SortNode(Compiler compiler, Sort rel) {
     super(compiler, rel);
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     final int offset =
         rel.offset == null
             ? 0
diff --git a/core/src/main/java/org/apache/calcite/interpreter/Source.java b/core/src/main/java/org/apache/calcite/interpreter/Source.java
index 6606f1974e3..4543e6206b4 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/Source.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/Source.java
@@ -25,5 +25,5 @@ public interface Source extends AutoCloseable {
   /** Reads a row. Null means end of data. */
   Row receive();
 
-  void close();
+  @Override void close();
 }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/TableScanNode.java b/core/src/main/java/org/apache/calcite/interpreter/TableScanNode.java
index a56505fdac2..427f0e6c47e 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/TableScanNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/TableScanNode.java
@@ -63,7 +63,7 @@ private TableScanNode(Compiler compiler, TableScan rel,
     compiler.enumerable(rel, enumerable);
   }
 
-  public void run() {
+  @Override public void run() {
     // nothing to do
   }
 
diff --git a/core/src/main/java/org/apache/calcite/interpreter/UnionNode.java b/core/src/main/java/org/apache/calcite/interpreter/UnionNode.java
index 520130c9812..55fc12a4952 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/UnionNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/UnionNode.java
@@ -45,7 +45,7 @@ public UnionNode(Compiler compiler, Union rel) {
     this.rel = rel;
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     final Set<Row> rows = rel.all ? null : new HashSet<>();
     for (Source source : sources) {
       Row row;
diff --git a/core/src/main/java/org/apache/calcite/interpreter/ValuesNode.java b/core/src/main/java/org/apache/calcite/interpreter/ValuesNode.java
index c7d41721791..ac399a6dfde 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/ValuesNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/ValuesNode.java
@@ -59,7 +59,7 @@ private ImmutableList<Row> createRows(Compiler compiler,
     return rows.build();
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     for (Row row : rows) {
       sink.send(row);
     }
diff --git a/core/src/main/java/org/apache/calcite/interpreter/WindowNode.java b/core/src/main/java/org/apache/calcite/interpreter/WindowNode.java
index 8bd67e2cf0f..c01f97b4c3c 100644
--- a/core/src/main/java/org/apache/calcite/interpreter/WindowNode.java
+++ b/core/src/main/java/org/apache/calcite/interpreter/WindowNode.java
@@ -27,7 +27,7 @@ public class WindowNode extends AbstractSingleNode<Window> {
     super(compiler, rel);
   }
 
-  public void run() throws InterruptedException {
+  @Override public void run() throws InterruptedException {
     Row row;
     while ((row = source.receive()) != null) {
       sink.send(row);
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CachingCalciteSchema.java b/core/src/main/java/org/apache/calcite/jdbc/CachingCalciteSchema.java
index 57494bd4114..23e144552a5 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CachingCalciteSchema.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CachingCalciteSchema.java
@@ -64,35 +64,35 @@ private CachingCalciteSchema(CalciteSchema parent, Schema schema,
         functionMap, functionNames, nullaryFunctionMap, path);
     this.implicitSubSchemaCache =
         new AbstractCached<SubSchemaCache>() {
-          public SubSchemaCache build() {
+          @Override public SubSchemaCache build() {
             return new SubSchemaCache(CachingCalciteSchema.this,
                 CachingCalciteSchema.this.schema.getSubSchemaNames());
           }
         };
     this.implicitTableCache =
         new AbstractCached<NameSet>() {
-          public NameSet build() {
+          @Override public NameSet build() {
             return NameSet.immutableCopyOf(
                 CachingCalciteSchema.this.schema.getTableNames());
           }
         };
     this.implicitFunctionCache =
         new AbstractCached<NameSet>() {
-          public NameSet build() {
+          @Override public NameSet build() {
             return NameSet.immutableCopyOf(
                 CachingCalciteSchema.this.schema.getFunctionNames());
           }
         };
     this.implicitTypeCache =
         new AbstractCached<NameSet>() {
-          public NameSet build() {
+          @Override public NameSet build() {
             return NameSet.immutableCopyOf(
                 CachingCalciteSchema.this.schema.getTypeNames());
           }
         };
   }
 
-  public void setCache(boolean cache) {
+  @Override public void setCache(boolean cache) {
     if (cache == this.cache) {
       return;
     }
@@ -103,11 +103,11 @@ public void setCache(boolean cache) {
     this.cache = cache;
   }
 
-  protected boolean isCacheEnabled() {
+  @Override protected boolean isCacheEnabled() {
     return this.cache;
   }
 
-  protected CalciteSchema getImplicitSubSchema(String schemaName,
+  @Override protected CalciteSchema getImplicitSubSchema(String schemaName,
       boolean caseSensitive) {
     final long now = System.currentTimeMillis();
     final SubSchemaCache subSchemaCache =
@@ -121,14 +121,14 @@ protected CalciteSchema getImplicitSubSchema(String schemaName,
   }
 
   /** Adds a child schema of this schema. */
-  public CalciteSchema add(String name, Schema schema) {
+  @Override public CalciteSchema add(String name, Schema schema) {
     final CalciteSchema calciteSchema =
         new CachingCalciteSchema(this, schema, name);
     subSchemaMap.put(name, calciteSchema);
     return calciteSchema;
   }
 
-  protected TableEntry getImplicitTable(String tableName,
+  @Override protected TableEntry getImplicitTable(String tableName,
       boolean caseSensitive) {
     final long now = System.currentTimeMillis();
     final NameSet implicitTableNames = implicitTableCache.get(now);
@@ -142,7 +142,7 @@ protected TableEntry getImplicitTable(String tableName,
     return null;
   }
 
-  protected TypeEntry getImplicitType(String name, boolean caseSensitive) {
+  @Override protected TypeEntry getImplicitType(String name, boolean caseSensitive) {
     final long now = System.currentTimeMillis();
     final NameSet implicitTypeNames = implicitTypeCache.get(now);
     for (String typeName
@@ -155,7 +155,7 @@ protected TypeEntry getImplicitType(String name, boolean caseSensitive) {
     return null;
   }
 
-  protected void addImplicitSubSchemaToBuilder(
+  @Override protected void addImplicitSubSchemaToBuilder(
       ImmutableSortedMap.Builder<String, CalciteSchema> builder) {
     ImmutableSortedMap<String, CalciteSchema> explicitSubSchemas = builder.build();
     final long now = System.currentTimeMillis();
@@ -169,7 +169,7 @@ protected void addImplicitSubSchemaToBuilder(
     }
   }
 
-  protected void addImplicitTableToBuilder(
+  @Override protected void addImplicitTableToBuilder(
       ImmutableSortedSet.Builder<String> builder) {
     // Add implicit tables, case-sensitive.
     final long now = System.currentTimeMillis();
@@ -177,7 +177,7 @@ protected void addImplicitTableToBuilder(
     builder.addAll(set.iterable());
   }
 
-  protected void addImplicitFunctionsToBuilder(
+  @Override protected void addImplicitFunctionsToBuilder(
       ImmutableList.Builder<Function> builder,
       String name, boolean caseSensitive) {
     // Add implicit functions, case-insensitive.
@@ -191,7 +191,7 @@ protected void addImplicitFunctionsToBuilder(
     }
   }
 
-  protected void addImplicitFuncNamesToBuilder(
+  @Override protected void addImplicitFuncNamesToBuilder(
       ImmutableSortedSet.Builder<String> builder) {
     // Add implicit functions, case-sensitive.
     final long now = System.currentTimeMillis();
@@ -199,14 +199,15 @@ protected void addImplicitFuncNamesToBuilder(
     builder.addAll(set.iterable());
   }
 
-  protected void addImplicitTypeNamesToBuilder(ImmutableSortedSet.Builder<String> builder) {
+  @Override protected void addImplicitTypeNamesToBuilder(
+      ImmutableSortedSet.Builder<String> builder) {
     // Add implicit types, case-sensitive.
     final long now = System.currentTimeMillis();
     final NameSet set = implicitTypeCache.get(now);
     builder.addAll(set.iterable());
   }
 
-  protected void addImplicitTablesBasedOnNullaryFunctionsToBuilder(
+  @Override protected void addImplicitTablesBasedOnNullaryFunctionsToBuilder(
       ImmutableSortedMap.Builder<String, Table> builder) {
     ImmutableSortedMap<String, Table> explicitTables = builder.build();
 
@@ -227,7 +228,7 @@ protected void addImplicitTablesBasedOnNullaryFunctionsToBuilder(
     }
   }
 
-  protected TableEntry getImplicitTableBasedOnNullaryFunction(String tableName,
+  @Override protected TableEntry getImplicitTableBasedOnNullaryFunction(String tableName,
       boolean caseSensitive) {
     final long now = System.currentTimeMillis();
     final NameSet set = implicitFunctionCache.get(now);
@@ -244,7 +245,7 @@ protected TableEntry getImplicitTableBasedOnNullaryFunction(String tableName,
     return null;
   }
 
-  protected CalciteSchema snapshot(CalciteSchema parent, SchemaVersion version) {
+  @Override protected CalciteSchema snapshot(CalciteSchema parent, SchemaVersion version) {
     CalciteSchema snapshot = new CachingCalciteSchema(parent,
         schema.snapshot(version), name, null, tableMap, latticeMap, typeMap,
         functionMap, functionNames, nullaryFunctionMap, getPath());
@@ -297,7 +298,7 @@ private abstract class AbstractCached<T> implements Cached<T> {
     T t;
     boolean built = false;
 
-    public T get(long now) {
+    @Override public T get(long now) {
       if (!CachingCalciteSchema.this.cache) {
         return build();
       }
@@ -308,7 +309,7 @@ public T get(long now) {
       return t;
     }
 
-    public void enable(long now, boolean enabled) {
+    @Override public void enable(long now, boolean enabled) {
       if (!enabled) {
         t = null;
       }
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CalciteConnection.java b/core/src/main/java/org/apache/calcite/jdbc/CalciteConnection.java
index 115d6755076..7706cae4b9b 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CalciteConnection.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CalciteConnection.java
@@ -71,10 +71,10 @@ public interface CalciteConnection extends Connection, QueryProvider {
   Properties getProperties();
 
   // in java.sql.Connection from JDK 1.7, but declare here to allow other JDKs
-  void setSchema(String schema) throws SQLException;
+  @Override void setSchema(String schema) throws SQLException;
 
   // in java.sql.Connection from JDK 1.7, but declare here to allow other JDKs
-  String getSchema() throws SQLException;
+  @Override String getSchema() throws SQLException;
 
   CalciteConnectionConfig config();
 
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CalciteConnectionImpl.java b/core/src/main/java/org/apache/calcite/jdbc/CalciteConnectionImpl.java
index 9c3e7243c2e..3bac79c1c6a 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CalciteConnectionImpl.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CalciteConnectionImpl.java
@@ -151,11 +151,11 @@ CalciteMetaImpl meta() {
     return (CalciteMetaImpl) meta;
   }
 
-  public CalciteConnectionConfig config() {
+  @Override public CalciteConnectionConfig config() {
     return new CalciteConnectionConfigImpl(info);
   }
 
-  public Context createPrepareContext() {
+  @Override public Context createPrepareContext() {
     return new ContextImpl(this);
   }
 
@@ -243,38 +243,38 @@ <T> CalcitePrepare.CalciteSignature<T> parseQuery(
 
   // CalciteConnection methods
 
-  public SchemaPlus getRootSchema() {
+  @Override public SchemaPlus getRootSchema() {
     return rootSchema.plus();
   }
 
-  public JavaTypeFactory getTypeFactory() {
+  @Override public JavaTypeFactory getTypeFactory() {
     return typeFactory;
   }
 
-  public Properties getProperties() {
+  @Override public Properties getProperties() {
     return info;
   }
 
   // QueryProvider methods
 
-  public <T> Queryable<T> createQuery(
+  @Override public <T> Queryable<T> createQuery(
       Expression expression, Class<T> rowType) {
     return new CalciteQueryable<>(this, rowType, expression);
   }
 
-  public <T> Queryable<T> createQuery(Expression expression, Type rowType) {
+  @Override public <T> Queryable<T> createQuery(Expression expression, Type rowType) {
     return new CalciteQueryable<>(this, rowType, expression);
   }
 
-  public <T> T execute(Expression expression, Type type) {
+  @Override public <T> T execute(Expression expression, Type type) {
     return null; // TODO:
   }
 
-  public <T> T execute(Expression expression, Class<T> type) {
+  @Override public <T> T execute(Expression expression, Class<T> type) {
     return null; // TODO:
   }
 
-  public <T> Enumerator<T> executeQuery(Queryable<T> queryable) {
+  @Override public <T> Enumerator<T> executeQuery(Queryable<T> queryable) {
     try {
       CalciteStatement statement = (CalciteStatement) createStatement();
       CalcitePrepare.CalciteSignature<T> signature =
@@ -351,11 +351,11 @@ public CalciteConnection getConnection() {
   private static class CalciteServerImpl implements CalciteServer {
     final Map<Integer, CalciteServerStatement> statementMap = new HashMap<>();
 
-    public void removeStatement(Meta.StatementHandle h) {
+    @Override public void removeStatement(Meta.StatementHandle h) {
       statementMap.remove(h.id);
     }
 
-    public void addStatement(CalciteConnection connection,
+    @Override public void addStatement(CalciteConnection connection,
         Meta.StatementHandle h) {
       final CalciteConnectionImpl c = (CalciteConnectionImpl) connection;
       final CalciteServerStatement previous =
@@ -365,7 +365,7 @@ public void addStatement(CalciteConnection connection,
       }
     }
 
-    public CalciteServerStatement getStatement(Meta.StatementHandle h)
+    @Override public CalciteServerStatement getStatement(Meta.StatementHandle h)
         throws NoSuchStatementException {
       CalciteServerStatement statement = statementMap.get(h.id);
       if (statement == null) {
@@ -445,7 +445,7 @@ static class DataContextImpl implements DataContext {
       map = builder.build();
     }
 
-    public synchronized Object get(String name) {
+    @Override public synchronized Object get(String name) {
       Object o = map.get(name);
       if (o == AvaticaSite.DUMMY_VALUE) {
         return null;
@@ -484,15 +484,15 @@ private SqlAdvisor getSqlAdvisor() {
       return new SqlAdvisor(validator, parserConfig);
     }
 
-    public SchemaPlus getRootSchema() {
+    @Override public SchemaPlus getRootSchema() {
       return rootSchema == null ? null : rootSchema.plus();
     }
 
-    public JavaTypeFactory getTypeFactory() {
+    @Override public JavaTypeFactory getTypeFactory() {
       return typeFactory;
     }
 
-    public QueryProvider getQueryProvider() {
+    @Override public QueryProvider getQueryProvider() {
       return queryProvider;
     }
   }
@@ -511,19 +511,19 @@ static class ContextImpl implements CalcitePrepare.Context {
       this.rootSchema = mutableRootSchema.createSnapshot(schemaVersion);
     }
 
-    public JavaTypeFactory getTypeFactory() {
+    @Override public JavaTypeFactory getTypeFactory() {
       return connection.typeFactory;
     }
 
-    public CalciteSchema getRootSchema() {
+    @Override public CalciteSchema getRootSchema() {
       return rootSchema;
     }
 
-    public CalciteSchema getMutableRootSchema() {
+    @Override public CalciteSchema getMutableRootSchema() {
       return mutableRootSchema;
     }
 
-    public List<String> getDefaultSchemaPath() {
+    @Override public List<String> getDefaultSchemaPath() {
       final String schemaName;
       try {
         schemaName = connection.getSchema();
@@ -535,20 +535,20 @@ public List<String> getDefaultSchemaPath() {
           : ImmutableList.of(schemaName);
     }
 
-    public List<String> getObjectPath() {
+    @Override public List<String> getObjectPath() {
       return null;
     }
 
-    public CalciteConnectionConfig config() {
+    @Override public CalciteConnectionConfig config() {
       return connection.config();
     }
 
-    public DataContext getDataContext() {
+    @Override public DataContext getDataContext() {
       return connection.createDataContext(ImmutableMap.of(),
           rootSchema);
     }
 
-    public RelRunner getRelRunner() {
+    @Override public RelRunner getRelRunner() {
       final RelRunner runner;
       try {
         runner = connection.unwrap(RelRunner.class);
@@ -561,7 +561,7 @@ public RelRunner getRelRunner() {
       return runner;
     }
 
-    public CalcitePrepare.SparkHandler spark() {
+    @Override public CalcitePrepare.SparkHandler spark() {
       final boolean enable = config().spark();
       return CalcitePrepare.Dummy.getSparkHandler(enable);
     }
@@ -570,19 +570,19 @@ public CalcitePrepare.SparkHandler spark() {
   /** Implementation of {@link DataContext} that has few variables and is
    * {@link Serializable}. For Spark. */
   private static class SlimDataContext implements DataContext, Serializable {
-    public SchemaPlus getRootSchema() {
+    @Override public SchemaPlus getRootSchema() {
       return null;
     }
 
-    public JavaTypeFactory getTypeFactory() {
+    @Override public JavaTypeFactory getTypeFactory() {
       return null;
     }
 
-    public QueryProvider getQueryProvider() {
+    @Override public QueryProvider getQueryProvider() {
       return null;
     }
 
-    public Object get(String name) {
+    @Override public Object get(String name) {
       return null;
     }
   }
@@ -599,27 +599,27 @@ static class CalciteServerStatementImpl
       this.connection = Objects.requireNonNull(connection);
     }
 
-    public Context createPrepareContext() {
+    @Override public Context createPrepareContext() {
       return connection.createPrepareContext();
     }
 
-    public CalciteConnection getConnection() {
+    @Override public CalciteConnection getConnection() {
       return connection;
     }
 
-    public void setSignature(Meta.Signature signature) {
+    @Override public void setSignature(Meta.Signature signature) {
       this.signature = signature;
     }
 
-    public Meta.Signature getSignature() {
+    @Override public Meta.Signature getSignature() {
       return signature;
     }
 
-    public Iterator<Object> getResultSet() {
+    @Override public Iterator<Object> getResultSet() {
       return iterator;
     }
 
-    public void setResultSet(Iterator<Object> iterator) {
+    @Override public void setResultSet(Iterator<Object> iterator) {
       this.iterator = iterator;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CalciteFactory.java b/core/src/main/java/org/apache/calcite/jdbc/CalciteFactory.java
index b13e4d76b49..1485d118f9c 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CalciteFactory.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CalciteFactory.java
@@ -37,15 +37,15 @@ protected CalciteFactory(int major, int minor) {
     this.minor = minor;
   }
 
-  public int getJdbcMajorVersion() {
+  @Override public int getJdbcMajorVersion() {
     return major;
   }
 
-  public int getJdbcMinorVersion() {
+  @Override public int getJdbcMinorVersion() {
     return minor;
   }
 
-  public final AvaticaConnection newConnection(
+  @Override public final AvaticaConnection newConnection(
       UnregisteredDriver driver,
       AvaticaFactory factory,
       String url,
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CalciteJdbc41Factory.java b/core/src/main/java/org/apache/calcite/jdbc/CalciteJdbc41Factory.java
index d4ba467c7fe..c71ae842316 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CalciteJdbc41Factory.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CalciteJdbc41Factory.java
@@ -53,20 +53,20 @@ protected CalciteJdbc41Factory(int major, int minor) {
     super(major, minor);
   }
 
-  public CalciteJdbc41Connection newConnection(UnregisteredDriver driver,
+  @Override public CalciteJdbc41Connection newConnection(UnregisteredDriver driver,
       AvaticaFactory factory, String url, Properties info,
       CalciteSchema rootSchema, JavaTypeFactory typeFactory) {
     return new CalciteJdbc41Connection(
         (Driver) driver, factory, url, info, rootSchema, typeFactory);
   }
 
-  public CalciteJdbc41DatabaseMetaData newDatabaseMetaData(
+  @Override public CalciteJdbc41DatabaseMetaData newDatabaseMetaData(
       AvaticaConnection connection) {
     return new CalciteJdbc41DatabaseMetaData(
         (CalciteConnectionImpl) connection);
   }
 
-  public CalciteJdbc41Statement newStatement(AvaticaConnection connection,
+  @Override public CalciteJdbc41Statement newStatement(AvaticaConnection connection,
       Meta.StatementHandle h,
       int resultSetType,
       int resultSetConcurrency,
@@ -78,7 +78,7 @@ public CalciteJdbc41Statement newStatement(AvaticaConnection connection,
         resultSetHoldability);
   }
 
-  public AvaticaPreparedStatement newPreparedStatement(
+  @Override public AvaticaPreparedStatement newPreparedStatement(
       AvaticaConnection connection,
       Meta.StatementHandle h,
       Meta.Signature signature,
@@ -91,7 +91,7 @@ public AvaticaPreparedStatement newPreparedStatement(
         resultSetConcurrency, resultSetHoldability);
   }
 
-  public CalciteResultSet newResultSet(AvaticaStatement statement, QueryState state,
+  @Override public CalciteResultSet newResultSet(AvaticaStatement statement, QueryState state,
       Meta.Signature signature, TimeZone timeZone, Meta.Frame firstFrame)
       throws SQLException {
     final ResultSetMetaData metaData =
@@ -102,7 +102,7 @@ public CalciteResultSet newResultSet(AvaticaStatement statement, QueryState stat
         firstFrame);
   }
 
-  public ResultSetMetaData newResultSetMetaData(AvaticaStatement statement,
+  @Override public ResultSetMetaData newResultSetMetaData(AvaticaStatement statement,
       Meta.Signature signature) {
     return new AvaticaResultSetMetaData(statement, null, signature);
   }
@@ -137,18 +137,18 @@ private static class CalciteJdbc41PreparedStatement
           resultSetHoldability);
     }
 
-    public void setRowId(
+    @Override public void setRowId(
         int parameterIndex,
         RowId x) throws SQLException {
       getSite(parameterIndex).setRowId(x);
     }
 
-    public void setNString(
+    @Override public void setNString(
         int parameterIndex, String value) throws SQLException {
       getSite(parameterIndex).setNString(value);
     }
 
-    public void setNCharacterStream(
+    @Override public void setNCharacterStream(
         int parameterIndex,
         Reader value,
         long length) throws SQLException {
@@ -156,13 +156,13 @@ public void setNCharacterStream(
           .setNCharacterStream(value, length);
     }
 
-    public void setNClob(
+    @Override public void setNClob(
         int parameterIndex,
         NClob value) throws SQLException {
       getSite(parameterIndex).setNClob(value);
     }
 
-    public void setClob(
+    @Override public void setClob(
         int parameterIndex,
         Reader reader,
         long length) throws SQLException {
@@ -170,7 +170,7 @@ public void setClob(
           .setClob(reader, length);
     }
 
-    public void setBlob(
+    @Override public void setBlob(
         int parameterIndex,
         InputStream inputStream,
         long length) throws SQLException {
@@ -178,19 +178,19 @@ public void setBlob(
           .setBlob(inputStream, length);
     }
 
-    public void setNClob(
+    @Override public void setNClob(
         int parameterIndex,
         Reader reader,
         long length) throws SQLException {
       getSite(parameterIndex).setNClob(reader, length);
     }
 
-    public void setSQLXML(
+    @Override public void setSQLXML(
         int parameterIndex, SQLXML xmlObject) throws SQLException {
       getSite(parameterIndex).setSQLXML(xmlObject);
     }
 
-    public void setAsciiStream(
+    @Override public void setAsciiStream(
         int parameterIndex,
         InputStream x,
         long length) throws SQLException {
@@ -198,7 +198,7 @@ public void setAsciiStream(
           .setAsciiStream(x, length);
     }
 
-    public void setBinaryStream(
+    @Override public void setBinaryStream(
         int parameterIndex,
         InputStream x,
         long length) throws SQLException {
@@ -206,7 +206,7 @@ public void setBinaryStream(
           .setBinaryStream(x, length);
     }
 
-    public void setCharacterStream(
+    @Override public void setCharacterStream(
         int parameterIndex,
         Reader reader,
         long length) throws SQLException {
@@ -214,41 +214,41 @@ public void setCharacterStream(
           .setCharacterStream(reader, length);
     }
 
-    public void setAsciiStream(
+    @Override public void setAsciiStream(
         int parameterIndex, InputStream x) throws SQLException {
       getSite(parameterIndex).setAsciiStream(x);
     }
 
-    public void setBinaryStream(
+    @Override public void setBinaryStream(
         int parameterIndex, InputStream x) throws SQLException {
       getSite(parameterIndex).setBinaryStream(x);
     }
 
-    public void setCharacterStream(
+    @Override public void setCharacterStream(
         int parameterIndex, Reader reader) throws SQLException {
       getSite(parameterIndex)
           .setCharacterStream(reader);
     }
 
-    public void setNCharacterStream(
+    @Override public void setNCharacterStream(
         int parameterIndex, Reader value) throws SQLException {
       getSite(parameterIndex)
           .setNCharacterStream(value);
     }
 
-    public void setClob(
+    @Override public void setClob(
         int parameterIndex,
         Reader reader) throws SQLException {
       getSite(parameterIndex).setClob(reader);
     }
 
-    public void setBlob(
+    @Override public void setBlob(
         int parameterIndex, InputStream inputStream) throws SQLException {
       getSite(parameterIndex)
           .setBlob(inputStream);
     }
 
-    public void setNClob(
+    @Override public void setNClob(
         int parameterIndex, Reader reader) throws SQLException {
       getSite(parameterIndex)
           .setNClob(reader);
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CalciteMetaImpl.java b/core/src/main/java/org/apache/calcite/jdbc/CalciteMetaImpl.java
index ccbb2e97b17..320ea5c6a72 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CalciteMetaImpl.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CalciteMetaImpl.java
@@ -193,7 +193,7 @@ private <E> MetaResultSet createResultSet(Enumerable<E> enumerable,
         cursorFactory, Frame.EMPTY);
   }
 
-  protected MetaResultSet createResultSet(
+  @Override protected MetaResultSet createResultSet(
       Map<String, Object> internalParameters, List<ColumnMetaData> columns,
       CursorFactory cursorFactory, final Frame firstFrame) {
     try {
@@ -249,7 +249,7 @@ private ImmutableMap.Builder<DatabaseProperty, Object> addProperty(
     }
   }
 
-  public MetaResultSet getTables(ConnectionHandle ch,
+  @Override public MetaResultSet getTables(ConnectionHandle ch,
       String catalog,
       final Pat schemaPattern,
       final Pat tableNamePattern,
@@ -278,7 +278,7 @@ public MetaResultSet getTables(ConnectionHandle ch,
         "REF_GENERATION");
   }
 
-  public MetaResultSet getTypeInfo(ConnectionHandle ch) {
+  @Override public MetaResultSet getTypeInfo(ConnectionHandle ch) {
     return createResultSet(allTypeInfo(),
         MetaTypeInfo.class,
         "TYPE_NAME",
@@ -301,7 +301,7 @@ public MetaResultSet getTypeInfo(ConnectionHandle ch) {
         "NUM_PREC_RADIX");
   }
 
-  public MetaResultSet getColumns(ConnectionHandle ch,
+  @Override public MetaResultSet getColumns(ConnectionHandle ch,
       String catalog,
       Pat schemaPattern,
       Pat tableNamePattern,
@@ -476,7 +476,8 @@ public Enumerable<MetaColumn> columns(final MetaTable table_) {
         });
   }
 
-  public MetaResultSet getSchemas(ConnectionHandle ch, String catalog, Pat schemaPattern) {
+  @Override public MetaResultSet getSchemas(ConnectionHandle ch, String catalog,
+      Pat schemaPattern) {
     final Predicate1<MetaSchema> schemaMatcher = namedMatcher(schemaPattern);
     return createResultSet(schemas(catalog).where(schemaMatcher),
         MetaSchema.class,
@@ -484,13 +485,13 @@ public MetaResultSet getSchemas(ConnectionHandle ch, String catalog, Pat schemaP
         "TABLE_CATALOG");
   }
 
-  public MetaResultSet getCatalogs(ConnectionHandle ch) {
+  @Override public MetaResultSet getCatalogs(ConnectionHandle ch) {
     return createResultSet(catalogs(),
         MetaCatalog.class,
         "TABLE_CAT");
   }
 
-  public MetaResultSet getTableTypes(ConnectionHandle ch) {
+  @Override public MetaResultSet getTableTypes(ConnectionHandle ch) {
     return createResultSet(tableTypes(),
         MetaTableType.class,
         "TABLE_TYPE");
@@ -676,19 +677,19 @@ private CalcitePrepare.Query<Object> toQuery(
           long updateCount;
           Signature signature;
 
-          public Object getMonitor() {
+          @Override public Object getMonitor() {
             return statement;
           }
 
-          public void clear() throws SQLException {}
+          @Override public void clear() throws SQLException {}
 
-          public void assign(Meta.Signature signature, Meta.Frame firstFrame,
+          @Override public void assign(Meta.Signature signature, Meta.Frame firstFrame,
               long updateCount) throws SQLException {
             this.signature = signature;
             this.updateCount = updateCount;
           }
 
-          public void execute() throws SQLException {
+          @Override public void execute() throws SQLException {
             if (signature.statementType.canUpdate()) {
               final Iterable<Object> iterable =
                   _createIterable(h, signature, ImmutableList.of(),
@@ -720,7 +721,7 @@ public static CalciteConnection connect(CalciteSchema schema,
     return DRIVER.connect(schema, typeFactory);
   }
 
-  public boolean syncResults(StatementHandle h, QueryState state, long offset)
+  @Override public boolean syncResults(StatementHandle h, QueryState state, long offset)
       throws NoSuchStatementException {
     // Doesn't have application in Calcite itself.
     throw new UnsupportedOperationException();
@@ -765,7 +766,7 @@ abstract static class MetadataTable<E> extends AbstractQueryableTable {
       super(clazz);
     }
 
-    public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+    @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
       return ((JavaTypeFactory) typeFactory).createType(elementType);
     }
 
@@ -780,12 +781,12 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
 
     protected abstract Enumerator<E> enumerator(CalciteMetaImpl connection);
 
-    public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+    @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
         SchemaPlus schema, String tableName) {
       return new AbstractTableQueryable<T>(queryProvider, schema, this,
           tableName) {
         @SuppressWarnings("unchecked")
-        public Enumerator<T> enumerator() {
+        @Override public Enumerator<T> enumerator() {
           return (Enumerator<T>) MetadataTable.this.enumerator(
               ((CalciteConnectionImpl) queryProvider).meta());
         }
@@ -814,16 +815,16 @@ static <E> Iterator<E> of(Iterator<E> iterator, long limit) {
       return new LimitIterator<>(iterator, limit);
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return iterator.hasNext() && i < limit;
     }
 
-    public E next() {
+    @Override public E next() {
       ++i;
       return iterator.next();
     }
 
-    public void remove() {
+    @Override public void remove() {
       throw new UnsupportedOperationException();
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CalcitePrepare.java b/core/src/main/java/org/apache/calcite/jdbc/CalcitePrepare.java
index 638f6251992..26e9eeb8b9f 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CalcitePrepare.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CalcitePrepare.java
@@ -209,23 +209,23 @@ public static void pop(Context context) {
     /** Implementation of {@link SparkHandler} that either does nothing or
      * throws for each method. Use this if Spark is not installed. */
     private static class TrivialSparkHandler implements SparkHandler {
-      public RelNode flattenTypes(RelOptPlanner planner, RelNode rootRel,
+      @Override public RelNode flattenTypes(RelOptPlanner planner, RelNode rootRel,
           boolean restructure) {
         return rootRel;
       }
 
-      public void registerRules(RuleSetBuilder builder) {
+      @Override public void registerRules(RuleSetBuilder builder) {
       }
 
-      public boolean enabled() {
+      @Override public boolean enabled() {
         return false;
       }
 
-      public ArrayBindable compile(ClassDeclaration expr, String s) {
+      @Override public ArrayBindable compile(ClassDeclaration expr, String s) {
         throw new UnsupportedOperationException();
       }
 
-      public Object sparkContext() {
+      @Override public Object sparkContext() {
         throw new UnsupportedOperationException();
       }
     }
diff --git a/core/src/main/java/org/apache/calcite/jdbc/CalciteSchema.java b/core/src/main/java/org/apache/calcite/jdbc/CalciteSchema.java
index 88f8f41ca5b..1a3a496e589 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/CalciteSchema.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/CalciteSchema.java
@@ -625,40 +625,40 @@ CalciteSchema calciteSchema() {
       return CalciteSchema.this;
     }
 
-    public SchemaPlus getParentSchema() {
+    @Override public SchemaPlus getParentSchema() {
       return parent == null ? null : parent.plus();
     }
 
-    public String getName() {
+    @Override public String getName() {
       return CalciteSchema.this.getName();
     }
 
-    public boolean isMutable() {
+    @Override public boolean isMutable() {
       return schema.isMutable();
     }
 
-    public void setCacheEnabled(boolean cache) {
+    @Override public void setCacheEnabled(boolean cache) {
       CalciteSchema.this.setCache(cache);
     }
 
-    public boolean isCacheEnabled() {
+    @Override public boolean isCacheEnabled() {
       return CalciteSchema.this.isCacheEnabled();
     }
 
-    public Schema snapshot(SchemaVersion version) {
+    @Override public Schema snapshot(SchemaVersion version) {
       throw new UnsupportedOperationException();
     }
 
-    public Expression getExpression(SchemaPlus parentSchema, String name) {
+    @Override public Expression getExpression(SchemaPlus parentSchema, String name) {
       return schema.getExpression(parentSchema, name);
     }
 
-    public Table getTable(String name) {
+    @Override public Table getTable(String name) {
       final TableEntry entry = CalciteSchema.this.getTable(name, true);
       return entry == null ? null : entry.getTable();
     }
 
-    public NavigableSet<String> getTableNames() {
+    @Override public NavigableSet<String> getTableNames() {
       return CalciteSchema.this.getTableNames();
     }
 
@@ -671,30 +671,30 @@ public NavigableSet<String> getTableNames() {
       return CalciteSchema.this.getTypeNames();
     }
 
-    public Collection<Function> getFunctions(String name) {
+    @Override public Collection<Function> getFunctions(String name) {
       return CalciteSchema.this.getFunctions(name, true);
     }
 
-    public NavigableSet<String> getFunctionNames() {
+    @Override public NavigableSet<String> getFunctionNames() {
       return CalciteSchema.this.getFunctionNames();
     }
 
-    public SchemaPlus getSubSchema(String name) {
+    @Override public SchemaPlus getSubSchema(String name) {
       final CalciteSchema subSchema =
           CalciteSchema.this.getSubSchema(name, true);
       return subSchema == null ? null : subSchema.plus();
     }
 
-    public Set<String> getSubSchemaNames() {
+    @Override public Set<String> getSubSchemaNames() {
       return CalciteSchema.this.getSubSchemaMap().keySet();
     }
 
-    public SchemaPlus add(String name, Schema schema) {
+    @Override public SchemaPlus add(String name, Schema schema) {
       final CalciteSchema calciteSchema = CalciteSchema.this.add(name, schema);
       return calciteSchema.plus();
     }
 
-    public <T> T unwrap(Class<T> clazz) {
+    @Override public <T> T unwrap(Class<T> clazz) {
       if (clazz.isInstance(this)) {
         return clazz.cast(this);
       }
@@ -715,23 +715,23 @@ public <T> T unwrap(Class<T> clazz) {
       throw new ClassCastException("not a " + clazz);
     }
 
-    public void setPath(ImmutableList<ImmutableList<String>> path) {
+    @Override public void setPath(ImmutableList<ImmutableList<String>> path) {
       CalciteSchema.this.path = path;
     }
 
-    public void add(String name, Table table) {
+    @Override public void add(String name, Table table) {
       CalciteSchema.this.add(name, table);
     }
 
-    public void add(String name, Function function) {
+    @Override public void add(String name, Function function) {
       CalciteSchema.this.add(name, function);
     }
 
-    public void add(String name, RelProtoDataType type) {
+    @Override public void add(String name, RelProtoDataType type) {
       CalciteSchema.this.add(name, type);
     }
 
-    public void add(String name, Lattice lattice) {
+    @Override public void add(String name, Lattice lattice) {
       CalciteSchema.this.add(name, lattice);
     }
   }
@@ -750,7 +750,7 @@ public TableEntryImpl(CalciteSchema schema, String name, Table table,
       this.table = Objects.requireNonNull(table);
     }
 
-    public Table getTable() {
+    @Override public Table getTable() {
       return table;
     }
   }
@@ -768,7 +768,7 @@ public TypeEntryImpl(CalciteSchema schema, String name, RelProtoDataType protoDa
       this.protoDataType = protoDataType;
     }
 
-    public RelProtoDataType getType() {
+    @Override public RelProtoDataType getType() {
       return protoDataType;
     }
   }
@@ -787,11 +787,11 @@ public FunctionEntryImpl(CalciteSchema schema, String name,
       this.function = function;
     }
 
-    public Function getFunction() {
+    @Override public Function getFunction() {
       return function;
     }
 
-    public boolean isMaterialization() {
+    @Override public boolean isMaterialization() {
       return function
           instanceof MaterializedViewTable.MaterializedViewTableMacro;
     }
@@ -816,11 +816,11 @@ public LatticeEntryImpl(CalciteSchema schema, String name,
       starTableEntry = schema.add(name, starTable);
     }
 
-    public Lattice getLattice() {
+    @Override public Lattice getLattice() {
       return lattice;
     }
 
-    public TableEntry getStarTable() {
+    @Override public TableEntry getStarTable() {
       return starTableEntry;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/jdbc/JavaTypeFactoryImpl.java b/core/src/main/java/org/apache/calcite/jdbc/JavaTypeFactoryImpl.java
index 8b2c6f686da..9aaef357493 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/JavaTypeFactoryImpl.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/JavaTypeFactoryImpl.java
@@ -70,7 +70,7 @@ public JavaTypeFactoryImpl(RelDataTypeSystem typeSystem) {
     super(typeSystem);
   }
 
-  public RelDataType createStructType(Class type) {
+  @Override public RelDataType createStructType(Class type) {
     final List<RelDataTypeField> list = new ArrayList<>();
     for (Field field : type.getFields()) {
       if (!Modifier.isStatic(field.getModifiers())) {
@@ -108,7 +108,7 @@ private Type fieldType(Field field) {
     return klass;
   }
 
-  public RelDataType createType(Type type) {
+  @Override public RelDataType createType(Type type) {
     if (type instanceof RelDataType) {
       return (RelDataType) type;
     }
@@ -160,7 +160,7 @@ public RelDataType createType(Type type) {
     }
   }
 
-  public Type getJavaClass(RelDataType type) {
+  @Override public Type getJavaClass(RelDataType type) {
     if (type instanceof JavaType) {
       JavaType javaType = (JavaType) type;
       return javaType.getJavaClass();
@@ -235,7 +235,7 @@ public Type getJavaClass(RelDataType type) {
     return null;
   }
 
-  public RelDataType toSql(RelDataType type) {
+  @Override public RelDataType toSql(RelDataType type) {
     return toSql(this, type);
   }
 
@@ -284,7 +284,7 @@ private static RelDataType toSqlTypeWithNullToAny(
     return toSql(typeFactory, type);
   }
 
-  public Type createSyntheticType(List<Type> types) {
+  @Override public Type createSyntheticType(List<Type> types) {
     if (types.isEmpty()) {
       // Unit is a pre-defined synthetic type to be used when there are 0
       // fields. Because all instances are the same, we use a singleton.
@@ -310,13 +310,13 @@ private SyntheticRecordType register(
       final SyntheticRecordType syntheticType) {
     final List<Pair<Type, Boolean>> key =
         new AbstractList<Pair<Type, Boolean>>() {
-          public Pair<Type, Boolean> get(int index) {
+          @Override public Pair<Type, Boolean> get(int index) {
             final Types.RecordField field =
                 syntheticType.getRecordFields().get(index);
             return Pair.of(field.getType(), field.nullable());
           }
 
-          public int size() {
+          @Override public int size() {
             return syntheticType.getRecordFields().size();
           }
         };
@@ -364,15 +364,15 @@ private SyntheticRecordType(RelDataType relType, String name) {
           : "field names not distinct: " + relType;
     }
 
-    public String getName() {
+    @Override public String getName() {
       return name;
     }
 
-    public List<Types.RecordField> getRecordFields() {
+    @Override public List<Types.RecordField> getRecordFields() {
       return fields;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return name;
     }
   }
@@ -400,27 +400,27 @@ private static class RecordFieldImpl implements Types.RecordField {
           : "type [" + type + "] can never be null";
     }
 
-    public Type getType() {
+    @Override public Type getType() {
       return type;
     }
 
-    public String getName() {
+    @Override public String getName() {
       return name;
     }
 
-    public int getModifiers() {
+    @Override public int getModifiers() {
       return modifiers;
     }
 
-    public boolean nullable() {
+    @Override public boolean nullable() {
       return nullable;
     }
 
-    public Object get(Object o) {
+    @Override public Object get(Object o) {
       throw new UnsupportedOperationException();
     }
 
-    public Type getDeclaringClass() {
+    @Override public Type getDeclaringClass() {
       return syntheticType;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/jdbc/MetadataSchema.java b/core/src/main/java/org/apache/calcite/jdbc/MetadataSchema.java
index 6f7664f7782..000c7180c7c 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/MetadataSchema.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/MetadataSchema.java
@@ -35,7 +35,7 @@ class MetadataSchema extends AbstractSchema {
       ImmutableMap.of(
           "COLUMNS",
           new CalciteMetaImpl.MetadataTable<MetaColumn>(MetaColumn.class) {
-            public Enumerator<MetaColumn> enumerator(
+            @Override public Enumerator<MetaColumn> enumerator(
                 final CalciteMetaImpl meta) {
               final String catalog;
               try {
@@ -49,7 +49,7 @@ public Enumerator<MetaColumn> enumerator(
           },
           "TABLES",
           new CalciteMetaImpl.MetadataTable<MetaTable>(MetaTable.class) {
-            public Enumerator<MetaTable> enumerator(CalciteMetaImpl meta) {
+            @Override public Enumerator<MetaTable> enumerator(CalciteMetaImpl meta) {
               final String catalog;
               try {
                 catalog = meta.getConnection().getCatalog();
diff --git a/core/src/main/java/org/apache/calcite/jdbc/SimpleCalciteSchema.java b/core/src/main/java/org/apache/calcite/jdbc/SimpleCalciteSchema.java
index 7e50886cf1f..ab08915b408 100644
--- a/core/src/main/java/org/apache/calcite/jdbc/SimpleCalciteSchema.java
+++ b/core/src/main/java/org/apache/calcite/jdbc/SimpleCalciteSchema.java
@@ -56,18 +56,18 @@ private SimpleCalciteSchema(CalciteSchema parent, Schema schema,
         functionMap, functionNames, nullaryFunctionMap, path);
   }
 
-  public void setCache(boolean cache) {
+  @Override public void setCache(boolean cache) {
     throw new UnsupportedOperationException();
   }
 
-  public CalciteSchema add(String name, Schema schema) {
+  @Override public CalciteSchema add(String name, Schema schema) {
     final CalciteSchema calciteSchema =
         new SimpleCalciteSchema(this, schema, name);
     subSchemaMap.put(name, calciteSchema);
     return calciteSchema;
   }
 
-  protected CalciteSchema getImplicitSubSchema(String schemaName,
+  @Override protected CalciteSchema getImplicitSubSchema(String schemaName,
       boolean caseSensitive) {
     // Check implicit schemas.
     Schema s = schema.getSubSchema(schemaName);
@@ -77,7 +77,7 @@ protected CalciteSchema getImplicitSubSchema(String schemaName,
     return null;
   }
 
-  protected TableEntry getImplicitTable(String tableName,
+  @Override protected TableEntry getImplicitTable(String tableName,
       boolean caseSensitive) {
     // Check implicit tables.
     Table table = schema.getTable(tableName);
@@ -87,7 +87,7 @@ protected TableEntry getImplicitTable(String tableName,
     return null;
   }
 
-  protected TypeEntry getImplicitType(String name, boolean caseSensitive) {
+  @Override protected TypeEntry getImplicitType(String name, boolean caseSensitive) {
     // Check implicit types.
     RelProtoDataType type = schema.getType(name);
     if (type != null) {
@@ -96,7 +96,7 @@ protected TypeEntry getImplicitType(String name, boolean caseSensitive) {
     return null;
   }
 
-  protected void addImplicitSubSchemaToBuilder(
+  @Override protected void addImplicitSubSchemaToBuilder(
       ImmutableSortedMap.Builder<String, CalciteSchema> builder) {
     ImmutableSortedMap<String, CalciteSchema> explicitSubSchemas = builder.build();
     for (String schemaName : schema.getSubSchemaNames()) {
@@ -112,11 +112,11 @@ protected void addImplicitSubSchemaToBuilder(
     }
   }
 
-  protected void addImplicitTableToBuilder(ImmutableSortedSet.Builder<String> builder) {
+  @Override protected void addImplicitTableToBuilder(ImmutableSortedSet.Builder<String> builder) {
     builder.addAll(schema.getTableNames());
   }
 
-  protected void addImplicitFunctionsToBuilder(
+  @Override protected void addImplicitFunctionsToBuilder(
       ImmutableList.Builder<Function> builder,
       String name, boolean caseSensitive) {
     Collection<Function> functions = schema.getFunctions(name);
@@ -125,7 +125,8 @@ protected void addImplicitFunctionsToBuilder(
     }
   }
 
-  protected void addImplicitFuncNamesToBuilder(ImmutableSortedSet.Builder<String> builder) {
+  @Override protected void addImplicitFuncNamesToBuilder(
+      ImmutableSortedSet.Builder<String> builder) {
     builder.addAll(schema.getFunctionNames());
   }
 
@@ -134,7 +135,7 @@ protected void addImplicitFuncNamesToBuilder(ImmutableSortedSet.Builder<String>
     builder.addAll(schema.getTypeNames());
   }
 
-  protected void addImplicitTablesBasedOnNullaryFunctionsToBuilder(
+  @Override protected void addImplicitTablesBasedOnNullaryFunctionsToBuilder(
       ImmutableSortedMap.Builder<String, Table> builder) {
     ImmutableSortedMap<String, Table> explicitTables = builder.build();
 
@@ -153,7 +154,7 @@ protected void addImplicitTablesBasedOnNullaryFunctionsToBuilder(
     }
   }
 
-  protected TableEntry getImplicitTableBasedOnNullaryFunction(String tableName,
+  @Override protected TableEntry getImplicitTableBasedOnNullaryFunction(String tableName,
       boolean caseSensitive) {
     Collection<Function> functions = schema.getFunctions(tableName);
     if (functions != null) {
@@ -168,7 +169,7 @@ protected TableEntry getImplicitTableBasedOnNullaryFunction(String tableName,
     return null;
   }
 
-  protected CalciteSchema snapshot(CalciteSchema parent, SchemaVersion version) {
+  @Override protected CalciteSchema snapshot(CalciteSchema parent, SchemaVersion version) {
     CalciteSchema snapshot = new SimpleCalciteSchema(parent,
         schema.snapshot(version), name, null, tableMap, latticeMap, typeMap,
         functionMap, functionNames, nullaryFunctionMap, getPath());
@@ -179,7 +180,7 @@ protected CalciteSchema snapshot(CalciteSchema parent, SchemaVersion version) {
     return snapshot;
   }
 
-  protected boolean isCacheEnabled() {
+  @Override protected boolean isCacheEnabled() {
     return false;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/materialize/CachingLatticeStatisticProvider.java b/core/src/main/java/org/apache/calcite/materialize/CachingLatticeStatisticProvider.java
index 544cba28d3b..5b20859537b 100644
--- a/core/src/main/java/org/apache/calcite/materialize/CachingLatticeStatisticProvider.java
+++ b/core/src/main/java/org/apache/calcite/materialize/CachingLatticeStatisticProvider.java
@@ -44,7 +44,7 @@ class CachingLatticeStatisticProvider implements LatticeStatisticProvider {
         CacheLoader.from(key -> provider.cardinality(ImmutableList.of(key))));
   }
 
-  public double cardinality(List<Lattice.Column> columns) {
+  @Override public double cardinality(List<Lattice.Column> columns) {
     final List<Double> counts = new ArrayList<>();
     for (Lattice.Column column : columns) {
       try {
diff --git a/core/src/main/java/org/apache/calcite/materialize/DelegatingLatticeStatisticProvider.java b/core/src/main/java/org/apache/calcite/materialize/DelegatingLatticeStatisticProvider.java
index 0a36e8a53e8..f928fbef037 100644
--- a/core/src/main/java/org/apache/calcite/materialize/DelegatingLatticeStatisticProvider.java
+++ b/core/src/main/java/org/apache/calcite/materialize/DelegatingLatticeStatisticProvider.java
@@ -35,7 +35,7 @@ protected DelegatingLatticeStatisticProvider(
     this.provider = provider;
   }
 
-  public double cardinality(List<Lattice.Column> columns) {
+  @Override public double cardinality(List<Lattice.Column> columns) {
     return provider.cardinality(columns);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/materialize/Lattice.java b/core/src/main/java/org/apache/calcite/materialize/Lattice.java
index 3f16f8c507b..2be85d2f0df 100644
--- a/core/src/main/java/org/apache/calcite/materialize/Lattice.java
+++ b/core/src/main/java/org/apache/calcite/materialize/Lattice.java
@@ -571,7 +571,7 @@ public Measure(SqlAggFunction agg, boolean distinct, @Nullable String name,
       this.digest = b.toString();
     }
 
-    public int compareTo(@Nonnull Measure measure) {
+    @Override public int compareTo(@Nonnull Measure measure) {
       int c = compare(args, measure.args);
       if (c == 0) {
         c = agg.getName().compareTo(measure.agg.getName());
@@ -655,7 +655,7 @@ static ImmutableBitSet toBitSet(List<Column> columns) {
       return builder.build();
     }
 
-    public int compareTo(Column column) {
+    @Override public int compareTo(Column column) {
       return Utilities.compare(ordinal, column.ordinal);
     }
 
@@ -700,11 +700,11 @@ public List<String> identifiers() {
       return ImmutableList.of(table, column);
     }
 
-    public void toSql(SqlWriter writer) {
+    @Override public void toSql(SqlWriter writer) {
       writer.dialect.quoteIdentifier(writer.buf, identifiers());
     }
 
-    public String defaultAlias() {
+    @Override public String defaultAlias() {
       return column;
     }
   }
@@ -725,11 +725,11 @@ private DerivedColumn(int ordinal, String alias, RexNode e,
       return Arrays.toString(new Object[] {e, alias});
     }
 
-    public void toSql(SqlWriter writer) {
+    @Override public void toSql(SqlWriter writer) {
       writer.write(e);
     }
 
-    public String defaultAlias() {
+    @Override public String defaultAlias() {
       // there is no default alias for an expression
       return null;
     }
diff --git a/core/src/main/java/org/apache/calcite/materialize/LatticeChildNode.java b/core/src/main/java/org/apache/calcite/materialize/LatticeChildNode.java
index 5f394a956ad..2782cb81cde 100644
--- a/core/src/main/java/org/apache/calcite/materialize/LatticeChildNode.java
+++ b/core/src/main/java/org/apache/calcite/materialize/LatticeChildNode.java
@@ -35,7 +35,7 @@ public class LatticeChildNode extends LatticeNode {
     this.link = ImmutableList.copyOf(mutableNode.step.keys);
   }
 
-  void use(List<LatticeNode> usedNodes) {
+  @Override void use(List<LatticeNode> usedNodes) {
     if (!usedNodes.contains(this)) {
       parent.use(usedNodes);
       usedNodes.add(this);
diff --git a/core/src/main/java/org/apache/calcite/materialize/LatticeRootNode.java b/core/src/main/java/org/apache/calcite/materialize/LatticeRootNode.java
index aef86d2e142..607b882de7b 100644
--- a/core/src/main/java/org/apache/calcite/materialize/LatticeRootNode.java
+++ b/core/src/main/java/org/apache/calcite/materialize/LatticeRootNode.java
@@ -46,7 +46,7 @@ private ImmutableList<Path> createPaths(LatticeSpace space) {
     return ImmutableList.copyOf(paths);
   }
 
-  void use(List<LatticeNode> usedNodes) {
+  @Override void use(List<LatticeNode> usedNodes) {
     if (!usedNodes.contains(this)) {
       usedNodes.add(this);
     }
diff --git a/core/src/main/java/org/apache/calcite/materialize/LatticeSuggester.java b/core/src/main/java/org/apache/calcite/materialize/LatticeSuggester.java
index 06f08047571..bae862e88e4 100644
--- a/core/src/main/java/org/apache/calcite/materialize/LatticeSuggester.java
+++ b/core/src/main/java/org/apache/calcite/materialize/LatticeSuggester.java
@@ -433,7 +433,7 @@ private Frame frame(final Query q, RelNode r) {
       }
       final int fieldCount = r.getRowType().getFieldCount();
       return new Frame(fieldCount, h.hops, measures, ImmutableList.of(h)) {
-        ColRef column(int offset) {
+        @Override ColRef column(int offset) {
           if (offset < aggregate.getGroupSet().cardinality()) {
             return h.column(aggregate.getGroupSet().nth(offset));
           }
@@ -459,7 +459,7 @@ ColRef column(int offset) {
           columns = columnBuilder.build();
         }
 
-        ColRef column(int offset) {
+        @Override ColRef column(int offset) {
           return columns.get(offset);
         }
 
@@ -515,7 +515,7 @@ private ColRef toColRef(RexNode e, String alias) {
       return new Frame(fieldCount, builder.build(),
           CompositeList.of(left.measures, right.measures),
           ImmutableList.of(left, right)) {
-        ColRef column(int offset) {
+        @Override ColRef column(int offset) {
           if (offset < leftCount) {
             return left.column(offset);
           } else {
@@ -529,7 +529,7 @@ ColRef column(int offset) {
       final int fieldCount = r.getRowType().getFieldCount();
       return new Frame(fieldCount, ImmutableList.of(),
           ImmutableList.of(), ImmutableSet.of(tableRef)) {
-        ColRef column(int offset) {
+        @Override ColRef column(int offset) {
           if (offset >= scan.getTable().getRowType().getFieldCount()) {
             throw new IndexOutOfBoundsException("field " + offset
                 + " out of range in " + scan.getTable().getRowType());
@@ -627,17 +627,17 @@ private TableRef(LatticeTable table, int ordinalInQuery) {
       this.ordinalInQuery = ordinalInQuery;
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       return ordinalInQuery;
     }
 
-    public boolean equals(Object obj) {
+    @Override public boolean equals(Object obj) {
       return this == obj
           || obj instanceof TableRef
           && ordinalInQuery == ((TableRef) obj).ordinalInQuery;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return table + ":" + ordinalInQuery;
     }
   }
@@ -680,11 +680,11 @@ TableRef target() {
     private static class Factory
         implements AttributedDirectedGraph.AttributedEdgeFactory<
             TableRef, StepRef> {
-      public StepRef createEdge(TableRef source, TableRef target) {
+      @Override public StepRef createEdge(TableRef source, TableRef target) {
         throw new UnsupportedOperationException();
       }
 
-      public StepRef createEdge(TableRef source, TableRef target,
+      @Override public StepRef createEdge(TableRef source, TableRef target,
             Object... attributes) {
         final Step step = (Step) attributes[0];
         final Integer ordinalInQuery = (Integer) attributes[1];
@@ -753,11 +753,11 @@ private BaseColRef(TableRef t, int c) {
       this.c = c;
     }
 
-    public TableRef tableRef() {
+    @Override public TableRef tableRef() {
       return t;
     }
 
-    public int col(LatticeSpace space) {
+    @Override public int col(LatticeSpace space) {
       return c;
     }
   }
@@ -787,11 +787,11 @@ private static class SingleTableDerivedColRef extends DerivedColRef
       super(ImmutableList.of(tableRef), e, alias);
     }
 
-    public TableRef tableRef() {
+    @Override public TableRef tableRef() {
       return tableRefs.get(0);
     }
 
-    public int col(LatticeSpace space) {
+    @Override public int col(LatticeSpace space) {
       return space.registerExpression(tableRef().table, e);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/materialize/MaterializationService.java b/core/src/main/java/org/apache/calcite/materialize/MaterializationService.java
index 90c5791170a..17f9a169d9f 100644
--- a/core/src/main/java/org/apache/calcite/materialize/MaterializationService.java
+++ b/core/src/main/java/org/apache/calcite/materialize/MaterializationService.java
@@ -358,7 +358,7 @@ Table createTable(CalciteSchema schema, String viewSql,
    * Creates a table using {@link CloneSchema}.
    */
   public static class DefaultTableFactory implements TableFactory {
-    public Table createTable(CalciteSchema schema, String viewSql,
+    @Override public Table createTable(CalciteSchema schema, String viewSql,
         List<String> viewSchemaPath) {
       final CalciteConnection connection =
           CalciteMetaImpl.connect(schema.root(), null);
@@ -372,26 +372,26 @@ public Table createTable(CalciteSchema schema, String viewSql,
           calciteSignature.getCollationList(),
           Util.transform(calciteSignature.columns, column -> column.type.rep),
           new AbstractQueryable<Object>() {
-            public Enumerator<Object> enumerator() {
+            @Override public Enumerator<Object> enumerator() {
               final DataContext dataContext =
                   Schemas.createDataContext(connection,
                       calciteSignature.rootSchema.plus());
               return calciteSignature.enumerable(dataContext).enumerator();
             }
 
-            public Type getElementType() {
+            @Override public Type getElementType() {
               return Object.class;
             }
 
-            public Expression getExpression() {
+            @Override public Expression getExpression() {
               throw new UnsupportedOperationException();
             }
 
-            public QueryProvider getProvider() {
+            @Override public QueryProvider getProvider() {
               return connection;
             }
 
-            public Iterator<Object> iterator() {
+            @Override public Iterator<Object> iterator() {
               final DataContext dataContext =
                   Schemas.createDataContext(connection,
                       calciteSignature.rootSchema.plus());
diff --git a/core/src/main/java/org/apache/calcite/materialize/MutableNode.java b/core/src/main/java/org/apache/calcite/materialize/MutableNode.java
index 48822701267..cc7b971b1a9 100644
--- a/core/src/main/java/org/apache/calcite/materialize/MutableNode.java
+++ b/core/src/main/java/org/apache/calcite/materialize/MutableNode.java
@@ -43,7 +43,7 @@ class MutableNode {
   static final Ordering<MutableNode> ORDERING =
       Ordering.from(
           new Comparator<MutableNode>() {
-            public int compare(MutableNode o1, MutableNode o2) {
+            @Override public int compare(MutableNode o1, MutableNode o2) {
               int c = Ordering.<String>natural().lexicographical().compare(
                   o1.table.t.getQualifiedName(), o2.table.t.getQualifiedName());
               if (c == 0) {
diff --git a/core/src/main/java/org/apache/calcite/materialize/ProfilerLatticeStatisticProvider.java b/core/src/main/java/org/apache/calcite/materialize/ProfilerLatticeStatisticProvider.java
index d22f56f8056..51dc46deb3e 100644
--- a/core/src/main/java/org/apache/calcite/materialize/ProfilerLatticeStatisticProvider.java
+++ b/core/src/main/java/org/apache/calcite/materialize/ProfilerLatticeStatisticProvider.java
@@ -78,7 +78,7 @@ private ProfilerLatticeStatisticProvider(Lattice lattice) {
     })::get;
   }
 
-  public double cardinality(List<Lattice.Column> columns) {
+  @Override public double cardinality(List<Lattice.Column> columns) {
     final ImmutableBitSet build = Lattice.Column.toBitSet(columns);
     final double cardinality = profile.get().cardinality(build);
 //    System.out.println(columns + ": " + cardinality);
diff --git a/core/src/main/java/org/apache/calcite/materialize/SqlLatticeStatisticProvider.java b/core/src/main/java/org/apache/calcite/materialize/SqlLatticeStatisticProvider.java
index 34df02d7e76..21802ad3828 100644
--- a/core/src/main/java/org/apache/calcite/materialize/SqlLatticeStatisticProvider.java
+++ b/core/src/main/java/org/apache/calcite/materialize/SqlLatticeStatisticProvider.java
@@ -46,7 +46,7 @@ private SqlLatticeStatisticProvider(Lattice lattice) {
     this.lattice = Objects.requireNonNull(lattice);
   }
 
-  public double cardinality(List<Lattice.Column> columns) {
+  @Override public double cardinality(List<Lattice.Column> columns) {
     final List<Double> counts = new ArrayList<>();
     for (Lattice.Column column : columns) {
       counts.add(cardinality(lattice, column));
diff --git a/core/src/main/java/org/apache/calcite/materialize/Step.java b/core/src/main/java/org/apache/calcite/materialize/Step.java
index 8c8fa8f446f..33e0c8e8e46 100644
--- a/core/src/main/java/org/apache/calcite/materialize/Step.java
+++ b/core/src/main/java/org/apache/calcite/materialize/Step.java
@@ -144,11 +144,11 @@ static class Factory implements AttributedDirectedGraph.AttributedEdgeFactory<
       this.space = Objects.requireNonNull(space);
     }
 
-    public Step createEdge(LatticeTable source, LatticeTable target) {
+    @Override public Step createEdge(LatticeTable source, LatticeTable target) {
       throw new UnsupportedOperationException();
     }
 
-    public Step createEdge(LatticeTable source, LatticeTable target,
+    @Override public Step createEdge(LatticeTable source, LatticeTable target,
         Object... attributes) {
       @SuppressWarnings("unchecked") final List<IntPair> keys =
           (List) attributes[0];
diff --git a/core/src/main/java/org/apache/calcite/materialize/TileSuggester.java b/core/src/main/java/org/apache/calcite/materialize/TileSuggester.java
index eb5680f62da..5ab233cbb45 100644
--- a/core/src/main/java/org/apache/calcite/materialize/TileSuggester.java
+++ b/core/src/main/java/org/apache/calcite/materialize/TileSuggester.java
@@ -101,31 +101,31 @@ private static class SchemaImpl implements Schema {
       this.attributes = attributeBuilder.build();
     }
 
-    public List<? extends Table> getTables() {
+    @Override public List<? extends Table> getTables() {
       return ImmutableList.of(table);
     }
 
-    public List<Measure> getMeasures() {
+    @Override public List<Measure> getMeasures() {
       throw new UnsupportedOperationException();
     }
 
-    public List<? extends Dimension> getDimensions() {
+    @Override public List<? extends Dimension> getDimensions() {
       throw new UnsupportedOperationException();
     }
 
-    public List<? extends Attribute> getAttributes() {
+    @Override public List<? extends Attribute> getAttributes() {
       return attributes;
     }
 
-    public StatisticsProvider getStatisticsProvider() {
+    @Override public StatisticsProvider getStatisticsProvider() {
       return statisticsProvider;
     }
 
-    public Dialect getDialect() {
+    @Override public Dialect getDialect() {
       throw new UnsupportedOperationException();
     }
 
-    public String generateAggregateSql(Aggregate aggregate,
+    @Override public String generateAggregateSql(Aggregate aggregate,
         List<String> columnNameList) {
       throw new UnsupportedOperationException();
     }
@@ -135,11 +135,11 @@ public String generateAggregateSql(Aggregate aggregate,
    * There is only one table (in this sense of table) in a lattice.
    * The algorithm does not really care about tables. */
   private static class TableImpl implements Table {
-    public String getLabel() {
+    @Override public String getLabel() {
       return "TABLE";
     }
 
-    public Table getParent() {
+    @Override public Table getParent() {
       return null;
     }
   }
@@ -158,27 +158,27 @@ private AttributeImpl(Lattice.Column column, TableImpl table) {
       return getLabel();
     }
 
-    public String getLabel() {
+    @Override public String getLabel() {
       return column.alias;
     }
 
-    public Table getTable() {
+    @Override public Table getTable() {
       return table;
     }
 
-    public double estimateSpace() {
+    @Override public double estimateSpace() {
       return 0;
     }
 
-    public String getCandidateColumnName() {
+    @Override public String getCandidateColumnName() {
       return null;
     }
 
-    public String getDatatype(Dialect dialect) {
+    @Override public String getDatatype(Dialect dialect) {
       return null;
     }
 
-    public List<Attribute> getAncestorAttributes() {
+    @Override public List<Attribute> getAncestorAttributes() {
       return ImmutableList.of();
     }
   }
@@ -192,20 +192,20 @@ private static class StatisticsProviderImpl implements StatisticsProvider {
       this.lattice = lattice;
     }
 
-    public double getFactRowCount() {
+    @Override public double getFactRowCount() {
       return lattice.getFactRowCount();
     }
 
-    public double getRowCount(List<Attribute> attributes) {
+    @Override public double getRowCount(List<Attribute> attributes) {
       return lattice.getRowCount(
           Util.transform(attributes, input -> ((AttributeImpl) input).column));
     }
 
-    public double getSpace(List<Attribute> attributes) {
+    @Override public double getSpace(List<Attribute> attributes) {
       return attributes.size();
     }
 
-    public double getLoadTime(List<Attribute> attributes) {
+    @Override public double getLoadTime(List<Attribute> attributes) {
       return getSpace(attributes) * getRowCount(attributes);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/model/JsonCustomSchema.java b/core/src/main/java/org/apache/calcite/model/JsonCustomSchema.java
index 36cea82424f..1491a02656e 100644
--- a/core/src/main/java/org/apache/calcite/model/JsonCustomSchema.java
+++ b/core/src/main/java/org/apache/calcite/model/JsonCustomSchema.java
@@ -41,7 +41,7 @@ public class JsonCustomSchema extends JsonMapSchema {
    */
   public Map<String, Object> operand;
 
-  public void accept(ModelHandler handler) {
+  @Override public void accept(ModelHandler handler) {
     handler.visit(this);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/model/JsonCustomTable.java b/core/src/main/java/org/apache/calcite/model/JsonCustomTable.java
index 09d01042d59..2bbab55c613 100644
--- a/core/src/main/java/org/apache/calcite/model/JsonCustomTable.java
+++ b/core/src/main/java/org/apache/calcite/model/JsonCustomTable.java
@@ -41,7 +41,7 @@ public class JsonCustomTable extends JsonTable {
    */
   public Map<String, Object> operand;
 
-  public void accept(ModelHandler handler) {
+  @Override public void accept(ModelHandler handler) {
     handler.visit(this);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/model/JsonView.java b/core/src/main/java/org/apache/calcite/model/JsonView.java
index 90467d1ec83..c2547bd6676 100644
--- a/core/src/main/java/org/apache/calcite/model/JsonView.java
+++ b/core/src/main/java/org/apache/calcite/model/JsonView.java
@@ -82,7 +82,7 @@ public class JsonView extends JsonTable {
    */
   public Boolean modifiable;
 
-  public void accept(ModelHandler handler) {
+  @Override public void accept(ModelHandler handler) {
     handler.visit(this);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/plan/AbstractRelOptPlanner.java b/core/src/main/java/org/apache/calcite/plan/AbstractRelOptPlanner.java
index b8428420a34..ed7b9179e83 100644
--- a/core/src/main/java/org/apache/calcite/plan/AbstractRelOptPlanner.java
+++ b/core/src/main/java/org/apache/calcite/plan/AbstractRelOptPlanner.java
@@ -113,18 +113,18 @@ protected AbstractRelOptPlanner(RelOptCostFactory costFactory,
 
   //~ Methods ----------------------------------------------------------------
 
-  public void clear() {}
+  @Override public void clear() {}
 
-  public Context getContext() {
+  @Override public Context getContext() {
     return context;
   }
 
-  public RelOptCostFactory getCostFactory() {
+  @Override public RelOptCostFactory getCostFactory() {
     return costFactory;
   }
 
   @SuppressWarnings("deprecation")
-  public void setCancelFlag(CancelFlag cancelFlag) {
+  @Override public void setCancelFlag(CancelFlag cancelFlag) {
     // ignored
   }
 
@@ -138,11 +138,11 @@ public void checkCancel() {
     }
   }
 
-  public List<RelOptRule> getRules() {
+  @Override public List<RelOptRule> getRules() {
     return ImmutableList.copyOf(mapDescToRule.values());
   }
 
-  public boolean addRule(RelOptRule rule) {
+  @Override public boolean addRule(RelOptRule rule) {
     // Check that there isn't a rule with the same description
     final String description = rule.toString();
     assert description != null;
@@ -162,7 +162,7 @@ public boolean addRule(RelOptRule rule) {
     return true;
   }
 
-  public boolean removeRule(RelOptRule rule) {
+  @Override public boolean removeRule(RelOptRule rule) {
     String description = rule.toString();
     RelOptRule removed = mapDescToRule.remove(description);
     return removed != null;
@@ -178,7 +178,7 @@ protected RelOptRule getRuleByDescription(String description) {
     return mapDescToRule.get(description);
   }
 
-  public void setRuleDescExclusionFilter(Pattern exclusionFilter) {
+  @Override public void setRuleDescExclusionFilter(Pattern exclusionFilter) {
     ruleDescExclusionFilter = exclusionFilter;
   }
 
@@ -193,38 +193,38 @@ public boolean isRuleExcluded(RelOptRule rule) {
         && ruleDescExclusionFilter.matcher(rule.toString()).matches();
   }
 
-  public RelOptPlanner chooseDelegate() {
+  @Override public RelOptPlanner chooseDelegate() {
     return this;
   }
 
-  public void addMaterialization(RelOptMaterialization materialization) {
+  @Override public void addMaterialization(RelOptMaterialization materialization) {
     // ignore - this planner does not support materializations
   }
 
-  public List<RelOptMaterialization> getMaterializations() {
+  @Override public List<RelOptMaterialization> getMaterializations() {
     return ImmutableList.of();
   }
 
-  public void addLattice(RelOptLattice lattice) {
+  @Override public void addLattice(RelOptLattice lattice) {
     // ignore - this planner does not support lattices
   }
 
-  public RelOptLattice getLattice(RelOptTable table) {
+  @Override public RelOptLattice getLattice(RelOptTable table) {
     // this planner does not support lattices
     return null;
   }
 
-  public void registerSchema(RelOptSchema schema) {
+  @Override public void registerSchema(RelOptSchema schema) {
   }
 
-  public long getRelMetadataTimestamp(RelNode rel) {
+  @Override public long getRelMetadataTimestamp(RelNode rel) {
     return 0;
   }
 
   @Override public void prune(RelNode rel) {
   }
 
-  public void registerClass(RelNode node) {
+  @Override public void registerClass(RelNode node) {
     final Class<? extends RelNode> clazz = node.getClass();
     if (classes.add(clazz)) {
       onNewClass(node);
@@ -239,49 +239,49 @@ protected void onNewClass(RelNode node) {
     node.register(this);
   }
 
-  public RelTraitSet emptyTraitSet() {
+  @Override public RelTraitSet emptyTraitSet() {
     return RelTraitSet.createEmpty();
   }
 
-  public RelOptCost getCost(RelNode rel, RelMetadataQuery mq) {
+  @Override public RelOptCost getCost(RelNode rel, RelMetadataQuery mq) {
     return mq.getCumulativeCost(rel);
   }
 
-  @SuppressWarnings("deprecation")
+  @Override @SuppressWarnings("deprecation")
   public RelOptCost getCost(RelNode rel) {
     final RelMetadataQuery mq = rel.getCluster().getMetadataQuery();
     return getCost(rel, mq);
   }
 
-  public void addListener(RelOptListener newListener) {
+  @Override public void addListener(RelOptListener newListener) {
     if (listener == null) {
       listener = new MulticastRelOptListener();
     }
     listener.addListener(newListener);
   }
 
-  public void registerMetadataProviders(List<RelMetadataProvider> list) {
+  @Override public void registerMetadataProviders(List<RelMetadataProvider> list) {
   }
 
-  public boolean addRelTraitDef(RelTraitDef relTraitDef) {
+  @Override public boolean addRelTraitDef(RelTraitDef relTraitDef) {
     return false;
   }
 
-  public void clearRelTraitDefs() {}
+  @Override public void clearRelTraitDefs() {}
 
-  public List<RelTraitDef> getRelTraitDefs() {
+  @Override public List<RelTraitDef> getRelTraitDefs() {
     return ImmutableList.of();
   }
 
-  public void setExecutor(RexExecutor executor) {
+  @Override public void setExecutor(RexExecutor executor) {
     this.executor = executor;
   }
 
-  public RexExecutor getExecutor() {
+  @Override public RexExecutor getExecutor() {
     return executor;
   }
 
-  public void onCopy(RelNode rel, RelNode newRel) {
+  @Override public void onCopy(RelNode rel, RelNode newRel) {
     // do nothing
   }
 
diff --git a/core/src/main/java/org/apache/calcite/plan/Contexts.java b/core/src/main/java/org/apache/calcite/plan/Contexts.java
index 05343d86330..ebcd34ad341 100644
--- a/core/src/main/java/org/apache/calcite/plan/Contexts.java
+++ b/core/src/main/java/org/apache/calcite/plan/Contexts.java
@@ -118,7 +118,7 @@ private static class WrapContext implements Context {
       this.target = Objects.requireNonNull(target);
     }
 
-    public <T> T unwrap(Class<T> clazz) {
+    @Override public <T> T unwrap(Class<T> clazz) {
       if (clazz.isInstance(target)) {
         return clazz.cast(target);
       }
@@ -128,7 +128,7 @@ public <T> T unwrap(Class<T> clazz) {
 
   /** Empty context. */
   static class EmptyContext implements Context {
-    public <T> T unwrap(Class<T> clazz) {
+    @Override public <T> T unwrap(Class<T> clazz) {
       return null;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/plan/Convention.java b/core/src/main/java/org/apache/calcite/plan/Convention.java
index 61cf9f12ee2..75915ae0f3a 100644
--- a/core/src/main/java/org/apache/calcite/plan/Convention.java
+++ b/core/src/main/java/org/apache/calcite/plan/Convention.java
@@ -104,21 +104,21 @@ public Impl(String name, Class<? extends RelNode> relClass) {
       return getName();
     }
 
-    public void register(RelOptPlanner planner) {}
+    @Override public void register(RelOptPlanner planner) {}
 
-    public boolean satisfies(RelTrait trait) {
+    @Override public boolean satisfies(RelTrait trait) {
       return this == trait;
     }
 
-    public Class getInterface() {
+    @Override public Class getInterface() {
       return relClass;
     }
 
-    public String getName() {
+    @Override public String getName() {
       return name;
     }
 
-    public RelTraitDef getTraitDef() {
+    @Override public RelTraitDef getTraitDef() {
       return ConventionTraitDef.INSTANCE;
     }
 
@@ -127,11 +127,11 @@ public RelTraitDef getTraitDef() {
       return null;
     }
 
-    public boolean canConvertConvention(Convention toConvention) {
+    @Override public boolean canConvertConvention(Convention toConvention) {
       return false;
     }
 
-    public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
+    @Override public boolean useAbstractConvertersForConversion(RelTraitSet fromTraits,
         RelTraitSet toTraits) {
       return false;
     }
diff --git a/core/src/main/java/org/apache/calcite/plan/ConventionTraitDef.java b/core/src/main/java/org/apache/calcite/plan/ConventionTraitDef.java
index d38d296ad0c..218ca09a42c 100644
--- a/core/src/main/java/org/apache/calcite/plan/ConventionTraitDef.java
+++ b/core/src/main/java/org/apache/calcite/plan/ConventionTraitDef.java
@@ -70,19 +70,19 @@ private ConventionTraitDef() {
   //~ Methods ----------------------------------------------------------------
 
   // implement RelTraitDef
-  public Class<Convention> getTraitClass() {
+  @Override public Class<Convention> getTraitClass() {
     return Convention.class;
   }
 
-  public String getSimpleName() {
+  @Override public String getSimpleName() {
     return "convention";
   }
 
-  public Convention getDefault() {
+  @Override public Convention getDefault() {
     return Convention.NONE;
   }
 
-  public void registerConverterRule(
+  @Override public void registerConverterRule(
       RelOptPlanner planner,
       ConverterRule converterRule) {
     if (converterRule.isGuaranteed()) {
@@ -101,7 +101,7 @@ public void registerConverterRule(
     }
   }
 
-  public void deregisterConverterRule(
+  @Override public void deregisterConverterRule(
       RelOptPlanner planner,
       ConverterRule converterRule) {
     if (converterRule.isGuaranteed()) {
@@ -122,7 +122,7 @@ public void deregisterConverterRule(
   }
 
   // implement RelTraitDef
-  public RelNode convert(
+  @Override public RelNode convert(
       RelOptPlanner planner,
       RelNode rel,
       Convention toConvention,
@@ -191,7 +191,7 @@ private RelNode changeConvention(
     return null;
   }
 
-  public boolean canConvert(
+  @Override public boolean canConvert(
       RelOptPlanner planner,
       Convention fromConvention,
       Convention toConvention) {
diff --git a/core/src/main/java/org/apache/calcite/plan/MulticastRelOptListener.java b/core/src/main/java/org/apache/calcite/plan/MulticastRelOptListener.java
index e707bbd7c50..af194f79758 100644
--- a/core/src/main/java/org/apache/calcite/plan/MulticastRelOptListener.java
+++ b/core/src/main/java/org/apache/calcite/plan/MulticastRelOptListener.java
@@ -49,35 +49,35 @@ public void addListener(RelOptListener listener) {
   }
 
   // implement RelOptListener
-  public void relEquivalenceFound(RelEquivalenceEvent event) {
+  @Override public void relEquivalenceFound(RelEquivalenceEvent event) {
     for (RelOptListener listener : listeners) {
       listener.relEquivalenceFound(event);
     }
   }
 
   // implement RelOptListener
-  public void ruleAttempted(RuleAttemptedEvent event) {
+  @Override public void ruleAttempted(RuleAttemptedEvent event) {
     for (RelOptListener listener : listeners) {
       listener.ruleAttempted(event);
     }
   }
 
   // implement RelOptListener
-  public void ruleProductionSucceeded(RuleProductionEvent event) {
+  @Override public void ruleProductionSucceeded(RuleProductionEvent event) {
     for (RelOptListener listener : listeners) {
       listener.ruleProductionSucceeded(event);
     }
   }
 
   // implement RelOptListener
-  public void relChosen(RelChosenEvent event) {
+  @Override public void relChosen(RelChosenEvent event) {
     for (RelOptListener listener : listeners) {
       listener.relChosen(event);
     }
   }
 
   // implement RelOptListener
-  public void relDiscarded(RelDiscardedEvent event) {
+  @Override public void relDiscarded(RelDiscardedEvent event) {
     for (RelOptListener listener : listeners) {
       listener.relDiscarded(event);
     }
diff --git a/core/src/main/java/org/apache/calcite/plan/RelCompositeTrait.java b/core/src/main/java/org/apache/calcite/plan/RelCompositeTrait.java
index ac8c705e314..8bb4efdd52d 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelCompositeTrait.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelCompositeTrait.java
@@ -70,7 +70,7 @@ static <T extends RelMultipleTrait> RelTrait of(RelTraitDef def,
     return def.canonize(compositeTrait);
   }
 
-  public RelTraitDef getTraitDef() {
+  @Override public RelTraitDef getTraitDef() {
     return traitDef;
   }
 
@@ -88,7 +88,7 @@ public RelTraitDef getTraitDef() {
     return Arrays.toString(traits);
   }
 
-  public boolean satisfies(RelTrait trait) {
+  @Override public boolean satisfies(RelTrait trait) {
     for (T t : traits) {
       if (t.satisfies(trait)) {
         return true;
@@ -97,7 +97,7 @@ public boolean satisfies(RelTrait trait) {
     return false;
   }
 
-  public void register(RelOptPlanner planner) {
+  @Override public void register(RelOptPlanner planner) {
   }
 
   /** Returns an immutable list of the traits in this composite trait. */
diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptAbstractTable.java b/core/src/main/java/org/apache/calcite/plan/RelOptAbstractTable.java
index ebee046a9cb..aae8ee42545 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptAbstractTable.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptAbstractTable.java
@@ -61,66 +61,66 @@ public String getName() {
     return name;
   }
 
-  public List<String> getQualifiedName() {
+  @Override public List<String> getQualifiedName() {
     return ImmutableList.of(name);
   }
 
-  public double getRowCount() {
+  @Override public double getRowCount() {
     return 100;
   }
 
-  public RelDataType getRowType() {
+  @Override public RelDataType getRowType() {
     return rowType;
   }
 
-  public RelOptSchema getRelOptSchema() {
+  @Override public RelOptSchema getRelOptSchema() {
     return schema;
   }
 
   // Override to define collations.
-  public List<RelCollation> getCollationList() {
+  @Override public List<RelCollation> getCollationList() {
     return Collections.emptyList();
   }
 
-  public RelDistribution getDistribution() {
+  @Override public RelDistribution getDistribution() {
     return RelDistributions.BROADCAST_DISTRIBUTED;
   }
 
-  public <T> T unwrap(Class<T> clazz) {
+  @Override public <T> T unwrap(Class<T> clazz) {
     return clazz.isInstance(this)
         ? clazz.cast(this)
         : null;
   }
 
   // Override to define keys
-  public boolean isKey(ImmutableBitSet columns) {
+  @Override public boolean isKey(ImmutableBitSet columns) {
     return false;
   }
 
   // Override to get unique keys
-  public List<ImmutableBitSet> getKeys() {
+  @Override public List<ImmutableBitSet> getKeys() {
     return Collections.emptyList();
   }
 
   // Override to define foreign keys
-  public List<RelReferentialConstraint> getReferentialConstraints() {
+  @Override public List<RelReferentialConstraint> getReferentialConstraints() {
     return Collections.emptyList();
   }
 
-  public RelNode toRel(ToRelContext context) {
+  @Override public RelNode toRel(ToRelContext context) {
     return LogicalTableScan.create(context.getCluster(), this,
         context.getTableHints());
   }
 
-  public Expression getExpression(Class clazz) {
+  @Override public Expression getExpression(Class clazz) {
     return null;
   }
 
-  public RelOptTable extend(List<RelDataTypeField> extendedFields) {
+  @Override public RelOptTable extend(List<RelDataTypeField> extendedFields) {
     throw new UnsupportedOperationException();
   }
 
-  public List<ColumnStrategy> getColumnStrategies() {
+  @Override public List<ColumnStrategy> getColumnStrategies() {
     return RelOptTableImpl.columnStrategies(this);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptCost.java b/core/src/main/java/org/apache/calcite/plan/RelOptCost.java
index 331d2abb08a..d963253e8bf 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptCost.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptCost.java
@@ -122,5 +122,5 @@ public interface RelOptCost {
    * Forces implementations to override {@link Object#toString} and provide a
    * good cost rendering to use during tracing.
    */
-  String toString();
+  @Override String toString();
 }
diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptCostImpl.java b/core/src/main/java/org/apache/calcite/plan/RelOptCostImpl.java
index 2ed57bd5d28..11f540aa989 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptCostImpl.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptCostImpl.java
@@ -38,32 +38,32 @@ public RelOptCostImpl(double value) {
   //~ Methods ----------------------------------------------------------------
 
   // implement RelOptCost
-  public double getRows() {
+  @Override public double getRows() {
     return value;
   }
 
   // implement RelOptCost
-  public double getIo() {
+  @Override public double getIo() {
     return 0;
   }
 
   // implement RelOptCost
-  public double getCpu() {
+  @Override public double getCpu() {
     return 0;
   }
 
   // implement RelOptCost
-  public boolean isInfinite() {
+  @Override public boolean isInfinite() {
     return Double.isInfinite(value);
   }
 
   // implement RelOptCost
-  public boolean isLe(RelOptCost other) {
+  @Override public boolean isLe(RelOptCost other) {
     return getRows() <= other.getRows();
   }
 
   // implement RelOptCost
-  public boolean isLt(RelOptCost other) {
+  @Override public boolean isLt(RelOptCost other) {
     return getRows() < other.getRows();
   }
 
@@ -72,7 +72,7 @@ public boolean isLt(RelOptCost other) {
   }
 
   // implement RelOptCost
-  public boolean equals(RelOptCost other) {
+  @Override public boolean equals(RelOptCost other) {
     return getRows() == other.getRows();
   }
 
@@ -84,32 +84,32 @@ public boolean equals(RelOptCost other) {
   }
 
   // implement RelOptCost
-  public boolean isEqWithEpsilon(RelOptCost other) {
+  @Override public boolean isEqWithEpsilon(RelOptCost other) {
     return Math.abs(getRows() - other.getRows()) < RelOptUtil.EPSILON;
   }
 
   // implement RelOptCost
-  public RelOptCost minus(RelOptCost other) {
+  @Override public RelOptCost minus(RelOptCost other) {
     return new RelOptCostImpl(getRows() - other.getRows());
   }
 
   // implement RelOptCost
-  public RelOptCost plus(RelOptCost other) {
+  @Override public RelOptCost plus(RelOptCost other) {
     return new RelOptCostImpl(getRows() + other.getRows());
   }
 
   // implement RelOptCost
-  public RelOptCost multiplyBy(double factor) {
+  @Override public RelOptCost multiplyBy(double factor) {
     return new RelOptCostImpl(getRows() * factor);
   }
 
-  public double divideBy(RelOptCost cost) {
+  @Override public double divideBy(RelOptCost cost) {
     RelOptCostImpl that = (RelOptCostImpl) cost;
     return this.getRows() / that.getRows();
   }
 
   // implement RelOptCost
-  public String toString() {
+  @Override public String toString() {
     if (value == Double.MAX_VALUE) {
       return "huge";
     } else {
@@ -121,7 +121,7 @@ public String toString() {
    * {@link RelOptCostImpl}s. */
   private static class Factory implements RelOptCostFactory {
     // implement RelOptPlanner
-    public RelOptCost makeCost(
+    @Override public RelOptCost makeCost(
         double dRows,
         double dCpu,
         double dIo) {
@@ -129,22 +129,22 @@ public RelOptCost makeCost(
     }
 
     // implement RelOptPlanner
-    public RelOptCost makeHugeCost() {
+    @Override public RelOptCost makeHugeCost() {
       return new RelOptCostImpl(Double.MAX_VALUE);
     }
 
     // implement RelOptPlanner
-    public RelOptCost makeInfiniteCost() {
+    @Override public RelOptCost makeInfiniteCost() {
       return new RelOptCostImpl(Double.POSITIVE_INFINITY);
     }
 
     // implement RelOptPlanner
-    public RelOptCost makeTinyCost() {
+    @Override public RelOptCost makeTinyCost() {
       return new RelOptCostImpl(1.0);
     }
 
     // implement RelOptPlanner
-    public RelOptCost makeZeroCost() {
+    @Override public RelOptCost makeZeroCost() {
       return new RelOptCostImpl(0.0);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptRule.java b/core/src/main/java/org/apache/calcite/plan/RelOptRule.java
index b06f0f46ef1..ce4d101bea8 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptRule.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptRule.java
@@ -455,7 +455,7 @@ public List<RelOptRuleOperand> getOperands() {
     return ImmutableList.copyOf(operands);
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     // Conventionally, hashCode() and equals() should use the same
     // criteria, whereas here we only look at the description. This is
     // okay, because the planner requires all rule instances to have
@@ -463,7 +463,7 @@ public int hashCode() {
     return description.hashCode();
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     return (obj instanceof RelOptRule)
         && equals((RelOptRule) obj);
   }
@@ -570,7 +570,7 @@ public RelTrait getOutTrait() {
    * <p>It must be unique (for rules that are not equal) and must consist of
    * only the characters A-Z, a-z, 0-9, '_', '.', '(', ')', '-', ',', '[', ']', ':', ' '.
    * It must start with a letter. */
-  public final String toString() {
+  @Override public final String toString() {
     return description;
   }
 
@@ -678,7 +678,7 @@ <R extends RelNode> ConverterRelOptRuleOperand(Class<R> clazz, RelTrait in,
           ImmutableList.of());
     }
 
-    public boolean matches(RelNode rel) {
+    @Override public boolean matches(RelNode rel) {
       // Don't apply converters to converters that operate
       // on the same RelTraitDef -- otherwise we get
       // an n^2 effect.
diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptRuleOperand.java b/core/src/main/java/org/apache/calcite/plan/RelOptRuleOperand.java
index 75dfc51e441..3db199922fb 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptRuleOperand.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptRuleOperand.java
@@ -166,11 +166,11 @@ public void setRule(RelOptRule rule) {
     this.rule = rule;
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return Objects.hash(clazz, trait, children);
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (this == obj) {
       return true;
     }
diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java b/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java
index 60803026938..ed83d724ae1 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java
@@ -3103,7 +3103,7 @@ public static boolean contains(RelNode ancestor, final RelNode target) {
     }
     try {
       new RelVisitor() {
-        public void visit(RelNode node, int ordinal, RelNode parent) {
+        @Override public void visit(RelNode node, int ordinal, RelNode parent) {
           if (node == target) {
             throw Util.FoundOne.NULL;
           }
@@ -3263,11 +3263,11 @@ public static RelNode createRename(
     assert fieldNames.size() == fields.size();
     final List<RexNode> refs =
         new AbstractList<RexNode>() {
-          public int size() {
+          @Override public int size() {
             return fields.size();
           }
 
-          public RexNode get(int index) {
+          @Override public RexNode get(int index) {
             return RexInputRef.of(index, fields);
           }
         };
@@ -3377,11 +3377,11 @@ public static RelNode createProject(final RelFactories.ProjectFactory factory,
     final RelBuilder relBuilder =
         RelBuilder.proto(factory).create(child.getCluster(), null);
     final List<RexNode> exprs = new AbstractList<RexNode>() {
-      public int size() {
+      @Override public int size() {
         return posList.size();
       }
 
-      public RexNode get(int index) {
+      @Override public RexNode get(int index) {
         final int pos = posList.get(index);
         return relBuilder.getRexBuilder().makeInputRef(child, pos);
       }
@@ -3540,11 +3540,11 @@ public static RelNode pushDownJoinConditions(Join originalJoin,
           relBuilder.peek().getRowType().getFieldList();
       final List<Pair<RexNode, String>> pairs =
           new AbstractList<Pair<RexNode, String>>() {
-            public int size() {
+            @Override public int size() {
               return leftCount + extraLeftExprs.size();
             }
 
-            public Pair<RexNode, String> get(int index) {
+            @Override public Pair<RexNode, String> get(int index) {
               if (index < leftCount) {
                 RelDataTypeField field = fields.get(index);
                 return Pair.of(
@@ -3564,11 +3564,11 @@ public Pair<RexNode, String> get(int index) {
       final int newLeftCount = leftCount + extraLeftExprs.size();
       final List<Pair<RexNode, String>> pairs =
           new AbstractList<Pair<RexNode, String>>() {
-            public int size() {
+            @Override public int size() {
               return rightCount + extraRightExprs.size();
             }
 
-            public Pair<RexNode, String> get(int index) {
+            @Override public Pair<RexNode, String> get(int index) {
               if (index < rightCount) {
                 RelDataTypeField field = fields.get(index);
                 return Pair.of(
@@ -3855,7 +3855,7 @@ private static class RelHintPropagateShuttle extends RelHomogeneousShuttle {
     /**
      * Visits a particular child of a parent.
      */
-    protected RelNode visitChild(RelNode parent, int i, RelNode child) {
+    @Override protected RelNode visitChild(RelNode parent, int i, RelNode child) {
       inheritPaths.forEach(inheritPath -> inheritPath.right.push(i));
       try {
         RelNode child2 = child.accept(this);
@@ -3870,7 +3870,7 @@ protected RelNode visitChild(RelNode parent, int i, RelNode child) {
       }
     }
 
-    public RelNode visit(RelNode other) {
+    @Override public RelNode visit(RelNode other) {
       if (other instanceof Hintable) {
         return visitHintable(other);
       } else {
@@ -3989,7 +3989,7 @@ private static class SubTreeHintPropagateShuttle extends RelHomogeneousShuttle {
     /**
      * Visits a particular child of a parent.
      */
-    protected RelNode visitChild(RelNode parent, int i, RelNode child) {
+    @Override protected RelNode visitChild(RelNode parent, int i, RelNode child) {
       appendPath.add(i);
       try {
         RelNode child2 = child.accept(this);
@@ -4005,7 +4005,7 @@ protected RelNode visitChild(RelNode parent, int i, RelNode child) {
       }
     }
 
-    public RelNode visit(RelNode other) {
+    @Override public RelNode visit(RelNode other) {
       if (this.appendPath.size() > 3) {
         // Returns early if the visiting depth is bigger than 3
         return other;
@@ -4087,7 +4087,7 @@ private static RelHint copyWithAppendPath(RelHint hint,
    * </ul>
    */
   private static class ResetHintsShuttle extends RelHomogeneousShuttle {
-    public RelNode visit(RelNode node) {
+    @Override public RelNode visit(RelNode node) {
       node = visitChildren(node);
       if (node instanceof Hintable) {
         node = resetHints((Hintable) node);
@@ -4112,7 +4112,7 @@ private static class VariableSetVisitor extends RelVisitor {
     final Set<CorrelationId> variables = new HashSet<>();
 
     // implement RelVisitor
-    public void visit(
+    @Override public void visit(
         RelNode p,
         int ordinal,
         RelNode parent) {
@@ -4163,7 +4163,7 @@ public VariableUsedVisitor(RelShuttle relShuttle) {
   public static class InputReferencedVisitor extends RexShuttle {
     public final SortedSet<Integer> inputPosReferenced = new TreeSet<>();
 
-    public RexNode visitInputRef(RexInputRef inputRef) {
+    @Override public RexNode visitInputRef(RexInputRef inputRef) {
       inputPosReferenced.add(inputRef.getIndex());
       return inputRef;
     }
@@ -4283,7 +4283,7 @@ public ImmutableBitSet build() {
       return bitBuilder.build();
     }
 
-    public Void visitInputRef(RexInputRef inputRef) {
+    @Override public Void visitInputRef(RexInputRef inputRef) {
       bitBuilder.set(inputRef.getIndex());
       return null;
     }
@@ -4383,7 +4383,7 @@ public RexInputConverter(
       this(rexBuilder, srcFields, null, null, null, adjustments);
     }
 
-    public RexNode visitInputRef(RexInputRef var) {
+    @Override public RexNode visitInputRef(RexInputRef var) {
       int srcIndex = var.getIndex();
       int destIndex = srcIndex + adjustments[srcIndex];
 
diff --git a/core/src/main/java/org/apache/calcite/plan/RelRule.java b/core/src/main/java/org/apache/calcite/plan/RelRule.java
index edf62de515b..0390ae0cd85 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelRule.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelRule.java
@@ -227,11 +227,11 @@ static RelOptRuleOperand operand(OperandTransform transform) {
       return b.operands.get(0);
     }
 
-    public <R extends RelNode> OperandDetailBuilder<R> operand(Class<R> relClass) {
+    @Override public <R extends RelNode> OperandDetailBuilder<R> operand(Class<R> relClass) {
       return new OperandDetailBuilderImpl<>(this, relClass);
     }
 
-    public Done exactly(RelOptRuleOperand operand) {
+    @Override public Done exactly(RelOptRuleOperand operand) {
       operands.add(operand);
       return DoneImpl.INSTANCE;
     }
@@ -253,12 +253,12 @@ private static class OperandDetailBuilderImpl<R extends RelNode>
       this.relClass = Objects.requireNonNull(relClass);
     }
 
-    public OperandDetailBuilderImpl<R> trait(@Nonnull RelTrait trait) {
+    @Override public OperandDetailBuilderImpl<R> trait(@Nonnull RelTrait trait) {
       this.trait = Objects.requireNonNull(trait);
       return this;
     }
 
-    public OperandDetailBuilderImpl<R> predicate(Predicate<? super R> predicate) {
+    @Override public OperandDetailBuilderImpl<R> predicate(Predicate<? super R> predicate) {
       this.predicate = predicate;
       return this;
     }
@@ -271,27 +271,27 @@ Done done(RelOptRuleOperandChildPolicy childPolicy) {
       return DoneImpl.INSTANCE;
     }
 
-    public Done convert(RelTrait in) {
+    @Override public Done convert(RelTrait in) {
       parent.operands.add(
           new ConverterRelOptRuleOperand(relClass, in, predicate));
       return DoneImpl.INSTANCE;
     }
 
-    public Done noInputs() {
+    @Override public Done noInputs() {
       return done(RelOptRuleOperandChildPolicy.LEAF);
     }
 
-    public Done anyInputs() {
+    @Override public Done anyInputs() {
       return done(RelOptRuleOperandChildPolicy.ANY);
     }
 
-    public Done oneInput(OperandTransform transform) {
+    @Override public Done oneInput(OperandTransform transform) {
       final Done done = transform.apply(inputBuilder);
       Objects.requireNonNull(done);
       return done(RelOptRuleOperandChildPolicy.SOME);
     }
 
-    public Done inputs(OperandTransform... transforms) {
+    @Override public Done inputs(OperandTransform... transforms) {
       for (OperandTransform transform : transforms) {
         final Done done = transform.apply(inputBuilder);
         Objects.requireNonNull(done);
@@ -299,7 +299,7 @@ public Done inputs(OperandTransform... transforms) {
       return done(RelOptRuleOperandChildPolicy.SOME);
     }
 
-    public Done unorderedInputs(OperandTransform... transforms) {
+    @Override public Done unorderedInputs(OperandTransform... transforms) {
       for (OperandTransform transform : transforms) {
         final Done done = transform.apply(inputBuilder);
         Objects.requireNonNull(done);
diff --git a/core/src/main/java/org/apache/calcite/plan/RelTrait.java b/core/src/main/java/org/apache/calcite/plan/RelTrait.java
index 37440a275c9..aa70ddd9f8a 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelTrait.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelTrait.java
@@ -48,12 +48,12 @@ public interface RelTrait {
   /**
    * See <a href="#EqualsHashCodeNote">note about equals() and hashCode()</a>.
    */
-  int hashCode();
+  @Override int hashCode();
 
   /**
    * See <a href="#EqualsHashCodeNote">note about equals() and hashCode()</a>.
    */
-  boolean equals(Object o);
+  @Override boolean equals(Object o);
 
   /**
    * Returns whether this trait satisfies a given trait.
@@ -78,7 +78,7 @@ public interface RelTrait {
    * Returns a succinct name for this trait. The planner may use this String
    * to describe the trait.
    */
-  String toString();
+  @Override String toString();
 
   /**
    * Registers a trait instance with the planner.
diff --git a/core/src/main/java/org/apache/calcite/plan/RelTraitPropagationVisitor.java b/core/src/main/java/org/apache/calcite/plan/RelTraitPropagationVisitor.java
index 080f28324ba..1474ad002d6 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelTraitPropagationVisitor.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelTraitPropagationVisitor.java
@@ -55,7 +55,7 @@ public RelTraitPropagationVisitor(
 
   //~ Methods ----------------------------------------------------------------
 
-  public void visit(RelNode rel, int ordinal, RelNode parent) {
+  @Override public void visit(RelNode rel, int ordinal, RelNode parent) {
     // REVIEW: SWZ: 1/31/06: We assume that any special RelNodes, such
     // as the VolcanoPlanner's RelSubset always have a full complement
     // of traits and that they either appear as registered or do nothing
diff --git a/core/src/main/java/org/apache/calcite/plan/RelTraitSet.java b/core/src/main/java/org/apache/calcite/plan/RelTraitSet.java
index 8e4766a5a15..9ea5323fa76 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelTraitSet.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelTraitSet.java
@@ -105,7 +105,7 @@ public <E extends RelMultipleTrait> List<E> getTraits(int index) {
     }
   }
 
-  public RelTrait get(int index) {
+  @Override public RelTrait get(int index) {
     return getTrait(index);
   }
 
@@ -393,7 +393,7 @@ public <T extends RelCollation> T getCollation() {
    *
    * @return the size of the RelTraitSet.
    */
-  public int size() {
+  @Override public int size() {
     return traits.length;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/plan/RexImplicationChecker.java b/core/src/main/java/org/apache/calcite/plan/RexImplicationChecker.java
index 2a94e612624..62fd4d7991f 100644
--- a/core/src/main/java/org/apache/calcite/plan/RexImplicationChecker.java
+++ b/core/src/main/java/org/apache/calcite/plan/RexImplicationChecker.java
@@ -436,7 +436,7 @@ private static class InputUsageFinder extends RexVisitorImpl<Void> {
       super(true);
     }
 
-    public Void visitInputRef(RexInputRef inputRef) {
+    @Override public Void visitInputRef(RexInputRef inputRef) {
       InputRefUsage<SqlOperator, RexNode> inputRefUse = getUsageMap(inputRef);
       inputRefUse.usageCount++;
       return null;
diff --git a/core/src/main/java/org/apache/calcite/plan/Strong.java b/core/src/main/java/org/apache/calcite/plan/Strong.java
index 057935e905c..52b7f2686e1 100644
--- a/core/src/main/java/org/apache/calcite/plan/Strong.java
+++ b/core/src/main/java/org/apache/calcite/plan/Strong.java
@@ -136,7 +136,7 @@ public static boolean isStrong(RexNode e) {
     final ImmutableBitSet.Builder nullColumns = ImmutableBitSet.builder();
     e.accept(
         new RexVisitorImpl<Void>(true) {
-          public Void visitInputRef(RexInputRef inputRef) {
+          @Override public Void visitInputRef(RexInputRef inputRef) {
             nullColumns.set(inputRef.getIndex());
             return super.visitInputRef(inputRef);
           }
diff --git a/core/src/main/java/org/apache/calcite/plan/SubstitutionVisitor.java b/core/src/main/java/org/apache/calcite/plan/SubstitutionVisitor.java
index c27394a932d..68321d682a1 100644
--- a/core/src/main/java/org/apache/calcite/plan/SubstitutionVisitor.java
+++ b/core/src/main/java/org/apache/calcite/plan/SubstitutionVisitor.java
@@ -203,7 +203,7 @@ public SubstitutionVisitor(RelNode target_, RelNode query_,
     final List<MutableRel> allNodes = new ArrayList<>();
     final MutableRelVisitor visitor =
         new MutableRelVisitor() {
-          public void visit(MutableRel node) {
+          @Override public void visit(MutableRel node) {
             parents.add(node.getParent());
             allNodes.add(node);
             super.visit(node);
@@ -1044,7 +1044,7 @@ private TrivialRule() {
       super(any(MutableRel.class), any(MutableRel.class), 0);
     }
 
-    public UnifyResult apply(UnifyRuleCall call) {
+    @Override public UnifyResult apply(UnifyRuleCall call) {
       if (call.query.equals(call.target)) {
         return call.result(call.target);
       }
@@ -1117,7 +1117,7 @@ private CalcToCalcUnifyRule() {
           operand(MutableCalc.class, target(0)), 1);
     }
 
-    public UnifyResult apply(UnifyRuleCall call) {
+    @Override public UnifyResult apply(UnifyRuleCall call) {
       final MutableCalc query = (MutableCalc) call.query;
       final Pair<RexNode, List<RexNode>> queryExplained = explainCalc(query);
       final RexNode queryCond = queryExplained.left;
@@ -1549,7 +1549,7 @@ private AggregateToAggregateUnifyRule() {
           operand(MutableAggregate.class, target(0)), 1);
     }
 
-    public UnifyResult apply(UnifyRuleCall call) {
+    @Override public UnifyResult apply(UnifyRuleCall call) {
       final MutableAggregate query = (MutableAggregate) call.query;
       final MutableAggregate target = (MutableAggregate) call.target;
       assert query != target;
@@ -1585,7 +1585,7 @@ private UnionToUnionUnifyRule() {
       super(any(MutableUnion.class), any(MutableUnion.class), 0);
     }
 
-    public UnifyResult apply(UnifyRuleCall call) {
+    @Override public UnifyResult apply(UnifyRuleCall call) {
       final MutableUnion query = (MutableUnion) call.query;
       final MutableUnion target = (MutableUnion) call.target;
       final List<MutableRel> queryInputs = new ArrayList<>(query.getInputs());
@@ -1612,7 +1612,7 @@ private UnionOnCalcsToUnionUnifyRule() {
       super(any(MutableUnion.class), any(MutableUnion.class), 0);
     }
 
-    public UnifyResult apply(UnifyRuleCall call) {
+    @Override public UnifyResult apply(UnifyRuleCall call) {
       return setOpApply(call);
     }
   }
@@ -1630,7 +1630,7 @@ private IntersectToIntersectUnifyRule() {
       super(any(MutableIntersect.class), any(MutableIntersect.class), 0);
     }
 
-    public UnifyResult apply(UnifyRuleCall call) {
+    @Override public UnifyResult apply(UnifyRuleCall call) {
       final MutableIntersect query = (MutableIntersect) call.query;
       final MutableIntersect target = (MutableIntersect) call.target;
       final List<MutableRel> queryInputs = new ArrayList<>(query.getInputs());
@@ -1657,7 +1657,7 @@ private IntersectOnCalcsToIntersectUnifyRule() {
       super(any(MutableIntersect.class), any(MutableIntersect.class), 0);
     }
 
-    public UnifyResult apply(UnifyRuleCall call) {
+    @Override public UnifyResult apply(UnifyRuleCall call) {
       return setOpApply(call);
     }
   }
@@ -1866,7 +1866,7 @@ public static MutableRel unifyAggregates(MutableAggregate query,
     Set<Integer> constantCondInputRefs = new HashSet<>();
     List<Integer> targetGroupByIndexList = target.groupSet.asList();
     RexShuttle rexShuttle = new RexShuttle() {
-      public RexNode visitInputRef(RexInputRef inputRef) {
+      @Override public RexNode visitInputRef(RexInputRef inputRef) {
         constantCondInputRefs.add(targetGroupByIndexList.get(inputRef.getIndex()));
         return super.visitInputRef(inputRef);
       }
diff --git a/core/src/main/java/org/apache/calcite/plan/TableAccessMap.java b/core/src/main/java/org/apache/calcite/plan/TableAccessMap.java
index b5810a2b3a5..fd9d6f4120f 100644
--- a/core/src/main/java/org/apache/calcite/plan/TableAccessMap.java
+++ b/core/src/main/java/org/apache/calcite/plan/TableAccessMap.java
@@ -170,7 +170,7 @@ public List<String> getQualifiedName(RelOptTable table) {
 
   /** Visitor that finds all tables in a tree. */
   private class TableRelVisitor extends RelVisitor {
-    public void visit(
+    @Override public void visit(
         RelNode p,
         int ordinal,
         RelNode parent) {
diff --git a/core/src/main/java/org/apache/calcite/plan/ViewExpanders.java b/core/src/main/java/org/apache/calcite/plan/ViewExpanders.java
index 72b80dabb69..f025489a181 100644
--- a/core/src/main/java/org/apache/calcite/plan/ViewExpanders.java
+++ b/core/src/main/java/org/apache/calcite/plan/ViewExpanders.java
@@ -39,15 +39,15 @@ public static RelOptTable.ToRelContext toRelContext(
       RelOptCluster cluster,
       List<RelHint> hints) {
     return new RelOptTable.ToRelContext() {
-      public RelOptCluster getCluster() {
+      @Override public RelOptCluster getCluster() {
         return cluster;
       }
 
-      public List<RelHint> getTableHints() {
+      @Override public List<RelHint> getTableHints() {
         return hints;
       }
 
-      public RelRoot expandView(RelDataType rowType, String queryString,
+      @Override public RelRoot expandView(RelDataType rowType, String queryString,
           List<String> schemaPath, List<String> viewPath) {
         return viewExpander.expandView(rowType, queryString, schemaPath,
             viewPath);
@@ -72,16 +72,16 @@ public static RelOptTable.ToRelContext simpleContext(
       RelOptCluster cluster,
       List<RelHint> hints) {
     return new RelOptTable.ToRelContext() {
-      public RelOptCluster getCluster() {
+      @Override public RelOptCluster getCluster() {
         return cluster;
       }
 
-      public RelRoot expandView(RelDataType rowType, String queryString,
+      @Override public RelRoot expandView(RelDataType rowType, String queryString,
           List<String> schemaPath, List<String> viewPath) {
         throw new UnsupportedOperationException();
       }
 
-      public List<RelHint> getTableHints() {
+      @Override public List<RelHint> getTableHints() {
         return hints;
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/plan/VisitorDataContext.java b/core/src/main/java/org/apache/calcite/plan/VisitorDataContext.java
index eae7e27b715..55c9be8ca9d 100644
--- a/core/src/main/java/org/apache/calcite/plan/VisitorDataContext.java
+++ b/core/src/main/java/org/apache/calcite/plan/VisitorDataContext.java
@@ -50,19 +50,19 @@ public VisitorDataContext(Object[] values) {
     this.values = values;
   }
 
-  public SchemaPlus getRootSchema() {
+  @Override public SchemaPlus getRootSchema() {
     throw new RuntimeException("Unsupported");
   }
 
-  public JavaTypeFactory getTypeFactory() {
+  @Override public JavaTypeFactory getTypeFactory() {
     throw new RuntimeException("Unsupported");
   }
 
-  public QueryProvider getQueryProvider() {
+  @Override public QueryProvider getQueryProvider() {
     throw new RuntimeException("Unsupported");
   }
 
-  public Object get(String name) {
+  @Override public Object get(String name) {
     if (name.equals("inputRecord")) {
       return values;
     } else {
diff --git a/core/src/main/java/org/apache/calcite/plan/hep/HepInstruction.java b/core/src/main/java/org/apache/calcite/plan/hep/HepInstruction.java
index 329f0fe27e6..11eaf271832 100644
--- a/core/src/main/java/org/apache/calcite/plan/hep/HepInstruction.java
+++ b/core/src/main/java/org/apache/calcite/plan/hep/HepInstruction.java
@@ -50,7 +50,7 @@ static class RuleClass<R extends RelOptRule> extends HepInstruction {
      */
     Set<RelOptRule> ruleSet;
 
-    void initialize(boolean clearCache) {
+    @Override void initialize(boolean clearCache) {
       if (!clearCache) {
         return;
       }
@@ -58,7 +58,7 @@ void initialize(boolean clearCache) {
       ruleSet = null;
     }
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -70,7 +70,7 @@ static class RuleCollection extends HepInstruction {
      */
     Collection<RelOptRule> rules;
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -85,7 +85,7 @@ static class ConverterRules extends HepInstruction {
      */
     Set<RelOptRule> ruleSet;
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -94,7 +94,7 @@ void execute(HepPlanner planner) {
   static class CommonRelSubExprRules extends HepInstruction {
     Set<RelOptRule> ruleSet;
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -112,7 +112,7 @@ static class RuleInstance extends HepInstruction {
      */
     RelOptRule rule;
 
-    void initialize(boolean clearCache) {
+    @Override void initialize(boolean clearCache) {
       if (!clearCache) {
         return;
       }
@@ -123,7 +123,7 @@ void initialize(boolean clearCache) {
       }
     }
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -132,7 +132,7 @@ void execute(HepPlanner planner) {
   static class MatchOrder extends HepInstruction {
     HepMatchOrder order;
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -141,7 +141,7 @@ void execute(HepPlanner planner) {
   static class MatchLimit extends HepInstruction {
     int limit;
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -150,11 +150,11 @@ void execute(HepPlanner planner) {
   static class Subprogram extends HepInstruction {
     HepProgram subprogram;
 
-    void initialize(boolean clearCache) {
+    @Override void initialize(boolean clearCache) {
       subprogram.initialize(clearCache);
     }
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -163,10 +163,10 @@ void execute(HepPlanner planner) {
   static class BeginGroup extends HepInstruction {
     EndGroup endGroup;
 
-    void initialize(boolean clearCache) {
+    @Override void initialize(boolean clearCache) {
     }
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
@@ -181,7 +181,7 @@ static class EndGroup extends HepInstruction {
 
     boolean collecting;
 
-    void initialize(boolean clearCache) {
+    @Override void initialize(boolean clearCache) {
       if (!clearCache) {
         return;
       }
@@ -190,7 +190,7 @@ void initialize(boolean clearCache) {
       collecting = true;
     }
 
-    void execute(HepPlanner planner) {
+    @Override void execute(HepPlanner planner) {
       planner.executeInstruction(this);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/plan/hep/HepPlanner.java b/core/src/main/java/org/apache/calcite/plan/hep/HepPlanner.java
index 77a11559d71..5170fd3b1f9 100644
--- a/core/src/main/java/org/apache/calcite/plan/hep/HepPlanner.java
+++ b/core/src/main/java/org/apache/calcite/plan/hep/HepPlanner.java
@@ -154,13 +154,13 @@ public HepPlanner(
   //~ Methods ----------------------------------------------------------------
 
   // implement RelOptPlanner
-  public void setRoot(RelNode rel) {
+  @Override public void setRoot(RelNode rel) {
     root = addRelToGraph(rel);
     dumpGraph();
   }
 
   // implement RelOptPlanner
-  public RelNode getRoot() {
+  @Override public RelNode getRoot() {
     return root;
   }
 
@@ -173,7 +173,7 @@ public RelNode getRoot() {
   }
 
   // implement RelOptPlanner
-  public RelNode changeTraits(RelNode rel, RelTraitSet toTraits) {
+  @Override public RelNode changeTraits(RelNode rel, RelTraitSet toTraits) {
     // Ignore traits, except for the root, where we remember
     // what the final conversion should be.
     if ((rel == root) || (rel == root.getCurrentRel())) {
@@ -183,7 +183,7 @@ public RelNode changeTraits(RelNode rel, RelTraitSet toTraits) {
   }
 
   // implement RelOptPlanner
-  public RelNode findBestExp() {
+  @Override public RelNode findBestExp() {
     assert root != null;
 
     executeProgram(mainProgram);
@@ -761,7 +761,7 @@ private HepRelVertex applyTransformationResults(
   }
 
   // implement RelOptPlanner
-  public RelNode register(
+  @Override public RelNode register(
       RelNode rel,
       RelNode equivRel) {
     // Ignore; this call is mostly to tell Volcano how to avoid
@@ -774,12 +774,12 @@ public RelNode register(
   }
 
   // implement RelOptPlanner
-  public RelNode ensureRegistered(RelNode rel, RelNode equivRel) {
+  @Override public RelNode ensureRegistered(RelNode rel, RelNode equivRel) {
     return rel;
   }
 
   // implement RelOptPlanner
-  public boolean isRegistered(RelNode rel) {
+  @Override public boolean isRegistered(RelNode rel) {
     return true;
   }
 
@@ -1028,12 +1028,12 @@ private void dumpGraph() {
   }
 
   // implement RelOptPlanner
-  public void registerMetadataProviders(List<RelMetadataProvider> list) {
+  @Override public void registerMetadataProviders(List<RelMetadataProvider> list) {
     list.add(0, new HepRelMetadataProvider());
   }
 
   // implement RelOptPlanner
-  public long getRelMetadataTimestamp(RelNode rel) {
+  @Override public long getRelMetadataTimestamp(RelNode rel) {
     // TODO jvs 20-Apr-2006: This is overly conservative.  Better would be
     // to keep a timestamp per HepRelVertex, and update only affected
     // vertices and all ancestors on each transformation.
diff --git a/core/src/main/java/org/apache/calcite/plan/hep/HepRelMetadataProvider.java b/core/src/main/java/org/apache/calcite/plan/hep/HepRelMetadataProvider.java
index 435e406a967..960f660b73b 100644
--- a/core/src/main/java/org/apache/calcite/plan/hep/HepRelMetadataProvider.java
+++ b/core/src/main/java/org/apache/calcite/plan/hep/HepRelMetadataProvider.java
@@ -43,7 +43,7 @@ class HepRelMetadataProvider implements RelMetadataProvider {
     return 107;
   }
 
-  public <M extends Metadata> UnboundMetadata<M> apply(
+  @Override public <M extends Metadata> UnboundMetadata<M> apply(
       Class<? extends RelNode> relClass,
       final Class<? extends M> metadataClass) {
     return (rel, mq) -> {
@@ -59,7 +59,7 @@ public <M extends Metadata> UnboundMetadata<M> apply(
     };
   }
 
-  public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
+  @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
       MetadataDef<M> def) {
     return ImmutableMultimap.of();
   }
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/AbstractConverter.java b/core/src/main/java/org/apache/calcite/plan/volcano/AbstractConverter.java
index 40a50ac65bc..7d36ee0fb2a 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/AbstractConverter.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/AbstractConverter.java
@@ -60,7 +60,7 @@ public AbstractConverter(
   //~ Methods ----------------------------------------------------------------
 
 
-  public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
+  @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
     return new AbstractConverter(
         getCluster(),
         (RelSubset) sole(inputs),
@@ -68,11 +68,11 @@ public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
         traitSet);
   }
 
-  public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
+  @Override public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
     return planner.getCostFactory().makeInfiniteCost();
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     super.explainTerms(pw);
     for (RelTrait trait : traitSet) {
       pw.item(trait.getTraitDef().getSimpleName(), trait);
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/Dumpers.java b/core/src/main/java/org/apache/calcite/plan/volcano/Dumpers.java
index 26da2230e3a..488bfcc632b 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/Dumpers.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/Dumpers.java
@@ -66,7 +66,7 @@ static String provenance(
     final PrintWriter pw = new PrintWriter(sw);
     final List<RelNode> nodes = new ArrayList<>();
     new RelVisitor() {
-      public void visit(RelNode node, int ordinal, RelNode parent) {
+      @Override public void visit(RelNode node, int ordinal, RelNode parent) {
         nodes.add(node);
         super.visit(node, ordinal, parent);
       }
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/IterativeRuleQueue.java b/core/src/main/java/org/apache/calcite/plan/volcano/IterativeRuleQueue.java
index 62394cca3e1..339b78d5196 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/IterativeRuleQueue.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/IterativeRuleQueue.java
@@ -72,7 +72,7 @@ class IterativeRuleQueue extends RuleQueue {
   /**
    * Add a rule match.
    */
-  public void addMatch(VolcanoRuleMatch match) {
+  @Override public void addMatch(VolcanoRuleMatch match) {
     final String matchName = match.toString();
 
     if (!matchList.names.add(matchName)) {
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/RelSubset.java b/core/src/main/java/org/apache/calcite/plan/volcano/RelSubset.java
index dccb95019f8..da6c88155af 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/RelSubset.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/RelSubset.java
@@ -212,7 +212,7 @@ public RelNode getOriginal() {
     return set.rel;
   }
 
-  public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
+  @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
     if (inputs.isEmpty()) {
       final RelTraitSet traitSet1 = traitSet.simplify();
       if (traitSet1.equals(this.traitSet)) {
@@ -223,11 +223,11 @@ public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
     throw new UnsupportedOperationException();
   }
 
-  public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
+  @Override public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
     return planner.getCostFactory().makeZeroCost();
   }
 
-  public double estimateRowCount(RelMetadataQuery mq) {
+  @Override public double estimateRowCount(RelMetadataQuery mq) {
     if (best != null) {
       return mq.getRowCount(best);
     } else {
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleDriver.java b/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleDriver.java
index 0115a05adf0..1380fee8f61 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleDriver.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleDriver.java
@@ -145,7 +145,7 @@ private void applyGenerator(GeneratorTask task, Procedure proc) {
     }
   }
 
-  public void onSetMerged(RelSet set) {
+  @Override public void onSetMerged(RelSet set) {
     // When RelSets get merged, an optimized group may get extra opportunities.
     // Clear the OPTIMISED state for the RelSubsets and all theirs ancestors
     // so that they will be optimized again
@@ -172,7 +172,7 @@ private void clearProcessed(RelSet set) {
   // a callback invoked when a RelNode is going to be added into a RelSubset,
   // either by Register or Reregister. The task driver should need to schedule
   // tasks for the new nodes.
-  public void onProduce(RelNode node, RelSubset subset) {
+  @Override public void onProduce(RelNode node, RelSubset subset) {
 
     // if the RelNode is added to another RelSubset, just ignore it.
     // It should be schedule in the later OptimizeGroup task
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleQueue.java b/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleQueue.java
index 2c142c1f601..7cb0528eb37 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleQueue.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/TopDownRuleQueue.java
@@ -41,7 +41,7 @@ class TopDownRuleQueue extends RuleQueue {
     super(planner);
   }
 
-  public void addMatch(VolcanoRuleMatch match) {
+  @Override public void addMatch(VolcanoRuleMatch match) {
     RelNode rel = match.rel(0);
     List<VolcanoRuleMatch> queue = matches.
         computeIfAbsent(rel, id -> new LinkedList<>());
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoCost.java b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoCost.java
index f8d67ec6cc0..76969e12963 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoCost.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoCost.java
@@ -36,28 +36,28 @@ class VolcanoCost implements RelOptCost {
           Double.POSITIVE_INFINITY,
           Double.POSITIVE_INFINITY,
           Double.POSITIVE_INFINITY) {
-        public String toString() {
+        @Override public String toString() {
           return "{inf}";
         }
       };
 
   static final VolcanoCost HUGE =
       new VolcanoCost(Double.MAX_VALUE, Double.MAX_VALUE, Double.MAX_VALUE) {
-        public String toString() {
+        @Override public String toString() {
           return "{huge}";
         }
       };
 
   static final VolcanoCost ZERO =
       new VolcanoCost(0.0, 0.0, 0.0) {
-        public String toString() {
+        @Override public String toString() {
           return "{0}";
         }
       };
 
   static final VolcanoCost TINY =
       new VolcanoCost(1.0, 1.0, 0.0) {
-        public String toString() {
+        @Override public String toString() {
           return "{tiny}";
         }
       };
@@ -80,22 +80,22 @@ public String toString() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public double getCpu() {
+  @Override public double getCpu() {
     return cpu;
   }
 
-  public boolean isInfinite() {
+  @Override public boolean isInfinite() {
     return (this == INFINITY)
         || (this.rowCount == Double.POSITIVE_INFINITY)
         || (this.cpu == Double.POSITIVE_INFINITY)
         || (this.io == Double.POSITIVE_INFINITY);
   }
 
-  public double getIo() {
+  @Override public double getIo() {
     return io;
   }
 
-  public boolean isLe(RelOptCost other) {
+  @Override public boolean isLe(RelOptCost other) {
     VolcanoCost that = (VolcanoCost) other;
     if (true) {
       return this == that
@@ -107,7 +107,7 @@ public boolean isLe(RelOptCost other) {
         && (this.io <= that.io));
   }
 
-  public boolean isLt(RelOptCost other) {
+  @Override public boolean isLt(RelOptCost other) {
     if (true) {
       VolcanoCost that = (VolcanoCost) other;
       return this.rowCount < that.rowCount;
@@ -115,7 +115,7 @@ public boolean isLt(RelOptCost other) {
     return isLe(other) && !equals(other);
   }
 
-  public double getRows() {
+  @Override public double getRows() {
     return rowCount;
   }
 
@@ -123,7 +123,7 @@ public double getRows() {
     return Objects.hash(rowCount, cpu, io);
   }
 
-  public boolean equals(RelOptCost other) {
+  @Override public boolean equals(RelOptCost other) {
     return this == other
         || other instanceof VolcanoCost
         && (this.rowCount == ((VolcanoCost) other).rowCount)
@@ -138,7 +138,7 @@ public boolean equals(RelOptCost other) {
     return false;
   }
 
-  public boolean isEqWithEpsilon(RelOptCost other) {
+  @Override public boolean isEqWithEpsilon(RelOptCost other) {
     if (!(other instanceof VolcanoCost)) {
       return false;
     }
@@ -149,7 +149,7 @@ public boolean isEqWithEpsilon(RelOptCost other) {
         && (Math.abs(this.io - that.io) < RelOptUtil.EPSILON));
   }
 
-  public RelOptCost minus(RelOptCost other) {
+  @Override public RelOptCost minus(RelOptCost other) {
     if (this == INFINITY) {
       return this;
     }
@@ -160,14 +160,14 @@ public RelOptCost minus(RelOptCost other) {
         this.io - that.io);
   }
 
-  public RelOptCost multiplyBy(double factor) {
+  @Override public RelOptCost multiplyBy(double factor) {
     if (this == INFINITY) {
       return this;
     }
     return new VolcanoCost(rowCount * factor, cpu * factor, io * factor);
   }
 
-  public double divideBy(RelOptCost cost) {
+  @Override public double divideBy(RelOptCost cost) {
     // Compute the geometric average of the ratios of all of the factors
     // which are non-zero and finite.
     VolcanoCost that = (VolcanoCost) cost;
@@ -200,7 +200,7 @@ public double divideBy(RelOptCost cost) {
     return Math.pow(d, 1 / n);
   }
 
-  public RelOptCost plus(RelOptCost other) {
+  @Override public RelOptCost plus(RelOptCost other) {
     VolcanoCost that = (VolcanoCost) other;
     if ((this == INFINITY) || (that == INFINITY)) {
       return INFINITY;
@@ -211,30 +211,30 @@ public RelOptCost plus(RelOptCost other) {
         this.io + that.io);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "{" + rowCount + " rows, " + cpu + " cpu, " + io + " io}";
   }
 
   /** Implementation of {@link org.apache.calcite.plan.RelOptCostFactory}
    * that creates {@link org.apache.calcite.plan.volcano.VolcanoCost}s. */
   private static class Factory implements RelOptCostFactory {
-    public RelOptCost makeCost(double dRows, double dCpu, double dIo) {
+    @Override public RelOptCost makeCost(double dRows, double dCpu, double dIo) {
       return new VolcanoCost(dRows, dCpu, dIo);
     }
 
-    public RelOptCost makeHugeCost() {
+    @Override public RelOptCost makeHugeCost() {
       return VolcanoCost.HUGE;
     }
 
-    public RelOptCost makeInfiniteCost() {
+    @Override public RelOptCost makeInfiniteCost() {
       return VolcanoCost.INFINITY;
     }
 
-    public RelOptCost makeTinyCost() {
+    @Override public RelOptCost makeTinyCost() {
       return VolcanoCost.TINY;
     }
 
-    public RelOptCost makeZeroCost() {
+    @Override public RelOptCost makeZeroCost() {
       return VolcanoCost.ZERO;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoPlanner.java b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoPlanner.java
index fa26892cb97..12ffe289f4a 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoPlanner.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoPlanner.java
@@ -252,11 +252,11 @@ public void setTopDownOpt(boolean value) {
   }
 
   // implement RelOptPlanner
-  public boolean isRegistered(RelNode rel) {
+  @Override public boolean isRegistered(RelNode rel) {
     return mapRel2Subset.get(rel) != null;
   }
 
-  public void setRoot(RelNode rel) {
+  @Override public void setRoot(RelNode rel) {
     // We've registered all the rules, and therefore RelNode classes,
     // we're interested in, and have not yet started calling metadata providers.
     // So now is a good time to tell the metadata layer what to expect.
@@ -271,7 +271,7 @@ public void setRoot(RelNode rel) {
     ensureRootConverters();
   }
 
-  public RelNode getRoot() {
+  @Override public RelNode getRoot() {
     return root;
   }
 
@@ -398,7 +398,7 @@ public RelSet getSet(RelNode rel) {
     this.provenanceMap.clear();
   }
 
-  public boolean addRule(RelOptRule rule) {
+  @Override public boolean addRule(RelOptRule rule) {
     if (locked) {
       return false;
     }
@@ -437,7 +437,7 @@ public boolean addRule(RelOptRule rule) {
     return true;
   }
 
-  public boolean removeRule(RelOptRule rule) {
+  @Override public boolean removeRule(RelOptRule rule) {
     // Remove description.
     if (!super.removeRule(rule)) {
       // Rule was not present.
@@ -479,7 +479,7 @@ public boolean removeRule(RelOptRule rule) {
     }
   }
 
-  public RelNode changeTraits(final RelNode rel, RelTraitSet toTraits) {
+  @Override public RelNode changeTraits(final RelNode rel, RelTraitSet toTraits) {
     assert !rel.getTraitSet().equals(toTraits);
     assert toTraits.allSimple();
 
@@ -492,7 +492,7 @@ public RelNode changeTraits(final RelNode rel, RelTraitSet toTraits) {
         rel.getCluster(), toTraits, true);
   }
 
-  public RelOptPlanner chooseDelegate() {
+  @Override public RelOptPlanner chooseDelegate() {
     return this;
   }
 
@@ -503,7 +503,7 @@ public RelOptPlanner chooseDelegate() {
    * @return the most efficient RelNode tree found for implementing the given
    * query
    */
-  public RelNode findBestExp() {
+  @Override public RelNode findBestExp() {
     ensureRootConverters();
     registerMaterializations();
 
@@ -569,7 +569,7 @@ void ensureRootConverters() {
     }
   }
 
-  public RelSubset register(
+  @Override public RelSubset register(
       RelNode rel,
       RelNode equivRel) {
     assert !isRegistered(rel) : "pre: isRegistered(rel)";
@@ -589,7 +589,7 @@ public RelSubset register(
     return registerImpl(rel, set);
   }
 
-  public RelSubset ensureRegistered(RelNode rel, RelNode equivRel) {
+  @Override public RelSubset ensureRegistered(RelNode rel, RelNode equivRel) {
     RelSubset result;
     final RelSubset subset = getSubset(rel);
     if (subset != null) {
@@ -674,7 +674,7 @@ public void registerAbstractRelationalRules() {
     RelOptUtil.registerAbstractRelationalRules(this);
   }
 
-  public void registerSchema(RelOptSchema schema) {
+  @Override public void registerSchema(RelOptSchema schema) {
     if (registeredSchemas.add(schema)) {
       try {
         schema.registerRules(this);
@@ -693,7 +693,7 @@ public void setNoneConventionHasInfiniteCost(boolean infinite) {
     this.noneConventionHasInfiniteCost = infinite;
   }
 
-  public RelOptCost getCost(RelNode rel, RelMetadataQuery mq) {
+  @Override public RelOptCost getCost(RelNode rel, RelMetadataQuery mq) {
     assert rel != null : "pre-condition: rel != null";
     if (rel instanceof RelSubset) {
       return ((RelSubset) rel).bestCost;
@@ -1290,12 +1290,12 @@ private RelSubset registerSubset(
   }
 
   // implement RelOptPlanner
-  public void registerMetadataProviders(List<RelMetadataProvider> list) {
+  @Override public void registerMetadataProviders(List<RelMetadataProvider> list) {
     list.add(0, new VolcanoRelMetadataProvider());
   }
 
   // implement RelOptPlanner
-  public long getRelMetadataTimestamp(RelNode rel) {
+  @Override public long getRelMetadataTimestamp(RelNode rel) {
     RelSubset subset = getSubset(rel);
     if (subset == null) {
       return 0;
@@ -1459,7 +1459,7 @@ private static class DeferringRuleCall extends VolcanoRuleCall {
      * Rather than invoking the rule (as the base method does), creates a
      * {@link VolcanoRuleMatch} which can be invoked later.
      */
-    protected void onMatch() {
+    @Override protected void onMatch() {
       final VolcanoRuleMatch match =
           new VolcanoRuleMatch(
               volcanoPlanner,
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRelMetadataProvider.java b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRelMetadataProvider.java
index 00c51642273..82223ce722e 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRelMetadataProvider.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRelMetadataProvider.java
@@ -43,7 +43,7 @@ public class VolcanoRelMetadataProvider implements RelMetadataProvider {
     return 103;
   }
 
-  public <M extends Metadata> UnboundMetadata<M> apply(
+  @Override public <M extends Metadata> UnboundMetadata<M> apply(
       Class<? extends RelNode> relClass,
       final Class<? extends M> metadataClass) {
     if (relClass != RelSubset.class) {
@@ -112,7 +112,7 @@ public <M extends Metadata> UnboundMetadata<M> apply(
     };
   }
 
-  public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
+  @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
       MetadataDef<M> def) {
     return ImmutableMultimap.of();
   }
diff --git a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRuleMatch.java b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRuleMatch.java
index beda1c5a4ca..01ccde743ec 100644
--- a/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRuleMatch.java
+++ b/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoRuleMatch.java
@@ -52,7 +52,7 @@ class VolcanoRuleMatch extends VolcanoRuleCall {
 
   //~ Methods ----------------------------------------------------------------
 
-  public String toString() {
+  @Override public String toString() {
     return digest;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/prepare/CalciteCatalogReader.java b/core/src/main/java/org/apache/calcite/prepare/CalciteCatalogReader.java
index e0f2f5cb2b0..fcede58c19f 100644
--- a/core/src/main/java/org/apache/calcite/prepare/CalciteCatalogReader.java
+++ b/core/src/main/java/org/apache/calcite/prepare/CalciteCatalogReader.java
@@ -108,12 +108,12 @@ protected CalciteCatalogReader(CalciteSchema rootSchema,
     this.config = config;
   }
 
-  public CalciteCatalogReader withSchemaPath(List<String> schemaPath) {
+  @Override public CalciteCatalogReader withSchemaPath(List<String> schemaPath) {
     return new CalciteCatalogReader(rootSchema, nameMatcher,
         ImmutableList.of(schemaPath, ImmutableList.of()), typeFactory, config);
   }
 
-  public Prepare.PreparingTable getTable(final List<String> names) {
+  @Override public Prepare.PreparingTable getTable(final List<String> names) {
     // First look in the default schema, if any.
     // If not found, look in the root schema.
     CalciteSchema.TableEntry entry = SqlValidatorUtil.getTableEntry(this, names);
@@ -171,7 +171,7 @@ private Collection<org.apache.calcite.schema.Function> getFunctionsFrom(
     return functions2;
   }
 
-  public RelDataType getNamedType(SqlIdentifier typeName) {
+  @Override public RelDataType getNamedType(SqlIdentifier typeName) {
     CalciteSchema.TypeEntry typeEntry = SqlValidatorUtil.getTypeEntry(getRootSchema(), typeName);
     if (typeEntry != null) {
       return typeEntry.getType().apply(typeFactory);
@@ -180,7 +180,7 @@ public RelDataType getNamedType(SqlIdentifier typeName) {
     }
   }
 
-  public List<SqlMoniker> getAllSchemaObjectNames(List<String> names) {
+  @Override public List<SqlMoniker> getAllSchemaObjectNames(List<String> names) {
     final CalciteSchema schema =
         SqlValidatorUtil.getSchema(rootSchema, names, nameMatcher);
     if (schema == null) {
@@ -221,31 +221,31 @@ private SqlMonikerImpl moniker(CalciteSchema schema, String name,
     return new SqlMonikerImpl(path, type);
   }
 
-  public List<List<String>> getSchemaPaths() {
+  @Override public List<List<String>> getSchemaPaths() {
     return schemaPaths;
   }
 
-  public Prepare.PreparingTable getTableForMember(List<String> names) {
+  @Override public Prepare.PreparingTable getTableForMember(List<String> names) {
     return getTable(names);
   }
 
-  @SuppressWarnings("deprecation")
+  @Override @SuppressWarnings("deprecation")
   public RelDataTypeField field(RelDataType rowType, String alias) {
     return nameMatcher.field(rowType, alias);
   }
 
   @SuppressWarnings("deprecation")
-  public boolean matches(String string, String name) {
+  @Override public boolean matches(String string, String name) {
     return nameMatcher.matches(string, name);
   }
 
-  public RelDataType createTypeFromProjection(final RelDataType type,
+  @Override public RelDataType createTypeFromProjection(final RelDataType type,
       final List<String> columnNameList) {
     return SqlValidatorUtil.createTypeFromProjection(type, columnNameList,
         typeFactory, nameMatcher.isCaseSensitive());
   }
 
-  public void lookupOperatorOverloads(final SqlIdentifier opName,
+  @Override public void lookupOperatorOverloads(final SqlIdentifier opName,
       SqlFunctionCategory category,
       SqlSyntax syntax,
       List<SqlOperator> operatorList,
@@ -409,7 +409,7 @@ private static RelDataType toSql(RelDataTypeFactory typeFactory,
     return JavaTypeFactoryImpl.toSql(typeFactory, type);
   }
 
-  public List<SqlOperator> getOperatorList() {
+  @Override public List<SqlOperator> getOperatorList() {
     final ImmutableList.Builder<SqlOperator> builder = ImmutableList.builder();
     for (List<String> schemaPath : schemaPaths) {
       CalciteSchema schema =
@@ -424,15 +424,15 @@ public List<SqlOperator> getOperatorList() {
     return builder.build();
   }
 
-  public CalciteSchema getRootSchema() {
+  @Override public CalciteSchema getRootSchema() {
     return rootSchema;
   }
 
-  public RelDataTypeFactory getTypeFactory() {
+  @Override public RelDataTypeFactory getTypeFactory() {
     return typeFactory;
   }
 
-  public void registerRules(RelOptPlanner planner) {
+  @Override public void registerRules(RelOptPlanner planner) {
   }
 
   @SuppressWarnings("deprecation")
@@ -440,7 +440,7 @@ public void registerRules(RelOptPlanner planner) {
     return nameMatcher.isCaseSensitive();
   }
 
-  public SqlNameMatcher nameMatcher() {
+  @Override public SqlNameMatcher nameMatcher() {
     return nameMatcher;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/prepare/CalciteMaterializer.java b/core/src/main/java/org/apache/calcite/prepare/CalciteMaterializer.java
index a779ff4562d..ffd6b9f8ca0 100644
--- a/core/src/main/java/org/apache/calcite/prepare/CalciteMaterializer.java
+++ b/core/src/main/java/org/apache/calcite/prepare/CalciteMaterializer.java
@@ -151,55 +151,55 @@ private Iterable<Callback> useStar(CalciteSchema schema, RelNode queryRel) {
   /** Implementation of {@link RelShuttle} that returns each relational
    * expression unchanged. It does not visit inputs. */
   static class RelNullShuttle implements RelShuttle {
-    public RelNode visit(TableScan scan) {
+    @Override public RelNode visit(TableScan scan) {
       return scan;
     }
-    public RelNode visit(TableFunctionScan scan) {
+    @Override public RelNode visit(TableFunctionScan scan) {
       return scan;
     }
-    public RelNode visit(LogicalValues values) {
+    @Override public RelNode visit(LogicalValues values) {
       return values;
     }
-    public RelNode visit(LogicalFilter filter) {
+    @Override public RelNode visit(LogicalFilter filter) {
       return filter;
     }
-    public RelNode visit(LogicalCalc calc) {
+    @Override public RelNode visit(LogicalCalc calc) {
       return calc;
     }
-    public RelNode visit(LogicalProject project) {
+    @Override public RelNode visit(LogicalProject project) {
       return project;
     }
-    public RelNode visit(LogicalJoin join) {
+    @Override public RelNode visit(LogicalJoin join) {
       return join;
     }
-    public RelNode visit(LogicalCorrelate correlate) {
+    @Override public RelNode visit(LogicalCorrelate correlate) {
       return correlate;
     }
-    public RelNode visit(LogicalUnion union) {
+    @Override public RelNode visit(LogicalUnion union) {
       return union;
     }
-    public RelNode visit(LogicalIntersect intersect) {
+    @Override public RelNode visit(LogicalIntersect intersect) {
       return intersect;
     }
-    public RelNode visit(LogicalMinus minus) {
+    @Override public RelNode visit(LogicalMinus minus) {
       return minus;
     }
-    public RelNode visit(LogicalAggregate aggregate) {
+    @Override public RelNode visit(LogicalAggregate aggregate) {
       return aggregate;
     }
-    public RelNode visit(LogicalMatch match) {
+    @Override public RelNode visit(LogicalMatch match) {
       return match;
     }
-    public RelNode visit(LogicalSort sort) {
+    @Override public RelNode visit(LogicalSort sort) {
       return sort;
     }
-    public RelNode visit(LogicalExchange exchange) {
+    @Override public RelNode visit(LogicalExchange exchange) {
       return exchange;
     }
-    public RelNode visit(LogicalTableModify modify) {
+    @Override public RelNode visit(LogicalTableModify modify) {
       return modify;
     }
-    public RelNode visit(RelNode other) {
+    @Override public RelNode visit(RelNode other) {
       return other;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/prepare/CalcitePrepareImpl.java b/core/src/main/java/org/apache/calcite/prepare/CalcitePrepareImpl.java
index 8221b028c1f..9cecb7a4344 100644
--- a/core/src/main/java/org/apache/calcite/prepare/CalcitePrepareImpl.java
+++ b/core/src/main/java/org/apache/calcite/prepare/CalcitePrepareImpl.java
@@ -164,16 +164,16 @@ public class CalcitePrepareImpl implements CalcitePrepare {
   public CalcitePrepareImpl() {
   }
 
-  public ParseResult parse(
+  @Override public ParseResult parse(
       Context context, String sql) {
     return parse_(context, sql, false, false, false);
   }
 
-  public ConvertResult convert(Context context, String sql) {
+  @Override public ConvertResult convert(Context context, String sql) {
     return (ConvertResult) parse_(context, sql, true, false, false);
   }
 
-  public AnalyzeViewResult analyzeView(Context context, String sql, boolean fail) {
+  @Override public AnalyzeViewResult analyzeView(Context context, String sql, boolean fail) {
     return (AnalyzeViewResult) parse_(context, sql, true, true, fail);
   }
 
@@ -449,11 +449,11 @@ protected RelOptPlanner createPlanner(
     if (spark.enabled()) {
       spark.registerRules(
           new SparkHandler.RuleSetBuilder() {
-            public void addRule(RelOptRule rule) {
+            @Override public void addRule(RelOptRule rule) {
               // TODO:
             }
 
-            public void removeRule(RelOptRule rule) {
+            @Override public void removeRule(RelOptRule rule) {
               // TODO:
             }
           });
@@ -463,14 +463,14 @@ public void removeRule(RelOptRule rule) {
     return planner;
   }
 
-  public <T> CalciteSignature<T> prepareQueryable(
+  @Override public <T> CalciteSignature<T> prepareQueryable(
       Context context,
       Queryable<T> queryable) {
     return prepare_(context, Query.of(queryable), queryable.getElementType(),
         -1);
   }
 
-  public <T> CalciteSignature<T> prepareSql(
+  @Override public <T> CalciteSignature<T> prepareSql(
       Context context,
       Query<T> query,
       Type elementType,
@@ -1145,15 +1145,15 @@ protected SqlValidator createSqlValidator(CatalogReader catalogReader) {
           root.rel,
           mapTableModOp(isDml, root.kind),
           isDml) {
-        public String getCode() {
+        @Override public String getCode() {
           throw new UnsupportedOperationException();
         }
 
-        public Bindable getBindable(Meta.CursorFactory cursorFactory) {
+        @Override public Bindable getBindable(Meta.CursorFactory cursorFactory) {
           return bindable;
         }
 
-        public Type getElementType() {
+        @Override public Type getElementType() {
           return ((Typed) bindable).getElementType();
         }
       };
@@ -1186,7 +1186,7 @@ private static class CalcitePreparedExplain extends Prepare.PreparedExplain {
       super(resultType, parameterRowType, root, format, detailLevel);
     }
 
-    public Bindable getBindable(final Meta.CursorFactory cursorFactory) {
+    @Override public Bindable getBindable(final Meta.CursorFactory cursorFactory) {
       final String explanation = getCode();
       return dataContext -> {
         switch (cursorFactory.style) {
@@ -1221,7 +1221,7 @@ public static ScalarTranslator empty(RexBuilder builder) {
       return new EmptyScalarTranslator(builder);
     }
 
-    public List<RexNode> toRexList(BlockStatement statement) {
+    @Override public List<RexNode> toRexList(BlockStatement statement) {
       final List<Expression> simpleList = simpleList(statement);
       final List<RexNode> list = new ArrayList<>();
       for (Expression expression1 : simpleList) {
@@ -1230,7 +1230,7 @@ public List<RexNode> toRexList(BlockStatement statement) {
       return list;
     }
 
-    public RexNode toRex(BlockStatement statement) {
+    @Override public RexNode toRex(BlockStatement statement) {
       return toRex(Blocks.simple(statement));
     }
 
@@ -1244,7 +1244,7 @@ private static List<Expression> simpleList(BlockStatement statement) {
       }
     }
 
-    public RexNode toRex(Expression expression) {
+    @Override public RexNode toRex(Expression expression) {
       switch (expression.getNodeType()) {
       case MemberAccess:
         // Case-sensitive name match because name was previously resolved.
@@ -1320,7 +1320,7 @@ protected RelDataType type(Expression expression) {
       return ((JavaTypeFactory) rexBuilder.getTypeFactory()).createType(type);
     }
 
-    public ScalarTranslator bind(
+    @Override public ScalarTranslator bind(
         List<ParameterExpression> parameterList, List<RexNode> values) {
       return new LambdaScalarTranslator(
           rexBuilder, parameterList, values);
@@ -1345,7 +1345,7 @@ private static class LambdaScalarTranslator extends EmptyScalarTranslator {
       this.values = values;
     }
 
-    public RexNode parameter(ParameterExpression param) {
+    @Override public RexNode parameter(ParameterExpression param) {
       int i = parameterList.indexOf(param);
       if (i >= 0) {
         return values.get(i);
diff --git a/core/src/main/java/org/apache/calcite/prepare/PlannerImpl.java b/core/src/main/java/org/apache/calcite/prepare/PlannerImpl.java
index 5417a64b1b7..39e77a95f9a 100644
--- a/core/src/main/java/org/apache/calcite/prepare/PlannerImpl.java
+++ b/core/src/main/java/org/apache/calcite/prepare/PlannerImpl.java
@@ -146,17 +146,17 @@ private void ensure(State state) {
     state.from(this);
   }
 
-  public RelTraitSet getEmptyTraitSet() {
+  @Override public RelTraitSet getEmptyTraitSet() {
     return planner.emptyTraitSet();
   }
 
-  public void close() {
+  @Override public void close() {
     open = false;
     typeFactory = null;
     state = State.STATE_0_CLOSED;
   }
 
-  public void reset() {
+  @Override public void reset() {
     ensure(State.STATE_0_CLOSED);
     open = true;
     state = State.STATE_1_RESET;
@@ -195,7 +195,7 @@ private void ready() {
     }
   }
 
-  public SqlNode parse(final Reader reader) throws SqlParseException {
+  @Override public SqlNode parse(final Reader reader) throws SqlParseException {
     switch (state) {
     case STATE_0_CLOSED:
     case STATE_1_RESET:
@@ -208,7 +208,7 @@ public SqlNode parse(final Reader reader) throws SqlParseException {
     return sqlNode;
   }
 
-  public SqlNode validate(SqlNode sqlNode) throws ValidationException {
+  @Override public SqlNode validate(SqlNode sqlNode) throws ValidationException {
     ensure(State.STATE_3_PARSED);
     this.validator = createSqlValidator(createCatalogReader());
     try {
@@ -220,7 +220,7 @@ public SqlNode validate(SqlNode sqlNode) throws ValidationException {
     return validatedSqlNode;
   }
 
-  public Pair<SqlNode, RelDataType> validateAndGetType(SqlNode sqlNode)
+  @Override public Pair<SqlNode, RelDataType> validateAndGetType(SqlNode sqlNode)
       throws ValidationException {
     final SqlNode validatedNode = this.validate(sqlNode);
     final RelDataType type =
@@ -229,11 +229,11 @@ public Pair<SqlNode, RelDataType> validateAndGetType(SqlNode sqlNode)
   }
 
   @SuppressWarnings("deprecation")
-  public final RelNode convert(SqlNode sql) {
+  @Override public final RelNode convert(SqlNode sql) {
     return rel(sql).rel;
   }
 
-  public RelRoot rel(SqlNode sql) {
+  @Override public RelRoot rel(SqlNode sql) {
     ensure(State.STATE_4_VALIDATED);
     assert validatedSqlNode != null;
     final RexBuilder rexBuilder = createRexBuilder();
@@ -262,7 +262,7 @@ public class ViewExpanderImpl implements ViewExpander {
     ViewExpanderImpl() {
     }
 
-    public RelRoot expandView(RelDataType rowType, String queryString,
+    @Override public RelRoot expandView(RelDataType rowType, String queryString,
         List<String> schemaPath, List<String> viewPath) {
       return PlannerImpl.this.expandView(rowType, queryString, schemaPath,
           viewPath);
@@ -341,11 +341,11 @@ private RexBuilder createRexBuilder() {
     return new RexBuilder(typeFactory);
   }
 
-  public JavaTypeFactory getTypeFactory() {
+  @Override public JavaTypeFactory getTypeFactory() {
     return typeFactory;
   }
 
-  public RelNode transform(int ruleSetIndex, RelTraitSet requiredOutputTraits,
+  @Override public RelNode transform(int ruleSetIndex, RelTraitSet requiredOutputTraits,
       RelNode rel) {
     ensure(State.STATE_5_CONVERTED);
     rel.getCluster().setMetadataProvider(
diff --git a/core/src/main/java/org/apache/calcite/prepare/Prepare.java b/core/src/main/java/org/apache/calcite/prepare/Prepare.java
index c52b1c07abd..29a3c304695 100644
--- a/core/src/main/java/org/apache/calcite/prepare/Prepare.java
+++ b/core/src/main/java/org/apache/calcite/prepare/Prepare.java
@@ -382,7 +382,7 @@ private boolean shouldTrim(RelNode rootRel) {
   /** Interface by which validator and planner can read table metadata. */
   public interface CatalogReader
       extends RelOptSchema, SqlValidatorCatalogReader, SqlOperatorTable {
-    PreparingTable getTableForMember(List<String> names);
+    @Override PreparingTable getTableForMember(List<String> names);
 
     /** Returns a catalog reader the same as this one but with a possibly
      * different schema path. */
@@ -403,7 +403,7 @@ public interface PreparingTable
   public abstract static class AbstractPreparingTable
       implements PreparingTable {
     @SuppressWarnings("deprecation")
-    public boolean columnHasDefaultValue(RelDataType rowType, int ordinal,
+    @Override public boolean columnHasDefaultValue(RelDataType rowType, int ordinal,
         InitializerContext initializerContext) {
       // This method is no longer used
       final Table table = this.unwrap(Table.class);
@@ -422,7 +422,7 @@ public boolean columnHasDefaultValue(RelDataType rowType, int ordinal,
       return !rowType.getFieldList().get(ordinal).getType().isNullable();
     }
 
-    public final RelOptTable extend(List<RelDataTypeField> extendedFields) {
+    @Override public final RelOptTable extend(List<RelDataTypeField> extendedFields) {
       final Table table = unwrap(Table.class);
 
       // Get the set of extended columns that do not have the same name as a column
@@ -452,7 +452,7 @@ public final RelOptTable extend(List<RelDataTypeField> extendedFields) {
      * based on a {@link Table} that has been extended. */
     protected abstract RelOptTable extend(Table extendedTable);
 
-    public List<ColumnStrategy> getColumnStrategies() {
+    @Override public List<ColumnStrategy> getColumnStrategies() {
       return RelOptTableImpl.columnStrategies(AbstractPreparingTable.this);
     }
   }
@@ -482,7 +482,7 @@ public PreparedExplain(
       this.detailLevel = detailLevel;
     }
 
-    public String getCode() {
+    @Override public String getCode() {
       if (root == null) {
         return RelOptUtil.dumpType(rowType);
       } else {
@@ -490,19 +490,19 @@ public String getCode() {
       }
     }
 
-    public RelDataType getParameterRowType() {
+    @Override public RelDataType getParameterRowType() {
       return parameterRowType;
     }
 
-    public boolean isDml() {
+    @Override public boolean isDml() {
       return false;
     }
 
-    public LogicalTableModify.Operation getTableModOp() {
+    @Override public LogicalTableModify.Operation getTableModOp() {
       return null;
     }
 
-    public List<List<String>> getFieldOrigins() {
+    @Override public List<List<String>> getFieldOrigins() {
       return Collections.singletonList(
           Collections.nCopies(4, null));
     }
@@ -580,19 +580,19 @@ public PreparedResultImpl(
       this.isDml = isDml;
     }
 
-    public boolean isDml() {
+    @Override public boolean isDml() {
       return isDml;
     }
 
-    public LogicalTableModify.Operation getTableModOp() {
+    @Override public LogicalTableModify.Operation getTableModOp() {
       return tableModOp;
     }
 
-    public List<List<String>> getFieldOrigins() {
+    @Override public List<List<String>> getFieldOrigins() {
       return fieldOrigins;
     }
 
-    public RelDataType getParameterRowType() {
+    @Override public RelDataType getParameterRowType() {
       return parameterRowType;
     }
 
@@ -605,7 +605,7 @@ public RelDataType getPhysicalRowType() {
       return rowType;
     }
 
-    public abstract Type getElementType();
+    @Override public abstract Type getElementType();
 
     public RelNode getRootRel() {
       return rootRel;
diff --git a/core/src/main/java/org/apache/calcite/prepare/QueryableRelBuilder.java b/core/src/main/java/org/apache/calcite/prepare/QueryableRelBuilder.java
index 96244701ec3..136ae6db1c2 100644
--- a/core/src/main/java/org/apache/calcite/prepare/QueryableRelBuilder.java
+++ b/core/src/main/java/org/apache/calcite/prepare/QueryableRelBuilder.java
@@ -117,7 +117,7 @@ private void setRel(RelNode rel) {
 
   // ~ Methods from QueryableFactory -----------------------------------------
 
-  public <TAccumulate, TResult> TResult aggregate(
+  @Override public <TAccumulate, TResult> TResult aggregate(
       Queryable<T> source,
       TAccumulate seed,
       FunctionExpression<Function2<TAccumulate, T, TAccumulate>> func,
@@ -125,164 +125,164 @@ public <TAccumulate, TResult> TResult aggregate(
     throw new UnsupportedOperationException();
   }
 
-  public T aggregate(
+  @Override public T aggregate(
       Queryable<T> source,
       FunctionExpression<Function2<T, T, T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TAccumulate> TAccumulate aggregate(
+  @Override public <TAccumulate> TAccumulate aggregate(
       Queryable<T> source,
       TAccumulate seed,
       FunctionExpression<Function2<TAccumulate, T, TAccumulate>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean all(
+  @Override public boolean all(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean any(Queryable<T> source) {
+  @Override public boolean any(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean any(
+  @Override public boolean any(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public BigDecimal averageBigDecimal(
+  @Override public BigDecimal averageBigDecimal(
       Queryable<T> source,
       FunctionExpression<BigDecimalFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public BigDecimal averageNullableBigDecimal(
+  @Override public BigDecimal averageNullableBigDecimal(
       Queryable<T> source,
       FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public double averageDouble(
+  @Override public double averageDouble(
       Queryable<T> source,
       FunctionExpression<DoubleFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Double averageNullableDouble(
+  @Override public Double averageNullableDouble(
       Queryable<T> source,
       FunctionExpression<NullableDoubleFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public int averageInteger(
+  @Override public int averageInteger(
       Queryable<T> source,
       FunctionExpression<IntegerFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Integer averageNullableInteger(
+  @Override public Integer averageNullableInteger(
       Queryable<T> source,
       FunctionExpression<NullableIntegerFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public float averageFloat(
+  @Override public float averageFloat(
       Queryable<T> source,
       FunctionExpression<FloatFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Float averageNullableFloat(
+  @Override public Float averageNullableFloat(
       Queryable<T> source,
       FunctionExpression<NullableFloatFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public long averageLong(
+  @Override public long averageLong(
       Queryable<T> source,
       FunctionExpression<LongFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Long averageNullableLong(
+  @Override public Long averageNullableLong(
       Queryable<T> source,
       FunctionExpression<NullableLongFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> concat(
+  @Override public Queryable<T> concat(
       Queryable<T> source, Enumerable<T> source2) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean contains(
+  @Override public boolean contains(
       Queryable<T> source, T element) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean contains(
+  @Override public boolean contains(
       Queryable<T> source, T element, EqualityComparer<T> comparer) {
     throw new UnsupportedOperationException();
   }
 
-  public int count(Queryable<T> source) {
+  @Override public int count(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public int count(
+  @Override public int count(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> defaultIfEmpty(Queryable<T> source) {
+  @Override public Queryable<T> defaultIfEmpty(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> defaultIfEmpty(Queryable<T> source, T value) {
+  @Override public Queryable<T> defaultIfEmpty(Queryable<T> source, T value) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> distinct(
+  @Override public Queryable<T> distinct(
       Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> distinct(
+  @Override public Queryable<T> distinct(
       Queryable<T> source, EqualityComparer<T> comparer) {
     throw new UnsupportedOperationException();
   }
 
-  public T elementAt(Queryable<T> source, int index) {
+  @Override public T elementAt(Queryable<T> source, int index) {
     throw new UnsupportedOperationException();
   }
 
-  public T elementAtOrDefault(Queryable<T> source, int index) {
+  @Override public T elementAtOrDefault(Queryable<T> source, int index) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> except(
+  @Override public Queryable<T> except(
       Queryable<T> source, Enumerable<T> enumerable) {
     return except(source, enumerable, false);
   }
 
-  public Queryable<T> except(
+  @Override public Queryable<T> except(
       Queryable<T> source, Enumerable<T> enumerable, boolean all) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> except(
+  @Override public Queryable<T> except(
       Queryable<T> source,
       Enumerable<T> enumerable,
       EqualityComparer<T> tEqualityComparer) {
     return except(source, enumerable, tEqualityComparer, false);
   }
 
-  public Queryable<T> except(
+  @Override public Queryable<T> except(
       Queryable<T> source,
       Enumerable<T> enumerable,
       EqualityComparer<T> tEqualityComparer,
@@ -290,48 +290,48 @@ public Queryable<T> except(
     throw new UnsupportedOperationException();
   }
 
-  public T first(Queryable<T> source) {
+  @Override public T first(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public T first(
+  @Override public T first(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public T firstOrDefault(
+  @Override public T firstOrDefault(
       Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public T firstOrDefault(
+  @Override public T firstOrDefault(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       EqualityComparer<TKey> comparer) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function2<TKey, Enumerable<T>, TResult>>
@@ -339,7 +339,7 @@ public <TKey, TResult> Queryable<TResult> groupByK(
     throw new UnsupportedOperationException();
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
@@ -347,7 +347,7 @@ public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
     throw new UnsupportedOperationException();
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function2<TKey, Enumerable<T>, TResult>>
@@ -356,7 +356,7 @@ public <TKey, TResult> Queryable<TResult> groupByK(
     throw new UnsupportedOperationException();
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
@@ -365,7 +365,7 @@ public <TKey, TElement, TResult> Queryable<TResult> groupBy(
     throw new UnsupportedOperationException();
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
@@ -375,7 +375,7 @@ public <TKey, TElement, TResult> Queryable<TResult> groupBy(
     throw new UnsupportedOperationException();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       Queryable<T> source,
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
@@ -385,7 +385,7 @@ public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
     throw new UnsupportedOperationException();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       Queryable<T> source,
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
@@ -396,31 +396,31 @@ public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> intersect(
+  @Override public Queryable<T> intersect(
       Queryable<T> source, Enumerable<T> enumerable) {
     return intersect(source, enumerable, false);
   }
 
-  public Queryable<T> intersect(
+  @Override public Queryable<T> intersect(
       Queryable<T> source, Enumerable<T> enumerable, boolean all) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> intersect(
+  @Override public Queryable<T> intersect(
       Queryable<T> source,
       Enumerable<T> enumerable,
       EqualityComparer<T> tEqualityComparer) {
     return intersect(source, enumerable, tEqualityComparer, false);
   }
 
-  public Queryable<T> intersect(
+  @Override public Queryable<T> intersect(
       Queryable<T> source,
       Enumerable<T> enumerable,
       EqualityComparer<T> tEqualityComparer, boolean all) {
     throw new UnsupportedOperationException();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       Queryable<T> source,
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
@@ -429,7 +429,7 @@ public <TInner, TKey, TResult> Queryable<TResult> join(
     throw new UnsupportedOperationException();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       Queryable<T> source,
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
@@ -439,100 +439,100 @@ public <TInner, TKey, TResult> Queryable<TResult> join(
     throw new UnsupportedOperationException();
   }
 
-  public T last(Queryable<T> source) {
+  @Override public T last(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public T last(
+  @Override public T last(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public T lastOrDefault(
+  @Override public T lastOrDefault(
       Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public T lastOrDefault(
+  @Override public T lastOrDefault(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public long longCount(Queryable<T> source) {
+  @Override public long longCount(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public long longCount(
+  @Override public long longCount(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public T max(Queryable<T> source) {
+  @Override public T max(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public <TResult extends Comparable<TResult>> TResult max(
+  @Override public <TResult extends Comparable<TResult>> TResult max(
       Queryable<T> source,
       FunctionExpression<Function1<T, TResult>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public T min(Queryable<T> source) {
+  @Override public T min(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public <TResult extends Comparable<TResult>> TResult min(
+  @Override public <TResult extends Comparable<TResult>> TResult min(
       Queryable<T> source,
       FunctionExpression<Function1<T, TResult>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TResult> Queryable<TResult> ofType(
+  @Override public <TResult> Queryable<TResult> ofType(
       Queryable<T> source, Class<TResult> clazz) {
     throw new UnsupportedOperationException();
   }
 
-  public <T2> Queryable<T2> cast(
+  @Override public <T2> Queryable<T2> cast(
       Queryable<T> source,
       Class<T2> clazz) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderBy(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey> OrderedQueryable<T> orderBy(
+  @Override public <TKey> OrderedQueryable<T> orderBy(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey> OrderedQueryable<T> orderByDescending(
+  @Override public <TKey> OrderedQueryable<T> orderByDescending(
       Queryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> reverse(
+  @Override public Queryable<T> reverse(
       Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public <TResult> Queryable<TResult> select(
+  @Override public <TResult> Queryable<TResult> select(
       Queryable<T> source,
       FunctionExpression<Function1<T, TResult>> selector) {
     RelNode child = toRel(source);
@@ -542,25 +542,25 @@ public <TResult> Queryable<TResult> select(
     return null;
   }
 
-  public <TResult> Queryable<TResult> selectN(
+  @Override public <TResult> Queryable<TResult> selectN(
       Queryable<T> source,
       FunctionExpression<Function2<T, Integer, TResult>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TResult> Queryable<TResult> selectMany(
+  @Override public <TResult> Queryable<TResult> selectMany(
       Queryable<T> source,
       FunctionExpression<Function1<T, Enumerable<TResult>>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TResult> Queryable<TResult> selectManyN(
+  @Override public <TResult> Queryable<TResult> selectManyN(
       Queryable<T> source,
       FunctionExpression<Function2<T, Integer, Enumerable<TResult>>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectMany(
+  @Override public <TCollection, TResult> Queryable<TResult> selectMany(
       Queryable<T> source,
       FunctionExpression<Function2<T, Integer, Enumerable<TCollection>>>
           collectionSelector,
@@ -568,7 +568,7 @@ public <TCollection, TResult> Queryable<TResult> selectMany(
     throw new UnsupportedOperationException();
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectManyN(
+  @Override public <TCollection, TResult> Queryable<TResult> selectManyN(
       Queryable<T> source,
       FunctionExpression<Function1<T, Enumerable<TCollection>>>
           collectionSelector,
@@ -576,171 +576,171 @@ public <TCollection, TResult> Queryable<TResult> selectManyN(
     throw new UnsupportedOperationException();
   }
 
-  public boolean sequenceEqual(
+  @Override public boolean sequenceEqual(
       Queryable<T> source, Enumerable<T> enumerable) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean sequenceEqual(
+  @Override public boolean sequenceEqual(
       Queryable<T> source,
       Enumerable<T> enumerable,
       EqualityComparer<T> tEqualityComparer) {
     throw new UnsupportedOperationException();
   }
 
-  public T single(Queryable<T> source) {
+  @Override public T single(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public T single(
+  @Override public T single(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public T singleOrDefault(Queryable<T> source) {
+  @Override public T singleOrDefault(Queryable<T> source) {
     throw new UnsupportedOperationException();
   }
 
-  public T singleOrDefault(
+  @Override public T singleOrDefault(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> skip(
+  @Override public Queryable<T> skip(
       Queryable<T> source, int count) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> skipWhile(
+  @Override public Queryable<T> skipWhile(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> skipWhileN(
+  @Override public Queryable<T> skipWhileN(
       Queryable<T> source,
       FunctionExpression<Predicate2<T, Integer>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public BigDecimal sumBigDecimal(
+  @Override public BigDecimal sumBigDecimal(
       Queryable<T> source,
       FunctionExpression<BigDecimalFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public BigDecimal sumNullableBigDecimal(
+  @Override public BigDecimal sumNullableBigDecimal(
       Queryable<T> source,
       FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public double sumDouble(
+  @Override public double sumDouble(
       Queryable<T> source,
       FunctionExpression<DoubleFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Double sumNullableDouble(
+  @Override public Double sumNullableDouble(
       Queryable<T> source,
       FunctionExpression<NullableDoubleFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public int sumInteger(
+  @Override public int sumInteger(
       Queryable<T> source,
       FunctionExpression<IntegerFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Integer sumNullableInteger(
+  @Override public Integer sumNullableInteger(
       Queryable<T> source,
       FunctionExpression<NullableIntegerFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public long sumLong(
+  @Override public long sumLong(
       Queryable<T> source,
       FunctionExpression<LongFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Long sumNullableLong(
+  @Override public Long sumNullableLong(
       Queryable<T> source,
       FunctionExpression<NullableLongFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public float sumFloat(
+  @Override public float sumFloat(
       Queryable<T> source,
       FunctionExpression<FloatFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Float sumNullableFloat(
+  @Override public Float sumNullableFloat(
       Queryable<T> source,
       FunctionExpression<NullableFloatFunction1<T>> selector) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> take(
+  @Override public Queryable<T> take(
       Queryable<T> source, int count) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> takeWhile(
+  @Override public Queryable<T> takeWhile(
       Queryable<T> source,
       FunctionExpression<Predicate1<T>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> takeWhileN(
+  @Override public Queryable<T> takeWhileN(
       Queryable<T> source,
       FunctionExpression<Predicate2<T, Integer>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
       OrderedQueryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey> OrderedQueryable<T> thenBy(
+  @Override public <TKey> OrderedQueryable<T> thenBy(
       OrderedQueryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
       OrderedQueryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector) {
     throw new UnsupportedOperationException();
   }
 
-  public <TKey> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey> OrderedQueryable<T> thenByDescending(
       OrderedQueryable<T> source,
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> union(
+  @Override public Queryable<T> union(
       Queryable<T> source, Enumerable<T> source1) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> union(
+  @Override public Queryable<T> union(
       Queryable<T> source,
       Enumerable<T> source1,
       EqualityComparer<T> tEqualityComparer) {
     throw new UnsupportedOperationException();
   }
 
-  public Queryable<T> where(
+  @Override public Queryable<T> where(
       Queryable<T> source,
       FunctionExpression<? extends Predicate1<T>> predicate) {
     RelNode child = toRel(source);
@@ -749,13 +749,13 @@ public Queryable<T> where(
     return source;
   }
 
-  public Queryable<T> whereN(
+  @Override public Queryable<T> whereN(
       Queryable<T> source,
       FunctionExpression<? extends Predicate2<T, Integer>> predicate) {
     throw new UnsupportedOperationException();
   }
 
-  public <T1, TResult> Queryable<TResult> zip(
+  @Override public <T1, TResult> Queryable<TResult> zip(
       Queryable<T> source,
       Enumerable<T1> source1,
       FunctionExpression<Function2<T, T1, TResult>> resultSelector) {
diff --git a/core/src/main/java/org/apache/calcite/prepare/RelOptTableImpl.java b/core/src/main/java/org/apache/calcite/prepare/RelOptTableImpl.java
index e5f8ded9ab4..0cf648e0372 100644
--- a/core/src/main/java/org/apache/calcite/prepare/RelOptTableImpl.java
+++ b/core/src/main/java/org/apache/calcite/prepare/RelOptTableImpl.java
@@ -186,7 +186,7 @@ public static RelOptTableImpl create(RelOptSchema schema,
     return new RelOptTableImpl(schema, rowType, names, table, null, null);
   }
 
-  public <T> T unwrap(Class<T> clazz) {
+  @Override public <T> T unwrap(Class<T> clazz) {
     if (clazz.isInstance(this)) {
       return clazz.cast(this);
     }
@@ -207,7 +207,7 @@ public <T> T unwrap(Class<T> clazz) {
     return null;
   }
 
-  public Expression getExpression(Class clazz) {
+  @Override public Expression getExpression(Class clazz) {
     if (expressionFunction == null) {
       return null;
     }
@@ -231,7 +231,7 @@ public Expression getExpression(Class clazz) {
     return (this.table == null)
         ? super.hashCode() : this.table.hashCode();
   }
-  public double getRowCount() {
+  @Override public double getRowCount() {
     if (rowCount != null) {
       return rowCount;
     }
@@ -244,11 +244,11 @@ public double getRowCount() {
     return 100d;
   }
 
-  public RelOptSchema getRelOptSchema() {
+  @Override public RelOptSchema getRelOptSchema() {
     return schema;
   }
 
-  public RelNode toRel(ToRelContext context) {
+  @Override public RelNode toRel(ToRelContext context) {
     // Make sure rowType's list is immutable. If rowType is DynamicRecordType, creates a new
     // RelOptTable by replacing with immutable RelRecordType using the same field list.
     if (this.getRowType().isDynamicStruct()) {
@@ -287,43 +287,43 @@ public RelNode toRel(ToRelContext context) {
     return LogicalTableScan.create(context.getCluster(), this, context.getTableHints());
   }
 
-  public List<RelCollation> getCollationList() {
+  @Override public List<RelCollation> getCollationList() {
     if (table != null) {
       return table.getStatistic().getCollations();
     }
     return ImmutableList.of();
   }
 
-  public RelDistribution getDistribution() {
+  @Override public RelDistribution getDistribution() {
     if (table != null) {
       return table.getStatistic().getDistribution();
     }
     return RelDistributionTraitDef.INSTANCE.getDefault();
   }
 
-  public boolean isKey(ImmutableBitSet columns) {
+  @Override public boolean isKey(ImmutableBitSet columns) {
     if (table != null) {
       return table.getStatistic().isKey(columns);
     }
     return false;
   }
 
-  public List<ImmutableBitSet> getKeys() {
+  @Override public List<ImmutableBitSet> getKeys() {
     return table.getStatistic().getKeys();
   }
 
-  public List<RelReferentialConstraint> getReferentialConstraints() {
+  @Override public List<RelReferentialConstraint> getReferentialConstraints() {
     if (table != null) {
       return table.getStatistic().getReferentialConstraints();
     }
     return ImmutableList.of();
   }
 
-  public RelDataType getRowType() {
+  @Override public RelDataType getRowType() {
     return rowType;
   }
 
-  public boolean supportsModality(SqlModality modality) {
+  @Override public boolean supportsModality(SqlModality modality) {
     switch (modality) {
     case STREAM:
       return table instanceof StreamableTable;
@@ -336,11 +336,11 @@ public boolean supportsModality(SqlModality modality) {
     return table instanceof TemporalTable;
   }
 
-  public List<String> getQualifiedName() {
+  @Override public List<String> getQualifiedName() {
     return names;
   }
 
-  public SqlMonotonicity getMonotonicity(String columnName) {
+  @Override public SqlMonotonicity getMonotonicity(String columnName) {
     List<RelCollation> collations = table.getStatistic().getCollations();
     if (collations == null) {
       return null;
@@ -357,7 +357,7 @@ public SqlMonotonicity getMonotonicity(String columnName) {
     return SqlMonotonicity.NOT_MONOTONIC;
   }
 
-  public SqlAccessType getAllowedAccess() {
+  @Override public SqlAccessType getAllowedAccess() {
     return SqlAccessType.ALL;
   }
 
@@ -368,11 +368,11 @@ public static List<ColumnStrategy> columnStrategies(final RelOptTable table) {
         Util.first(table.unwrap(InitializerExpressionFactory.class),
             NullInitializerExpressionFactory.INSTANCE);
     return new AbstractList<ColumnStrategy>() {
-      public int size() {
+      @Override public int size() {
         return fieldCount;
       }
 
-      public ColumnStrategy get(int index) {
+      @Override public ColumnStrategy get(int index) {
         return ief.generationStrategy(table, index);
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/profile/Profiler.java b/core/src/main/java/org/apache/calcite/profile/Profiler.java
index 7ab6988194b..cd389854eaa 100644
--- a/core/src/main/java/org/apache/calcite/profile/Profiler.java
+++ b/core/src/main/java/org/apache/calcite/profile/Profiler.java
@@ -109,7 +109,7 @@ public RowCount(int rowCount) {
       this.rowCount = rowCount;
     }
 
-    public Object toMap(JsonBuilder jsonBuilder) {
+    @Override public Object toMap(JsonBuilder jsonBuilder) {
       final Map<String, Object> map = jsonBuilder.map();
       map.put("type", "rowCount");
       map.put("rowCount", rowCount);
@@ -125,7 +125,7 @@ public Unique(SortedSet<Column> columns) {
       this.columns = ImmutableSortedSet.copyOf(columns);
     }
 
-    public Object toMap(JsonBuilder jsonBuilder) {
+    @Override public Object toMap(JsonBuilder jsonBuilder) {
       final Map<String, Object> map = jsonBuilder.map();
       map.put("type", "unique");
       map.put("columns", FunctionalDependency.getObjects(jsonBuilder, columns));
@@ -143,7 +143,7 @@ class FunctionalDependency implements Statistic {
       this.dependentColumn = dependentColumn;
     }
 
-    public Object toMap(JsonBuilder jsonBuilder) {
+    @Override public Object toMap(JsonBuilder jsonBuilder) {
       final Map<String, Object> map = jsonBuilder.map();
       map.put("type", "fd");
       map.put("columns", getObjects(jsonBuilder, columns));
@@ -199,7 +199,7 @@ public Distribution(SortedSet<Column> columns, SortedSet<Comparable> values,
       this.minimal = minimal;
     }
 
-    public Object toMap(JsonBuilder jsonBuilder) {
+    @Override public Object toMap(JsonBuilder jsonBuilder) {
       final Map<String, Object> map = jsonBuilder.map();
       map.put("type", "distribution");
       map.put("columns", FunctionalDependency.getObjects(jsonBuilder, columns));
diff --git a/core/src/main/java/org/apache/calcite/profile/ProfilerImpl.java b/core/src/main/java/org/apache/calcite/profile/ProfilerImpl.java
index e276e620ceb..3f7cf107184 100644
--- a/core/src/main/java/org/apache/calcite/profile/ProfilerImpl.java
+++ b/core/src/main/java/org/apache/calcite/profile/ProfilerImpl.java
@@ -97,7 +97,7 @@ public static Builder builder() {
     this.predicate = predicate;
   }
 
-  public Profile profile(Iterable<List<Comparable>> rows,
+  @Override public Profile profile(Iterable<List<Comparable>> rows,
       final List<Column> columns, Collection<ImmutableBitSet> initialGroups) {
     return new Run(columns, initialGroups).profile(rows);
   }
@@ -543,7 +543,7 @@ static class SingletonCollector extends Collector {
       this.sketchThreshold = sketchThreshold;
     }
 
-    public void add(List<Comparable> row) {
+    @Override public void add(List<Comparable> row) {
       final Comparable v = row.get(columnOrdinal);
       if (v == NullSentinel.INSTANCE) {
         nullCount++;
@@ -560,7 +560,7 @@ public void add(List<Comparable> row) {
       }
     }
 
-    public void finish() {
+    @Override public void finish() {
       space.nullCount = nullCount;
       space.cardinality = values.size() + (nullCount > 0 ? 1 : 0);
       space.valueSet = values.size() < 20 ? values : null;
@@ -583,7 +583,7 @@ static class CompositeCollector extends Collector {
       this.sketchThreshold = sketchThreshold;
     }
 
-    public void add(List<Comparable> row) {
+    @Override public void add(List<Comparable> row) {
       if (space.columnOrdinals.equals(OF)) {
         Util.discard(0);
       }
@@ -619,7 +619,7 @@ public void add(List<Comparable> row) {
       }
     }
 
-    public void finish() {
+    @Override public void finish() {
       // number of input rows (not distinct values)
       // that were null or partially null
       space.nullCount = nullCount;
@@ -660,7 +660,7 @@ protected void add(Comparable value) {
       }
     }
 
-    public void finish() {
+    @Override public void finish() {
       space.nullCount = nullCount;
       space.cardinality = (int) sketch.getEstimate();
       space.valueSet = null;
@@ -676,7 +676,7 @@ static class HllSingletonCollector extends HllCollector {
       this.columnOrdinal = columnOrdinal;
     }
 
-    public void add(List<Comparable> row) {
+    @Override public void add(List<Comparable> row) {
       final Comparable value = row.get(columnOrdinal);
       if (value == NullSentinel.INSTANCE) {
         nullCount++;
@@ -698,7 +698,7 @@ static class HllCompositeCollector extends HllCollector {
       this.columnOrdinals = columnOrdinals;
     }
 
-    public void add(List<Comparable> row) {
+    @Override public void add(List<Comparable> row) {
       if (space.columnOrdinals.equals(OF)) {
         Util.discard(0);
       }
diff --git a/core/src/main/java/org/apache/calcite/profile/SimpleProfiler.java b/core/src/main/java/org/apache/calcite/profile/SimpleProfiler.java
index a251714389f..725a40d9fe7 100644
--- a/core/src/main/java/org/apache/calcite/profile/SimpleProfiler.java
+++ b/core/src/main/java/org/apache/calcite/profile/SimpleProfiler.java
@@ -45,7 +45,7 @@
  */
 public class SimpleProfiler implements Profiler {
 
-  public Profile profile(Iterable<List<Comparable>> rows,
+  @Override public Profile profile(Iterable<List<Comparable>> rows,
       final List<Column> columns, Collection<ImmutableBitSet> initialGroups) {
     Util.discard(initialGroups); // this profiler ignores initial groups
     return new Run(columns).profile(rows);
@@ -309,7 +309,7 @@ static class Space implements Comparable<Space> {
           && columnOrdinals.equals(((Space) o).columnOrdinals);
     }
 
-    public int compareTo(@Nonnull Space o) {
+    @Override public int compareTo(@Nonnull Space o) {
       return columnOrdinals.equals(o.columnOrdinals) ? 0
           : columnOrdinals.contains(o.columnOrdinals) ? 1
               : -1;
diff --git a/core/src/main/java/org/apache/calcite/rel/AbstractRelNode.java b/core/src/main/java/org/apache/calcite/rel/AbstractRelNode.java
index 206503de3df..0b8dccc1ac5 100644
--- a/core/src/main/java/org/apache/calcite/rel/AbstractRelNode.java
+++ b/core/src/main/java/org/apache/calcite/rel/AbstractRelNode.java
@@ -98,7 +98,7 @@ public AbstractRelNode(RelOptCluster cluster, RelTraitSet traitSet) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
+  @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
     // Note that empty set equals empty set, so relational expressions
     // with zero inputs do not generally need to implement their own copy
     // method.
@@ -118,37 +118,37 @@ protected static <T> T sole(List<T> collection) {
     return collection.get(0);
   }
 
-  public final RelOptCluster getCluster() {
+  @Override public final RelOptCluster getCluster() {
     return cluster;
   }
 
-  public final Convention getConvention() {
+  @Override public final Convention getConvention() {
     return traitSet.getTrait(ConventionTraitDef.INSTANCE);
   }
 
-  public RelTraitSet getTraitSet() {
+  @Override public RelTraitSet getTraitSet() {
     return traitSet;
   }
 
-  public String getCorrelVariable() {
+  @Override public String getCorrelVariable() {
     return null;
   }
 
-  public int getId() {
+  @Override public int getId() {
     return id;
   }
 
-  public RelNode getInput(int i) {
+  @Override public RelNode getInput(int i) {
     List<RelNode> inputs = getInputs();
     return inputs.get(i);
   }
 
-  public void register(RelOptPlanner planner) {
+  @Override public void register(RelOptPlanner planner) {
     Util.discard(planner);
   }
 
   // It is not recommended to override this method, but sub-classes can do it at their own risk.
-  public String getRelTypeName() {
+  @Override public String getRelTypeName() {
     String cn = getClass().getName();
     int i = cn.length();
     while (--i >= 0) {
@@ -159,11 +159,11 @@ public String getRelTypeName() {
     return cn;
   }
 
-  public boolean isValid(Litmus litmus, Context context) {
+  @Override public boolean isValid(Litmus litmus, Context context) {
     return litmus.succeed();
   }
 
-  public final RelDataType getRowType() {
+  @Override public final RelDataType getRowType() {
     if (rowType == null) {
       rowType = deriveRowType();
       assert rowType != null : this;
@@ -177,58 +177,58 @@ protected RelDataType deriveRowType() {
     throw new UnsupportedOperationException();
   }
 
-  public RelDataType getExpectedInputRowType(int ordinalInParent) {
+  @Override public RelDataType getExpectedInputRowType(int ordinalInParent) {
     return getRowType();
   }
 
-  public List<RelNode> getInputs() {
+  @Override public List<RelNode> getInputs() {
     return Collections.emptyList();
   }
 
-  public double estimateRowCount(RelMetadataQuery mq) {
+  @Override public double estimateRowCount(RelMetadataQuery mq) {
     return 1.0;
   }
 
-  public Set<CorrelationId> getVariablesSet() {
+  @Override public Set<CorrelationId> getVariablesSet() {
     return ImmutableSet.of();
   }
 
-  public void collectVariablesUsed(Set<CorrelationId> variableSet) {
+  @Override public void collectVariablesUsed(Set<CorrelationId> variableSet) {
     // for default case, nothing to do
   }
 
-  public boolean isEnforcer() {
+  @Override public boolean isEnforcer() {
     return false;
   }
 
-  public void collectVariablesSet(Set<CorrelationId> variableSet) {
+  @Override public void collectVariablesSet(Set<CorrelationId> variableSet) {
   }
 
-  public void childrenAccept(RelVisitor visitor) {
+  @Override public void childrenAccept(RelVisitor visitor) {
     List<RelNode> inputs = getInputs();
     for (int i = 0; i < inputs.size(); i++) {
       visitor.visit(inputs.get(i), i, this);
     }
   }
 
-  public RelNode accept(RelShuttle shuttle) {
+  @Override public RelNode accept(RelShuttle shuttle) {
     // Call fall-back method. Specific logical types (such as LogicalProject
     // and LogicalJoin) have their own RelShuttle.visit methods.
     return shuttle.visit(this);
   }
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     return this;
   }
 
-  public RelOptCost computeSelfCost(RelOptPlanner planner,
+  @Override public RelOptCost computeSelfCost(RelOptPlanner planner,
       RelMetadataQuery mq) {
     // by default, assume cost is proportional to number of rows
     double rowCount = mq.getRowCount(this);
     return planner.getCostFactory().makeCost(rowCount, rowCount, 0);
   }
 
-  public final <M extends Metadata> M metadata(Class<M> metadataClass,
+  @Override public final <M extends Metadata> M metadata(Class<M> metadataClass,
       RelMetadataQuery mq) {
     final MetadataFactory factory = cluster.getMetadataFactory();
     final M metadata = factory.query(this, mq, metadataClass);
@@ -242,7 +242,7 @@ public final <M extends Metadata> M metadata(Class<M> metadataClass,
     return metadata;
   }
 
-  public void explain(RelWriter pw) {
+  @Override public void explain(RelWriter pw) {
     explainTerms(pw).done(this);
   }
 
@@ -261,7 +261,7 @@ public RelWriter explainTerms(RelWriter pw) {
     return pw;
   }
 
-  public RelNode onRegister(RelOptPlanner planner) {
+  @Override public RelNode onRegister(RelOptPlanner planner) {
     List<RelNode> oldInputs = getInputs();
     List<RelNode> inputs = new ArrayList<>(oldInputs.size());
     for (final RelNode input : oldInputs) {
@@ -282,35 +282,35 @@ public RelNode onRegister(RelOptPlanner planner) {
     return r;
   }
 
-  public void recomputeDigest() {
+  @Override public void recomputeDigest() {
     digest.clear();
   }
 
-  public void replaceInput(
+  @Override public void replaceInput(
       int ordinalInParent,
       RelNode p) {
     throw new UnsupportedOperationException("replaceInput called on " + this);
   }
 
   /** Description; consists of id plus digest. */
-  public String toString() {
+  @Override public String toString() {
     return "rel#" + id + ':' + getDigest();
   }
 
   @Deprecated // to be removed before 2.0
-  public final String getDescription() {
+  @Override public final String getDescription() {
     return this.toString();
   }
 
-  public String getDigest() {
+  @Override public String getDigest() {
     return digest.toString();
   }
 
-  public final RelDigest getRelDigest() {
+  @Override public final RelDigest getRelDigest() {
     return digest;
   }
 
-  public RelOptTable getTable() {
+  @Override public RelOptTable getTable() {
     return null;
   }
 
@@ -349,7 +349,7 @@ public RelOptTable getTable() {
    * @return Whether the 2 RelNodes are equivalent or have the same digest.
    * @see #deepHashCode()
    */
-  @API(since = "1.25", status = API.Status.MAINTAINED)
+  @Override @API(since = "1.25", status = API.Status.MAINTAINED)
   public boolean deepEquals(Object obj) {
     if (this == obj) {
       return true;
@@ -386,7 +386,7 @@ public boolean deepEquals(Object obj) {
    * @see #deepEquals(Object)
    */
   @API(since = "1.25", status = API.Status.MAINTAINED)
-  public int deepHashCode() {
+  @Override public int deepHashCode() {
     int result = 31 + getTraitSet().hashCode();
     List<Pair<String, Object>> items = this.getDigestItems();
     for (Pair<String, Object> item : items) {
diff --git a/core/src/main/java/org/apache/calcite/rel/BiRel.java b/core/src/main/java/org/apache/calcite/rel/BiRel.java
index baafd46332c..2c12a21156a 100644
--- a/core/src/main/java/org/apache/calcite/rel/BiRel.java
+++ b/core/src/main/java/org/apache/calcite/rel/BiRel.java
@@ -41,12 +41,12 @@ public BiRel(
     this.right = right;
   }
 
-  public void childrenAccept(RelVisitor visitor) {
+  @Override public void childrenAccept(RelVisitor visitor) {
     visitor.visit(left, 0, this);
     visitor.visit(right, 1, this);
   }
 
-  public List<RelNode> getInputs() {
+  @Override public List<RelNode> getInputs() {
     return FlatLists.of(left, right);
   }
 
@@ -58,7 +58,7 @@ public RelNode getRight() {
     return right;
   }
 
-  public void replaceInput(
+  @Override public void replaceInput(
       int ordinalInParent,
       RelNode p) {
     switch (ordinalInParent) {
diff --git a/core/src/main/java/org/apache/calcite/rel/RelCollationImpl.java b/core/src/main/java/org/apache/calcite/rel/RelCollationImpl.java
index f06c84c1cd6..3853f46b0d1 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelCollationImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelCollationImpl.java
@@ -71,19 +71,19 @@ public static RelCollation of(List<RelFieldCollation> fieldCollations) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelTraitDef getTraitDef() {
+  @Override public RelTraitDef getTraitDef() {
     return RelCollationTraitDef.INSTANCE;
   }
 
-  public List<RelFieldCollation> getFieldCollations() {
+  @Override public List<RelFieldCollation> getFieldCollations() {
     return fieldCollations;
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return fieldCollations.hashCode();
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (this == obj) {
       return true;
     }
@@ -94,11 +94,11 @@ public boolean equals(Object obj) {
     return false;
   }
 
-  public boolean isTop() {
+  @Override public boolean isTop() {
     return fieldCollations.isEmpty();
   }
 
-  public int compareTo(@Nonnull RelMultipleTrait o) {
+  @Override public int compareTo(@Nonnull RelMultipleTrait o) {
     final RelCollationImpl that = (RelCollationImpl) o;
     final UnmodifiableIterator<RelFieldCollation> iterator =
         that.fieldCollations.iterator();
@@ -115,7 +115,7 @@ public int compareTo(@Nonnull RelMultipleTrait o) {
     return iterator.hasNext() ? -1 : 0;
   }
 
-  public void register(RelOptPlanner planner) {}
+  @Override public void register(RelOptPlanner planner) {}
 
   /**
    * Applies mapping to a given collation.
@@ -140,7 +140,7 @@ public void register(RelOptPlanner planner) {}
     return (RelCollationImpl) RexUtil.apply(mapping, this);
   }
 
-  public boolean satisfies(RelTrait trait) {
+  @Override public boolean satisfies(RelTrait trait) {
     return this == trait
         || trait instanceof RelCollationImpl
         && Util.startsWith(fieldCollations,
@@ -150,7 +150,7 @@ public boolean satisfies(RelTrait trait) {
   /** Returns a string representation of this collation, suitably terse given
    * that it will appear in plan traces. Examples:
    * "[]", "[2]", "[0 DESC, 1]", "[0 DESC, 1 ASC NULLS LAST]". */
-  public String toString() {
+  @Override public String toString() {
     Iterator<RelFieldCollation> it = fieldCollations.iterator();
     if (! it.hasNext()) {
       return "[]";
diff --git a/core/src/main/java/org/apache/calcite/rel/RelCollationTraitDef.java b/core/src/main/java/org/apache/calcite/rel/RelCollationTraitDef.java
index bab96ab019e..ad6d9fa2d7a 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelCollationTraitDef.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelCollationTraitDef.java
@@ -43,11 +43,11 @@ public class RelCollationTraitDef extends RelTraitDef<RelCollation> {
   private RelCollationTraitDef() {
   }
 
-  public Class<RelCollation> getTraitClass() {
+  @Override public Class<RelCollation> getTraitClass() {
     return RelCollation.class;
   }
 
-  public String getSimpleName() {
+  @Override public String getSimpleName() {
     return "sort";
   }
 
@@ -55,11 +55,11 @@ public String getSimpleName() {
     return true;
   }
 
-  public RelCollation getDefault() {
+  @Override public RelCollation getDefault() {
     return RelCollations.EMPTY;
   }
 
-  public RelNode convert(
+  @Override public RelNode convert(
       RelOptPlanner planner,
       RelNode rel,
       RelCollation toCollation,
@@ -81,7 +81,7 @@ public RelNode convert(
     return newRel;
   }
 
-  public boolean canConvert(
+  @Override public boolean canConvert(
       RelOptPlanner planner, RelCollation fromTrait, RelCollation toTrait) {
     return true;
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/RelCollations.java b/core/src/main/java/org/apache/calcite/rel/RelCollations.java
index ed522780444..8071f7f645d 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelCollations.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelCollations.java
@@ -53,7 +53,7 @@ public class RelCollations {
       RelCollationTraitDef.INSTANCE.canonize(
           new RelCollationImpl(
               ImmutableList.of(new RelFieldCollation(-1))) {
-            public String toString() {
+            @Override public String toString() {
               return "PRESERVE";
             }
           });
diff --git a/core/src/main/java/org/apache/calcite/rel/RelDistribution.java b/core/src/main/java/org/apache/calcite/rel/RelDistribution.java
index cf2dc035259..cc4d96b39f6 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelDistribution.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelDistribution.java
@@ -66,7 +66,7 @@ public interface RelDistribution extends RelMultipleTrait {
    * @param mapping   Mapping
    * @return distribution with mapping applied
    */
-  RelDistribution apply(Mappings.TargetMapping mapping);
+  @Override RelDistribution apply(Mappings.TargetMapping mapping);
 
   /** Type of distribution. */
   enum Type {
diff --git a/core/src/main/java/org/apache/calcite/rel/RelDistributionTraitDef.java b/core/src/main/java/org/apache/calcite/rel/RelDistributionTraitDef.java
index 72dd253f736..1582e32e66f 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelDistributionTraitDef.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelDistributionTraitDef.java
@@ -36,19 +36,19 @@ public class RelDistributionTraitDef extends RelTraitDef<RelDistribution> {
   private RelDistributionTraitDef() {
   }
 
-  public Class<RelDistribution> getTraitClass() {
+  @Override public Class<RelDistribution> getTraitClass() {
     return RelDistribution.class;
   }
 
-  public String getSimpleName() {
+  @Override public String getSimpleName() {
     return "dist";
   }
 
-  public RelDistribution getDefault() {
+  @Override public RelDistribution getDefault() {
     return RelDistributions.ANY;
   }
 
-  public RelNode convert(RelOptPlanner planner, RelNode rel,
+  @Override public RelNode convert(RelOptPlanner planner, RelNode rel,
       RelDistribution toDistribution, boolean allowInfiniteCostConverters) {
     if (toDistribution == RelDistributions.ANY) {
       return rel;
@@ -66,7 +66,7 @@ public RelNode convert(RelOptPlanner planner, RelNode rel,
     return newRel;
   }
 
-  public boolean canConvert(RelOptPlanner planner, RelDistribution fromTrait,
+  @Override public boolean canConvert(RelOptPlanner planner, RelDistribution fromTrait,
       RelDistribution toTrait) {
     return true;
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/RelDistributions.java b/core/src/main/java/org/apache/calcite/rel/RelDistributions.java
index 9b7b10eb9c0..05f55392c04 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelDistributions.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelDistributions.java
@@ -125,19 +125,19 @@ private RelDistributionImpl(Type type, ImmutableIntList keys) {
       }
     }
 
-    @Nonnull public Type getType() {
+    @Override @Nonnull public Type getType() {
       return type;
     }
 
-    @Nonnull public List<Integer> getKeys() {
+    @Override @Nonnull public List<Integer> getKeys() {
       return keys;
     }
 
-    public RelDistributionTraitDef getTraitDef() {
+    @Override public RelDistributionTraitDef getTraitDef() {
       return RelDistributionTraitDef.INSTANCE;
     }
 
-    public RelDistribution apply(Mappings.TargetMapping mapping) {
+    @Override public RelDistribution apply(Mappings.TargetMapping mapping) {
       if (keys.isEmpty()) {
         return this;
       }
@@ -151,7 +151,7 @@ public RelDistribution apply(Mappings.TargetMapping mapping) {
       return of(type, mappedKeys);
     }
 
-    public boolean satisfies(RelTrait trait) {
+    @Override public boolean satisfies(RelTrait trait) {
       if (trait == this || trait == ANY) {
         return true;
       }
@@ -181,7 +181,7 @@ public boolean satisfies(RelTrait trait) {
       return false;
     }
 
-    public void register(RelOptPlanner planner) {
+    @Override public void register(RelOptPlanner planner) {
     }
 
     @Override public boolean isTop() {
diff --git a/core/src/main/java/org/apache/calcite/rel/RelFieldCollation.java b/core/src/main/java/org/apache/calcite/rel/RelFieldCollation.java
index 38ecccef9a4..37a956027c9 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelFieldCollation.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelFieldCollation.java
@@ -268,7 +268,7 @@ public RelFieldCollation.Direction getDirection() {
     return direction;
   }
 
-  public String toString() {
+  @Override public String toString() {
     if (direction == Direction.ASCENDING
         && nullDirection == direction.defaultNullDirection()) {
       return String.valueOf(fieldIndex);
diff --git a/core/src/main/java/org/apache/calcite/rel/RelNode.java b/core/src/main/java/org/apache/calcite/rel/RelNode.java
index bd865f6b355..284052f3520 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelNode.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelNode.java
@@ -109,7 +109,7 @@ public interface RelNode extends RelOptNode, Cloneable {
   /**
    * Returns the type of the rows returned by this relational expression.
    */
-  RelDataType getRowType();
+  @Override RelDataType getRowType();
 
   /**
    * Returns the type of the rows expected for an input. Defaults to
@@ -127,7 +127,7 @@ public interface RelNode extends RelOptNode, Cloneable {
    *
    * @return Array of this relational expression's inputs
    */
-  List<RelNode> getInputs();
+  @Override List<RelNode> getInputs();
 
   /**
    * Returns an estimate of the number of rows this relational expression will
@@ -259,7 +259,7 @@ default String explain() {
    *
    * @see #getRelDigest()
    */
-  default String getDigest() {
+  @Override default String getDigest() {
     return getRelDigest().toString();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/RelNodes.java b/core/src/main/java/org/apache/calcite/rel/RelNodes.java
index a7d98c4b077..dab3b5e5f63 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelNodes.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelNodes.java
@@ -53,7 +53,7 @@ public static int compareRels(RelNode[] rels0, RelNode[] rels1) {
 
   /** Arbitrary stable comparator for {@link RelNode}s. */
   private static class RelNodeComparator implements Comparator<RelNode> {
-    public int compare(RelNode o1, RelNode o2) {
+    @Override public int compare(RelNode o1, RelNode o2) {
       // Compare on field count first. It is more stable than id (when rules
       // are added to the set of active rules).
       final int c = Utilities.compare(o1.getRowType().getFieldCount(),
diff --git a/core/src/main/java/org/apache/calcite/rel/RelShuttleImpl.java b/core/src/main/java/org/apache/calcite/rel/RelShuttleImpl.java
index 9b622df8ab1..35b4aa28eb1 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelShuttleImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelShuttleImpl.java
@@ -73,71 +73,71 @@ protected RelNode visitChildren(RelNode rel) {
     return rel;
   }
 
-  public RelNode visit(LogicalAggregate aggregate) {
+  @Override public RelNode visit(LogicalAggregate aggregate) {
     return visitChild(aggregate, 0, aggregate.getInput());
   }
 
-  public RelNode visit(LogicalMatch match) {
+  @Override public RelNode visit(LogicalMatch match) {
     return visitChild(match, 0, match.getInput());
   }
 
-  public RelNode visit(TableScan scan) {
+  @Override public RelNode visit(TableScan scan) {
     return scan;
   }
 
-  public RelNode visit(TableFunctionScan scan) {
+  @Override public RelNode visit(TableFunctionScan scan) {
     return visitChildren(scan);
   }
 
-  public RelNode visit(LogicalValues values) {
+  @Override public RelNode visit(LogicalValues values) {
     return values;
   }
 
-  public RelNode visit(LogicalFilter filter) {
+  @Override public RelNode visit(LogicalFilter filter) {
     return visitChild(filter, 0, filter.getInput());
   }
 
-  public RelNode visit(LogicalCalc calc) {
+  @Override public RelNode visit(LogicalCalc calc) {
     return visitChildren(calc);
   }
 
-  public RelNode visit(LogicalProject project) {
+  @Override public RelNode visit(LogicalProject project) {
     return visitChild(project, 0, project.getInput());
   }
 
-  public RelNode visit(LogicalJoin join) {
+  @Override public RelNode visit(LogicalJoin join) {
     return visitChildren(join);
   }
 
-  public RelNode visit(LogicalCorrelate correlate) {
+  @Override public RelNode visit(LogicalCorrelate correlate) {
     return visitChildren(correlate);
   }
 
-  public RelNode visit(LogicalUnion union) {
+  @Override public RelNode visit(LogicalUnion union) {
     return visitChildren(union);
   }
 
-  public RelNode visit(LogicalIntersect intersect) {
+  @Override public RelNode visit(LogicalIntersect intersect) {
     return visitChildren(intersect);
   }
 
-  public RelNode visit(LogicalMinus minus) {
+  @Override public RelNode visit(LogicalMinus minus) {
     return visitChildren(minus);
   }
 
-  public RelNode visit(LogicalSort sort) {
+  @Override public RelNode visit(LogicalSort sort) {
     return visitChildren(sort);
   }
 
-  public RelNode visit(LogicalExchange exchange) {
+  @Override public RelNode visit(LogicalExchange exchange) {
     return visitChildren(exchange);
   }
 
-  public RelNode visit(LogicalTableModify modify) {
+  @Override public RelNode visit(LogicalTableModify modify) {
     return visitChildren(modify);
   }
 
-  public RelNode visit(RelNode other) {
+  @Override public RelNode visit(RelNode other) {
     return visitChildren(other);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/rel/SingleRel.java b/core/src/main/java/org/apache/calcite/rel/SingleRel.java
index ef06c96e39b..403d5c1fa06 100644
--- a/core/src/main/java/org/apache/calcite/rel/SingleRel.java
+++ b/core/src/main/java/org/apache/calcite/rel/SingleRel.java
@@ -72,7 +72,7 @@ public RelNode getInput() {
     visitor.visit(input, 0, this);
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     return super.explainTerms(pw)
         .input("input", getInput());
   }
@@ -85,7 +85,7 @@ public RelWriter explainTerms(RelWriter pw) {
     recomputeDigest();
   }
 
-  protected RelDataType deriveRowType() {
+  @Override protected RelDataType deriveRowType() {
     return input.getRowType();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/rel/convert/ConverterImpl.java b/core/src/main/java/org/apache/calcite/rel/convert/ConverterImpl.java
index 310cf629073..b542b962087 100644
--- a/core/src/main/java/org/apache/calcite/rel/convert/ConverterImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/convert/ConverterImpl.java
@@ -71,11 +71,11 @@ protected Error cannotImplement() {
         + inTraits + " traits");
   }
 
-  public RelTraitSet getInputTraits() {
+  @Override public RelTraitSet getInputTraits() {
     return inTraits;
   }
 
-  public RelTraitDef getTraitDef() {
+  @Override public RelTraitDef getTraitDef() {
     return traitDef;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/convert/ConverterRule.java b/core/src/main/java/org/apache/calcite/rel/convert/ConverterRule.java
index 0d78259110a..45ac09f7697 100644
--- a/core/src/main/java/org/apache/calcite/rel/convert/ConverterRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/convert/ConverterRule.java
@@ -124,7 +124,7 @@ public <R extends RelNode> ConverterRule(Class<R> clazz,
     return (Convention) outTrait;
   }
 
-  public RelTrait getOutTrait() {
+  @Override public RelTrait getOutTrait() {
     return outTrait;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/convert/NoneConverter.java b/core/src/main/java/org/apache/calcite/rel/convert/NoneConverter.java
index 8f08a913a1e..70e89a2ce1f 100644
--- a/core/src/main/java/org/apache/calcite/rel/convert/NoneConverter.java
+++ b/core/src/main/java/org/apache/calcite/rel/convert/NoneConverter.java
@@ -46,7 +46,7 @@ public NoneConverter(
   //~ Methods ----------------------------------------------------------------
 
 
-  public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
+  @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
     assert traitSet.comprises(Convention.NONE);
     return new NoneConverter(
         getCluster(),
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Aggregate.java b/core/src/main/java/org/apache/calcite/rel/core/Aggregate.java
index 634e0fbeeff..f728a523a5f 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Aggregate.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Aggregate.java
@@ -318,7 +318,7 @@ public ImmutableList<ImmutableBitSet> getGroupSets() {
     return groupSets;
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     // We skip the "groups" element if it is a singleton of "group".
     super.explainTerms(pw)
         .item("group", groupSet)
@@ -364,7 +364,7 @@ public RelWriter explainTerms(RelWriter pw) {
     return planner.getCostFactory().makeCost(rowCount * multiplier, 0, 0);
   }
 
-  protected RelDataType deriveRowType() {
+  @Override protected RelDataType deriveRowType() {
     return deriveRowType(getCluster().getTypeFactory(), getInput().getRowType(),
         false, groupSet, groupSets, aggCalls);
   }
@@ -416,7 +416,7 @@ public static RelDataType deriveRowType(RelDataTypeFactory typeFactory,
     return builder.build();
   }
 
-  public boolean isValid(Litmus litmus, Context context) {
+  @Override public boolean isValid(Litmus litmus, Context context) {
     return super.isValid(litmus, context)
         && litmus.check(Util.isDistinct(getRowType().getFieldNames()),
             "distinct field names: {}", getRowType());
@@ -600,15 +600,15 @@ public AggCallBinding(RelDataTypeFactory typeFactory,
       return filter;
     }
 
-    public int getOperandCount() {
+    @Override public int getOperandCount() {
       return operands.size();
     }
 
-    public RelDataType getOperandType(int ordinal) {
+    @Override public RelDataType getOperandType(int ordinal) {
       return operands.get(ordinal);
     }
 
-    public CalciteException newError(
+    @Override public CalciteException newError(
         Resources.ExInst<SqlValidatorException> e) {
       return SqlUtil.newContextException(SqlParserPos.ZERO, e);
     }
diff --git a/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java b/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java
index 8880389f4a2..2eed5d7c484 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java
@@ -291,7 +291,7 @@ public AggregateCall rename(String name) {
         name);
   }
 
-  public String toString() {
+  @Override public String toString() {
     StringBuilder buf = new StringBuilder(aggFunction.toString());
     buf.append("(");
     if (approximate) {
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Calc.java b/core/src/main/java/org/apache/calcite/rel/core/Calc.java
index 4f1f208cee7..a85853ab307 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Calc.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Calc.java
@@ -136,7 +136,7 @@ public final boolean containsOver() {
     return RexOver.containsOver(program);
   }
 
-  public boolean isValid(Litmus litmus, Context context) {
+  @Override public boolean isValid(Litmus litmus, Context context) {
     if (!RelOptUtil.equal(
         "program's input type",
         program.getInputRowType(),
@@ -174,11 +174,11 @@ public RexProgram getProgram() {
     return planner.getCostFactory().makeCost(dRows, dCpu, dIo);
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     return program.explainCalc(super.explainTerms(pw));
   }
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     List<RexNode> oldExprs = program.getExprList();
     List<RexNode> exprs = shuttle.apply(oldExprs);
     List<RexLocalRef> oldProjects = program.getProjectList();
diff --git a/core/src/main/java/org/apache/calcite/rel/core/CorrelationId.java b/core/src/main/java/org/apache/calcite/rel/core/CorrelationId.java
index 11be21b632b..f34f216052e 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/CorrelationId.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/CorrelationId.java
@@ -81,11 +81,11 @@ public String getName() {
     return name;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return name;
   }
 
-  public int compareTo(CorrelationId other) {
+  @Override public int compareTo(CorrelationId other) {
     return id - other.id;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Exchange.java b/core/src/main/java/org/apache/calcite/rel/core/Exchange.java
index 79999bd8ac7..31f94a3c30e 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Exchange.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Exchange.java
@@ -98,7 +98,7 @@ public RelDistribution getDistribution() {
         Util.nLogN(rowCount) * bytesPerRow, rowCount, 0);
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     return super.explainTerms(pw)
         .item("distribution", distribution);
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Filter.java b/core/src/main/java/org/apache/calcite/rel/core/Filter.java
index e3ba20aa19d..ef4d9276198 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Filter.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Filter.java
@@ -97,7 +97,7 @@ protected Filter(RelInput input) {
   public abstract Filter copy(RelTraitSet traitSet, RelNode input,
       RexNode condition);
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     RexNode condition = shuttle.apply(this.condition);
     if (this.condition == condition) {
       return this;
@@ -151,7 +151,7 @@ public static double estimateFilteredRows(RelNode child, RexNode condition) {
     return RelMdUtil.estimateFilteredRows(child, condition, mq);
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     return super.explainTerms(pw)
         .item("condition", condition);
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Project.java b/core/src/main/java/org/apache/calcite/rel/core/Project.java
index 51e8271e5a7..053a36721e6 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Project.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Project.java
@@ -153,7 +153,7 @@ public boolean isBoxed() {
     return true;
   }
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     List<RexNode> exps = shuttle.apply(this.exps);
     if (this.exps == exps) {
       return this;
@@ -200,7 +200,7 @@ public final boolean containsOver() {
     return RexOver.containsOver(getProjects(), null);
   }
 
-  public boolean isValid(Litmus litmus, Context context) {
+  @Override public boolean isValid(Litmus litmus, Context context) {
     if (!super.isValid(litmus, context)) {
       return litmus.fail(null);
     }
@@ -259,7 +259,7 @@ private static int countTrivial(List<RexNode> refs) {
     return refs.size();
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     super.explainTerms(pw);
     // Skip writing field names so the optimizer can reuse the projects that differ in
     // field names only
diff --git a/core/src/main/java/org/apache/calcite/rel/core/RelFactories.java b/core/src/main/java/org/apache/calcite/rel/core/RelFactories.java
index 62a133c7f46..18b0a78f6ec 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/RelFactories.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/RelFactories.java
@@ -172,7 +172,7 @@ RelNode createProject(RelNode input, List<RelHint> hints,
    * {@link org.apache.calcite.rel.logical.LogicalProject}.
    */
   private static class ProjectFactoryImpl implements ProjectFactory {
-    public RelNode createProject(RelNode input, List<RelHint> hints,
+    @Override public RelNode createProject(RelNode input, List<RelHint> hints,
         List<? extends RexNode> childExprs, List<String> fieldNames) {
       return LogicalProject.create(input, hints, childExprs, fieldNames);
     }
@@ -199,7 +199,7 @@ default RelNode createSort(RelTraitSet traitSet, RelNode input,
    * returns a vanilla {@link Sort}.
    */
   private static class SortFactoryImpl implements SortFactory {
-    public RelNode createSort(RelNode input, RelCollation collation,
+    @Override public RelNode createSort(RelNode input, RelCollation collation,
         RexNode offset, RexNode fetch) {
       return LogicalSort.create(input, collation, offset, fetch);
     }
@@ -270,7 +270,7 @@ public interface SetOpFactory {
    * operation (UNION, EXCEPT, INTERSECT).
    */
   private static class SetOpFactoryImpl implements SetOpFactory {
-    public RelNode createSetOp(SqlKind kind, List<RelNode> inputs,
+    @Override public RelNode createSetOp(SqlKind kind, List<RelNode> inputs,
         boolean all) {
       switch (kind) {
       case UNION:
@@ -300,7 +300,7 @@ RelNode createAggregate(RelNode input, List<RelHint> hints, ImmutableBitSet grou
    * that returns a vanilla {@link LogicalAggregate}.
    */
   private static class AggregateFactoryImpl implements AggregateFactory {
-    public RelNode createAggregate(RelNode input, List<RelHint> hints,
+    @Override public RelNode createAggregate(RelNode input, List<RelHint> hints,
         ImmutableBitSet groupSet, ImmutableList<ImmutableBitSet> groupSets,
         List<AggregateCall> aggCalls) {
       return LogicalAggregate.create(input, hints, groupSet, groupSets, aggCalls);
@@ -339,7 +339,7 @@ default RelNode createFilter(RelNode input, RexNode condition) {
    * returns a vanilla {@link LogicalFilter}.
    */
   private static class FilterFactoryImpl implements FilterFactory {
-    public RelNode createFilter(RelNode input, RexNode condition,
+    @Override public RelNode createFilter(RelNode input, RexNode condition,
         Set<CorrelationId> variablesSet) {
       return LogicalFilter.create(input, condition,
           ImmutableSet.copyOf(variablesSet));
@@ -376,7 +376,7 @@ RelNode createJoin(RelNode left, RelNode right, List<RelHint> hints,
    * {@link org.apache.calcite.rel.logical.LogicalJoin}.
    */
   private static class JoinFactoryImpl implements JoinFactory {
-    public RelNode createJoin(RelNode left, RelNode right, List<RelHint> hints,
+    @Override public RelNode createJoin(RelNode left, RelNode right, List<RelHint> hints,
         RexNode condition, Set<CorrelationId> variablesSet,
         JoinRelType joinType, boolean semiJoinDone) {
       return LogicalJoin.create(left, right, hints, condition, variablesSet, joinType,
@@ -410,7 +410,7 @@ RelNode createCorrelate(RelNode left, RelNode right,
    * {@link org.apache.calcite.rel.logical.LogicalCorrelate}.
    */
   private static class CorrelateFactoryImpl implements CorrelateFactory {
-    public RelNode createCorrelate(RelNode left, RelNode right,
+    @Override public RelNode createCorrelate(RelNode left, RelNode right,
         CorrelationId correlationId, ImmutableBitSet requiredColumns,
         JoinRelType joinType) {
       return LogicalCorrelate.create(left, right, correlationId,
@@ -444,7 +444,7 @@ public interface SemiJoinFactory {
    */
   @Deprecated  // to be removed before 2.0
   private static class SemiJoinFactoryImpl implements SemiJoinFactory {
-    public RelNode createSemiJoin(RelNode left, RelNode right,
+    @Override public RelNode createSemiJoin(RelNode left, RelNode right,
         RexNode condition) {
       return LogicalJoin.create(left, right, ImmutableList.of(), condition,
           ImmutableSet.of(), JoinRelType.SEMI, false, ImmutableList.of());
@@ -468,7 +468,7 @@ RelNode createValues(RelOptCluster cluster, RelDataType rowType,
    * {@link LogicalValues}.
    */
   private static class ValuesFactoryImpl implements ValuesFactory {
-    public RelNode createValues(RelOptCluster cluster, RelDataType rowType,
+    @Override public RelNode createValues(RelOptCluster cluster, RelDataType rowType,
         List<ImmutableList<RexLiteral>> tuples) {
       return LogicalValues.create(cluster, rowType,
           ImmutableList.copyOf(tuples));
@@ -491,7 +491,7 @@ public interface TableScanFactory {
    * {@link LogicalTableScan}.
    */
   private static class TableScanFactoryImpl implements TableScanFactory {
-    public RelNode createScan(RelOptTable.ToRelContext toRelContext, RelOptTable table) {
+    @Override public RelNode createScan(RelOptTable.ToRelContext toRelContext, RelOptTable table) {
       return table.toRel(toRelContext);
     }
   }
@@ -556,7 +556,7 @@ public interface SnapshotFactory {
    * returns a vanilla {@link LogicalSnapshot}.
    */
   public static class SnapshotFactoryImpl implements SnapshotFactory {
-    public RelNode createSnapshot(RelNode input, RexNode period) {
+    @Override public RelNode createSnapshot(RelNode input, RexNode period) {
       return LogicalSnapshot.create(input, period);
     }
   }
@@ -580,7 +580,7 @@ RelNode createMatch(RelNode input, RexNode pattern,
    * that returns a {@link LogicalMatch}.
    */
   private static class MatchFactoryImpl implements MatchFactory {
-    public RelNode createMatch(RelNode input, RexNode pattern,
+    @Override public RelNode createMatch(RelNode input, RexNode pattern,
         RelDataType rowType, boolean strictStart, boolean strictEnd,
         Map<String, RexNode> patternDefinitions, Map<String, RexNode> measures,
         RexNode after, Map<String, ? extends SortedSet<String>> subsets,
@@ -608,7 +608,7 @@ RelNode createTableSpool(RelNode input, Spool.Type readType,
    * that returns Logical Spools.
    */
   private static class SpoolFactoryImpl implements SpoolFactory {
-    public RelNode createTableSpool(RelNode input, Spool.Type readType,
+    @Override public RelNode createTableSpool(RelNode input, Spool.Type readType,
         Spool.Type writeType, RelOptTable table) {
       return LogicalTableSpool.create(input, readType, writeType, table);
     }
@@ -630,7 +630,7 @@ RelNode createRepeatUnion(RelNode seed, RelNode iterative, boolean all,
    * that returns a {@link LogicalRepeatUnion}.
    */
   private static class RepeatUnionFactoryImpl implements RepeatUnionFactory {
-    public RelNode createRepeatUnion(RelNode seed, RelNode iterative,
+    @Override public RelNode createRepeatUnion(RelNode seed, RelNode iterative,
         boolean all, int iterationLimit) {
       return LogicalRepeatUnion.create(seed, iterative, all, iterationLimit);
     }
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Sample.java b/core/src/main/java/org/apache/calcite/rel/core/Sample.java
index d78f2fdb165..bab6e2c805c 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Sample.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Sample.java
@@ -66,7 +66,7 @@ private static RelOptSamplingParameters getSamplingParameters(
         repeatable ? ((Number) repeatableSeed).intValue() : 0);
   }
 
-  public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
+  @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
     assert traitSet.containsIfApplicable(Convention.NONE);
     return new Sample(getCluster(), sole(inputs), params);
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Snapshot.java b/core/src/main/java/org/apache/calcite/rel/core/Snapshot.java
index eaba15dd600..ae5c795ab89 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Snapshot.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Snapshot.java
@@ -74,7 +74,7 @@ protected Snapshot(RelOptCluster cluster, RelTraitSet traitSet, RelNode input,
 
   public abstract Snapshot copy(RelTraitSet traitSet, RelNode input, RexNode period);
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     RexNode condition = shuttle.apply(this.period);
     if (this.period == condition) {
       return this;
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Sort.java b/core/src/main/java/org/apache/calcite/rel/core/Sort.java
index 4de02914eac..c7ece1f02fe 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Sort.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Sort.java
@@ -130,7 +130,7 @@ public abstract Sort copy(RelTraitSet traitSet, RelNode newInput,
     return planner.getCostFactory().makeCost(rowCount, cpu, 0);
   }
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     RexNode offset = shuttle.apply(this.offset);
     RexNode fetch = shuttle.apply(this.fetch);
     List<RexNode> originalSortExps = getSortExps();
@@ -174,7 +174,7 @@ public List<RexNode> getSortExps() {
             Objects.requireNonNull(field).getFieldIndex()));
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     super.explainTerms(pw);
     if (pw.nest()) {
       pw.item("collation", collation);
diff --git a/core/src/main/java/org/apache/calcite/rel/core/SortExchange.java b/core/src/main/java/org/apache/calcite/rel/core/SortExchange.java
index eba52a4fdd2..dc9a7114dd8 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/SortExchange.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/SortExchange.java
@@ -103,7 +103,7 @@ public RelCollation getCollation() {
     return collation;
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     return super.explainTerms(pw)
         .item("collation", collation);
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/core/TableFunctionScan.java b/core/src/main/java/org/apache/calcite/rel/core/TableFunctionScan.java
index c79e0a582fa..b33ca3d790a 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/TableFunctionScan.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/TableFunctionScan.java
@@ -133,7 +133,7 @@ public abstract TableFunctionScan copy(
     return inputs;
   }
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     RexNode rexCall = shuttle.apply(this.rexCall);
     if (rexCall == this.rexCall) {
       return this;
@@ -181,7 +181,7 @@ public RexNode getCall() {
     return rexCall;
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     super.explainTerms(pw);
     for (Ord<RelNode> ord : Ord.zip(inputs)) {
       pw.input("input#" + ord.i, ord.e);
diff --git a/core/src/main/java/org/apache/calcite/rel/core/TableModify.java b/core/src/main/java/org/apache/calcite/rel/core/TableModify.java
index 162eb2df815..8a5744675c3 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/TableModify.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/TableModify.java
@@ -158,7 +158,7 @@ public Prepare.CatalogReader getCatalogReader() {
     return catalogReader;
   }
 
-  public RelOptTable getTable() {
+  @Override public RelOptTable getTable() {
     return table;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/core/TableSpool.java b/core/src/main/java/org/apache/calcite/rel/core/TableSpool.java
index cb7ec14ba0d..7c39e84728e 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/TableSpool.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/TableSpool.java
@@ -42,7 +42,7 @@ protected TableSpool(RelOptCluster cluster, RelTraitSet traitSet,
     this.table = Objects.requireNonNull(table);
   }
 
-  public RelOptTable getTable() {
+  @Override public RelOptTable getTable() {
     return table;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Uncollect.java b/core/src/main/java/org/apache/calcite/rel/core/Uncollect.java
index 45caa41f0d4..cbf5b6a89e3 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Uncollect.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Uncollect.java
@@ -122,7 +122,7 @@ public RelNode copy(RelTraitSet traitSet, RelNode input) {
     return new Uncollect(getCluster(), traitSet, input, withOrdinality, itemAliases);
   }
 
-  protected RelDataType deriveRowType() {
+  @Override protected RelDataType deriveRowType() {
     return deriveUncollectRowType(input, withOrdinality, itemAliases);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Values.java b/core/src/main/java/org/apache/calcite/rel/core/Values.java
index 8f25815fb96..0943ff4b1ea 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Values.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Values.java
@@ -166,12 +166,12 @@ private boolean assertRowType() {
   }
 
   // implement RelNode
-  public double estimateRowCount(RelMetadataQuery mq) {
+  @Override public double estimateRowCount(RelMetadataQuery mq) {
     return tuples.size();
   }
 
   // implement RelNode
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     // A little adapter just to get the tuples to come out
     // with curly brackets instead of square brackets.  Plus
     // more whitespace for readability.
diff --git a/core/src/main/java/org/apache/calcite/rel/core/Window.java b/core/src/main/java/org/apache/calcite/rel/core/Window.java
index dc364ea5b7c..48ddcff32d1 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/Window.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/Window.java
@@ -123,7 +123,7 @@ public Window(RelOptCluster cluster, RelTraitSet traitSet, RelNode input,
     return litmus.succeed();
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     super.explainTerms(pw);
     for (Ord<Group> window : Ord.zip(groups)) {
       pw.item("window#" + window.i, window.e.toString());
@@ -134,11 +134,11 @@ public RelWriter explainTerms(RelWriter pw) {
   public static ImmutableIntList getProjectOrdinals(final List<RexNode> exprs) {
     return ImmutableIntList.copyOf(
         new AbstractList<Integer>() {
-          public Integer get(int index) {
+          @Override public Integer get(int index) {
             return ((RexSlot) exprs.get(index)).getIndex();
           }
 
-          public int size() {
+          @Override public int size() {
             return exprs.size();
           }
         });
@@ -148,7 +148,7 @@ public static RelCollation getCollation(
       final List<RexFieldCollation> collations) {
     return RelCollations.of(
         new AbstractList<RelFieldCollation>() {
-          public RelFieldCollation get(int index) {
+          @Override public RelFieldCollation get(int index) {
             final RexFieldCollation collation = collations.get(index);
             return new RelFieldCollation(
                 ((RexLocalRef) collation.left).getIndex(),
@@ -156,7 +156,7 @@ public RelFieldCollation get(int index) {
                 collation.getNullDirection());
           }
 
-          public int size() {
+          @Override public int size() {
             return collations.size();
           }
         });
@@ -239,7 +239,7 @@ public Group(
       this.digest = computeString();
     }
 
-    public String toString() {
+    @Override public String toString() {
       return digest;
     }
 
@@ -325,11 +325,11 @@ public List<AggregateCall> getAggregateCalls(Window windowRel) {
           Util.skip(windowRel.getRowType().getFieldNames(),
               windowRel.getInput().getRowType().getFieldCount());
       return new AbstractList<AggregateCall>() {
-        public int size() {
+        @Override public int size() {
           return aggCalls.size();
         }
 
-        public AggregateCall get(int index) {
+        @Override public AggregateCall get(int index) {
           final RexWinAggCall aggCall = aggCalls.get(index);
           final SqlAggFunction op = (SqlAggFunction) aggCall.getOperator();
           return AggregateCall.create(op, aggCall.distinct, false,
diff --git a/core/src/main/java/org/apache/calcite/rel/externalize/RelDotWriter.java b/core/src/main/java/org/apache/calcite/rel/externalize/RelDotWriter.java
index d2b2b47398f..96c73387efb 100644
--- a/core/src/main/java/org/apache/calcite/rel/externalize/RelDotWriter.java
+++ b/core/src/main/java/org/apache/calcite/rel/externalize/RelDotWriter.java
@@ -73,7 +73,7 @@ public RelDotWriter(
 
   //~ Methods ----------------------------------------------------------------
 
-  protected void explain_(RelNode rel,
+  @Override protected void explain_(RelNode rel,
                           List<Pair<String, Object>> values) {
     // get inputs
     List<RelNode> inputs = getInputs(rel);
@@ -179,7 +179,7 @@ private void explainInputs(List<RelNode> inputs) {
     }
   }
 
-  public RelWriter done(RelNode node) {
+  @Override public RelWriter done(RelNode node) {
     int numOfVisitedNodes = nodeLabels.size();
     super.done(node);
     if (numOfVisitedNodes == 0) {
diff --git a/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonReader.java b/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonReader.java
index a4db821b03c..b9caf290ccb 100644
--- a/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonReader.java
+++ b/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonReader.java
@@ -97,26 +97,26 @@ private void readRel(final Map<String, Object> jsonRel) {
     String type = (String) jsonRel.get("relOp");
     Constructor constructor = relJson.getConstructor(type);
     RelInput input = new RelInput() {
-      public RelOptCluster getCluster() {
+      @Override public RelOptCluster getCluster() {
         return cluster;
       }
 
-      public RelTraitSet getTraitSet() {
+      @Override public RelTraitSet getTraitSet() {
         return cluster.traitSetOf(Convention.NONE);
       }
 
-      public RelOptTable getTable(String table) {
+      @Override public RelOptTable getTable(String table) {
         final List<String> list = getStringList(table);
         return relOptSchema.getTableForMember(list);
       }
 
-      public RelNode getInput() {
+      @Override public RelNode getInput() {
         final List<RelNode> inputs = getInputs();
         assert inputs.size() == 1;
         return inputs.get(0);
       }
 
-      public List<RelNode> getInputs() {
+      @Override public List<RelNode> getInputs() {
         final List<String> jsonInputs = getStringList("inputs");
         if (jsonInputs == null) {
           return ImmutableList.of(lastRel);
@@ -128,15 +128,15 @@ public List<RelNode> getInputs() {
         return inputs;
       }
 
-      public RexNode getExpression(String tag) {
+      @Override public RexNode getExpression(String tag) {
         return relJson.toRex(this, jsonRel.get(tag));
       }
 
-      public ImmutableBitSet getBitSet(String tag) {
+      @Override public ImmutableBitSet getBitSet(String tag) {
         return ImmutableBitSet.of(getIntegerList(tag));
       }
 
-      public List<ImmutableBitSet> getBitSetList(String tag) {
+      @Override public List<ImmutableBitSet> getBitSetList(String tag) {
         List<List<Integer>> list = getIntegerListList(tag);
         if (list == null) {
           return null;
@@ -149,22 +149,22 @@ public List<ImmutableBitSet> getBitSetList(String tag) {
         return builder.build();
       }
 
-      public List<String> getStringList(String tag) {
+      @Override public List<String> getStringList(String tag) {
         //noinspection unchecked
         return (List<String>) jsonRel.get(tag);
       }
 
-      public List<Integer> getIntegerList(String tag) {
+      @Override public List<Integer> getIntegerList(String tag) {
         //noinspection unchecked
         return (List<Integer>) jsonRel.get(tag);
       }
 
-      public List<List<Integer>> getIntegerListList(String tag) {
+      @Override public List<List<Integer>> getIntegerListList(String tag) {
         //noinspection unchecked
         return (List<List<Integer>>) jsonRel.get(tag);
       }
 
-      public List<AggregateCall> getAggregateCalls(String tag) {
+      @Override public List<AggregateCall> getAggregateCalls(String tag) {
         @SuppressWarnings("unchecked")
         final List<Map<String, Object>> jsonAggs = (List) jsonRel.get(tag);
         final List<AggregateCall> inputs = new ArrayList<>();
@@ -174,29 +174,29 @@ public List<AggregateCall> getAggregateCalls(String tag) {
         return inputs;
       }
 
-      public Object get(String tag) {
+      @Override public Object get(String tag) {
         return jsonRel.get(tag);
       }
 
-      public String getString(String tag) {
+      @Override public String getString(String tag) {
         return (String) jsonRel.get(tag);
       }
 
-      public float getFloat(String tag) {
+      @Override public float getFloat(String tag) {
         return ((Number) jsonRel.get(tag)).floatValue();
       }
 
-      public boolean getBoolean(String tag, boolean default_) {
+      @Override public boolean getBoolean(String tag, boolean default_) {
         final Boolean b = (Boolean) jsonRel.get(tag);
         return b != null ? b : default_;
       }
 
-      public <E extends Enum<E>> E getEnum(String tag, Class<E> enumClass) {
+      @Override public <E extends Enum<E>> E getEnum(String tag, Class<E> enumClass) {
         return Util.enumVal(enumClass,
             getString(tag).toUpperCase(Locale.ROOT));
       }
 
-      public List<RexNode> getExpressionList(String tag) {
+      @Override public List<RexNode> getExpressionList(String tag) {
         @SuppressWarnings("unchecked")
         final List<Object> jsonNodes = (List) jsonRel.get(tag);
         if (jsonNodes == null) {
@@ -209,12 +209,12 @@ public List<RexNode> getExpressionList(String tag) {
         return nodes;
       }
 
-      public RelDataType getRowType(String tag) {
+      @Override public RelDataType getRowType(String tag) {
         final Object o = jsonRel.get(tag);
         return relJson.toType(cluster.getTypeFactory(), o);
       }
 
-      public RelDataType getRowType(String expressionsTag, String fieldsTag) {
+      @Override public RelDataType getRowType(String expressionsTag, String fieldsTag) {
         final List<RexNode> expressionList = getExpressionList(expressionsTag);
         @SuppressWarnings("unchecked") final List<String> names =
             (List<String>) get(fieldsTag);
@@ -231,16 +231,16 @@ public RelDataType getRowType(String expressionsTag, String fieldsTag) {
             });
       }
 
-      public RelCollation getCollation() {
+      @Override public RelCollation getCollation() {
         //noinspection unchecked
         return relJson.toCollation((List) get("collation"));
       }
 
-      public RelDistribution getDistribution() {
+      @Override public RelDistribution getDistribution() {
         return relJson.toDistribution((Map<String, Object>) get("distribution"));
       }
 
-      public ImmutableList<ImmutableList<RexLiteral>> getTuples(String tag) {
+      @Override public ImmutableList<ImmutableList<RexLiteral>> getTuples(String tag) {
         //noinspection unchecked
         final List<List> jsonTuples = (List) get(tag);
         final ImmutableList.Builder<ImmutableList<RexLiteral>> builder =
diff --git a/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonWriter.java b/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonWriter.java
index 5b6a346e675..6600effc714 100644
--- a/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonWriter.java
+++ b/core/src/main/java/org/apache/calcite/rel/externalize/RelJsonWriter.java
@@ -96,15 +96,15 @@ private List<Object> explainInputs(List<RelNode> inputs) {
     return list;
   }
 
-  public final void explain(RelNode rel, List<Pair<String, Object>> valueList) {
+  @Override public final void explain(RelNode rel, List<Pair<String, Object>> valueList) {
     explain_(rel, valueList);
   }
 
-  public SqlExplainLevel getDetailLevel() {
+  @Override public SqlExplainLevel getDetailLevel() {
     return SqlExplainLevel.ALL_ATTRIBUTES;
   }
 
-  public RelWriter item(String term, Object value) {
+  @Override public RelWriter item(String term, Object value) {
     values.add(Pair.of(term, value));
     return this;
   }
@@ -121,7 +121,7 @@ private List<Object> getList(List<Pair<String, Object>> values, String tag) {
     return list;
   }
 
-  public RelWriter done(RelNode node) {
+  @Override public RelWriter done(RelNode node) {
     final List<Pair<String, Object>> valuesCopy =
         ImmutableList.copyOf(values);
     values.clear();
diff --git a/core/src/main/java/org/apache/calcite/rel/externalize/RelWriterImpl.java b/core/src/main/java/org/apache/calcite/rel/externalize/RelWriterImpl.java
index 9fa52d82696..4ac6b7e7d41 100644
--- a/core/src/main/java/org/apache/calcite/rel/externalize/RelWriterImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/externalize/RelWriterImpl.java
@@ -123,20 +123,20 @@ private void explainInputs(List<RelNode> inputs) {
     }
   }
 
-  public final void explain(RelNode rel, List<Pair<String, Object>> valueList) {
+  @Override public final void explain(RelNode rel, List<Pair<String, Object>> valueList) {
     explain_(rel, valueList);
   }
 
-  public SqlExplainLevel getDetailLevel() {
+  @Override public SqlExplainLevel getDetailLevel() {
     return detailLevel;
   }
 
-  public RelWriter item(String term, Object value) {
+  @Override public RelWriter item(String term, Object value) {
     values.add(Pair.of(term, value));
     return this;
   }
 
-  public RelWriter done(RelNode node) {
+  @Override public RelWriter done(RelNode node) {
     assert checkInputsPresentInExplain(node);
     final List<Pair<String, Object>> valuesCopy =
         ImmutableList.copyOf(values);
diff --git a/core/src/main/java/org/apache/calcite/rel/externalize/RelXmlWriter.java b/core/src/main/java/org/apache/calcite/rel/externalize/RelXmlWriter.java
index 9d2d06065cc..17bfc38bf99 100644
--- a/core/src/main/java/org/apache/calcite/rel/externalize/RelXmlWriter.java
+++ b/core/src/main/java/org/apache/calcite/rel/externalize/RelXmlWriter.java
@@ -49,7 +49,7 @@ public RelXmlWriter(PrintWriter pw, SqlExplainLevel detailLevel) {
 
   //~ Methods ----------------------------------------------------------------
 
-  protected void explain_(
+  @Override protected void explain_(
       RelNode rel,
       List<Pair<String, Object>> values) {
     if (generic) {
diff --git a/core/src/main/java/org/apache/calcite/rel/hint/HintStrategyTable.java b/core/src/main/java/org/apache/calcite/rel/hint/HintStrategyTable.java
index fc4db46ae4f..31c0e8c92a9 100644
--- a/core/src/main/java/org/apache/calcite/rel/hint/HintStrategyTable.java
+++ b/core/src/main/java/org/apache/calcite/rel/hint/HintStrategyTable.java
@@ -229,16 +229,16 @@ public static class HintErrorLogger implements Litmus {
 
     public static final HintErrorLogger INSTANCE = new HintErrorLogger();
 
-    public boolean fail(String message, Object... args) {
+    @Override public boolean fail(String message, Object... args) {
       LOGGER.warn(message, args);
       return false;
     }
 
-    public boolean succeed() {
+    @Override public boolean succeed() {
       return true;
     }
 
-    public boolean check(boolean condition, String message, Object... args) {
+    @Override public boolean check(boolean condition, String message, Object... args) {
       if (condition) {
         return succeed();
       } else {
diff --git a/core/src/main/java/org/apache/calcite/rel/logical/LogicalFilter.java b/core/src/main/java/org/apache/calcite/rel/logical/LogicalFilter.java
index 740469bda49..8248fbc969f 100644
--- a/core/src/main/java/org/apache/calcite/rel/logical/LogicalFilter.java
+++ b/core/src/main/java/org/apache/calcite/rel/logical/LogicalFilter.java
@@ -120,7 +120,7 @@ public static LogicalFilter create(final RelNode input, RexNode condition,
     return variablesSet;
   }
 
-  public LogicalFilter copy(RelTraitSet traitSet, RelNode input,
+  @Override public LogicalFilter copy(RelTraitSet traitSet, RelNode input,
       RexNode condition) {
     assert traitSet.containsIfApplicable(Convention.NONE);
     return new LogicalFilter(getCluster(), traitSet, input, condition,
diff --git a/core/src/main/java/org/apache/calcite/rel/logical/LogicalJoin.java b/core/src/main/java/org/apache/calcite/rel/logical/LogicalJoin.java
index baf87ec454b..d8e50720b52 100644
--- a/core/src/main/java/org/apache/calcite/rel/logical/LogicalJoin.java
+++ b/core/src/main/java/org/apache/calcite/rel/logical/LogicalJoin.java
@@ -184,7 +184,7 @@ public static LogicalJoin create(RelNode left, RelNode right, List<RelHint> hint
     return shuttle.visit(this);
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     // Don't ever print semiJoinDone=false. This way, we
     // don't clutter things up in optimizers that don't use semi-joins.
     return super.explainTerms(pw)
@@ -208,7 +208,7 @@ public RelWriter explainTerms(RelWriter pw) {
     return semiJoinDone;
   }
 
-  public List<RelDataTypeField> getSystemFieldList() {
+  @Override public List<RelDataTypeField> getSystemFieldList() {
     return systemFieldList;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/logical/LogicalTableFunctionScan.java b/core/src/main/java/org/apache/calcite/rel/logical/LogicalTableFunctionScan.java
index fbd1869f452..9b5510ed55f 100644
--- a/core/src/main/java/org/apache/calcite/rel/logical/LogicalTableFunctionScan.java
+++ b/core/src/main/java/org/apache/calcite/rel/logical/LogicalTableFunctionScan.java
@@ -113,7 +113,7 @@ public static LogicalTableFunctionScan create(
         columnMappings);
   }
 
-  public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
+  @Override public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
     // REVIEW jvs 8-Jan-2006:  what is supposed to be here
     // for an abstract rel?
     return planner.getCostFactory().makeHugeCost();
diff --git a/core/src/main/java/org/apache/calcite/rel/logical/LogicalUnion.java b/core/src/main/java/org/apache/calcite/rel/logical/LogicalUnion.java
index 535ca8193b3..a56ba115673 100644
--- a/core/src/main/java/org/apache/calcite/rel/logical/LogicalUnion.java
+++ b/core/src/main/java/org/apache/calcite/rel/logical/LogicalUnion.java
@@ -67,7 +67,7 @@ public static LogicalUnion create(List<RelNode> inputs, boolean all) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public LogicalUnion copy(
+  @Override public LogicalUnion copy(
       RelTraitSet traitSet, List<RelNode> inputs, boolean all) {
     assert traitSet.containsIfApplicable(Convention.NONE);
     return new LogicalUnion(getCluster(), traitSet, inputs, all);
diff --git a/core/src/main/java/org/apache/calcite/rel/logical/LogicalWindow.java b/core/src/main/java/org/apache/calcite/rel/logical/LogicalWindow.java
index 7272a5796b8..6cbfeb0c054 100644
--- a/core/src/main/java/org/apache/calcite/rel/logical/LogicalWindow.java
+++ b/core/src/main/java/org/apache/calcite/rel/logical/LogicalWindow.java
@@ -212,7 +212,7 @@ public static RelNode create(RelOptCluster cluster,
     // the output calc (if it exists).
     RexShuttle shuttle =
         new RexShuttle() {
-          public RexNode visitOver(RexOver over) {
+          @Override public RexNode visitOver(RexOver over) {
             // Look up the aggCall which this expr was translated to.
             final Window.RexWinAggCall aggCall =
                 aggMap.get(origToNewOver.get(over));
@@ -243,7 +243,7 @@ public RexNode visitOver(RexOver over) {
                 over.getType());
           }
 
-          public RexNode visitLocalRef(RexLocalRef localRef) {
+          @Override public RexNode visitLocalRef(RexLocalRef localRef) {
             final int index = localRef.getIndex();
             if (index < inputFieldCount) {
               // Reference to input field.
@@ -281,11 +281,11 @@ public RexNode visitLocalRef(RexLocalRef localRef) {
   private static List<RexNode> toInputRefs(
       final List<? extends RexNode> operands) {
     return new AbstractList<RexNode>() {
-      public int size() {
+      @Override public int size() {
         return operands.size();
       }
 
-      public RexNode get(int index) {
+      @Override public RexNode get(int index) {
         final RexNode operand = operands.get(index);
         if (operand instanceof RexInputRef) {
           return operand;
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/CachingRelMetadataProvider.java b/core/src/main/java/org/apache/calcite/rel/metadata/CachingRelMetadataProvider.java
index 03f80e190a5..d1a69285eb8 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/CachingRelMetadataProvider.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/CachingRelMetadataProvider.java
@@ -55,7 +55,7 @@ public CachingRelMetadataProvider(
 
   //~ Methods ----------------------------------------------------------------
 
-  public <M extends Metadata> UnboundMetadata<M> apply(
+  @Override public <M extends Metadata> UnboundMetadata<M> apply(
       Class<? extends RelNode> relClass,
       final Class<? extends M> metadataClass) {
     final UnboundMetadata<M> function =
@@ -75,7 +75,7 @@ public <M extends Metadata> UnboundMetadata<M> apply(
     };
   }
 
-  public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
+  @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
       MetadataDef<M> def) {
     return underlyingProvider.handlers(def);
   }
@@ -103,7 +103,7 @@ private class CachingInvocationHandler implements InvocationHandler {
       this.metadata = Objects.requireNonNull(metadata);
     }
 
-    public Object invoke(Object proxy, Method method, Object[] args)
+    @Override public Object invoke(Object proxy, Method method, Object[] args)
         throws Throwable {
       // Compute hash key.
       final ImmutableList.Builder<Object> builder = ImmutableList.builder();
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/ChainedRelMetadataProvider.java b/core/src/main/java/org/apache/calcite/rel/metadata/ChainedRelMetadataProvider.java
index d1cf705d1c1..2ece0454dfa 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/ChainedRelMetadataProvider.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/ChainedRelMetadataProvider.java
@@ -67,7 +67,7 @@ protected ChainedRelMetadataProvider(
     return providers.hashCode();
   }
 
-  public <M extends Metadata> UnboundMetadata<M> apply(
+  @Override public <M extends Metadata> UnboundMetadata<M> apply(
       Class<? extends RelNode> relClass,
       final Class<? extends M> metadataClass) {
     final List<UnboundMetadata<M>> functions = new ArrayList<>();
@@ -101,7 +101,7 @@ public <M extends Metadata> UnboundMetadata<M> apply(
     }
   }
 
-  public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
+  @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
       MetadataDef<M> def) {
     final ImmutableMultimap.Builder<Method, MetadataHandler<M>> builder =
         ImmutableMultimap.builder();
@@ -125,7 +125,7 @@ private static class ChainedInvocationHandler implements InvocationHandler {
       this.metadataList = ImmutableList.copyOf(metadataList);
     }
 
-    public Object invoke(Object proxy, Method method, Object[] args)
+    @Override public Object invoke(Object proxy, Method method, Object[] args)
         throws Throwable {
       for (Metadata metadata : metadataList) {
         try {
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/JaninoRelMetadataProvider.java b/core/src/main/java/org/apache/calcite/rel/metadata/JaninoRelMetadataProvider.java
index 78584a1b5c3..d18cf07dd15 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/JaninoRelMetadataProvider.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/JaninoRelMetadataProvider.java
@@ -181,12 +181,12 @@ private static <K, V> CacheBuilder<K, V> maxSize(CacheBuilder<K, V> builder,
     return 109 + provider.hashCode();
   }
 
-  public <M extends Metadata> UnboundMetadata<M> apply(
+  @Override public <M extends Metadata> UnboundMetadata<M> apply(
       Class<? extends RelNode> relClass, Class<? extends M> metadataClass) {
     throw new UnsupportedOperationException();
   }
 
-  public <M extends Metadata> Multimap<Method, MetadataHandler<M>>
+  @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>>
       handlers(MetadataDef<M> def) {
     return provider.handlers(def);
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/MetadataFactoryImpl.java b/core/src/main/java/org/apache/calcite/rel/metadata/MetadataFactoryImpl.java
index c4fa662064f..d92c267bd8c 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/MetadataFactoryImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/MetadataFactoryImpl.java
@@ -55,7 +55,7 @@ UnboundMetadata<Metadata>> loader(final RelMetadataProvider provider) {
     });
   }
 
-  public <M extends Metadata> M query(RelNode rel, RelMetadataQuery mq,
+  @Override public <M extends Metadata> M query(RelNode rel, RelMetadataQuery mq,
       Class<M> metadataClazz) {
     try {
       //noinspection unchecked
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/ReflectiveRelMetadataProvider.java b/core/src/main/java/org/apache/calcite/rel/metadata/ReflectiveRelMetadataProvider.java
index 61681796be8..aa2662e1569 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/ReflectiveRelMetadataProvider.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/ReflectiveRelMetadataProvider.java
@@ -198,7 +198,7 @@ private static RelMetadataProvider reflectiveSource(
         space.providerMap);
   }
 
-  public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
+  @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
       MetadataDef<M> def) {
     final ImmutableMultimap.Builder<Method, MetadataHandler<M>> builder =
         ImmutableMultimap.builder();
@@ -228,7 +228,7 @@ private static boolean couldImplement(Method handlerMethod, Method method) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public <M extends Metadata> UnboundMetadata<M> apply(
+  @Override public <M extends Metadata> UnboundMetadata<M> apply(
       Class<? extends RelNode> relClass, Class<? extends M> metadataClass) {
     if (metadataClass == metadataClass0) {
       return apply(relClass);
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelColumnOrigin.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelColumnOrigin.java
index 6a3d7e5ae15..2cdaaa5627b 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelColumnOrigin.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelColumnOrigin.java
@@ -70,7 +70,7 @@ public boolean isDerived() {
   }
 
   // override Object
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (!(obj instanceof RelColumnOrigin)) {
       return false;
     }
@@ -82,7 +82,7 @@ public boolean equals(Object obj) {
   }
 
   // override Object
-  public int hashCode() {
+  @Override public int hashCode() {
     return originTable.getQualifiedName().hashCode()
         + iOriginColumn + (isDerived ? 313 : 0);
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdAllPredicates.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdAllPredicates.java
index 2ae457156df..10ad7a04771 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdAllPredicates.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdAllPredicates.java
@@ -77,7 +77,7 @@ public class RelMdAllPredicates
   public static final RelMetadataProvider SOURCE = ReflectiveRelMetadataProvider
       .reflectiveSource(BuiltInMethod.ALL_PREDICATES.method, new RelMdAllPredicates());
 
-  public MetadataDef<BuiltInMetadata.AllPredicates> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.AllPredicates> getDef() {
     return BuiltInMetadata.AllPredicates.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdCollation.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdCollation.java
index 8de027553a3..be9314e222c 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdCollation.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdCollation.java
@@ -88,7 +88,7 @@ private RelMdCollation() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.Collation> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.Collation> getDef() {
     return BuiltInMetadata.Collation.DEF;
   }
 
@@ -416,7 +416,7 @@ public static Ordering<List<RexLiteral>> comparator(
     switch (fieldCollation.direction) {
     case ASCENDING:
       return new Ordering<List<RexLiteral>>() {
-        public int compare(List<RexLiteral> o1, List<RexLiteral> o2) {
+        @Override public int compare(List<RexLiteral> o1, List<RexLiteral> o2) {
           final Comparable c1 = o1.get(x).getValueAs(Comparable.class);
           final Comparable c2 = o2.get(x).getValueAs(Comparable.class);
           return RelFieldCollation.compare(c1, c2, nullComparison);
@@ -424,7 +424,7 @@ public int compare(List<RexLiteral> o1, List<RexLiteral> o2) {
       };
     default:
       return new Ordering<List<RexLiteral>>() {
-        public int compare(List<RexLiteral> o1, List<RexLiteral> o2) {
+        @Override public int compare(List<RexLiteral> o1, List<RexLiteral> o2) {
           final Comparable c1 = o1.get(x).getValueAs(Comparable.class);
           final Comparable c2 = o2.get(x).getValueAs(Comparable.class);
           return RelFieldCollation.compare(c2, c1, -nullComparison);
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnOrigins.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnOrigins.java
index ed1b9cc647f..dbe3aff4844 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnOrigins.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnOrigins.java
@@ -58,7 +58,7 @@ private RelMdColumnOrigins() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.ColumnOrigin> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.ColumnOrigin> getDef() {
     return BuiltInMetadata.ColumnOrigin.DEF;
   }
 
@@ -272,7 +272,7 @@ private Set<RelColumnOrigin> getMultipleColumns(RexNode rexNode, RelNode input,
     final Set<RelColumnOrigin> set = new HashSet<>();
     final RexVisitor<Void> visitor =
         new RexVisitorImpl<Void>(true) {
-          public Void visitInputRef(RexInputRef inputRef) {
+          @Override public Void visitInputRef(RexInputRef inputRef) {
             Set<RelColumnOrigin> inputSet =
                 mq.getColumnOrigins(input, inputRef.getIndex());
             if (inputSet != null) {
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnUniqueness.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnUniqueness.java
index 5815cfc0581..77140d6dab1 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnUniqueness.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnUniqueness.java
@@ -74,7 +74,7 @@ private RelMdColumnUniqueness() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.ColumnUniqueness> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.ColumnUniqueness> getDef() {
     return BuiltInMetadata.ColumnUniqueness.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistinctRowCount.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistinctRowCount.java
index 971f4f3aab9..ba6d4fa5db0 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistinctRowCount.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistinctRowCount.java
@@ -61,7 +61,7 @@ protected RelMdDistinctRowCount() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.DistinctRowCount> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.DistinctRowCount> getDef() {
     return BuiltInMetadata.DistinctRowCount.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistribution.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistribution.java
index adbab6bdc4a..82b5479ad7a 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistribution.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistribution.java
@@ -60,7 +60,7 @@ private RelMdDistribution() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.Distribution> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.Distribution> getDef() {
     return BuiltInMetadata.Distribution.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExplainVisibility.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExplainVisibility.java
index 474f29f5661..6d73fad5165 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExplainVisibility.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExplainVisibility.java
@@ -37,7 +37,7 @@ private RelMdExplainVisibility() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.ExplainVisibility> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.ExplainVisibility> getDef() {
     return BuiltInMetadata.ExplainVisibility.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExpressionLineage.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExpressionLineage.java
index f560cbd744b..41189a02247 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExpressionLineage.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdExpressionLineage.java
@@ -87,7 +87,7 @@ protected RelMdExpressionLineage() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.ExpressionLineage> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.ExpressionLineage> getDef() {
     return BuiltInMetadata.ExpressionLineage.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdLowerBoundCost.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdLowerBoundCost.java
index f7ea60a3376..2a18df5a5aa 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdLowerBoundCost.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdLowerBoundCost.java
@@ -40,7 +40,7 @@ protected RelMdLowerBoundCost() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<LowerBoundCost> getDef() {
+  @Override public MetadataDef<LowerBoundCost> getDef() {
     return BuiltInMetadata.LowerBoundCost.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMaxRowCount.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMaxRowCount.java
index e6255a31e31..dcf59a639c0 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMaxRowCount.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMaxRowCount.java
@@ -51,7 +51,7 @@ public class RelMdMaxRowCount
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.MaxRowCount> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.MaxRowCount> getDef() {
     return BuiltInMetadata.MaxRowCount.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMemory.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMemory.java
index 80864f82969..5d2d215767f 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMemory.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMemory.java
@@ -42,7 +42,7 @@ protected RelMdMemory() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.Memory> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.Memory> getDef() {
     return BuiltInMetadata.Memory.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMinRowCount.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMinRowCount.java
index 069e40ff112..2bdce84dc5c 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMinRowCount.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMinRowCount.java
@@ -49,7 +49,7 @@ public class RelMdMinRowCount
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.MinRowCount> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.MinRowCount> getDef() {
     return BuiltInMetadata.MinRowCount.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdNodeTypes.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdNodeTypes.java
index 5259b3ffca5..f47db4ac151 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdNodeTypes.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdNodeTypes.java
@@ -54,7 +54,7 @@ public class RelMdNodeTypes
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.NodeTypes> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.NodeTypes> getDef() {
     return BuiltInMetadata.NodeTypes.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdParallelism.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdParallelism.java
index c4443862260..4f2a371f26b 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdParallelism.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdParallelism.java
@@ -45,7 +45,7 @@ protected RelMdParallelism() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.Parallelism> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.Parallelism> getDef() {
     return BuiltInMetadata.Parallelism.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPercentageOriginalRows.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPercentageOriginalRows.java
index a68082c335c..081bac0b9e5 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPercentageOriginalRows.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPercentageOriginalRows.java
@@ -54,7 +54,7 @@ public class RelMdPercentageOriginalRows
 
   private RelMdPercentageOriginalRows() {}
 
-  public MetadataDef<BuiltInMetadata.PercentageOriginalRows> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.PercentageOriginalRows> getDef() {
     return BuiltInMetadata.PercentageOriginalRows.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPopulationSize.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPopulationSize.java
index 093958dbf19..f725293bbf6 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPopulationSize.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPopulationSize.java
@@ -48,7 +48,7 @@ private RelMdPopulationSize() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.PopulationSize> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.PopulationSize> getDef() {
     return BuiltInMetadata.PopulationSize.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPredicates.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPredicates.java
index 698b05926be..6745e07d40b 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPredicates.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPredicates.java
@@ -132,7 +132,7 @@ public class RelMdPredicates
 
   private static final List<RexNode> EMPTY_LIST = ImmutableList.of();
 
-  public MetadataDef<BuiltInMetadata.Predicates> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.Predicates> getDef() {
     return BuiltInMetadata.Predicates.DEF;
   }
 
@@ -840,7 +840,7 @@ class ExprsItr implements Iterator<Mapping> {
         firstCall = true;
       }
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         if (firstCall) {
           initializeMapping();
           firstCall = false;
@@ -850,11 +850,11 @@ public boolean hasNext() {
         return nextMapping != null;
       }
 
-      public Mapping next() {
+      @Override public Mapping next() {
         return nextMapping;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException();
       }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdRowCount.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdRowCount.java
index a42ed2ab093..4cf6209ead1 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdRowCount.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdRowCount.java
@@ -53,7 +53,7 @@ public class RelMdRowCount
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.RowCount> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.RowCount> getDef() {
     return BuiltInMetadata.RowCount.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSelectivity.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSelectivity.java
index ec181f9778c..192cca05475 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSelectivity.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSelectivity.java
@@ -55,7 +55,7 @@ protected RelMdSelectivity() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.Selectivity> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.Selectivity> getDef() {
     return BuiltInMetadata.Selectivity.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSize.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSize.java
index 458df6b3448..00b78c55790 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSize.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSize.java
@@ -74,7 +74,7 @@ protected RelMdSize() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.Size> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.Size> getDef() {
     return BuiltInMetadata.Size.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdTableReferences.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdTableReferences.java
index e554728e0be..dd9e797dce8 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdTableReferences.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdTableReferences.java
@@ -71,7 +71,7 @@ protected RelMdTableReferences() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.TableReferences> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.TableReferences> getDef() {
     return BuiltInMetadata.TableReferences.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUniqueKeys.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUniqueKeys.java
index 9ce85970c8a..85d6ddd0f24 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUniqueKeys.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUniqueKeys.java
@@ -66,7 +66,7 @@ private RelMdUniqueKeys() {}
 
   //~ Methods ----------------------------------------------------------------
 
-  public MetadataDef<BuiltInMetadata.UniqueKeys> getDef() {
+  @Override public MetadataDef<BuiltInMetadata.UniqueKeys> getDef() {
     return BuiltInMetadata.UniqueKeys.DEF;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUtil.java b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUtil.java
index 4f642a22428..75ee15281a6 100644
--- a/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUtil.java
+++ b/core/src/main/java/org/apache/calcite/rel/metadata/RelMdUtil.java
@@ -811,7 +811,7 @@ private static class CardOfProjExpr extends RexVisitorImpl<Double> {
       this.rel = rel;
     }
 
-    public Double visitInputRef(RexInputRef var) {
+    @Override public Double visitInputRef(RexInputRef var) {
       int index = var.getIndex();
       ImmutableBitSet col = ImmutableBitSet.of(index);
       Double distinctRowCount =
@@ -823,11 +823,11 @@ public Double visitInputRef(RexInputRef var) {
       }
     }
 
-    public Double visitLiteral(RexLiteral literal) {
+    @Override public Double visitLiteral(RexLiteral literal) {
       return numDistinctVals(1.0, mq.getRowCount(rel));
     }
 
-    public Double visitCall(RexCall call) {
+    @Override public Double visitCall(RexCall call) {
       Double distinctRowCount;
       Double rowCount = mq.getRowCount(rel);
       if (call.isA(SqlKind.MINUS_PREFIX)) {
diff --git a/core/src/main/java/org/apache/calcite/rel/mutable/MutableBiRel.java b/core/src/main/java/org/apache/calcite/rel/mutable/MutableBiRel.java
index 46d1f2d3c19..e7475226cc2 100644
--- a/core/src/main/java/org/apache/calcite/rel/mutable/MutableBiRel.java
+++ b/core/src/main/java/org/apache/calcite/rel/mutable/MutableBiRel.java
@@ -40,7 +40,7 @@ protected MutableBiRel(MutableRelType type, RelOptCluster cluster,
     right.ordinalInParent = 1;
   }
 
-  public void setInput(int ordinalInParent, MutableRel input) {
+  @Override public void setInput(int ordinalInParent, MutableRel input) {
     if (ordinalInParent > 1) {
       throw new IllegalArgumentException();
     }
@@ -55,7 +55,7 @@ public void setInput(int ordinalInParent, MutableRel input) {
     }
   }
 
-  public List<MutableRel> getInputs() {
+  @Override public List<MutableRel> getInputs() {
     return ImmutableList.of(left, right);
   }
 
@@ -67,7 +67,7 @@ public MutableRel getRight() {
     return right;
   }
 
-  public void childrenAccept(MutableRelVisitor visitor) {
+  @Override public void childrenAccept(MutableRelVisitor visitor) {
 
     visitor.visit(left);
     visitor.visit(right);
diff --git a/core/src/main/java/org/apache/calcite/rel/mutable/MutableLeafRel.java b/core/src/main/java/org/apache/calcite/rel/mutable/MutableLeafRel.java
index f34f58f29af..500c0b002f9 100644
--- a/core/src/main/java/org/apache/calcite/rel/mutable/MutableLeafRel.java
+++ b/core/src/main/java/org/apache/calcite/rel/mutable/MutableLeafRel.java
@@ -32,15 +32,15 @@ protected MutableLeafRel(MutableRelType type, RelNode rel) {
     this.rel = rel;
   }
 
-  public void setInput(int ordinalInParent, MutableRel input) {
+  @Override public void setInput(int ordinalInParent, MutableRel input) {
     throw new IllegalArgumentException();
   }
 
-  public List<MutableRel> getInputs() {
+  @Override public List<MutableRel> getInputs() {
     return ImmutableList.of();
   }
 
-  public void childrenAccept(MutableRelVisitor visitor) {
+  @Override public void childrenAccept(MutableRelVisitor visitor) {
     // no children - nothing to do
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/rel/mutable/MutableRel.java b/core/src/main/java/org/apache/calcite/rel/mutable/MutableRel.java
index 06fcf2f87c8..f15e9847737 100644
--- a/core/src/main/java/org/apache/calcite/rel/mutable/MutableRel.java
+++ b/core/src/main/java/org/apache/calcite/rel/mutable/MutableRel.java
@@ -82,7 +82,7 @@ public MutableRel getParent() {
 
   public abstract List<MutableRel> getInputs();
 
-  public abstract MutableRel clone();
+  @Override public abstract MutableRel clone();
 
   public abstract void childrenAccept(MutableRelVisitor visitor);
 
diff --git a/core/src/main/java/org/apache/calcite/rel/mutable/MutableRels.java b/core/src/main/java/org/apache/calcite/rel/mutable/MutableRels.java
index bb646844220..996e44c2ee1 100644
--- a/core/src/main/java/org/apache/calcite/rel/mutable/MutableRels.java
+++ b/core/src/main/java/org/apache/calcite/rel/mutable/MutableRels.java
@@ -153,11 +153,11 @@ public static MutableRel createProject(final MutableRel child,
         RelOptUtil.permute(child.cluster.getTypeFactory(), rowType, mapping),
         child,
         new AbstractList<RexNode>() {
-          public int size() {
+          @Override public int size() {
             return posList.size();
           }
 
-          public RexNode get(int index) {
+          @Override public RexNode get(int index) {
             final int pos = posList.get(index);
             return RexInputRef.of(pos, rowType);
           }
diff --git a/core/src/main/java/org/apache/calcite/rel/mutable/MutableSingleRel.java b/core/src/main/java/org/apache/calcite/rel/mutable/MutableSingleRel.java
index 133061ab622..3b7e4788c64 100644
--- a/core/src/main/java/org/apache/calcite/rel/mutable/MutableSingleRel.java
+++ b/core/src/main/java/org/apache/calcite/rel/mutable/MutableSingleRel.java
@@ -34,7 +34,7 @@ protected MutableSingleRel(MutableRelType type,
     input.ordinalInParent = 0;
   }
 
-  public void setInput(int ordinalInParent, MutableRel input) {
+  @Override public void setInput(int ordinalInParent, MutableRel input) {
     if (ordinalInParent > 0) {
       throw new IllegalArgumentException();
     }
@@ -45,11 +45,11 @@ public void setInput(int ordinalInParent, MutableRel input) {
     }
   }
 
-  public List<MutableRel> getInputs() {
+  @Override public List<MutableRel> getInputs() {
     return ImmutableList.of(input);
   }
 
-  public void childrenAccept(MutableRelVisitor visitor) {
+  @Override public void childrenAccept(MutableRelVisitor visitor) {
     visitor.visit(input);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java b/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
index e3e4231e1de..7b88b3fce25 100644
--- a/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
+++ b/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
@@ -131,7 +131,7 @@ protected Result dispatch(RelNode e) {
     return dispatcher.invoke(e);
   }
 
-  public Result visitInput(RelNode parent, int i, boolean anon,
+  @Override public Result visitInput(RelNode parent, int i, boolean anon,
       boolean ignoreClauses, Set<Clause> expectedClauses) {
     try {
       final RelNode e = parent.getInput(i);
diff --git a/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java b/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java
index 7fa48594c25..a60111d59aa 100644
--- a/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java
+++ b/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java
@@ -1067,11 +1067,11 @@ private List<SqlNode> toSql(RexProgram program, List<RexNode> operandList) {
 
     public List<SqlNode> fieldList() {
       return new AbstractList<SqlNode>() {
-        public SqlNode get(int index) {
+        @Override public SqlNode get(int index) {
           return field(index);
         }
 
-        public int size() {
+        @Override public int size() {
           return fieldCount;
         }
       };
@@ -1359,7 +1359,7 @@ public SimpleContext(SqlDialect dialect, IntFunction<SqlNode> field) {
       throw new UnsupportedOperationException();
     }
 
-    public SqlNode field(int ordinal) {
+    @Override public SqlNode field(int ordinal) {
       return field.apply(ordinal);
     }
   }
@@ -1438,7 +1438,7 @@ protected AliasContext(SqlDialect dialect,
       this.qualified = qualified;
     }
 
-    public SqlNode field(int ordinal) {
+    @Override public SqlNode field(int ordinal) {
       for (Map.Entry<String, RelDataType> alias : aliases.entrySet()) {
         final List<RelDataTypeField> fields = alias.getValue().getFieldList();
         if (ordinal < fields.size()) {
@@ -1469,7 +1469,7 @@ private JoinContext(SqlDialect dialect, Context leftContext,
       this.rightContext = rightContext;
     }
 
-    public SqlNode field(int ordinal) {
+    @Override public SqlNode field(int ordinal) {
       if (ordinal < leftContext.fieldCount) {
         return leftContext.field(ordinal);
       } else {
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/AggregateStarTableRule.java b/core/src/main/java/org/apache/calcite/rel/rules/AggregateStarTableRule.java
index 859150c1e7d..d7ee66cc38e 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/AggregateStarTableRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/AggregateStarTableRule.java
@@ -165,7 +165,7 @@ protected void apply(RelOptRuleCall call, Project postProject,
               new AbstractSourceMapping(
                   tileKey.dimensions.cardinality() + tileKey.measures.size(),
                   aggregate.getRowType().getFieldCount()) {
-                public int getSourceOpt(int source) {
+                @Override public int getSourceOpt(int source) {
                   if (source < aggregate.getGroupCount()) {
                     int in = tileKey.dimensions.nth(source);
                     return aggregate.getGroupSet().indexOf(in);
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/CalcRelSplitter.java b/core/src/main/java/org/apache/calcite/rel/rules/CalcRelSplitter.java
index 6d0b8406491..cfd99940535 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/CalcRelSplitter.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/CalcRelSplitter.java
@@ -444,7 +444,7 @@ private List<Integer> computeTopologicalOrdering(
       }
       expr.accept(
           new RexVisitorImpl<Void>(true) {
-            public Void visitLocalRef(RexLocalRef localRef) {
+            @Override public Void visitLocalRef(RexLocalRef localRef) {
               for (Integer target : targets) {
                 graph.addEdge(localRef.getIndex(), target);
               }
@@ -750,7 +750,7 @@ public RelType(String name) {
       this.name = name;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return name;
     }
 
@@ -828,28 +828,28 @@ private static class ImplementTester extends RexVisitorImpl<Void> {
       this.relType = relType;
     }
 
-    public Void visitCall(RexCall call) {
+    @Override public Void visitCall(RexCall call) {
       if (!relType.canImplement(call)) {
         throw CannotImplement.INSTANCE;
       }
       return null;
     }
 
-    public Void visitDynamicParam(RexDynamicParam dynamicParam) {
+    @Override public Void visitDynamicParam(RexDynamicParam dynamicParam) {
       if (!relType.canImplement(dynamicParam)) {
         throw CannotImplement.INSTANCE;
       }
       return null;
     }
 
-    public Void visitFieldAccess(RexFieldAccess fieldAccess) {
+    @Override public Void visitFieldAccess(RexFieldAccess fieldAccess) {
       if (!relType.canImplement(fieldAccess)) {
         throw CannotImplement.INSTANCE;
       }
       return null;
     }
 
-    public Void visitLiteral(RexLiteral literal) {
+    @Override public Void visitLiteral(RexLiteral literal) {
       if (!relType.canImplement(literal)) {
         throw CannotImplement.INSTANCE;
       }
@@ -889,7 +889,7 @@ private static class InputToCommonExprConverter extends RexShuttle {
       this.allExprs = allExprs;
     }
 
-    public RexNode visitInputRef(RexInputRef input) {
+    @Override public RexNode visitInputRef(RexInputRef input) {
       final int index = exprInverseOrdinals[input.getIndex()];
       assert index >= 0;
       return new RexLocalRef(
@@ -897,7 +897,7 @@ public RexNode visitInputRef(RexInputRef input) {
           input.getType());
     }
 
-    public RexNode visitLocalRef(RexLocalRef local) {
+    @Override public RexNode visitLocalRef(RexLocalRef local) {
       // A reference to a local variable becomes a reference to an input
       // if the local was computed at a previous level.
       final int localIndex = local.getIndex();
@@ -935,7 +935,7 @@ private static class MaxInputFinder extends RexVisitorImpl<Void> {
       this.exprLevels = exprLevels;
     }
 
-    public Void visitLocalRef(RexLocalRef localRef) {
+    @Override public Void visitLocalRef(RexLocalRef localRef) {
       int inputLevel = exprLevels[localRef.getIndex()];
       level = Math.max(level, inputLevel);
       return null;
@@ -980,7 +980,7 @@ public int[] getMaxUsingLevelOrdinals() {
       return maxUsingLevelOrdinals;
     }
 
-    public Void visitLocalRef(RexLocalRef ref) {
+    @Override public Void visitLocalRef(RexLocalRef ref) {
       final int index = ref.getIndex();
       maxUsingLevelOrdinals[index] =
           Math.max(maxUsingLevelOrdinals[index], currentLevel);
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/DateRangeRules.java b/core/src/main/java/org/apache/calcite/rel/rules/DateRangeRules.java
index ba2a7777653..68f89a9c4ac 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/DateRangeRules.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/DateRangeRules.java
@@ -253,7 +253,7 @@ private ExtractFinder() {
       return super.visitCall(call);
     }
 
-    public void close() {
+    @Override public void close() {
       timeUnits.clear();
       opKinds.clear();
     }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/JoinToMultiJoinRule.java b/core/src/main/java/org/apache/calcite/rel/rules/JoinToMultiJoinRule.java
index 2f1d18b181c..58040bd203e 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/JoinToMultiJoinRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/JoinToMultiJoinRule.java
@@ -564,7 +564,7 @@ private class InputReferenceCounter extends RexVisitorImpl<Void> {
       this.refCounts = refCounts;
     }
 
-    public Void visitInputRef(RexInputRef inputRef) {
+    @Override public Void visitInputRef(RexInputRef inputRef) {
       refCounts[inputRef.getIndex()]++;
       return null;
     }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/LoptJoinTree.java b/core/src/main/java/org/apache/calcite/rel/rules/LoptJoinTree.java
index de8de4b31d3..e73c5e27e0b 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/LoptJoinTree.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/LoptJoinTree.java
@@ -180,7 +180,7 @@ public int getId() {
       return id;
     }
 
-    public void getTreeOrder(List<Integer> treeOrder) {
+    @Override public void getTreeOrder(List<Integer> treeOrder) {
       treeOrder.add(id);
     }
   }
@@ -204,7 +204,7 @@ public BinaryTree getRight() {
       return right;
     }
 
-    public void getTreeOrder(List<Integer> treeOrder) {
+    @Override public void getTreeOrder(List<Integer> treeOrder) {
       left.getTreeOrder(treeOrder);
       right.getTreeOrder(treeOrder);
     }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/LoptSemiJoinOptimizer.java b/core/src/main/java/org/apache/calcite/rel/rules/LoptSemiJoinOptimizer.java
index 77e2109fcbb..927ab585551 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/LoptSemiJoinOptimizer.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/LoptSemiJoinOptimizer.java
@@ -803,7 +803,7 @@ public RelNode getChosenSemiJoin(int factIdx) {
   /** Compares factors. */
   private class FactorCostComparator
       implements Comparator<Integer> {
-    public int compare(Integer rel1Idx, Integer rel2Idx) {
+    @Override public int compare(Integer rel1Idx, Integer rel2Idx) {
       RelOptCost c1 =
           mq.getCumulativeCost(chosenSemiJoins[rel1Idx]);
       RelOptCost c2 =
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/MultiJoin.java b/core/src/main/java/org/apache/calcite/rel/rules/MultiJoin.java
index 90d3119b702..3b72fd4a419 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/MultiJoin.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/MultiJoin.java
@@ -142,7 +142,7 @@ private Map<Integer, int[]> cloneJoinFieldRefCountsMap() {
     return clonedMap;
   }
 
-  public RelWriter explainTerms(RelWriter pw) {
+  @Override public RelWriter explainTerms(RelWriter pw) {
     List<String> joinTypeNames = new ArrayList<>();
     List<String> outerJoinConds = new ArrayList<>();
     List<String> projFieldObjects = new ArrayList<>();
@@ -172,15 +172,15 @@ public RelWriter explainTerms(RelWriter pw) {
         .itemIf("postJoinFilter", postJoinFilter, postJoinFilter != null);
   }
 
-  public RelDataType deriveRowType() {
+  @Override public RelDataType deriveRowType() {
     return rowType;
   }
 
-  public List<RelNode> getInputs() {
+  @Override public List<RelNode> getInputs() {
     return inputs;
   }
 
-  public RelNode accept(RexShuttle shuttle) {
+  @Override public RelNode accept(RexShuttle shuttle) {
     RexNode joinFilter = shuttle.apply(this.joinFilter);
     List<RexNode> outerJoinConditions = shuttle.apply(this.outerJoinConditions);
     RexNode postJoinFilter = shuttle.apply(this.postJoinFilter);
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/MultiJoinOptimizeBushyRule.java b/core/src/main/java/org/apache/calcite/rel/rules/MultiJoinOptimizeBushyRule.java
index 33fec8e8c56..6ec18352c60 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/MultiJoinOptimizeBushyRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/MultiJoinOptimizeBushyRule.java
@@ -123,7 +123,7 @@ public MultiJoinOptimizeBushyRule(RelFactories.JoinFactory joinFactory,
     // a large difference in the number of rows on LHS and RHS.
     final Comparator<LoptMultiJoin.Edge> edgeComparator =
         new Comparator<LoptMultiJoin.Edge>() {
-          public int compare(LoptMultiJoin.Edge e0, LoptMultiJoin.Edge e1) {
+          @Override public int compare(LoptMultiJoin.Edge e0, LoptMultiJoin.Edge e1) {
             return Double.compare(rowCountDiff(e0), rowCountDiff(e1));
           }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/ProjectTableScanRule.java b/core/src/main/java/org/apache/calcite/rel/rules/ProjectTableScanRule.java
index 8614f69098f..4d9129a1a77 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/ProjectTableScanRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/ProjectTableScanRule.java
@@ -103,7 +103,7 @@ protected void apply(RelOptRuleCall call, Project project, TableScan scan) {
 
     final List<Integer> selectedColumns = new ArrayList<>();
     final RexVisitorImpl<Void> visitor = new RexVisitorImpl<Void>(true) {
-      public Void visitInputRef(RexInputRef inputRef) {
+      @Override public Void visitInputRef(RexInputRef inputRef) {
         if (!selectedColumns.contains(inputRef.getIndex())) {
           selectedColumns.add(inputRef.getIndex());
         }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/ProjectToWindowRule.java b/core/src/main/java/org/apache/calcite/rel/rules/ProjectToWindowRule.java
index e188b7d9a6b..5ee5c9e3892 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/ProjectToWindowRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/ProjectToWindowRule.java
@@ -206,23 +206,23 @@ public interface Config extends ProjectToWindowRule.Config {
   static class WindowedAggRelSplitter extends CalcRelSplitter {
     private static final RelType[] REL_TYPES = {
         new RelType("CalcRelType") {
-            protected boolean canImplement(RexFieldAccess field) {
+            @Override protected boolean canImplement(RexFieldAccess field) {
               return true;
             }
 
-            protected boolean canImplement(RexDynamicParam param) {
+            @Override protected boolean canImplement(RexDynamicParam param) {
               return true;
             }
 
-            protected boolean canImplement(RexLiteral literal) {
+            @Override protected boolean canImplement(RexLiteral literal) {
               return true;
             }
 
-            protected boolean canImplement(RexCall call) {
+            @Override protected boolean canImplement(RexCall call) {
               return !(call instanceof RexOver);
             }
 
-            protected RelNode makeRel(RelOptCluster cluster,
+            @Override protected RelNode makeRel(RelOptCluster cluster,
                 RelTraitSet traitSet, RelBuilder relBuilder, RelNode input,
                 RexProgram program) {
               assert !program.containsAggs();
@@ -232,27 +232,27 @@ protected RelNode makeRel(RelOptCluster cluster,
             }
         },
         new RelType("WinAggRelType") {
-          protected boolean canImplement(RexFieldAccess field) {
+          @Override protected boolean canImplement(RexFieldAccess field) {
             return false;
           }
 
-          protected boolean canImplement(RexDynamicParam param) {
+          @Override protected boolean canImplement(RexDynamicParam param) {
             return false;
           }
 
-          protected boolean canImplement(RexLiteral literal) {
+          @Override protected boolean canImplement(RexLiteral literal) {
             return false;
           }
 
-          protected boolean canImplement(RexCall call) {
+          @Override protected boolean canImplement(RexCall call) {
             return call instanceof RexOver;
           }
 
-          protected boolean supportsCondition() {
+          @Override protected boolean supportsCondition() {
             return false;
           }
 
-          protected RelNode makeRel(RelOptCluster cluster, RelTraitSet traitSet,
+          @Override protected RelNode makeRel(RelOptCluster cluster, RelTraitSet traitSet,
               RelBuilder relBuilder, RelNode input, RexProgram program) {
             Preconditions.checkArgument(program.getCondition() == null,
                 "WindowedAggregateRel cannot accept a condition");
@@ -373,7 +373,7 @@ private DirectedGraph<Integer, DefaultEdge> createGraphFromExpression(
       }
 
       new RexBiVisitorImpl<Void, Integer>(true) {
-        public Void visitLocalRef(RexLocalRef localRef, Integer i) {
+        @Override public Void visitLocalRef(RexLocalRef localRef, Integer i) {
           graph.addEdge(localRef.getIndex(), i);
           return null;
         }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/PushProjector.java b/core/src/main/java/org/apache/calcite/rel/rules/PushProjector.java
index 58075401684..51b4767cca1 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/PushProjector.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/PushProjector.java
@@ -691,7 +691,7 @@ private class InputSpecialOpFinder extends RexVisitorImpl<Void> {
       this.strong = Strong.of(strongFields);
     }
 
-    public Void visitCall(RexCall call) {
+    @Override public Void visitCall(RexCall call) {
       if (preserve(call)) {
         return null;
       }
@@ -737,7 +737,7 @@ private boolean preserve(RexNode call) {
       return false;
     }
 
-    public Void visitInputRef(RexInputRef inputRef) {
+    @Override public Void visitInputRef(RexInputRef inputRef) {
       rexRefs.set(inputRef.getIndex());
       return null;
     }
@@ -770,7 +770,7 @@ private class RefAndExprConverter extends RelOptUtil.RexInputConverter {
       this.firstRightRef = firstRightRef;
     }
 
-    public RexNode visitCall(RexCall call) {
+    @Override public RexNode visitCall(RexCall call) {
       // if the expression corresponds to one that needs to be preserved,
       // convert it to a field reference; otherwise, convert the entire
       // expression
@@ -837,7 +837,7 @@ public interface ExprCondition extends Predicate<RexNode> {
      * @param expr Expression
      * @return result of evaluating the condition
      */
-    boolean test(RexNode expr);
+    @Override boolean test(RexNode expr);
 
     /**
      * Constant condition that replies {@code false} for all expressions.
@@ -866,7 +866,7 @@ class OperatorExprCondition implements ExprCondition {
       this.operatorSet = ImmutableSet.copyOf(operatorSet);
     }
 
-    public boolean test(RexNode expr) {
+    @Override public boolean test(RexNode expr) {
       return expr instanceof RexCall
           && operatorSet.contains(((RexCall) expr).getOperator());
     }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/ReduceDecimalsRule.java b/core/src/main/java/org/apache/calcite/rel/rules/ReduceDecimalsRule.java
index bbf1c8442b1..f7903c3bff5 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/ReduceDecimalsRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/ReduceDecimalsRule.java
@@ -146,7 +146,7 @@ public static class DecimalShuttle extends RexShuttle {
      * </ol>
      * </ol>
      */
-    public RexNode visitCall(RexCall call) {
+    @Override public RexNode visitCall(RexCall call) {
       RexNode savedResult = lookup(call);
       if (savedResult != null) {
         return savedResult;
@@ -721,7 +721,7 @@ private CastExpander(RexBuilder builder) {
     }
 
     // implement RexExpander
-    public RexNode expand(RexCall call) {
+    @Override public RexNode expand(RexCall call) {
       List<RexNode> operands = call.operands;
       assert call.isA(SqlKind.CAST);
       assert operands.size() == 1;
@@ -1010,7 +1010,7 @@ private FloorExpander(RexBuilder rexBuilder) {
       super(rexBuilder);
     }
 
-    public RexNode expand(RexCall call) {
+    @Override public RexNode expand(RexCall call) {
       assert call.getOperator() == SqlStdOperatorTable.FLOOR;
       RexNode decValue = call.operands.get(0);
       int scale = decValue.getType().getScale();
@@ -1060,7 +1060,7 @@ private CeilExpander(RexBuilder rexBuilder) {
       super(rexBuilder);
     }
 
-    public RexNode expand(RexCall call) {
+    @Override public RexNode expand(RexCall call) {
       assert call.getOperator() == SqlStdOperatorTable.CEIL;
       RexNode decValue = call.operands.get(0);
       int scale = decValue.getType().getScale();
@@ -1111,7 +1111,7 @@ private CaseExpander(RexBuilder rexBuilder) {
       super(rexBuilder);
     }
 
-    public RexNode expand(RexCall call) {
+    @Override public RexNode expand(RexCall call) {
       RelDataType retType = call.getType();
       int argCount = call.operands.size();
       ImmutableList.Builder<RexNode> opBuilder = ImmutableList.builder();
@@ -1152,7 +1152,7 @@ private PassThroughExpander(RexBuilder builder) {
       return RexUtil.requiresDecimalExpansion(call, false);
     }
 
-    public RexNode expand(RexCall call) {
+    @Override public RexNode expand(RexCall call) {
       ImmutableList.Builder<RexNode> opBuilder = ImmutableList.builder();
       for (RexNode operand : call.operands) {
         if (SqlTypeUtil.isNumeric(operand.getType())) {
@@ -1183,7 +1183,7 @@ private CastArgAsDoubleExpander(RexBuilder builder) {
       super(builder);
     }
 
-    public RelDataType getArgType(RexCall call, int ordinal) {
+    @Override public RelDataType getArgType(RexCall call, int ordinal) {
       RelDataType type = real8;
       if (call.operands.get(ordinal).getType().isNullable()) {
         type =
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java b/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java
index 4c009473d30..0074a8b97ae 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java
@@ -447,7 +447,7 @@ public CalcReduceExpressionsRule(Class<? extends Calc> calcClass,
       final List<RexNode> expandedExprList = new ArrayList<>();
       final RexShuttle shuttle =
           new RexShuttle() {
-            public RexNode visitLocalRef(RexLocalRef localRef) {
+            @Override public RexNode visitLocalRef(RexLocalRef localRef) {
               return expandedExprList.get(localRef.getIndex());
             }
           };
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/ValuesReduceRule.java b/core/src/main/java/org/apache/calcite/rel/rules/ValuesReduceRule.java
index dcd6d2c2c70..6550a73d84a 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/ValuesReduceRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/ValuesReduceRule.java
@@ -237,7 +237,7 @@ protected void apply(RelOptRuleCall call, LogicalProject project,
   private static class MyRexShuttle extends RexShuttle {
     private List<RexLiteral> literalList;
 
-    public RexNode visitInputRef(RexInputRef inputRef) {
+    @Override public RexNode visitInputRef(RexInputRef inputRef) {
       return literalList.get(inputRef.getIndex());
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectFilterRule.java b/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectFilterRule.java
index e73fad09f68..e4021447aff 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectFilterRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectFilterRule.java
@@ -64,7 +64,7 @@ public interface Config extends MaterializedViewJoinRule.Config {
         .withFastBailOut(true)
         .as(Config.class);
 
-    default MaterializedViewProjectFilterRule toRule() {
+    @Override default MaterializedViewProjectFilterRule toRule() {
       return new MaterializedViewProjectFilterRule(this);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectJoinRule.java b/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectJoinRule.java
index 352af89b9be..17b8e14250b 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectJoinRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewProjectJoinRule.java
@@ -64,7 +64,7 @@ public interface Config extends MaterializedViewJoinRule.Config {
         .withFastBailOut(true)
         .as(Config.class);
 
-    default MaterializedViewProjectJoinRule toRule() {
+    @Override default MaterializedViewProjectJoinRule toRule() {
       return new MaterializedViewProjectJoinRule(this);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewRule.java b/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewRule.java
index 14bae0e70ed..1951ca4af16 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/materialize/MaterializedViewRule.java
@@ -1348,7 +1348,7 @@ protected static class Edge extends DefaultEdge {
       super(source, target);
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "{" + source + " -> " + target + "}";
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/rel/type/DelegatingTypeSystem.java b/core/src/main/java/org/apache/calcite/rel/type/DelegatingTypeSystem.java
index ba3b45b9ca5..74b02c52fcd 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/DelegatingTypeSystem.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/DelegatingTypeSystem.java
@@ -28,70 +28,70 @@ protected DelegatingTypeSystem(RelDataTypeSystem typeSystem) {
     this.typeSystem = typeSystem;
   }
 
-  public int getMaxScale(SqlTypeName typeName) {
+  @Override public int getMaxScale(SqlTypeName typeName) {
     return typeSystem.getMaxScale(typeName);
   }
 
-  public int getDefaultPrecision(SqlTypeName typeName) {
+  @Override public int getDefaultPrecision(SqlTypeName typeName) {
     return typeSystem.getDefaultPrecision(typeName);
   }
 
-  public int getMaxPrecision(SqlTypeName typeName) {
+  @Override public int getMaxPrecision(SqlTypeName typeName) {
     return typeSystem.getMaxPrecision(typeName);
   }
 
-  public int getMaxNumericScale() {
+  @Override public int getMaxNumericScale() {
     return typeSystem.getMaxNumericScale();
   }
 
-  public int getMaxNumericPrecision() {
+  @Override public int getMaxNumericPrecision() {
     return typeSystem.getMaxNumericPrecision();
   }
 
-  public String getLiteral(SqlTypeName typeName, boolean isPrefix) {
+  @Override public String getLiteral(SqlTypeName typeName, boolean isPrefix) {
     return typeSystem.getLiteral(typeName, isPrefix);
   }
 
-  public boolean isCaseSensitive(SqlTypeName typeName) {
+  @Override public boolean isCaseSensitive(SqlTypeName typeName) {
     return typeSystem.isCaseSensitive(typeName);
   }
 
-  public boolean isAutoincrement(SqlTypeName typeName) {
+  @Override public boolean isAutoincrement(SqlTypeName typeName) {
     return typeSystem.isAutoincrement(typeName);
   }
 
-  public int getNumTypeRadix(SqlTypeName typeName) {
+  @Override public int getNumTypeRadix(SqlTypeName typeName) {
     return typeSystem.getNumTypeRadix(typeName);
   }
 
-  public RelDataType deriveSumType(RelDataTypeFactory typeFactory,
+  @Override public RelDataType deriveSumType(RelDataTypeFactory typeFactory,
       RelDataType argumentType) {
     return typeSystem.deriveSumType(typeFactory, argumentType);
   }
 
-  public RelDataType deriveAvgAggType(RelDataTypeFactory typeFactory,
+  @Override public RelDataType deriveAvgAggType(RelDataTypeFactory typeFactory,
       RelDataType argumentType) {
     return typeSystem.deriveAvgAggType(typeFactory, argumentType);
   }
 
-  public RelDataType deriveCovarType(RelDataTypeFactory typeFactory,
+  @Override public RelDataType deriveCovarType(RelDataTypeFactory typeFactory,
       RelDataType arg0Type, RelDataType arg1Type) {
     return typeSystem.deriveCovarType(typeFactory, arg0Type, arg1Type);
   }
 
-  public RelDataType deriveFractionalRankType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType deriveFractionalRankType(RelDataTypeFactory typeFactory) {
     return typeSystem.deriveFractionalRankType(typeFactory);
   }
 
-  public RelDataType deriveRankType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType deriveRankType(RelDataTypeFactory typeFactory) {
     return typeSystem.deriveRankType(typeFactory);
   }
 
-  public boolean isSchemaCaseSensitive() {
+  @Override public boolean isSchemaCaseSensitive() {
     return typeSystem.isSchemaCaseSensitive();
   }
 
-  public boolean shouldConvertRaggedUnionTypesToVarying() {
+  @Override public boolean shouldConvertRaggedUnionTypesToVarying() {
     return typeSystem.shouldConvertRaggedUnionTypesToVarying();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordType.java b/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordType.java
index 196e3a00f26..a76e147c559 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordType.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordType.java
@@ -26,7 +26,7 @@ public abstract class DynamicRecordType extends RelDataTypeImpl {
   // The prefix string for dynamic star column name
   public static final String DYNAMIC_STAR_PREFIX = "**";
 
-  public boolean isDynamicStruct() {
+  @Override public boolean isDynamicStruct() {
     return true;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordTypeImpl.java b/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordTypeImpl.java
index 36a960f8f8e..7ef18134d0a 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordTypeImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/DynamicRecordTypeImpl.java
@@ -73,7 +73,7 @@ public DynamicRecordTypeImpl(RelDataTypeFactory typeFactory) {
     return new SqlTypeExplicitPrecedenceList(ImmutableList.of());
   }
 
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     sb.append("(DynamicRecordRow").append(getFieldNames()).append(")");
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/type/RelCrossType.java b/core/src/main/java/org/apache/calcite/rel/type/RelCrossType.java
index 6af0d96a0b6..5c8fcd8fe93 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/RelCrossType.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/RelCrossType.java
@@ -57,7 +57,7 @@ public RelCrossType(
     return false;
   }
 
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     sb.append("CrossType(");
     for (Ord<RelDataType> type : Ord.zip(types)) {
       if (type.i > 0) {
diff --git a/core/src/main/java/org/apache/calcite/rel/type/RelDataType.java b/core/src/main/java/org/apache/calcite/rel/type/RelDataType.java
index 07223dc82f3..21fe0e13445 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/RelDataType.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/RelDataType.java
@@ -207,7 +207,7 @@ RelDataTypeField getField(String fieldName, boolean caseSensitive,
    *
    * @return abbreviated type string
    */
-  String toString();
+  @Override String toString();
 
   /**
    * Gets a string representation of this type with full detail such as
diff --git a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFactoryImpl.java b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFactoryImpl.java
index 1cd3a2085c3..0f5ff19cf64 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFactoryImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFactoryImpl.java
@@ -109,12 +109,12 @@ protected RelDataTypeFactoryImpl(RelDataTypeSystem typeSystem) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataTypeSystem getTypeSystem() {
+  @Override public RelDataTypeSystem getTypeSystem() {
     return typeSystem;
   }
 
   // implement RelDataTypeFactory
-  public RelDataType createJavaType(Class clazz) {
+  @Override public RelDataType createJavaType(Class clazz) {
     final JavaType javaType =
         clazz == String.class
             ? new JavaType(clazz, true, getDefaultCharset(),
@@ -124,7 +124,7 @@ public RelDataType createJavaType(Class clazz) {
   }
 
   // implement RelDataTypeFactory
-  public RelDataType createJoinType(RelDataType... types) {
+  @Override public RelDataType createJoinType(RelDataType... types) {
     assert types != null;
     assert types.length >= 1;
     final List<RelDataType> flattenedTypes = new ArrayList<>();
@@ -133,14 +133,14 @@ public RelDataType createJoinType(RelDataType... types) {
         new RelCrossType(flattenedTypes, getFieldList(flattenedTypes)));
   }
 
-  public RelDataType createStructType(
+  @Override public RelDataType createStructType(
       final List<RelDataType> typeList,
       final List<String> fieldNameList) {
     return createStructType(StructKind.FULLY_QUALIFIED, typeList,
         fieldNameList);
   }
 
-  public RelDataType createStructType(StructKind kind,
+  @Override public RelDataType createStructType(StructKind kind,
       final List<RelDataType> typeList,
       final List<String> fieldNameList) {
     return createStructType(kind, typeList,
@@ -156,7 +156,7 @@ private RelDataType createStructType(StructKind kind,
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType createStructType(
+  @Override public RelDataType createStructType(
       final RelDataTypeFactory.FieldInfo fieldInfo) {
     return canonize(StructKind.FULLY_QUALIFIED,
         new AbstractList<String>() {
@@ -179,7 +179,7 @@ public RelDataType createStructType(
         });
   }
 
-  public final RelDataType createStructType(
+  @Override public final RelDataType createStructType(
       final List<? extends Map.Entry<String, RelDataType>> fieldList) {
     return createStructType(fieldList, false);
   }
@@ -207,7 +207,7 @@ private RelDataType createStructType(
         }, nullable);
   }
 
-  public RelDataType leastRestrictive(List<RelDataType> types) {
+  @Override public RelDataType leastRestrictive(List<RelDataType> types) {
     assert types != null;
     assert types.size() >= 1;
     RelDataType type0 = types.get(0);
@@ -245,11 +245,11 @@ protected RelDataType leastRestrictiveStructuredType(
           type0.getFieldList().get(j).getName(),
           leastRestrictive(
               new AbstractList<RelDataType>() {
-                public RelDataType get(int index) {
+                @Override public RelDataType get(int index) {
                   return types.get(index).getFieldList().get(k).getType();
                 }
 
-                public int size() {
+                @Override public int size() {
                   return types.size();
                 }
               }));
@@ -310,12 +310,12 @@ private RelDataType copyRecordType(
   }
 
   // implement RelDataTypeFactory
-  public RelDataType copyType(RelDataType type) {
+  @Override public RelDataType copyType(RelDataType type) {
     return createTypeWithNullability(type, type.isNullable());
   }
 
   // implement RelDataTypeFactory
-  public RelDataType createTypeWithNullability(
+  @Override public RelDataType createTypeWithNullability(
       final RelDataType type,
       final boolean nullable) {
     Objects.requireNonNull(type);
@@ -460,7 +460,7 @@ private List<RelDataTypeFieldImpl> fieldsOf(Class clazz) {
    * {@link RelDataTypeSystem#deriveDecimalMultiplyType(RelDataTypeFactory, RelDataType, RelDataType)}
    * to get the return type for the operation.
    */
-  @Deprecated
+  @Override @Deprecated
   public RelDataType createDecimalProduct(
       RelDataType type1,
       RelDataType type2) {
@@ -473,7 +473,7 @@ public RelDataType createDecimalProduct(
    * to get if double should be used for multiplication.
    */
   @Deprecated
-  public boolean useDoubleMultiplication(
+  @Override public boolean useDoubleMultiplication(
       RelDataType type1,
       RelDataType type2) {
     return typeSystem.shouldUseDoubleMultiplication(this, type1, type2);
@@ -484,14 +484,14 @@ public boolean useDoubleMultiplication(
    * {@link RelDataTypeSystem#deriveDecimalDivideType(RelDataTypeFactory, RelDataType, RelDataType)}
    * to get the return type for the operation.
    */
-  @Deprecated
+  @Override @Deprecated
   public RelDataType createDecimalQuotient(
       RelDataType type1,
       RelDataType type2) {
     return typeSystem.deriveDecimalDivideType(this, type1, type2);
   }
 
-  public RelDataType decimalOf(RelDataType type) {
+  @Override public RelDataType decimalOf(RelDataType type) {
     // create decimal type and sync nullability
     return createTypeWithNullability(decimalOf2(type), type.isNullable());
   }
@@ -530,12 +530,12 @@ private RelDataType decimalOf2(RelDataType type) {
     }
   }
 
-  public Charset getDefaultCharset() {
+  @Override public Charset getDefaultCharset() {
     return Util.getDefaultCharset();
   }
 
   @SuppressWarnings("deprecation")
-  public FieldInfoBuilder builder() {
+  @Override public FieldInfoBuilder builder() {
     return new FieldInfoBuilder(this);
   }
 
@@ -581,7 +581,7 @@ public Class getJavaClass() {
       return clazz;
     }
 
-    public boolean isNullable() {
+    @Override public boolean isNullable() {
       return nullable;
     }
 
@@ -590,13 +590,13 @@ public boolean isNullable() {
       return family != null ? family : this;
     }
 
-    protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+    @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
       sb.append("JavaType(");
       sb.append(clazz);
       sb.append(")");
     }
 
-    public RelDataType getComponentType() {
+    @Override public RelDataType getComponentType() {
       final Class componentType = clazz.getComponentType();
       if (componentType == null) {
         return null;
@@ -631,15 +631,15 @@ public RelDataType getComponentType() {
       }
     }
 
-    public Charset getCharset() {
+    @Override public Charset getCharset() {
       return this.charset;
     }
 
-    public SqlCollation getCollation() {
+    @Override public SqlCollation getCollation() {
       return this.collation;
     }
 
-    public SqlTypeName getSqlTypeName() {
+    @Override public SqlTypeName getSqlTypeName() {
       final SqlTypeName typeName =
           JavaToSqlTypeConversionRules.instance().lookup(clazz);
       if (typeName == null) {
diff --git a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFieldImpl.java b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFieldImpl.java
index 4d1ac981376..909da959a4c 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFieldImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeFieldImpl.java
@@ -67,41 +67,41 @@ public RelDataTypeFieldImpl(
   }
 
   // implement RelDataTypeField
-  public String getName() {
+  @Override public String getName() {
     return name;
   }
 
   // implement RelDataTypeField
-  public int getIndex() {
+  @Override public int getIndex() {
     return index;
   }
 
   // implement RelDataTypeField
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     return type;
   }
 
   // implement Map.Entry
-  public final String getKey() {
+  @Override public final String getKey() {
     return getName();
   }
 
   // implement Map.Entry
-  public final RelDataType getValue() {
+  @Override public final RelDataType getValue() {
     return getType();
   }
 
   // implement Map.Entry
-  public RelDataType setValue(RelDataType value) {
+  @Override public RelDataType setValue(RelDataType value) {
     throw new UnsupportedOperationException();
   }
 
   // for debugging
-  public String toString() {
+  @Override public String toString() {
     return "#" + index + ": " + name + " " + type;
   }
 
-  public boolean isDynamicStar() {
+  @Override public boolean isDynamicStar() {
     return type.getSqlTypeName() == SqlTypeName.DYNAMIC_STAR;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeImpl.java b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeImpl.java
index 979d8a2f927..512b0e6f7f4 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeImpl.java
@@ -77,7 +77,7 @@ protected RelDataTypeImpl() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataTypeField getField(String fieldName, boolean caseSensitive,
+  @Override public RelDataTypeField getField(String fieldName, boolean caseSensitive,
       boolean elideRecord) {
     for (RelDataTypeField field : fieldList) {
       if (Util.matches(caseSensitive, field.getName(), fieldName)) {
@@ -142,41 +142,41 @@ private static void getFieldRecurse(List<Slot> slots, RelDataType type,
     }
   }
 
-  public List<RelDataTypeField> getFieldList() {
+  @Override public List<RelDataTypeField> getFieldList() {
     assert fieldList != null : "fieldList must not be null, type = " + this;
     return fieldList;
   }
 
-  public List<String> getFieldNames() {
+  @Override public List<String> getFieldNames() {
     assert fieldList != null : "fieldList must not be null, type = " + this;
     return Pair.left(fieldList);
   }
 
-  public int getFieldCount() {
+  @Override public int getFieldCount() {
     assert fieldList != null : "fieldList must not be null, type = " + this;
     return fieldList.size();
   }
 
-  public StructKind getStructKind() {
+  @Override public StructKind getStructKind() {
     return isStruct() ? StructKind.FULLY_QUALIFIED : StructKind.NONE;
   }
 
-  public RelDataType getComponentType() {
+  @Override public RelDataType getComponentType() {
     // this is not a collection type
     return null;
   }
 
-  public RelDataType getKeyType() {
+  @Override public RelDataType getKeyType() {
     // this is not a map type
     return null;
   }
 
-  public RelDataType getValueType() {
+  @Override public RelDataType getValueType() {
     // this is not a map type
     return null;
   }
 
-  public boolean isStruct() {
+  @Override public boolean isStruct() {
     return fieldList != null;
   }
 
@@ -190,31 +190,31 @@ public boolean isStruct() {
     return digest.hashCode();
   }
 
-  public String getFullTypeString() {
+  @Override public String getFullTypeString() {
     return digest;
   }
 
-  public boolean isNullable() {
+  @Override public boolean isNullable() {
     return false;
   }
 
-  public Charset getCharset() {
+  @Override public Charset getCharset() {
     return null;
   }
 
-  public SqlCollation getCollation() {
+  @Override public SqlCollation getCollation() {
     return null;
   }
 
-  public SqlIntervalQualifier getIntervalQualifier() {
+  @Override public SqlIntervalQualifier getIntervalQualifier() {
     return null;
   }
 
-  public int getPrecision() {
+  @Override public int getPrecision() {
     return PRECISION_NOT_SPECIFIED;
   }
 
-  public int getScale() {
+  @Override public int getScale() {
     return SCALE_NOT_SPECIFIED;
   }
 
@@ -224,11 +224,11 @@ public int getScale() {
    *
    * @return SqlTypeName, never null
    */
-  public SqlTypeName getSqlTypeName() {
+  @Override public SqlTypeName getSqlTypeName() {
     return null;
   }
 
-  public SqlIdentifier getSqlIdentifier() {
+  @Override public SqlIdentifier getSqlIdentifier() {
     SqlTypeName typeName = getSqlTypeName();
     if (typeName == null) {
       return null;
@@ -238,7 +238,7 @@ public SqlIdentifier getSqlIdentifier() {
         SqlParserPos.ZERO);
   }
 
-  public RelDataTypeFamily getFamily() {
+  @Override public RelDataTypeFamily getFamily() {
     // by default, put each type into its own family
     return this;
   }
@@ -274,15 +274,15 @@ protected void computeDigest() {
     return sb.toString();
   }
 
-  public RelDataTypePrecedenceList getPrecedenceList() {
+  @Override public RelDataTypePrecedenceList getPrecedenceList() {
     // by default, make each type have a precedence list containing
     // only other types in the same family
     return new RelDataTypePrecedenceList() {
-      public boolean containsType(RelDataType type) {
+      @Override public boolean containsType(RelDataType type) {
         return getFamily() == type.getFamily();
       }
 
-      public int compareTypePrecedence(
+      @Override public int compareTypePrecedence(
           RelDataType type1,
           RelDataType type2) {
         assert containsType(type1);
@@ -292,7 +292,7 @@ public int compareTypePrecedence(
     };
   }
 
-  public RelDataTypeComparability getComparability() {
+  @Override public RelDataTypeComparability getComparability() {
     return RelDataTypeComparability.ALL;
   }
 
@@ -379,7 +379,7 @@ public static RelDataTypeField extra(RelDataType rowType) {
     return rowType.getField("_extra", true, false);
   }
 
-  public boolean isDynamicStruct() {
+  @Override public boolean isDynamicStruct() {
     return false;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeSystemImpl.java b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeSystemImpl.java
index 32cbc34edce..65c32aaedb7 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeSystemImpl.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/RelDataTypeSystemImpl.java
@@ -34,7 +34,7 @@
  * </table>
  */
 public abstract class RelDataTypeSystemImpl implements RelDataTypeSystem {
-  public int getMaxScale(SqlTypeName typeName) {
+  @Override public int getMaxScale(SqlTypeName typeName) {
     switch (typeName) {
     case DECIMAL:
       return getMaxNumericScale();
@@ -256,11 +256,11 @@ && getDefaultPrecision(typeName) != -1) {
         typeFactory.createSqlType(SqlTypeName.BIGINT), false);
   }
 
-  public boolean isSchemaCaseSensitive() {
+  @Override public boolean isSchemaCaseSensitive() {
     return true;
   }
 
-  public boolean shouldConvertRaggedUnionTypesToVarying() {
+  @Override public boolean shouldConvertRaggedUnionTypesToVarying() {
     return false;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rel/type/RelRecordType.java b/core/src/main/java/org/apache/calcite/rel/type/RelRecordType.java
index 751e6a10725..55da7154a45 100644
--- a/core/src/main/java/org/apache/calcite/rel/type/RelRecordType.java
+++ b/core/src/main/java/org/apache/calcite/rel/type/RelRecordType.java
@@ -84,7 +84,7 @@ public RelRecordType(List<RelDataTypeField> fields) {
     return kind;
   }
 
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     sb.append("RecordType");
     switch (kind) {
     case PEEK_FIELDS:
diff --git a/core/src/main/java/org/apache/calcite/rex/RexBiVisitorImpl.java b/core/src/main/java/org/apache/calcite/rex/RexBiVisitorImpl.java
index ed5ba2694e4..83a834308e7 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexBiVisitorImpl.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexBiVisitorImpl.java
@@ -36,19 +36,19 @@ protected RexBiVisitorImpl(boolean deep) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public R visitInputRef(RexInputRef inputRef, P arg) {
+  @Override public R visitInputRef(RexInputRef inputRef, P arg) {
     return null;
   }
 
-  public R visitLocalRef(RexLocalRef localRef, P arg) {
+  @Override public R visitLocalRef(RexLocalRef localRef, P arg) {
     return null;
   }
 
-  public R visitLiteral(RexLiteral literal, P arg) {
+  @Override public R visitLiteral(RexLiteral literal, P arg) {
     return null;
   }
 
-  public R visitOver(RexOver over, P arg) {
+  @Override public R visitOver(RexOver over, P arg) {
     R r = visitCall(over, arg);
     if (!deep) {
       return null;
@@ -65,11 +65,11 @@ public R visitOver(RexOver over, P arg) {
     return r;
   }
 
-  public R visitCorrelVariable(RexCorrelVariable correlVariable, P arg) {
+  @Override public R visitCorrelVariable(RexCorrelVariable correlVariable, P arg) {
     return null;
   }
 
-  public R visitCall(RexCall call, P arg) {
+  @Override public R visitCall(RexCall call, P arg) {
     if (!deep) {
       return null;
     }
@@ -81,15 +81,15 @@ public R visitCall(RexCall call, P arg) {
     return r;
   }
 
-  public R visitDynamicParam(RexDynamicParam dynamicParam, P arg) {
+  @Override public R visitDynamicParam(RexDynamicParam dynamicParam, P arg) {
     return null;
   }
 
-  public R visitRangeRef(RexRangeRef rangeRef, P arg) {
+  @Override public R visitRangeRef(RexRangeRef rangeRef, P arg) {
     return null;
   }
 
-  public R visitFieldAccess(RexFieldAccess fieldAccess, P arg) {
+  @Override public R visitFieldAccess(RexFieldAccess fieldAccess, P arg) {
     if (!deep) {
       return null;
     }
@@ -97,7 +97,7 @@ public R visitFieldAccess(RexFieldAccess fieldAccess, P arg) {
     return expr.accept(this, arg);
   }
 
-  public R visitSubQuery(RexSubQuery subQuery, P arg) {
+  @Override public R visitSubQuery(RexSubQuery subQuery, P arg) {
     if (!deep) {
       return null;
     }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexCall.java b/core/src/main/java/org/apache/calcite/rex/RexCall.java
index 8d21072feaa..5bea803685a 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexCall.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexCall.java
@@ -170,15 +170,15 @@ private boolean digestWithType() {
     return isA(SqlKind.CAST) || isA(SqlKind.NEW_SPECIFICATION);
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitCall(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitCall(this, arg);
   }
 
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     return type;
   }
 
@@ -218,7 +218,7 @@ public RelDataType getType() {
     }
   }
 
-  public SqlKind getKind() {
+  @Override public SqlKind getKind() {
     return op.kind;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexCallBinding.java b/core/src/main/java/org/apache/calcite/rex/RexCallBinding.java
index a4316526740..da51ac6868c 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexCallBinding.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexCallBinding.java
@@ -127,16 +127,16 @@ public List<RexNode> operands() {
   }
 
   // implement SqlOperatorBinding
-  public int getOperandCount() {
+  @Override public int getOperandCount() {
     return operands.size();
   }
 
   // implement SqlOperatorBinding
-  public RelDataType getOperandType(int ordinal) {
+  @Override public RelDataType getOperandType(int ordinal) {
     return operands.get(ordinal).getType();
   }
 
-  public CalciteException newError(
+  @Override public CalciteException newError(
       Resources.ExInst<SqlValidatorException> e) {
     return SqlUtil.newContextException(SqlParserPos.ZERO, e);
   }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexCopier.java b/core/src/main/java/org/apache/calcite/rex/RexCopier.java
index 8a371fb0366..e73a68d5f6f 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexCopier.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexCopier.java
@@ -48,49 +48,49 @@ private RelDataType copy(RelDataType type) {
     return builder.getTypeFactory().copyType(type);
   }
 
-  public RexNode visitOver(RexOver over) {
+  @Override public RexNode visitOver(RexOver over) {
     final boolean[] update = null;
     return new RexOver(copy(over.getType()), over.getAggOperator(),
         visitList(over.getOperands(), update), visitWindow(over.getWindow()),
         over.isDistinct(), over.ignoreNulls());
   }
 
-  public RexNode visitCall(final RexCall call) {
+  @Override public RexNode visitCall(final RexCall call) {
     final boolean[] update = null;
     return builder.makeCall(copy(call.getType()),
         call.getOperator(),
         visitList(call.getOperands(), update));
   }
 
-  public RexNode visitCorrelVariable(RexCorrelVariable variable) {
+  @Override public RexNode visitCorrelVariable(RexCorrelVariable variable) {
     return builder.makeCorrel(copy(variable.getType()), variable.id);
   }
 
-  public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
+  @Override public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
     return builder.makeFieldAccess(fieldAccess.getReferenceExpr().accept(this),
         fieldAccess.getField().getIndex());
   }
 
-  public RexNode visitInputRef(RexInputRef inputRef) {
+  @Override public RexNode visitInputRef(RexInputRef inputRef) {
     return builder.makeInputRef(copy(inputRef.getType()), inputRef.getIndex());
   }
 
-  public RexNode visitLocalRef(RexLocalRef localRef) {
+  @Override public RexNode visitLocalRef(RexLocalRef localRef) {
     return new RexLocalRef(localRef.getIndex(), copy(localRef.getType()));
   }
 
-  public RexNode visitLiteral(RexLiteral literal) {
+  @Override public RexNode visitLiteral(RexLiteral literal) {
     // Get the value as is
     return new RexLiteral(RexLiteral.value(literal), copy(literal.getType()),
         literal.getTypeName());
   }
 
-  public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
+  @Override public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
     return builder.makeDynamicParam(copy(dynamicParam.getType()),
         dynamicParam.getIndex());
   }
 
-  public RexNode visitRangeRef(RexRangeRef rangeRef) {
+  @Override public RexNode visitRangeRef(RexRangeRef rangeRef) {
     return builder.makeRangeReference(copy(rangeRef.getType()),
         rangeRef.getOffset(), false);
   }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexCorrelVariable.java b/core/src/main/java/org/apache/calcite/rex/RexCorrelVariable.java
index 7c3408cede4..2e2b35ae449 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexCorrelVariable.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexCorrelVariable.java
@@ -43,11 +43,11 @@ public class RexCorrelVariable extends RexVariable {
 
   //~ Methods ----------------------------------------------------------------
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitCorrelVariable(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitCorrelVariable(this, arg);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexDynamicParam.java b/core/src/main/java/org/apache/calcite/rex/RexDynamicParam.java
index dab2907c247..6477566ff32 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexDynamicParam.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexDynamicParam.java
@@ -46,7 +46,7 @@ public RexDynamicParam(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlKind getKind() {
+  @Override public SqlKind getKind() {
     return SqlKind.DYNAMIC_PARAM;
   }
 
@@ -54,11 +54,11 @@ public int getIndex() {
     return index;
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitDynamicParam(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitDynamicParam(this, arg);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexExecutorImpl.java b/core/src/main/java/org/apache/calcite/rex/RexExecutorImpl.java
index c77033d3f5e..605c019771b 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexExecutorImpl.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexExecutorImpl.java
@@ -123,7 +123,7 @@ public static RexExecutable getExecutable(RexBuilder rexBuilder, List<RexNode> e
   /**
    * Do constant reduction using generated code.
    */
-  public void reduce(RexBuilder rexBuilder, List<RexNode> constExps,
+  @Override public void reduce(RexBuilder rexBuilder, List<RexNode> constExps,
       List<RexNode> reducedValues) {
     final String code = compile(rexBuilder, constExps,
         (list, index, storageType) -> {
@@ -151,7 +151,7 @@ private static class DataContextInputGetter implements InputGetter {
       this.typeFactory = typeFactory;
     }
 
-    public Expression field(BlockBuilder list, int index, Type storageType) {
+    @Override public Expression field(BlockBuilder list, int index, Type storageType) {
       MethodCallExpression recFromCtx = Expressions.call(
           DataContext.ROOT,
           BuiltInMethod.DATA_CONTEXT_GET.method,
diff --git a/core/src/main/java/org/apache/calcite/rex/RexFieldAccess.java b/core/src/main/java/org/apache/calcite/rex/RexFieldAccess.java
index bd052020435..f8fc8f14db3 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexFieldAccess.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexFieldAccess.java
@@ -80,19 +80,19 @@ public RelDataTypeField getField() {
     return field;
   }
 
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     return field.getType();
   }
 
-  public SqlKind getKind() {
+  @Override public SqlKind getKind() {
     return SqlKind.FIELD_ACCESS;
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitFieldAccess(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitFieldAccess(this, arg);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexInputRef.java b/core/src/main/java/org/apache/calcite/rex/RexInputRef.java
index e264a6d2181..d7124bd933c 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexInputRef.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexInputRef.java
@@ -108,11 +108,11 @@ public static Pair<RexNode, String> of2(
     return SqlKind.INPUT_REF;
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitInputRef(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitInputRef(this, arg);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexInterpreter.java b/core/src/main/java/org/apache/calcite/rex/RexInterpreter.java
index 11d91ae2764..f7336b12c8b 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexInterpreter.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexInterpreter.java
@@ -90,51 +90,51 @@ private Comparable getOrUnbound(RexNode e) {
     throw unbound(e);
   }
 
-  public Comparable visitInputRef(RexInputRef inputRef) {
+  @Override public Comparable visitInputRef(RexInputRef inputRef) {
     return getOrUnbound(inputRef);
   }
 
-  public Comparable visitLocalRef(RexLocalRef localRef) {
+  @Override public Comparable visitLocalRef(RexLocalRef localRef) {
     throw unbound(localRef);
   }
 
-  public Comparable visitLiteral(RexLiteral literal) {
+  @Override public Comparable visitLiteral(RexLiteral literal) {
     return Util.first(literal.getValue4(), N);
   }
 
-  public Comparable visitOver(RexOver over) {
+  @Override public Comparable visitOver(RexOver over) {
     throw unbound(over);
   }
 
-  public Comparable visitCorrelVariable(RexCorrelVariable correlVariable) {
+  @Override public Comparable visitCorrelVariable(RexCorrelVariable correlVariable) {
     return getOrUnbound(correlVariable);
   }
 
-  public Comparable visitDynamicParam(RexDynamicParam dynamicParam) {
+  @Override public Comparable visitDynamicParam(RexDynamicParam dynamicParam) {
     return getOrUnbound(dynamicParam);
   }
 
-  public Comparable visitRangeRef(RexRangeRef rangeRef) {
+  @Override public Comparable visitRangeRef(RexRangeRef rangeRef) {
     throw unbound(rangeRef);
   }
 
-  public Comparable visitFieldAccess(RexFieldAccess fieldAccess) {
+  @Override public Comparable visitFieldAccess(RexFieldAccess fieldAccess) {
     return getOrUnbound(fieldAccess);
   }
 
-  public Comparable visitSubQuery(RexSubQuery subQuery) {
+  @Override public Comparable visitSubQuery(RexSubQuery subQuery) {
     throw unbound(subQuery);
   }
 
-  public Comparable visitTableInputRef(RexTableInputRef fieldRef) {
+  @Override public Comparable visitTableInputRef(RexTableInputRef fieldRef) {
     throw unbound(fieldRef);
   }
 
-  public Comparable visitPatternFieldRef(RexPatternFieldRef fieldRef) {
+  @Override public Comparable visitPatternFieldRef(RexPatternFieldRef fieldRef) {
     throw unbound(fieldRef);
   }
 
-  public Comparable visitCall(RexCall call) {
+  @Override public Comparable visitCall(RexCall call) {
     final List<Comparable> values = visitList(call.operands);
     switch (call.getKind()) {
     case IS_NOT_DISTINCT_FROM:
diff --git a/core/src/main/java/org/apache/calcite/rex/RexLiteral.java b/core/src/main/java/org/apache/calcite/rex/RexLiteral.java
index a4dd9c31fd7..d66336aab8b 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexLiteral.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexLiteral.java
@@ -871,7 +871,7 @@ public SqlTypeName getTypeName() {
     return typeName;
   }
 
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     return type;
   }
 
@@ -1114,21 +1114,21 @@ public static boolean booleanValue(RexNode node) {
     return (Boolean) ((RexLiteral) node).value;
   }
 
-  public boolean isAlwaysTrue() {
+  @Override public boolean isAlwaysTrue() {
     if (typeName != SqlTypeName.BOOLEAN) {
       return false;
     }
     return booleanValue(this);
   }
 
-  public boolean isAlwaysFalse() {
+  @Override public boolean isAlwaysFalse() {
     if (typeName != SqlTypeName.BOOLEAN) {
       return false;
     }
     return !booleanValue(this);
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (this == obj) {
       return true;
     }
@@ -1137,7 +1137,7 @@ && equals(((RexLiteral) obj).value, value)
         && equals(((RexLiteral) obj).type, type);
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return Objects.hash(value, type);
   }
 
@@ -1183,11 +1183,11 @@ private static boolean equals(Object o1, Object o2) {
     return Objects.equals(o1, o2);
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitLiteral(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitLiteral(this, arg);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexLocalRef.java b/core/src/main/java/org/apache/calcite/rex/RexLocalRef.java
index f242496e48e..7cc31e9d402 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexLocalRef.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexLocalRef.java
@@ -60,22 +60,22 @@ public RexLocalRef(int index, RelDataType type) {
     return SqlKind.LOCAL_REF;
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     return this == obj
         || obj instanceof RexLocalRef
         && Objects.equals(this.type, ((RexLocalRef) obj).type)
         && this.index == ((RexLocalRef) obj).index;
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return Objects.hash(type, index);
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitLocalRef(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitLocalRef(this, arg);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexMultisetUtil.java b/core/src/main/java/org/apache/calcite/rex/RexMultisetUtil.java
index f0606e2160f..953a00145df 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexMultisetUtil.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexMultisetUtil.java
@@ -188,7 +188,7 @@ void reset() {
       multisetCount = 0;
     }
 
-    public Void visitCall(RexCall call) {
+    @Override public Void visitCall(RexCall call) {
       ++totalCount;
       if (MULTISET_OPERATORS.contains(call.getOperator())) {
         if (!call.getOperator().equals(SqlStdOperatorTable.CAST)
diff --git a/core/src/main/java/org/apache/calcite/rex/RexNode.java b/core/src/main/java/org/apache/calcite/rex/RexNode.java
index 8a42b9d2ded..55bf69cd1e8 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexNode.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexNode.java
@@ -79,7 +79,7 @@ public SqlKind getKind() {
     return SqlKind.OTHER;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return digest;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexOver.java b/core/src/main/java/org/apache/calcite/rex/RexOver.java
index 6e006c9edd9..dcfee0b00c5 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexOver.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexOver.java
@@ -117,11 +117,11 @@ public boolean ignoreNulls() {
     return sb.toString();
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitOver(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitOver(this, arg);
   }
 
@@ -192,7 +192,7 @@ private static class Finder extends RexVisitorImpl<Void> {
       super(true);
     }
 
-    public Void visitOver(RexOver over) {
+    @Override public Void visitOver(RexOver over) {
       throw OverFound.INSTANCE;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexPermutationShuttle.java b/core/src/main/java/org/apache/calcite/rex/RexPermutationShuttle.java
index 87dd07818d5..812a311e293 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexPermutationShuttle.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexPermutationShuttle.java
@@ -37,7 +37,7 @@ public RexPermutationShuttle(Permutation permutation) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RexNode visitLocalRef(RexLocalRef local) {
+  @Override public RexNode visitLocalRef(RexLocalRef local) {
     final int index = local.getIndex();
     int target = permutation.getTarget(index);
     return new RexLocalRef(
diff --git a/core/src/main/java/org/apache/calcite/rex/RexProgram.java b/core/src/main/java/org/apache/calcite/rex/RexProgram.java
index 24e41949df8..96a7267b0d5 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexProgram.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexProgram.java
@@ -153,11 +153,11 @@ public List<RexLocalRef> getProjectList() {
    */
   public List<Pair<RexLocalRef, String>> getNamedProjects() {
     return new AbstractList<Pair<RexLocalRef, String>>() {
-      public int size() {
+      @Override public int size() {
         return projects.size();
       }
 
-      public Pair<RexLocalRef, String> get(int index) {
+      @Override public Pair<RexLocalRef, String> get(int index) {
         return Pair.of(
             projects.get(index),
             outputRowType.getFieldList().get(index).getName());
@@ -247,7 +247,7 @@ public static RexProgram create(RelInput input) {
   }
 
   // description of this calc, chiefly intended for debugging
-  public String toString() {
+  @Override public String toString() {
     // Intended to produce similar output to explainCalc,
     // but without requiring a RelNode or RelOptPlanWriter.
     final RelWriterImpl pw =
@@ -761,7 +761,7 @@ public Set<String> getCorrelVariableNames() {
     final Set<String> paramIdSet = new HashSet<>();
     RexUtil.apply(
         new RexVisitorImpl<Void>(true) {
-          public Void visitCorrelVariable(
+          @Override public Void visitCorrelVariable(
               RexCorrelVariable correlVariable) {
             paramIdSet.add(correlVariable.getName());
             return null;
@@ -900,7 +900,7 @@ static class ExpansionShuttle extends RexShuttle {
       this.exprs = exprs;
     }
 
-    public RexNode visitLocalRef(RexLocalRef localRef) {
+    @Override public RexNode visitLocalRef(RexLocalRef localRef) {
       RexNode tree = exprs.get(localRef.getIndex());
       return tree.accept(this);
     }
@@ -935,20 +935,20 @@ private class Marshaller extends RexVisitorImpl<RexNode> {
       super(false);
     }
 
-    public RexNode visitInputRef(RexInputRef inputRef) {
+    @Override public RexNode visitInputRef(RexInputRef inputRef) {
       return inputRef;
     }
 
-    public RexNode visitLocalRef(RexLocalRef localRef) {
+    @Override public RexNode visitLocalRef(RexLocalRef localRef) {
       final RexNode expr = exprs.get(localRef.index);
       return expr.accept(this);
     }
 
-    public RexNode visitLiteral(RexLiteral literal) {
+    @Override public RexNode visitLiteral(RexLiteral literal) {
       return literal;
     }
 
-    public RexNode visitCall(RexCall call) {
+    @Override public RexNode visitCall(RexCall call) {
       final List<RexNode> newOperands = new ArrayList<>();
       for (RexNode operand : call.getOperands()) {
         newOperands.add(operand.accept(this));
@@ -956,23 +956,23 @@ public RexNode visitCall(RexCall call) {
       return call.clone(call.getType(), newOperands);
     }
 
-    public RexNode visitOver(RexOver over) {
+    @Override public RexNode visitOver(RexOver over) {
       return visitCall(over);
     }
 
-    public RexNode visitCorrelVariable(RexCorrelVariable correlVariable) {
+    @Override public RexNode visitCorrelVariable(RexCorrelVariable correlVariable) {
       return correlVariable;
     }
 
-    public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
+    @Override public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
       return dynamicParam;
     }
 
-    public RexNode visitRangeRef(RexRangeRef rangeRef) {
+    @Override public RexNode visitRangeRef(RexRangeRef rangeRef) {
       return rangeRef;
     }
 
-    public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
+    @Override public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
       final RexNode referenceExpr =
           fieldAccess.getReferenceExpr().accept(this);
       return new RexFieldAccess(
@@ -989,7 +989,7 @@ private class ReferenceCounter extends RexVisitorImpl<Void> {
       super(true);
     }
 
-    public Void visitLocalRef(RexLocalRef localRef) {
+    @Override public Void visitLocalRef(RexLocalRef localRef) {
       final int index = localRef.getIndex();
       refCounts[index]++;
       return null;
diff --git a/core/src/main/java/org/apache/calcite/rex/RexProgramBuilder.java b/core/src/main/java/org/apache/calcite/rex/RexProgramBuilder.java
index 488b2a0111b..1e63e3a4045 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexProgramBuilder.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexProgramBuilder.java
@@ -164,7 +164,7 @@ private static boolean assertionsAreEnabled() {
   private void validate(final RexNode expr, final int fieldOrdinal) {
     final RexVisitor<Void> validator =
         new RexVisitorImpl<Void>(true) {
-          public Void visitInputRef(RexInputRef input) {
+          @Override public Void visitInputRef(RexInputRef input) {
             final int index = input.getIndex();
             final List<RelDataTypeField> fields =
                 inputRowType.getFieldList();
@@ -885,32 +885,32 @@ public List<RexLocalRef> getProjectList() {
   /** Shuttle that visits a tree of {@link RexNode} and registers them
    * in a program. */
   private abstract class RegisterShuttle extends RexShuttle {
-    public RexNode visitCall(RexCall call) {
+    @Override public RexNode visitCall(RexCall call) {
       final RexNode expr = super.visitCall(call);
       return registerInternal(expr, false);
     }
 
-    public RexNode visitOver(RexOver over) {
+    @Override public RexNode visitOver(RexOver over) {
       final RexNode expr = super.visitOver(over);
       return registerInternal(expr, false);
     }
 
-    public RexNode visitLiteral(RexLiteral literal) {
+    @Override public RexNode visitLiteral(RexLiteral literal) {
       final RexNode expr = super.visitLiteral(literal);
       return registerInternal(expr, false);
     }
 
-    public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
+    @Override public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
       final RexNode expr = super.visitFieldAccess(fieldAccess);
       return registerInternal(expr, false);
     }
 
-    public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
+    @Override public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
       final RexNode expr = super.visitDynamicParam(dynamicParam);
       return registerInternal(expr, false);
     }
 
-    public RexNode visitCorrelVariable(RexCorrelVariable variable) {
+    @Override public RexNode visitCorrelVariable(RexCorrelVariable variable) {
       final RexNode expr = super.visitCorrelVariable(variable);
       return registerInternal(expr, false);
     }
@@ -928,7 +928,7 @@ protected RegisterInputShuttle(boolean valid) {
       this.valid = valid;
     }
 
-    public RexNode visitInputRef(RexInputRef input) {
+    @Override public RexNode visitInputRef(RexInputRef input) {
       final int index = input.getIndex();
       if (valid) {
         // The expression should already be valid. Check that its
@@ -954,7 +954,7 @@ public RexNode visitInputRef(RexInputRef input) {
       return ref;
     }
 
-    public RexNode visitLocalRef(RexLocalRef local) {
+    @Override public RexNode visitLocalRef(RexLocalRef local) {
       if (valid) {
         // The expression should already be valid.
         final int index = local.getIndex();
@@ -1003,7 +1003,7 @@ protected RegisterMidputShuttle(
       this.localExprList = localExprList;
     }
 
-    public RexNode visitLocalRef(RexLocalRef local) {
+    @Override public RexNode visitLocalRef(RexLocalRef local) {
       // Convert a local ref into the common-subexpression it references.
       final int index = local.getIndex();
       return localExprList.get(index).accept(this);
@@ -1023,7 +1023,7 @@ private class RegisterOutputShuttle extends RegisterShuttle {
       this.localExprList = localExprList;
     }
 
-    public RexNode visitInputRef(RexInputRef input) {
+    @Override public RexNode visitInputRef(RexInputRef input) {
       // This expression refers to the Nth project column. Lookup that
       // column and find out what common sub-expression IT refers to.
       final int index = input.getIndex();
@@ -1037,7 +1037,7 @@ public RexNode visitInputRef(RexInputRef input) {
       return local;
     }
 
-    public RexNode visitLocalRef(RexLocalRef local) {
+    @Override public RexNode visitLocalRef(RexLocalRef local) {
       // Convert a local ref into the common-subexpression it references.
       final int index = local.getIndex();
       return localExprList.get(index).accept(this);
@@ -1055,7 +1055,7 @@ private UpdateRefShuttle(List<RexLocalRef> newRefs) {
       this.newRefs = newRefs;
     }
 
-    public RexNode visitLocalRef(RexLocalRef localRef) {
+    @Override public RexNode visitLocalRef(RexLocalRef localRef) {
       return newRefs.get(localRef.getIndex());
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexRangeRef.java b/core/src/main/java/org/apache/calcite/rex/RexRangeRef.java
index 3c57f95bba9..c64751a90aa 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexRangeRef.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexRangeRef.java
@@ -61,7 +61,7 @@ public class RexRangeRef extends RexNode {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     return type;
   }
 
@@ -69,11 +69,11 @@ public int getOffset() {
     return offset;
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitRangeRef(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitRangeRef(this, arg);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexShuttle.java b/core/src/main/java/org/apache/calcite/rex/RexShuttle.java
index 740c995588c..8936644d713 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexShuttle.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexShuttle.java
@@ -33,7 +33,7 @@
 public class RexShuttle implements RexVisitor<RexNode> {
   //~ Methods ----------------------------------------------------------------
 
-  public RexNode visitOver(RexOver over) {
+  @Override public RexNode visitOver(RexOver over) {
     boolean[] update = {false};
     List<RexNode> clonedOperands = visitList(over.operands, update);
     RexWindow window = visitWindow(over.getWindow());
@@ -87,7 +87,7 @@ public RexWindow visitWindow(RexWindow window) {
         rows);
   }
 
-  public RexNode visitSubQuery(RexSubQuery subQuery) {
+  @Override public RexNode visitSubQuery(RexSubQuery subQuery) {
     boolean[] update = {false};
     List<RexNode> clonedOperands = visitList(subQuery.operands, update);
     if (update[0]) {
@@ -105,7 +105,7 @@ public RexNode visitSubQuery(RexSubQuery subQuery) {
     return fieldRef;
   }
 
-  public RexNode visitCall(final RexCall call) {
+  @Override public RexNode visitCall(final RexCall call) {
     boolean[] update = {false};
     List<RexNode> clonedOperands = visitList(call.operands, update);
     if (update[0]) {
@@ -189,11 +189,11 @@ protected List<RexFieldCollation> visitFieldCollations(
     return clonedOperands.build();
   }
 
-  public RexNode visitCorrelVariable(RexCorrelVariable variable) {
+  @Override public RexNode visitCorrelVariable(RexCorrelVariable variable) {
     return variable;
   }
 
-  public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
+  @Override public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
     RexNode before = fieldAccess.getReferenceExpr();
     RexNode after = before.accept(this);
 
@@ -206,23 +206,23 @@ public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
     }
   }
 
-  public RexNode visitInputRef(RexInputRef inputRef) {
+  @Override public RexNode visitInputRef(RexInputRef inputRef) {
     return inputRef;
   }
 
-  public RexNode visitLocalRef(RexLocalRef localRef) {
+  @Override public RexNode visitLocalRef(RexLocalRef localRef) {
     return localRef;
   }
 
-  public RexNode visitLiteral(RexLiteral literal) {
+  @Override public RexNode visitLiteral(RexLiteral literal) {
     return literal;
   }
 
-  public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
+  @Override public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
     return dynamicParam;
   }
 
-  public RexNode visitRangeRef(RexRangeRef rangeRef) {
+  @Override public RexNode visitRangeRef(RexRangeRef rangeRef) {
     return rangeRef;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexSlot.java b/core/src/main/java/org/apache/calcite/rex/RexSlot.java
index 7ce5d491519..bf6dc1459cc 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexSlot.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexSlot.java
@@ -71,11 +71,11 @@ private static AbstractList<String> fromTo(
         final int start,
         final int end) {
       return new AbstractList<String>() {
-        public String get(int index) {
+        @Override public String get(int index) {
           return prefix + (index + start);
         }
 
-        public int size() {
+        @Override public int size() {
           return end - start;
         }
       };
diff --git a/core/src/main/java/org/apache/calcite/rex/RexSqlReflectiveConvertletTable.java b/core/src/main/java/org/apache/calcite/rex/RexSqlReflectiveConvertletTable.java
index 65d4fc673b7..1b2fdc00a80 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexSqlReflectiveConvertletTable.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexSqlReflectiveConvertletTable.java
@@ -36,7 +36,7 @@ public RexSqlReflectiveConvertletTable() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RexSqlConvertlet get(RexCall call) {
+  @Override public RexSqlConvertlet get(RexCall call) {
     RexSqlConvertlet convertlet;
     final SqlOperator op = call.getOperator();
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexSqlStandardConvertletTable.java b/core/src/main/java/org/apache/calcite/rex/RexSqlStandardConvertletTable.java
index 217a6ff306c..952e1a76a4f 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexSqlStandardConvertletTable.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexSqlStandardConvertletTable.java
@@ -249,7 +249,7 @@ private class EquivConvertlet implements RexSqlConvertlet {
       this.op = op;
     }
 
-    public SqlNode convertCall(RexToSqlNodeConverter converter, RexCall call) {
+    @Override public SqlNode convertCall(RexToSqlNodeConverter converter, RexCall call) {
       SqlNode[] operands = convertExpressionList(converter, call.operands);
       if (operands == null) {
         return null;
diff --git a/core/src/main/java/org/apache/calcite/rex/RexSubQuery.java b/core/src/main/java/org/apache/calcite/rex/RexSubQuery.java
index df1ae2959b0..378551bb5a2 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexSubQuery.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexSubQuery.java
@@ -107,11 +107,11 @@ public static RexSubQuery scalar(RelNode rel) {
         ImmutableList.of(), rel);
   }
 
-  public <R> R accept(RexVisitor<R> visitor) {
+  @Override public <R> R accept(RexVisitor<R> visitor) {
     return visitor.visitSubQuery(this);
   }
 
-  public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
+  @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
     return visitor.visitSubQuery(this, arg);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexToSqlNodeConverterImpl.java b/core/src/main/java/org/apache/calcite/rex/RexToSqlNodeConverterImpl.java
index 1b9c2e1c4ca..1dd4ae7fc9c 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexToSqlNodeConverterImpl.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexToSqlNodeConverterImpl.java
@@ -42,7 +42,7 @@ public RexToSqlNodeConverterImpl(RexSqlConvertletTable convertletTable) {
   //~ Methods ----------------------------------------------------------------
 
   // implement RexToSqlNodeConverter
-  public SqlNode convertNode(RexNode node) {
+  @Override public SqlNode convertNode(RexNode node) {
     if (node instanceof RexLiteral) {
       return convertLiteral((RexLiteral) node);
     } else if (node instanceof RexInputRef) {
@@ -54,7 +54,7 @@ public SqlNode convertNode(RexNode node) {
   }
 
   // implement RexToSqlNodeConverter
-  public SqlNode convertCall(RexCall call) {
+  @Override public SqlNode convertCall(RexCall call) {
     final RexSqlConvertlet convertlet = convertletTable.get(call);
     if (convertlet != null) {
       return convertlet.convertCall(this, call);
@@ -64,7 +64,7 @@ public SqlNode convertCall(RexCall call) {
   }
 
   // implement RexToSqlNodeConverter
-  public SqlNode convertLiteral(RexLiteral literal) {
+  @Override public SqlNode convertLiteral(RexLiteral literal) {
     // Numeric
     if (SqlTypeFamily.EXACT_NUMERIC.getTypeNames().contains(
         literal.getTypeName())) {
@@ -131,7 +131,7 @@ public SqlNode convertLiteral(RexLiteral literal) {
   }
 
   // implement RexToSqlNodeConverter
-  public SqlNode convertInputRef(RexInputRef ref) {
+  @Override public SqlNode convertInputRef(RexInputRef ref) {
     return null;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexUtil.java b/core/src/main/java/org/apache/calcite/rex/RexUtil.java
index d513be4ec00..586f2523ce2 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexUtil.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexUtil.java
@@ -625,23 +625,23 @@ private static RexNode deref(RexProgram program, RexNode node) {
   static class ConstantFinder implements RexVisitor<Boolean> {
     static final ConstantFinder INSTANCE = new ConstantFinder();
 
-    public Boolean visitLiteral(RexLiteral literal) {
+    @Override public Boolean visitLiteral(RexLiteral literal) {
       return true;
     }
 
-    public Boolean visitInputRef(RexInputRef inputRef) {
+    @Override public Boolean visitInputRef(RexInputRef inputRef) {
       return false;
     }
 
-    public Boolean visitLocalRef(RexLocalRef localRef) {
+    @Override public Boolean visitLocalRef(RexLocalRef localRef) {
       return false;
     }
 
-    public Boolean visitOver(RexOver over) {
+    @Override public Boolean visitOver(RexOver over) {
       return false;
     }
 
-    public Boolean visitSubQuery(RexSubQuery subQuery) {
+    @Override public Boolean visitSubQuery(RexSubQuery subQuery) {
       return false;
     }
 
@@ -653,19 +653,19 @@ public Boolean visitSubQuery(RexSubQuery subQuery) {
       return false;
     }
 
-    public Boolean visitCorrelVariable(RexCorrelVariable correlVariable) {
+    @Override public Boolean visitCorrelVariable(RexCorrelVariable correlVariable) {
       // Correlating variables change when there is an internal restart.
       // Not good enough for our purposes.
       return false;
     }
 
-    public Boolean visitDynamicParam(RexDynamicParam dynamicParam) {
+    @Override public Boolean visitDynamicParam(RexDynamicParam dynamicParam) {
       // Dynamic parameters are constant WITHIN AN EXECUTION, so that's
       // good enough.
       return true;
     }
 
-    public Boolean visitCall(RexCall call) {
+    @Override public Boolean visitCall(RexCall call) {
       // Constant if operator meets the following conditions:
       // 1. It is deterministic;
       // 2. All its operands are constant.
@@ -673,11 +673,11 @@ public Boolean visitCall(RexCall call) {
           && RexVisitorImpl.visitArrayAnd(this, call.getOperands());
     }
 
-    public Boolean visitRangeRef(RexRangeRef rangeRef) {
+    @Override public Boolean visitRangeRef(RexRangeRef rangeRef) {
       return false;
     }
 
-    public Boolean visitFieldAccess(RexFieldAccess fieldAccess) {
+    @Override public Boolean visitFieldAccess(RexFieldAccess fieldAccess) {
       // "<expr>.FIELD" is constant iff "<expr>" is constant.
       return fieldAccess.getReferenceExpr().accept(this);
     }
@@ -740,7 +740,7 @@ public static RexCall findOperatorCall(
     try {
       RexVisitor<Void> visitor =
           new RexVisitorImpl<Void>(true) {
-            public Void visitCall(RexCall call) {
+            @Override public Void visitCall(RexCall call) {
               if (call.getOperator().equals(operator)) {
                 throw new Util.FoundOne(call);
               }
@@ -765,7 +765,7 @@ public static boolean containsInputRef(
     try {
       RexVisitor<Void> visitor =
           new RexVisitorImpl<Void>(true) {
-            public Void visitInputRef(RexInputRef inputRef) {
+            @Override public Void visitInputRef(RexInputRef inputRef) {
               throw new Util.FoundOne(inputRef);
             }
           };
@@ -787,7 +787,7 @@ public static boolean containsFieldAccess(RexNode node) {
     try {
       RexVisitor<Void> visitor =
           new RexVisitorImpl<Void>(true) {
-            public Void visitFieldAccess(RexFieldAccess fieldAccess) {
+            @Override public Void visitFieldAccess(RexFieldAccess fieldAccess) {
               throw new Util.FoundOne(fieldAccess);
             }
           };
@@ -1017,7 +1017,7 @@ public static RexTableInputRef containsTableInputRef(RexNode node) {
     try {
       RexVisitor<Void> visitor =
           new RexVisitorImpl<Void>(true) {
-            public Void visitTableInputRef(RexTableInputRef inputRef) {
+            @Override public Void visitTableInputRef(RexTableInputRef inputRef) {
               throw new Util.FoundOne(inputRef);
             }
           };
@@ -2279,19 +2279,19 @@ protected RexNode lookup(RexNode expr) {
       return map.get(expr);
     }
 
-    public RexNode visitInputRef(RexInputRef inputRef) {
+    @Override public RexNode visitInputRef(RexInputRef inputRef) {
       return register(inputRef);
     }
 
-    public RexNode visitLiteral(RexLiteral literal) {
+    @Override public RexNode visitLiteral(RexLiteral literal) {
       return register(literal);
     }
 
-    public RexNode visitCorrelVariable(RexCorrelVariable correlVariable) {
+    @Override public RexNode visitCorrelVariable(RexCorrelVariable correlVariable) {
       return register(correlVariable);
     }
 
-    public RexNode visitCall(RexCall call) {
+    @Override public RexNode visitCall(RexCall call) {
       List<RexNode> normalizedOperands = new ArrayList<>();
       int diffCount = 0;
       for (RexNode operand : call.getOperands()) {
@@ -2311,15 +2311,15 @@ public RexNode visitCall(RexCall call) {
       return register(call);
     }
 
-    public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
+    @Override public RexNode visitDynamicParam(RexDynamicParam dynamicParam) {
       return register(dynamicParam);
     }
 
-    public RexNode visitRangeRef(RexRangeRef rangeRef) {
+    @Override public RexNode visitRangeRef(RexRangeRef rangeRef) {
       return register(rangeRef);
     }
 
-    public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
+    @Override public RexNode visitFieldAccess(RexFieldAccess fieldAccess) {
       final RexNode expr = fieldAccess.getReferenceExpr();
       expr.accept(this);
       final RexNode normalizedExpr = lookup(expr);
@@ -2357,7 +2357,7 @@ private static class ForwardRefFinder extends RexVisitorImpl<Void> {
       this.inputRowType = inputRowType;
     }
 
-    public Void visitInputRef(RexInputRef inputRef) {
+    @Override public Void visitInputRef(RexInputRef inputRef) {
       super.visitInputRef(inputRef);
       if (inputRef.getIndex() >= inputRowType.getFieldCount()) {
         throw new IllegalForwardRefException();
@@ -2365,7 +2365,7 @@ public Void visitInputRef(RexInputRef inputRef) {
       return null;
     }
 
-    public Void visitLocalRef(RexLocalRef inputRef) {
+    @Override public Void visitLocalRef(RexLocalRef inputRef) {
       super.visitLocalRef(inputRef);
       if (inputRef.getIndex() >= limit) {
         throw new IllegalForwardRefException();
@@ -2394,12 +2394,12 @@ public FieldAccessFinder() {
       fieldAccessList = new ArrayList<>();
     }
 
-    public Void visitFieldAccess(RexFieldAccess fieldAccess) {
+    @Override public Void visitFieldAccess(RexFieldAccess fieldAccess) {
       fieldAccessList.add(fieldAccess);
       return null;
     }
 
-    public Void visitCall(RexCall call) {
+    @Override public Void visitCall(RexCall call) {
       visitEach(call.operands);
       return null;
     }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexVariable.java b/core/src/main/java/org/apache/calcite/rex/RexVariable.java
index 77fdd7e875c..37634f618d4 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexVariable.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexVariable.java
@@ -41,7 +41,7 @@ protected RexVariable(
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     return type;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/rex/RexVisitorImpl.java b/core/src/main/java/org/apache/calcite/rex/RexVisitorImpl.java
index c4808786a79..8a07b37668c 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexVisitorImpl.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexVisitorImpl.java
@@ -37,19 +37,19 @@ protected RexVisitorImpl(boolean deep) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public R visitInputRef(RexInputRef inputRef) {
+  @Override public R visitInputRef(RexInputRef inputRef) {
     return null;
   }
 
-  public R visitLocalRef(RexLocalRef localRef) {
+  @Override public R visitLocalRef(RexLocalRef localRef) {
     return null;
   }
 
-  public R visitLiteral(RexLiteral literal) {
+  @Override public R visitLiteral(RexLiteral literal) {
     return null;
   }
 
-  public R visitOver(RexOver over) {
+  @Override public R visitOver(RexOver over) {
     R r = visitCall(over);
     if (!deep) {
       return null;
@@ -64,11 +64,11 @@ public R visitOver(RexOver over) {
     return r;
   }
 
-  public R visitCorrelVariable(RexCorrelVariable correlVariable) {
+  @Override public R visitCorrelVariable(RexCorrelVariable correlVariable) {
     return null;
   }
 
-  public R visitCall(RexCall call) {
+  @Override public R visitCall(RexCall call) {
     if (!deep) {
       return null;
     }
@@ -80,15 +80,15 @@ public R visitCall(RexCall call) {
     return r;
   }
 
-  public R visitDynamicParam(RexDynamicParam dynamicParam) {
+  @Override public R visitDynamicParam(RexDynamicParam dynamicParam) {
     return null;
   }
 
-  public R visitRangeRef(RexRangeRef rangeRef) {
+  @Override public R visitRangeRef(RexRangeRef rangeRef) {
     return null;
   }
 
-  public R visitFieldAccess(RexFieldAccess fieldAccess) {
+  @Override public R visitFieldAccess(RexFieldAccess fieldAccess) {
     if (!deep) {
       return null;
     }
@@ -96,7 +96,7 @@ public R visitFieldAccess(RexFieldAccess fieldAccess) {
     return expr.accept(this);
   }
 
-  public R visitSubQuery(RexSubQuery subQuery) {
+  @Override public R visitSubQuery(RexSubQuery subQuery) {
     if (!deep) {
       return null;
     }
diff --git a/core/src/main/java/org/apache/calcite/rex/RexWindow.java b/core/src/main/java/org/apache/calcite/rex/RexWindow.java
index 3793fc5ad68..ca0b0358676 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexWindow.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexWindow.java
@@ -88,15 +88,15 @@ public class RexWindow {
 
   //~ Methods ----------------------------------------------------------------
 
-  public String toString() {
+  @Override public String toString() {
     return digest;
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return digest.hashCode();
   }
 
-  public boolean equals(Object that) {
+  @Override public boolean equals(Object that) {
     if (that instanceof RexWindow) {
       RexWindow window = (RexWindow) that;
       return digest.equals(window.digest);
diff --git a/core/src/main/java/org/apache/calcite/runtime/AbstractImmutableList.java b/core/src/main/java/org/apache/calcite/runtime/AbstractImmutableList.java
index cc58a001389..422b0414097 100644
--- a/core/src/main/java/org/apache/calcite/runtime/AbstractImmutableList.java
+++ b/core/src/main/java/org/apache/calcite/runtime/AbstractImmutableList.java
@@ -30,67 +30,67 @@
 abstract class AbstractImmutableList<E> implements List<E> {
   protected abstract List<E> toList();
 
-  @Nonnull public Iterator<E> iterator() {
+  @Override @Nonnull public Iterator<E> iterator() {
     return toList().iterator();
   }
 
-  @Nonnull public ListIterator<E> listIterator() {
+  @Override @Nonnull public ListIterator<E> listIterator() {
     return toList().listIterator();
   }
 
-  public boolean isEmpty() {
+  @Override public boolean isEmpty() {
     return false;
   }
 
-  public boolean add(E t) {
+  @Override public boolean add(E t) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean addAll(@Nonnull Collection<? extends E> c) {
+  @Override public boolean addAll(@Nonnull Collection<? extends E> c) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean addAll(int index, @Nonnull Collection<? extends E> c) {
+  @Override public boolean addAll(int index, @Nonnull Collection<? extends E> c) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean removeAll(@Nonnull Collection<?> c) {
+  @Override public boolean removeAll(@Nonnull Collection<?> c) {
     throw new UnsupportedOperationException();
   }
 
-  public boolean retainAll(@Nonnull Collection<?> c) {
+  @Override public boolean retainAll(@Nonnull Collection<?> c) {
     throw new UnsupportedOperationException();
   }
 
-  public void clear() {
+  @Override public void clear() {
     throw new UnsupportedOperationException();
   }
 
-  public E set(int index, E element) {
+  @Override public E set(int index, E element) {
     throw new UnsupportedOperationException();
   }
 
-  public void add(int index, E element) {
+  @Override public void add(int index, E element) {
     throw new UnsupportedOperationException();
   }
 
-  public E remove(int index) {
+  @Override public E remove(int index) {
     throw new UnsupportedOperationException();
   }
 
-  @Nonnull public ListIterator<E> listIterator(int index) {
+  @Override @Nonnull public ListIterator<E> listIterator(int index) {
     return toList().listIterator(index);
   }
 
-  @Nonnull public List<E> subList(int fromIndex, int toIndex) {
+  @Override @Nonnull public List<E> subList(int fromIndex, int toIndex) {
     return toList().subList(fromIndex, toIndex);
   }
 
-  public boolean contains(Object o) {
+  @Override public boolean contains(Object o) {
     return indexOf(o) >= 0;
   }
 
-  public boolean containsAll(@Nonnull Collection<?> c) {
+  @Override public boolean containsAll(@Nonnull Collection<?> c) {
     for (Object o : c) {
       if (!contains(o)) {
         return false;
@@ -99,7 +99,7 @@ public boolean containsAll(@Nonnull Collection<?> c) {
     return true;
   }
 
-  public boolean remove(Object o) {
+  @Override public boolean remove(Object o) {
     throw new UnsupportedOperationException();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/ArrayBindable.java b/core/src/main/java/org/apache/calcite/runtime/ArrayBindable.java
index d40bfa5a4b8..a88bc861f48 100644
--- a/core/src/main/java/org/apache/calcite/runtime/ArrayBindable.java
+++ b/core/src/main/java/org/apache/calcite/runtime/ArrayBindable.java
@@ -24,5 +24,5 @@
  */
 public interface ArrayBindable extends Bindable<Object[]>, Typed {
   // override
-  Class<Object[]> getElementType();
+  @Override Class<Object[]> getElementType();
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/ArrayComparator.java b/core/src/main/java/org/apache/calcite/runtime/ArrayComparator.java
index a44c4794b0e..f72e9cc2e40 100644
--- a/core/src/main/java/org/apache/calcite/runtime/ArrayComparator.java
+++ b/core/src/main/java/org/apache/calcite/runtime/ArrayComparator.java
@@ -47,7 +47,7 @@ private static Comparator[] comparators(boolean[] descendings) {
     return comparators;
   }
 
-  public int compare(Object[] o1, Object[] o2) {
+  @Override public int compare(Object[] o1, Object[] o2) {
     for (int i = 0; i < comparators.length; i++) {
       Comparator comparator = comparators[i];
       int c = comparator.compare(o1[i], o2[i]);
diff --git a/core/src/main/java/org/apache/calcite/runtime/ArrayEnumeratorCursor.java b/core/src/main/java/org/apache/calcite/runtime/ArrayEnumeratorCursor.java
index 6775340f5ef..11a8bc1a300 100644
--- a/core/src/main/java/org/apache/calcite/runtime/ArrayEnumeratorCursor.java
+++ b/core/src/main/java/org/apache/calcite/runtime/ArrayEnumeratorCursor.java
@@ -33,7 +33,7 @@ public ArrayEnumeratorCursor(Enumerator<Object[]> enumerator) {
     super(enumerator);
   }
 
-  protected Getter createGetter(int ordinal) {
+  @Override protected Getter createGetter(int ordinal) {
     return new ArrayGetter(ordinal);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/ConsList.java b/core/src/main/java/org/apache/calcite/runtime/ConsList.java
index 445cf7e1b1d..83cc303d41c 100644
--- a/core/src/main/java/org/apache/calcite/runtime/ConsList.java
+++ b/core/src/main/java/org/apache/calcite/runtime/ConsList.java
@@ -53,7 +53,7 @@ private ConsList(E first, List<E> rest) {
     this.rest = rest;
   }
 
-  public E get(int index) {
+  @Override public E get(int index) {
     for (ConsList<E> c = this;; c = (ConsList<E>) c.rest) {
       if (index == 0) {
         return c.first;
@@ -65,7 +65,7 @@ public E get(int index) {
     }
   }
 
-  public int size() {
+  @Override public int size() {
     int s = 1;
     for (ConsList c = this;; c = (ConsList) c.rest, ++s) {
       if (!(c.rest instanceof ConsList)) {
@@ -88,7 +88,7 @@ public int size() {
     return toList().toString();
   }
 
-  protected final List<E> toList() {
+  @Override protected final List<E> toList() {
     final List<E> list = new ArrayList<>();
     for (ConsList<E> c = this;; c = (ConsList<E>) c.rest) {
       list.add(c.first);
@@ -111,11 +111,11 @@ protected final List<E> toList() {
     return toList().listIterator(index);
   }
 
-  @Nonnull public Object[] toArray() {
+  @Override @Nonnull public Object[] toArray() {
     return toList().toArray();
   }
 
-  @Nonnull public <T> T[] toArray(@Nonnull T[] a) {
+  @Override @Nonnull public <T> T[] toArray(@Nonnull T[] a) {
     final int s = size();
     if (s > a.length) {
       a = Arrays.copyOf(a, s);
@@ -135,11 +135,11 @@ protected final List<E> toList() {
     }
   }
 
-  public int indexOf(Object o) {
+  @Override public int indexOf(Object o) {
     return toList().indexOf(o);
   }
 
-  public int lastIndexOf(Object o) {
+  @Override public int lastIndexOf(Object o) {
     return toList().lastIndexOf(o);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/Enumerables.java b/core/src/main/java/org/apache/calcite/runtime/Enumerables.java
index 11143910211..ce45f39eccf 100644
--- a/core/src/main/java/org/apache/calcite/runtime/Enumerables.java
+++ b/core/src/main/java/org/apache/calcite/runtime/Enumerables.java
@@ -76,7 +76,7 @@ public static <E, TKey, TResult> Enumerable<TResult> match(
       Matcher<E> matcher,
       Emitter<E, TResult> emitter, int history, int future) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           final Enumerator<E> inputEnumerator = enumerable.enumerator();
 
@@ -94,12 +94,12 @@ public Enumerator<TResult> enumerator() {
           /** Match counter is 1-based in Oracle. */
           final AtomicInteger matchCounter = new AtomicInteger(1);
 
-          public TResult current() {
+          @Override public TResult current() {
             Objects.requireNonNull(resultRow);
             return resultRow;
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             for (;;) {
               resultRow = emitRows.pollFirst();
               if (resultRow != null) {
@@ -170,11 +170,11 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             throw new UnsupportedOperationException();
           }
 
-          public void close() {
+          @Override public void close() {
             inputEnumerator.close();
           }
         };
diff --git a/core/src/main/java/org/apache/calcite/runtime/EnumeratorCursor.java b/core/src/main/java/org/apache/calcite/runtime/EnumeratorCursor.java
index 042f88c31d0..43923030ad5 100644
--- a/core/src/main/java/org/apache/calcite/runtime/EnumeratorCursor.java
+++ b/core/src/main/java/org/apache/calcite/runtime/EnumeratorCursor.java
@@ -43,15 +43,15 @@ protected EnumeratorCursor(Enumerator<T> enumerator) {
     this.enumerator = enumerator;
   }
 
-  protected T current() {
+  @Override protected T current() {
     return enumerator.current();
   }
 
-  public boolean next() {
+  @Override public boolean next() {
     return enumerator.moveNext();
   }
 
-  public void close() {
+  @Override public void close() {
     enumerator.close();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/FlatLists.java b/core/src/main/java/org/apache/calcite/runtime/FlatLists.java
index 84c4b3b33c2..41bde64f8d1 100644
--- a/core/src/main/java/org/apache/calcite/runtime/FlatLists.java
+++ b/core/src/main/java/org/apache/calcite/runtime/FlatLists.java
@@ -278,7 +278,7 @@ public static <K, V> ImmutableMap<K, V> append(Map<K, V> map, K k, V v) {
    * @param <T> element type */
   public abstract static class AbstractFlatList<T>
       extends AbstractImmutableList<T> implements RandomAccess {
-    protected final List<T> toList() {
+    @Override protected final List<T> toList() {
       //noinspection unchecked
       return Arrays.asList((T[]) toArray());
     }
@@ -311,11 +311,11 @@ protected static class Flat1List<T>
       this.t0 = t0;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "[" + t0 + "]";
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       switch (index) {
       case 0:
         return t0;
@@ -324,15 +324,15 @@ public T get(int index) {
       }
     }
 
-    public int size() {
+    @Override public int size() {
       return 1;
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return Collections.singletonList(t0).iterator();
     }
 
-    public boolean equals(Object o) {
+    @Override public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
@@ -345,13 +345,13 @@ public boolean equals(Object o) {
           && Objects.equals(t0, ((List) o).get(0));
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       int h = 1;
       h = h * 31 + Utilities.hash(t0);
       return h;
     }
 
-    public int indexOf(Object o) {
+    @Override public int indexOf(Object o) {
       if (o == null) {
         if (t0 == null) {
           return 0;
@@ -364,7 +364,7 @@ public int indexOf(Object o) {
       return -1;
     }
 
-    public int lastIndexOf(Object o) {
+    @Override public int lastIndexOf(Object o) {
       if (o == null) {
         if (t0 == null) {
           return 0;
@@ -377,7 +377,7 @@ public int lastIndexOf(Object o) {
       return -1;
     }
 
-    @SuppressWarnings({"unchecked" })
+    @Override @SuppressWarnings({"unchecked" })
     public <T2> T2[] toArray(T2[] a) {
       if (a.length < 1) {
         // Make a new array of a's runtime type, but my contents:
@@ -387,15 +387,15 @@ public <T2> T2[] toArray(T2[] a) {
       return a;
     }
 
-    public Object[] toArray() {
+    @Override public Object[] toArray() {
       return new Object[] {t0};
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return ComparableListImpl.compare((List) this, o);
     }
 
-    public List<T> append(T e) {
+    @Override public List<T> append(T e) {
       return new Flat2List<>(t0, e);
     }
   }
@@ -425,11 +425,11 @@ protected static class Flat2List<T>
       this.t1 = t1;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "[" + t0 + ", " + t1 + "]";
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       switch (index) {
       case 0:
         return t0;
@@ -440,15 +440,15 @@ public T get(int index) {
       }
     }
 
-    public int size() {
+    @Override public int size() {
       return 2;
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return Arrays.asList(t0, t1).iterator();
     }
 
-    public boolean equals(Object o) {
+    @Override public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
@@ -464,14 +464,14 @@ public boolean equals(Object o) {
       return false;
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       int h = 1;
       h = h * 31 + Utilities.hash(t0);
       h = h * 31 + Utilities.hash(t1);
       return h;
     }
 
-    public int indexOf(Object o) {
+    @Override public int indexOf(Object o) {
       if (o == null) {
         if (t0 == null) {
           return 0;
@@ -490,7 +490,7 @@ public int indexOf(Object o) {
       return -1;
     }
 
-    public int lastIndexOf(Object o) {
+    @Override public int lastIndexOf(Object o) {
       if (o == null) {
         if (t1 == null) {
           return 1;
@@ -509,7 +509,7 @@ public int lastIndexOf(Object o) {
       return -1;
     }
 
-    @SuppressWarnings({"unchecked" })
+    @Override @SuppressWarnings({"unchecked" })
     public <T2> T2[] toArray(T2[] a) {
       if (a.length < 2) {
         // Make a new array of a's runtime type, but my contents:
@@ -520,15 +520,15 @@ public <T2> T2[] toArray(T2[] a) {
       return a;
     }
 
-    public Object[] toArray() {
+    @Override public Object[] toArray() {
       return new Object[] {t0, t1};
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return ComparableListImpl.compare((List) this, o);
     }
 
-    public List<T> append(T e) {
+    @Override public List<T> append(T e) {
       return new Flat3List<>(t0, t1, e);
     }
   }
@@ -560,11 +560,11 @@ protected static class Flat3List<T>
       this.t2 = t2;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "[" + t0 + ", " + t1 + ", " + t2 + "]";
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       switch (index) {
       case 0:
         return t0;
@@ -577,15 +577,15 @@ public T get(int index) {
       }
     }
 
-    public int size() {
+    @Override public int size() {
       return 3;
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return Arrays.asList(t0, t1, t2).iterator();
     }
 
-    public boolean equals(Object o) {
+    @Override public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
@@ -600,7 +600,7 @@ public boolean equals(Object o) {
           && Arrays.asList(t0, t1, t2).equals(o);
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       int h = 1;
       h = h * 31 + Utilities.hash(t0);
       h = h * 31 + Utilities.hash(t1);
@@ -608,7 +608,7 @@ public int hashCode() {
       return h;
     }
 
-    public int indexOf(Object o) {
+    @Override public int indexOf(Object o) {
       if (o == null) {
         if (t0 == null) {
           return 0;
@@ -633,7 +633,7 @@ public int indexOf(Object o) {
       return -1;
     }
 
-    public int lastIndexOf(Object o) {
+    @Override public int lastIndexOf(Object o) {
       if (o == null) {
         if (t2 == null) {
           return 2;
@@ -658,7 +658,7 @@ public int lastIndexOf(Object o) {
       return -1;
     }
 
-    @SuppressWarnings({"unchecked" })
+    @Override @SuppressWarnings({"unchecked" })
     public <T2> T2[] toArray(T2[] a) {
       if (a.length < 3) {
         // Make a new array of a's runtime type, but my contents:
@@ -670,15 +670,15 @@ public <T2> T2[] toArray(T2[] a) {
       return a;
     }
 
-    public Object[] toArray() {
+    @Override public Object[] toArray() {
       return new Object[] {t0, t1, t2};
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return ComparableListImpl.compare((List) this, o);
     }
 
-    public List<T> append(T e) {
+    @Override public List<T> append(T e) {
       return new Flat4List<>(t0, t1, t2, e);
     }
   }
@@ -712,11 +712,11 @@ protected static class Flat4List<T>
       this.t3 = t3;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "[" + t0 + ", " + t1 + ", " + t2 + ", " + t3 + "]";
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       switch (index) {
       case 0:
         return t0;
@@ -731,15 +731,15 @@ public T get(int index) {
       }
     }
 
-    public int size() {
+    @Override public int size() {
       return 4;
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return Arrays.asList(t0, t1, t2, t3).iterator();
     }
 
-    public boolean equals(Object o) {
+    @Override public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
@@ -755,7 +755,7 @@ public boolean equals(Object o) {
           && Arrays.asList(t0, t1, t2, t3).equals(o);
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       int h = 1;
       h = h * 31 + Utilities.hash(t0);
       h = h * 31 + Utilities.hash(t1);
@@ -764,7 +764,7 @@ public int hashCode() {
       return h;
     }
 
-    public int indexOf(Object o) {
+    @Override public int indexOf(Object o) {
       if (o == null) {
         if (t0 == null) {
           return 0;
@@ -795,7 +795,7 @@ public int indexOf(Object o) {
       return -1;
     }
 
-    public int lastIndexOf(Object o) {
+    @Override public int lastIndexOf(Object o) {
       if (o == null) {
         if (t3 == null) {
           return 3;
@@ -826,7 +826,7 @@ public int lastIndexOf(Object o) {
       return -1;
     }
 
-    @SuppressWarnings({"unchecked" })
+    @Override @SuppressWarnings({"unchecked" })
     public <T2> T2[] toArray(T2[] a) {
       if (a.length < 4) {
         // Make a new array of a's runtime type, but my contents:
@@ -839,15 +839,15 @@ public <T2> T2[] toArray(T2[] a) {
       return a;
     }
 
-    public Object[] toArray() {
+    @Override public Object[] toArray() {
       return new Object[] {t0, t1, t2, t3};
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return ComparableListImpl.compare((List) this, o);
     }
 
-    public List<T> append(T e) {
+    @Override public List<T> append(T e) {
       return new Flat5List<>(t0, t1, t2, t3, e);
     }
   }
@@ -883,11 +883,11 @@ protected static class Flat5List<T>
       this.t4 = t4;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "[" + t0 + ", " + t1 + ", " + t2 + ", " + t3 + ", " + t4 + "]";
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       switch (index) {
       case 0:
         return t0;
@@ -904,15 +904,15 @@ public T get(int index) {
       }
     }
 
-    public int size() {
+    @Override public int size() {
       return 5;
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return Arrays.asList(t0, t1, t2, t3, t4).iterator();
     }
 
-    public boolean equals(Object o) {
+    @Override public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
@@ -929,7 +929,7 @@ public boolean equals(Object o) {
           && Arrays.asList(t0, t1, t2, t3, t4).equals(o);
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       int h = 1;
       h = h * 31 + Utilities.hash(t0);
       h = h * 31 + Utilities.hash(t1);
@@ -939,7 +939,7 @@ public int hashCode() {
       return h;
     }
 
-    public int indexOf(Object o) {
+    @Override public int indexOf(Object o) {
       if (o == null) {
         if (t0 == null) {
           return 0;
@@ -976,7 +976,7 @@ public int indexOf(Object o) {
       return -1;
     }
 
-    public int lastIndexOf(Object o) {
+    @Override public int lastIndexOf(Object o) {
       if (o == null) {
         if (t4 == null) {
           return 4;
@@ -1013,7 +1013,7 @@ public int lastIndexOf(Object o) {
       return -1;
     }
 
-    @SuppressWarnings({"unchecked" })
+    @Override @SuppressWarnings({"unchecked" })
     public <T2> T2[] toArray(T2[] a) {
       if (a.length < 5) {
         // Make a new array of a's runtime type, but my contents:
@@ -1027,15 +1027,15 @@ public <T2> T2[] toArray(T2[] a) {
       return a;
     }
 
-    public Object[] toArray() {
+    @Override public Object[] toArray() {
       return new Object[] {t0, t1, t2, t3, t4};
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return ComparableListImpl.compare((List) this, o);
     }
 
-    public List<T> append(T e) {
+    @Override public List<T> append(T e) {
       return new Flat6List<>(t0, t1, t2, t3, t4, e);
     }
   }
@@ -1073,12 +1073,12 @@ protected static class Flat6List<T>
       this.t5 = t5;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "[" + t0 + ", " + t1 + ", " + t2 + ", " + t3 + ", " + t4
           + ", " + t5 + "]";
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       switch (index) {
       case 0:
         return t0;
@@ -1097,15 +1097,15 @@ public T get(int index) {
       }
     }
 
-    public int size() {
+    @Override public int size() {
       return 6;
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return Arrays.asList(t0, t1, t2, t3, t4, t5).iterator();
     }
 
-    public boolean equals(Object o) {
+    @Override public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
@@ -1123,7 +1123,7 @@ public boolean equals(Object o) {
           && Arrays.asList(t0, t1, t2, t3, t4, t5).equals(o);
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       int h = 1;
       h = h * 31 + Utilities.hash(t0);
       h = h * 31 + Utilities.hash(t1);
@@ -1134,7 +1134,7 @@ public int hashCode() {
       return h;
     }
 
-    public int indexOf(Object o) {
+    @Override public int indexOf(Object o) {
       if (o == null) {
         if (t0 == null) {
           return 0;
@@ -1177,7 +1177,7 @@ public int indexOf(Object o) {
       return -1;
     }
 
-    public int lastIndexOf(Object o) {
+    @Override public int lastIndexOf(Object o) {
       if (o == null) {
         if (t5 == null) {
           return 5;
@@ -1220,7 +1220,7 @@ public int lastIndexOf(Object o) {
       return -1;
     }
 
-    @SuppressWarnings({"unchecked" })
+    @Override @SuppressWarnings({"unchecked" })
     public <T2> T2[] toArray(T2[] a) {
       if (a.length < 6) {
         // Make a new array of a's runtime type, but my contents:
@@ -1235,15 +1235,15 @@ public <T2> T2[] toArray(T2[] a) {
       return a;
     }
 
-    public Object[] toArray() {
+    @Override public Object[] toArray() {
       return new Object[] {t0, t1, t2, t3, t4, t5};
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return ComparableListImpl.compare((List) this, o);
     }
 
-    public List<T> append(T e) {
+    @Override public List<T> append(T e) {
       return ImmutableNullableList.of(t0, t1, t2, t3, t5, e);
     }
   }
@@ -1257,24 +1257,24 @@ private static class ComparableEmptyList<T>
     private ComparableEmptyList() {
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       throw new IndexOutOfBoundsException();
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       return 1; // same as Collections.emptyList()
     }
 
-    public boolean equals(Object o) {
+    @Override public boolean equals(Object o) {
       return o == this
           || o instanceof List && ((List) o).isEmpty();
     }
 
-    public int size() {
+    @Override public int size() {
       return 0;
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return ComparableListImpl.compare((List) this, o);
     }
   }
@@ -1305,15 +1305,15 @@ protected ComparableListImpl(List<T> list) {
       this.list = list;
     }
 
-    public T get(int index) {
+    @Override public T get(int index) {
       return list.get(index);
     }
 
-    public int size() {
+    @Override public int size() {
       return list.size();
     }
 
-    public int compareTo(List o) {
+    @Override public int compareTo(List o) {
       return compare(list, o);
     }
 
diff --git a/core/src/main/java/org/apache/calcite/runtime/GeoFunctions.java b/core/src/main/java/org/apache/calcite/runtime/GeoFunctions.java
index c7c2019f4b9..7b1fb251b0f 100644
--- a/core/src/main/java/org/apache/calcite/runtime/GeoFunctions.java
+++ b/core/src/main/java/org/apache/calcite/runtime/GeoFunctions.java
@@ -568,15 +568,15 @@ public GridEnumerable(Envelope envelope, BigDecimal deltaX,
           return new Object[] {geom, id, x + 1, y + 1, baseX + x, baseY + y};
         }
 
-        public boolean moveNext() {
+        @Override public boolean moveNext() {
           return ++id < area;
         }
 
-        public void reset() {
+        @Override public void reset() {
           id = -1;
         }
 
-        public void close() {
+        @Override public void close() {
         }
       };
     }
diff --git a/core/src/main/java/org/apache/calcite/runtime/Geometries.java b/core/src/main/java/org/apache/calcite/runtime/Geometries.java
index c8e9919cd75..0805a81d649 100644
--- a/core/src/main/java/org/apache/calcite/runtime/Geometries.java
+++ b/core/src/main/java/org/apache/calcite/runtime/Geometries.java
@@ -222,30 +222,30 @@ static class SimpleGeom implements Geom {
       return g.toString();
     }
 
-    public int compareTo(Geom o) {
+    @Override public int compareTo(Geom o) {
       return toString().compareTo(o.toString());
     }
 
-    public Geometry g() {
+    @Override public Geometry g() {
       return g;
     }
 
-    public Type type() {
+    @Override public Type type() {
       return Geometries.type(g);
     }
 
-    public SpatialReference sr() {
+    @Override public SpatialReference sr() {
       return SPATIAL_REFERENCE;
     }
 
-    public Geom transform(int srid) {
+    @Override public Geom transform(int srid) {
       if (srid == SPATIAL_REFERENCE.getID()) {
         return this;
       }
       return bind(g, srid);
     }
 
-    public Geom wrap(Geometry g) {
+    @Override public Geom wrap(Geometry g) {
       return new SimpleGeom(g);
     }
   }
@@ -262,23 +262,23 @@ static class MapGeom implements Geom {
       return mg.toString();
     }
 
-    public int compareTo(Geom o) {
+    @Override public int compareTo(Geom o) {
       return toString().compareTo(o.toString());
     }
 
-    public Geometry g() {
+    @Override public Geometry g() {
       return mg.getGeometry();
     }
 
-    public Type type() {
+    @Override public Type type() {
       return Geometries.type(mg.getGeometry());
     }
 
-    public SpatialReference sr() {
+    @Override public SpatialReference sr() {
       return mg.getSpatialReference();
     }
 
-    public Geom transform(int srid) {
+    @Override public Geom transform(int srid) {
       if (srid == NO_SRID) {
         return new SimpleGeom(mg.getGeometry());
       }
@@ -288,7 +288,7 @@ public Geom transform(int srid) {
       return bind(mg.getGeometry(), srid);
     }
 
-    public Geom wrap(Geometry g) {
+    @Override public Geom wrap(Geometry g) {
       return bind(g, this.mg.getSpatialReference());
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/runtime/HilbertCurve2D.java b/core/src/main/java/org/apache/calcite/runtime/HilbertCurve2D.java
index 6a32a30c788..c4b0c6500e3 100644
--- a/core/src/main/java/org/apache/calcite/runtime/HilbertCurve2D.java
+++ b/core/src/main/java/org/apache/calcite/runtime/HilbertCurve2D.java
@@ -75,7 +75,7 @@ long setNormalizedLongitude(long lonNormal) {
     return (long) (lonNormal * 360d / (precision - 1));
   }
 
-  public long toIndex(double x, double y) {
+  @Override public long toIndex(double x, double y) {
     final long normX = getNormalizedLongitude(x);
     final long normY = getNormalizedLatitude(y);
     final BitVector[] p = {
@@ -92,7 +92,7 @@ public long toIndex(double x, double y) {
     return hilbert.toLong();
   }
 
-  public Point toPoint(long i) {
+  @Override public Point toPoint(long i) {
     final BitVector h = BitVectorFactories.OPTIMAL.apply(resolution * 2);
     h.copyFrom(i);
     final BitVector[] p = {
@@ -107,7 +107,7 @@ public Point toPoint(long i) {
     return new Point((double) x, (double) y);
   }
 
-  public List<IndexRange> toRanges(double xMin, double yMin, double xMax,
+  @Override public List<IndexRange> toRanges(double xMin, double yMin, double xMax,
       double yMax, RangeComputeHints hints) {
     final CompactHilbertCurve chc =
         new CompactHilbertCurve(new int[] {resolution, resolution});
diff --git a/core/src/main/java/org/apache/calcite/runtime/ObjectEnumeratorCursor.java b/core/src/main/java/org/apache/calcite/runtime/ObjectEnumeratorCursor.java
index 233ffa3be53..43818820d8c 100644
--- a/core/src/main/java/org/apache/calcite/runtime/ObjectEnumeratorCursor.java
+++ b/core/src/main/java/org/apache/calcite/runtime/ObjectEnumeratorCursor.java
@@ -36,19 +36,19 @@ public ObjectEnumeratorCursor(Enumerator<Object> enumerator) {
     this.enumerator = enumerator;
   }
 
-  protected Getter createGetter(int ordinal) {
+  @Override protected Getter createGetter(int ordinal) {
     return new ObjectGetter(ordinal);
   }
 
-  protected Object current() {
+  @Override protected Object current() {
     return enumerator.current();
   }
 
-  public boolean next() {
+  @Override public boolean next() {
     return enumerator.moveNext();
   }
 
-  public void close() {
+  @Override public void close() {
     enumerator.close();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/Pattern.java b/core/src/main/java/org/apache/calcite/runtime/Pattern.java
index 1818fb6cc4a..e555380de30 100644
--- a/core/src/main/java/org/apache/calcite/runtime/Pattern.java
+++ b/core/src/main/java/org/apache/calcite/runtime/Pattern.java
@@ -154,7 +154,7 @@ abstract class AbstractPattern implements Pattern {
       this.op = Objects.requireNonNull(op);
     }
 
-    public Automaton toAutomaton() {
+    @Override public Automaton toAutomaton() {
       return new AutomatonBuilder().add(this).build();
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/runtime/PredicateImpl.java b/core/src/main/java/org/apache/calcite/runtime/PredicateImpl.java
index db80565978d..614a22f0a7e 100644
--- a/core/src/main/java/org/apache/calcite/runtime/PredicateImpl.java
+++ b/core/src/main/java/org/apache/calcite/runtime/PredicateImpl.java
@@ -35,10 +35,10 @@
  * implement {@link java.util.function.Predicate} directly.
  */
 public abstract class PredicateImpl<T> implements Predicate<T> {
-  public final boolean apply(@Nullable T input) {
+  @Override public final boolean apply(@Nullable T input) {
     return test(input);
   }
 
   /** Overrides {@code java.util.function.Predicate#test} in JDK8 and higher. */
-  public abstract boolean test(@Nullable T t);
+  @Override public abstract boolean test(@Nullable T t);
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/RecordEnumeratorCursor.java b/core/src/main/java/org/apache/calcite/runtime/RecordEnumeratorCursor.java
index e1efdcf4891..d470c913ecf 100644
--- a/core/src/main/java/org/apache/calcite/runtime/RecordEnumeratorCursor.java
+++ b/core/src/main/java/org/apache/calcite/runtime/RecordEnumeratorCursor.java
@@ -42,7 +42,7 @@ public RecordEnumeratorCursor(
     this.clazz = clazz;
   }
 
-  protected Getter createGetter(int ordinal) {
+  @Override protected Getter createGetter(int ordinal) {
     return new FieldGetter(clazz.getFields()[ordinal]);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/runtime/Resources.java b/core/src/main/java/org/apache/calcite/runtime/Resources.java
index 17dc7efab68..8bccaeeb6ac 100644
--- a/core/src/main/java/org/apache/calcite/runtime/Resources.java
+++ b/core/src/main/java/org/apache/calcite/runtime/Resources.java
@@ -137,6 +137,7 @@ private static <T> T create(final String base,
         new InvocationHandler() {
           final Map<String, Object> cache = new ConcurrentHashMap<>();
 
+          @Override
           public Object invoke(Object proxy, Method method, Object[] args)
               throws Throwable {
             if (args == null || args.length == 0) {
@@ -752,38 +753,47 @@ public interface PropertyAccessor {
   enum EmptyPropertyAccessor implements PropertyAccessor {
     INSTANCE;
 
+    @Override
     public boolean isSet(Prop p) {
       return false;
     }
 
+    @Override
     public int intValue(IntProp p) {
       return p.defaultValue();
     }
 
+    @Override
     public int intValue(IntProp p, int defaultValue) {
       return defaultValue;
     }
 
+    @Override
     public String stringValue(StringProp p) {
       return p.defaultValue();
     }
 
+    @Override
     public String stringValue(StringProp p, String defaultValue) {
       return defaultValue;
     }
 
+    @Override
     public boolean booleanValue(BooleanProp p) {
       return p.defaultValue();
     }
 
+    @Override
     public boolean booleanValue(BooleanProp p, boolean defaultValue) {
       return defaultValue;
     }
 
+    @Override
     public double doubleValue(DoubleProp p) {
       return p.defaultValue();
     }
 
+    @Override
     public double doubleValue(DoubleProp p, double defaultValue) {
       return defaultValue;
     }
@@ -937,10 +947,12 @@ private static InputStream openPropertiesFile(Class clazz) {
           });
     }
 
+    @Override
     public Enumeration<String> getKeys() {
       return bundle.getKeys();
     }
 
+    @Override
     protected Object handleGetObject(String key) {
       return bundle.getObject(key);
     }
@@ -1040,10 +1052,12 @@ private static class PropertiesAccessor implements PropertyAccessor {
       this.properties = properties;
     }
 
+    @Override
     public boolean isSet(Prop p) {
       return properties.containsKey(p.key);
     }
 
+    @Override
     public int intValue(IntProp p) {
       final String s = properties.getProperty(p.key);
       if (s != null) {
@@ -1053,11 +1067,13 @@ public int intValue(IntProp p) {
       return p.defaultValue;
     }
 
+    @Override
     public int intValue(IntProp p, int defaultValue) {
       final String s = properties.getProperty(p.key);
       return s == null ? defaultValue : Integer.parseInt(s, 10);
     }
 
+    @Override
     public String stringValue(StringProp p) {
       final String s = properties.getProperty(p.key);
       if (s != null) {
@@ -1067,11 +1083,13 @@ public String stringValue(StringProp p) {
       return p.defaultValue;
     }
 
+    @Override
     public String stringValue(StringProp p, String defaultValue) {
       final String s = properties.getProperty(p.key);
       return s == null ? defaultValue : s;
     }
 
+    @Override
     public boolean booleanValue(BooleanProp p) {
       final String s = properties.getProperty(p.key);
       if (s != null) {
@@ -1081,11 +1099,13 @@ public boolean booleanValue(BooleanProp p) {
       return p.defaultValue;
     }
 
+    @Override
     public boolean booleanValue(BooleanProp p, boolean defaultValue) {
       final String s = properties.getProperty(p.key);
       return s == null ? defaultValue : Boolean.parseBoolean(s);
     }
 
+    @Override
     public double doubleValue(DoubleProp p) {
       final String s = properties.getProperty(p.key);
       if (s != null) {
@@ -1095,6 +1115,7 @@ public double doubleValue(DoubleProp p) {
       return p.defaultValue;
     }
 
+    @Override
     public double doubleValue(DoubleProp p, double defaultValue) {
       final String s = properties.getProperty(p.key);
       return s == null ? defaultValue : Double.parseDouble(s);
diff --git a/core/src/main/java/org/apache/calcite/runtime/ResultSetEnumerable.java b/core/src/main/java/org/apache/calcite/runtime/ResultSetEnumerable.java
index b29e890a27a..9dc39a7893a 100644
--- a/core/src/main/java/org/apache/calcite/runtime/ResultSetEnumerable.java
+++ b/core/src/main/java/org/apache/calcite/runtime/ResultSetEnumerable.java
@@ -246,7 +246,7 @@ private static void setDynamicParam(PreparedStatement preparedStatement,
     }
   }
 
-  public Enumerator<T> enumerator() {
+  @Override public Enumerator<T> enumerator() {
     if (preparedStatementEnricher == null) {
       return enumeratorBasedOnStatement();
     } else {
@@ -361,11 +361,11 @@ private static class ResultSetEnumerator<T> implements Enumerator<T> {
       this.rowBuilder = rowBuilderFactory.apply(resultSet);
     }
 
-    public T current() {
+    @Override public T current() {
       return rowBuilder.apply();
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       try {
         return resultSet.next();
       } catch (SQLException e) {
@@ -373,7 +373,7 @@ public boolean moveNext() {
       }
     }
 
-    public void reset() {
+    @Override public void reset() {
       try {
         resultSet.beforeFirst();
       } catch (SQLException e) {
@@ -381,7 +381,7 @@ public void reset() {
       }
     }
 
-    public void close() {
+    @Override public void close() {
       ResultSet savedResultSet = resultSet;
       if (savedResultSet != null) {
         try {
diff --git a/core/src/main/java/org/apache/calcite/runtime/SortedMultiMap.java b/core/src/main/java/org/apache/calcite/runtime/SortedMultiMap.java
index 0f162e4c18c..7b2448c5c94 100644
--- a/core/src/main/java/org/apache/calcite/runtime/SortedMultiMap.java
+++ b/core/src/main/java/org/apache/calcite/runtime/SortedMultiMap.java
@@ -47,11 +47,11 @@ public void putMulti(K key, V value) {
   public Iterator<V[]> arrays(final Comparator<V> comparator) {
     final Iterator<List<V>> iterator = values().iterator();
     return new Iterator<V[]>() {
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return iterator.hasNext();
       }
 
-      public V[] next() {
+      @Override public V[] next() {
         List<V> list = iterator.next();
         @SuppressWarnings("unchecked")
         final V[] vs = (V[]) list.toArray();
@@ -59,7 +59,7 @@ public V[] next() {
         return vs;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException();
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/runtime/SpaceFillingCurve2D.java b/core/src/main/java/org/apache/calcite/runtime/SpaceFillingCurve2D.java
index c685bb383f5..bde003d8201 100644
--- a/core/src/main/java/org/apache/calcite/runtime/SpaceFillingCurve2D.java
+++ b/core/src/main/java/org/apache/calcite/runtime/SpaceFillingCurve2D.java
@@ -70,15 +70,15 @@ protected AbstractRange(long lower, long upper) {
       this.upper = upper;
     }
 
-    public long lower() {
+    @Override public long lower() {
       return lower;
     }
 
-    public long upper() {
+    @Override public long upper() {
       return upper;
     }
 
-    public IndexRangeTuple tuple() {
+    @Override public IndexRangeTuple tuple() {
       return new IndexRangeTuple(lower, upper, contained());
     }
   }
@@ -89,7 +89,7 @@ class CoveredRange extends AbstractRange {
       super(lower, upper);
     }
 
-    public boolean contained() {
+    @Override public boolean contained() {
       return true;
     }
 
@@ -104,7 +104,7 @@ class OverlappingRange extends AbstractRange {
       super(lower, upper);
     }
 
-    public boolean contained() {
+    @Override public boolean contained() {
       return false;
     }
 
@@ -115,7 +115,7 @@ public boolean contained() {
 
   /** Lexicographic ordering for {@link IndexRange}. */
   class IndexRangeOrdering extends Ordering<IndexRange> {
-    public int compare(IndexRange x, IndexRange y) {
+    @Override public int compare(IndexRange x, IndexRange y) {
       final int c1 = Long.compare(x.lower(), y.lower());
       if (c1 != 0) {
         return c1;
diff --git a/core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java b/core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java
index 2c552909e5a..95eeb04f54d 100644
--- a/core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java
+++ b/core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java
@@ -128,7 +128,7 @@ public class SqlFunctions {
         }
         final Enumerator<List<Object>> product = Linq4j.product(enumerators);
         return new AbstractEnumerable<Object[]>() {
-          public Enumerator<Object[]> enumerator() {
+          @Override public Enumerator<Object[]> enumerator() {
             return Linq4j.transform(product, List::toArray);
           }
         };
@@ -2727,7 +2727,7 @@ public static Function1<Object, Enumerable<Comparable>> flatList() {
       final List list = (List) inputObject;
       final Enumerator<List<Object>> enumerator = Linq4j.enumerator(list);
       return new AbstractEnumerable<Comparable>() {
-        public Enumerator<Comparable> enumerator() {
+        @Override public Enumerator<Comparable> enumerator() {
           return new Enumerator<Comparable>() {
 
             @Override public boolean moveNext() {
@@ -2831,7 +2831,7 @@ public static <E extends Comparable> Enumerable<FlatLists.ComparableList<E>> pro
       final List<Enumerator<List<E>>> enumerators, final int fieldCount,
       final boolean withOrdinality) {
     return new AbstractEnumerable<FlatLists.ComparableList<E>>() {
-      public Enumerator<FlatLists.ComparableList<E>> enumerator() {
+      @Override public Enumerator<FlatLists.ComparableList<E>> enumerator() {
         return new ProductComparableListEnumerator<>(enumerators, fieldCount,
             withOrdinality);
       }
@@ -2985,7 +2985,7 @@ private static class ProductComparableListEnumerator<E extends Comparable>
       return hasNext;
     }
 
-    public FlatLists.ComparableList<E> current() {
+    @Override public FlatLists.ComparableList<E> current() {
       int i = 0;
       for (Object element : (Object[]) elements) {
         Object[] a;
diff --git a/core/src/main/java/org/apache/calcite/runtime/TrustAllSslSocketFactory.java b/core/src/main/java/org/apache/calcite/runtime/TrustAllSslSocketFactory.java
index 9218bdb0af3..b5ef3899f40 100644
--- a/core/src/main/java/org/apache/calcite/runtime/TrustAllSslSocketFactory.java
+++ b/core/src/main/java/org/apache/calcite/runtime/TrustAllSslSocketFactory.java
@@ -112,16 +112,16 @@ public static SSLSocketFactory createSSLSocketFactory() {
   /** Implementation of {@link X509TrustManager} that trusts all
    * certificates. */
   private static class DummyTrustManager implements X509TrustManager {
-    public X509Certificate[] getAcceptedIssuers() {
+    @Override public X509Certificate[] getAcceptedIssuers() {
       return null;
     }
 
-    public void checkClientTrusted(
+    @Override public void checkClientTrusted(
         X509Certificate[] certs,
         String authType) {
     }
 
-    public void checkServerTrusted(
+    @Override public void checkServerTrusted(
         X509Certificate[] certs,
         String authType) {
     }
diff --git a/core/src/main/java/org/apache/calcite/runtime/Unit.java b/core/src/main/java/org/apache/calcite/runtime/Unit.java
index 9422029e4df..77d2847a919 100644
--- a/core/src/main/java/org/apache/calcite/runtime/Unit.java
+++ b/core/src/main/java/org/apache/calcite/runtime/Unit.java
@@ -27,11 +27,11 @@ public class Unit implements Comparable<Unit> {
   private Unit() {
   }
 
-  public int compareTo(Unit that) {
+  @Override public int compareTo(Unit that) {
     return 0;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "{}";
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/schema/SchemaPlus.java b/core/src/main/java/org/apache/calcite/schema/SchemaPlus.java
index 8043560394f..b57da521206 100644
--- a/core/src/main/java/org/apache/calcite/schema/SchemaPlus.java
+++ b/core/src/main/java/org/apache/calcite/schema/SchemaPlus.java
@@ -57,7 +57,7 @@ public interface SchemaPlus extends Schema {
   String getName();
 
   // override with stricter return
-  SchemaPlus getSubSchema(String name);
+  @Override SchemaPlus getSubSchema(String name);
 
   /** Adds a schema as a sub-schema of this schema, and returns the wrapped
    * object. */
@@ -75,7 +75,7 @@ public interface SchemaPlus extends Schema {
   /** Adds a lattice to this schema. */
   void add(String name, Lattice lattice);
 
-  boolean isMutable();
+  @Override boolean isMutable();
 
   /** Returns an underlying object. */
   <T> T unwrap(Class<T> clazz);
diff --git a/core/src/main/java/org/apache/calcite/schema/Schemas.java b/core/src/main/java/org/apache/calcite/schema/Schemas.java
index 126e7e1eae3..1f9ba5391f5 100644
--- a/core/src/main/java/org/apache/calcite/schema/Schemas.java
+++ b/core/src/main/java/org/apache/calcite/schema/Schemas.java
@@ -380,19 +380,19 @@ private static CalcitePrepare.Context makeContext(
     final ImmutableList<String> objectPath =
         objectPath_ == null ? null : ImmutableList.copyOf(objectPath_);
     return new CalcitePrepare.Context() {
-      public JavaTypeFactory getTypeFactory() {
+      @Override public JavaTypeFactory getTypeFactory() {
         return typeFactory;
       }
 
-      public CalciteSchema getRootSchema() {
+      @Override public CalciteSchema getRootSchema() {
         return schema.root();
       }
 
-      public CalciteSchema getMutableRootSchema() {
+      @Override public CalciteSchema getMutableRootSchema() {
         return getRootSchema();
       }
 
-      public List<String> getDefaultSchemaPath() {
+      @Override public List<String> getDefaultSchemaPath() {
         // schemaPath is usually null. If specified, it overrides schema
         // as the context within which the SQL is validated.
         if (schemaPath == null) {
@@ -401,23 +401,23 @@ public List<String> getDefaultSchemaPath() {
         return schemaPath;
       }
 
-      public List<String> getObjectPath() {
+      @Override public List<String> getObjectPath() {
         return objectPath;
       }
 
-      public CalciteConnectionConfig config() {
+      @Override public CalciteConnectionConfig config() {
         return connectionConfig;
       }
 
-      public DataContext getDataContext() {
+      @Override public DataContext getDataContext() {
         return dataContext;
       }
 
-      public RelRunner getRelRunner() {
+      @Override public RelRunner getRelRunner() {
         throw new UnsupportedOperationException();
       }
 
-      public CalcitePrepare.SparkHandler spark() {
+      @Override public CalcitePrepare.SparkHandler spark() {
         final boolean enable = config().spark();
         return CalcitePrepare.Dummy.getSparkHandler(enable);
       }
@@ -555,19 +555,19 @@ private static class DummyDataContext implements DataContext {
       this.map = ImmutableMap.of();
     }
 
-    public SchemaPlus getRootSchema() {
+    @Override public SchemaPlus getRootSchema() {
       return rootSchema;
     }
 
-    public JavaTypeFactory getTypeFactory() {
+    @Override public JavaTypeFactory getTypeFactory() {
       return connection.getTypeFactory();
     }
 
-    public QueryProvider getQueryProvider() {
+    @Override public QueryProvider getQueryProvider() {
       return connection;
     }
 
-    public Object get(String name) {
+    @Override public Object get(String name) {
       return map.get(name);
     }
   }
@@ -594,34 +594,34 @@ private static class PathImpl
       return pairs.hashCode();
     }
 
-    public Pair<String, Schema> get(int index) {
+    @Override public Pair<String, Schema> get(int index) {
       return pairs.get(index);
     }
 
-    public int size() {
+    @Override public int size() {
       return pairs.size();
     }
 
-    public Path parent() {
+    @Override public Path parent() {
       if (pairs.isEmpty()) {
         throw new IllegalArgumentException("at root");
       }
       return new PathImpl(pairs.subList(0, pairs.size() - 1));
     }
 
-    public List<String> names() {
+    @Override public List<String> names() {
       return new AbstractList<String>() {
-        public String get(int index) {
+        @Override public String get(int index) {
           return pairs.get(index + 1).left;
         }
 
-        public int size() {
+        @Override public int size() {
           return pairs.size() - 1;
         }
       };
     }
 
-    public List<Schema> schemas() {
+    @Override public List<Schema> schemas() {
       return Pair.right(pairs);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/schema/Statistics.java b/core/src/main/java/org/apache/calcite/schema/Statistics.java
index 21e8ab62451..c9bc7273de7 100644
--- a/core/src/main/java/org/apache/calcite/schema/Statistics.java
+++ b/core/src/main/java/org/apache/calcite/schema/Statistics.java
@@ -70,11 +70,11 @@ public static Statistic of(final Double rowCount,
         collations == null ? null : ImmutableList.copyOf(collations);
 
     return new Statistic() {
-      public Double getRowCount() {
+      @Override public Double getRowCount() {
         return rowCount;
       }
 
-      public boolean isKey(ImmutableBitSet columns) {
+      @Override public boolean isKey(ImmutableBitSet columns) {
         for (ImmutableBitSet key : keysCopy) {
           if (columns.contains(key)) {
             return true;
@@ -83,15 +83,15 @@ public boolean isKey(ImmutableBitSet columns) {
         return false;
       }
 
-      public List<ImmutableBitSet> getKeys() {
+      @Override public List<ImmutableBitSet> getKeys() {
         return keysCopy;
       }
 
-      public List<RelReferentialConstraint> getReferentialConstraints() {
+      @Override public List<RelReferentialConstraint> getReferentialConstraints() {
         return referentialConstraintsCopy;
       }
 
-      public List<RelCollation> getCollations() {
+      @Override public List<RelCollation> getCollations() {
         return collationsCopy;
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/AbstractSchema.java b/core/src/main/java/org/apache/calcite/schema/impl/AbstractSchema.java
index 2c01b1958eb..2888a658045 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/AbstractSchema.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/AbstractSchema.java
@@ -55,15 +55,15 @@ public class AbstractSchema implements Schema {
   public AbstractSchema() {
   }
 
-  public boolean isMutable() {
+  @Override public boolean isMutable() {
     return true;
   }
 
-  public Schema snapshot(SchemaVersion version) {
+  @Override public Schema snapshot(SchemaVersion version) {
     return this;
   }
 
-  public Expression getExpression(SchemaPlus parentSchema, String name) {
+  @Override public Expression getExpression(SchemaPlus parentSchema, String name) {
     return Schemas.subSchemaExpression(parentSchema, name, getClass());
   }
 
@@ -81,11 +81,11 @@ protected Map<String, Table> getTableMap() {
     return ImmutableMap.of();
   }
 
-  public final Set<String> getTableNames() {
+  @Override public final Set<String> getTableNames() {
     return getTableMap().keySet();
   }
 
-  public final Table getTable(String name) {
+  @Override public final Table getTable(String name) {
     return getTableMap().get(name);
   }
 
@@ -103,11 +103,11 @@ protected Map<String, RelProtoDataType> getTypeMap() {
     return ImmutableMap.of();
   }
 
-  public RelProtoDataType getType(String name) {
+  @Override public RelProtoDataType getType(String name) {
     return getTypeMap().get(name);
   }
 
-  public Set<String> getTypeNames() {
+  @Override public Set<String> getTypeNames() {
     return getTypeMap().keySet();
   }
 
@@ -128,11 +128,11 @@ protected Multimap<String, Function> getFunctionMultimap() {
     return ImmutableMultimap.of();
   }
 
-  public final Collection<Function> getFunctions(String name) {
+  @Override public final Collection<Function> getFunctions(String name) {
     return getFunctionMultimap().get(name); // never null
   }
 
-  public final Set<String> getFunctionNames() {
+  @Override public final Set<String> getFunctionNames() {
     return getFunctionMultimap().keySet();
   }
 
@@ -150,11 +150,11 @@ protected Map<String, Schema> getSubSchemaMap() {
     return ImmutableMap.of();
   }
 
-  public final Set<String> getSubSchemaNames() {
+  @Override public final Set<String> getSubSchemaNames() {
     return getSubSchemaMap().keySet();
   }
 
-  public final Schema getSubSchema(String name) {
+  @Override public final Schema getSubSchema(String name) {
     return getSubSchemaMap().get(name);
   }
 
@@ -165,7 +165,7 @@ public static class Factory implements SchemaFactory {
 
     private Factory() {}
 
-    public Schema create(SchemaPlus parentSchema, String name,
+    @Override public Schema create(SchemaPlus parentSchema, String name,
         Map<String, Object> operand) {
       return new AbstractSchema();
     }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/AbstractTable.java b/core/src/main/java/org/apache/calcite/schema/impl/AbstractTable.java
index 3f93c7ee380..dad2035878f 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/AbstractTable.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/AbstractTable.java
@@ -38,15 +38,15 @@ protected AbstractTable() {
   }
 
   // Default implementation. Override if you have statistics.
-  public Statistic getStatistic() {
+  @Override public Statistic getStatistic() {
     return Statistics.UNKNOWN;
   }
 
-  public Schema.TableType getJdbcTableType() {
+  @Override public Schema.TableType getJdbcTableType() {
     return Schema.TableType.TABLE;
   }
 
-  public <C> C unwrap(Class<C> aClass) {
+  @Override public <C> C unwrap(Class<C> aClass) {
     if (aClass.isInstance(this)) {
       return aClass.cast(this);
     }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/AbstractTableQueryable.java b/core/src/main/java/org/apache/calcite/schema/impl/AbstractTableQueryable.java
index f28651e931f..48ae55ab9a2 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/AbstractTableQueryable.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/AbstractTableQueryable.java
@@ -50,19 +50,19 @@ public AbstractTableQueryable(QueryProvider queryProvider,
     this.tableName = tableName;
   }
 
-  public Expression getExpression() {
+  @Override public Expression getExpression() {
     return table.getExpression(schema, tableName, Queryable.class);
   }
 
-  public QueryProvider getProvider() {
+  @Override public QueryProvider getProvider() {
     return queryProvider;
   }
 
-  public Type getElementType() {
+  @Override public Type getElementType() {
     return table.getElementType();
   }
 
-  public Iterator<T> iterator() {
+  @Override public Iterator<T> iterator() {
     return Linq4j.enumeratorIterator(enumerator());
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/AggregateFunctionImpl.java b/core/src/main/java/org/apache/calcite/schema/impl/AggregateFunctionImpl.java
index 45d83beffbc..47157ccc7ba 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/AggregateFunctionImpl.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/AggregateFunctionImpl.java
@@ -129,15 +129,15 @@ public static AggregateFunctionImpl create(Class<?> clazz) {
     return null;
   }
 
-  public List<FunctionParameter> getParameters() {
+  @Override public List<FunctionParameter> getParameters() {
     return parameters;
   }
 
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return typeFactory.createJavaType(resultType);
   }
 
-  public AggImplementor getImplementor(boolean windowContext) {
+  @Override public AggImplementor getImplementor(boolean windowContext) {
     return new RexImpTable.UserDefinedAggReflectiveImplementor(this);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/DelegatingSchema.java b/core/src/main/java/org/apache/calcite/schema/impl/DelegatingSchema.java
index 4cd1af3d4c9..91a0e82083e 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/DelegatingSchema.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/DelegatingSchema.java
@@ -47,47 +47,47 @@ public DelegatingSchema(Schema schema) {
     return "DelegatingSchema(delegate=" + schema + ")";
   }
 
-  public boolean isMutable() {
+  @Override public boolean isMutable() {
     return schema.isMutable();
   }
 
-  public Schema snapshot(SchemaVersion version) {
+  @Override public Schema snapshot(SchemaVersion version) {
     return schema.snapshot(version);
   }
 
-  public Expression getExpression(SchemaPlus parentSchema, String name) {
+  @Override public Expression getExpression(SchemaPlus parentSchema, String name) {
     return schema.getExpression(parentSchema, name);
   }
 
-  public Table getTable(String name) {
+  @Override public Table getTable(String name) {
     return schema.getTable(name);
   }
 
-  public Set<String> getTableNames() {
+  @Override public Set<String> getTableNames() {
     return schema.getTableNames();
   }
 
-  public RelProtoDataType getType(String name) {
+  @Override public RelProtoDataType getType(String name) {
     return schema.getType(name);
   }
 
-  public Set<String> getTypeNames() {
+  @Override public Set<String> getTypeNames() {
     return schema.getTypeNames();
   }
 
-  public Collection<Function> getFunctions(String name) {
+  @Override public Collection<Function> getFunctions(String name) {
     return schema.getFunctions(name);
   }
 
-  public Set<String> getFunctionNames() {
+  @Override public Set<String> getFunctionNames() {
     return schema.getFunctionNames();
   }
 
-  public Schema getSubSchema(String name) {
+  @Override public Schema getSubSchema(String name) {
     return schema.getSubSchema(name);
   }
 
-  public Set<String> getSubSchemaNames() {
+  @Override public Set<String> getSubSchemaNames() {
     return schema.getSubSchemaNames();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/ListTransientTable.java b/core/src/main/java/org/apache/calcite/schema/impl/ListTransientTable.java
index f07cda4ace8..12485e7f6e7 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/ListTransientTable.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/ListTransientTable.java
@@ -91,7 +91,7 @@ public ListTransientTable(String name, RelDataType rowType) {
     final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
 
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         return new Enumerator<Object[]>() {
           private final List list = new ArrayList(rows);
           private int i = -1;
@@ -123,7 +123,7 @@ public Enumerator<Object[]> enumerator() {
     };
   }
 
-  public Expression getExpression(SchemaPlus schema, String tableName,
+  @Override public Expression getExpression(SchemaPlus schema, String tableName,
                                   Class clazz) {
     return Schemas.tableExpression(schema, elementType, tableName, clazz);
   }
@@ -131,7 +131,7 @@ public Expression getExpression(SchemaPlus schema, String tableName,
   @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
                                                 SchemaPlus schema, String tableName) {
     return new AbstractTableQueryable<T>(queryProvider, schema, this, tableName) {
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         //noinspection unchecked
         return (Enumerator<T>) Linq4j.enumerator(rows);
       }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/LongSchemaVersion.java b/core/src/main/java/org/apache/calcite/schema/impl/LongSchemaVersion.java
index 399d1b3436c..fc52962fc26 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/LongSchemaVersion.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/LongSchemaVersion.java
@@ -26,7 +26,7 @@ public LongSchemaVersion(long value) {
     this.value = value;
   }
 
-  public boolean isBefore(SchemaVersion other) {
+  @Override public boolean isBefore(SchemaVersion other) {
     if (!(other instanceof LongSchemaVersion)) {
       throw new IllegalArgumentException(
           "Cannot compare a LongSchemaVersion object with a "
@@ -36,7 +36,7 @@ public boolean isBefore(SchemaVersion other) {
     return this.value < ((LongSchemaVersion) other).value;
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (this == obj) {
       return true;
     }
@@ -48,11 +48,11 @@ public boolean equals(Object obj) {
     return this.value == ((LongSchemaVersion) obj).value;
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return Long.valueOf(value).hashCode();
   }
 
-  public String toString() {
+  @Override public String toString() {
     return String.valueOf(value);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/ModifiableViewTable.java b/core/src/main/java/org/apache/calcite/schema/impl/ModifiableViewTable.java
index 2caa91d123d..18331fe6d4d 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/ModifiableViewTable.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/ModifiableViewTable.java
@@ -70,20 +70,20 @@ public ModifiableViewTable(Type elementType, RelProtoDataType rowType,
     this.initializerExpressionFactory = new ModifiableViewTableInitializerExpressionFactory();
   }
 
-  public RexNode getConstraint(RexBuilder rexBuilder,
+  @Override public RexNode getConstraint(RexBuilder rexBuilder,
       RelDataType tableRowType) {
     return rexBuilder.copy(constraint);
   }
 
-  public ImmutableIntList getColumnMapping() {
+  @Override public ImmutableIntList getColumnMapping() {
     return columnMapping;
   }
 
-  public Table getTable() {
+  @Override public Table getTable() {
     return table;
   }
 
-  public Path getTablePath() {
+  @Override public Path getTablePath() {
     return tablePath;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/ReflectiveFunctionBase.java b/core/src/main/java/org/apache/calcite/schema/impl/ReflectiveFunctionBase.java
index d01daf7c74f..85aca05a7fd 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/ReflectiveFunctionBase.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/ReflectiveFunctionBase.java
@@ -56,7 +56,7 @@ public ReflectiveFunctionBase(Method method) {
    *
    * @return Parameters; never null
    */
-  public List<FunctionParameter> getParameters() {
+  @Override public List<FunctionParameter> getParameters() {
     return parameters;
   }
 
@@ -118,19 +118,19 @@ public ParameterListBuilder add(final Class<?> type, final String name,
                   + (optional ? "?" : "");
             }
 
-            public int getOrdinal() {
+            @Override public int getOrdinal() {
               return ordinal;
             }
 
-            public String getName() {
+            @Override public String getName() {
               return name;
             }
 
-            public RelDataType getType(RelDataTypeFactory typeFactory) {
+            @Override public RelDataType getType(RelDataTypeFactory typeFactory) {
               return typeFactory.createJavaType(type);
             }
 
-            public boolean isOptional() {
+            @Override public boolean isOptional() {
               return optional;
             }
           });
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/ScalarFunctionImpl.java b/core/src/main/java/org/apache/calcite/schema/impl/ScalarFunctionImpl.java
index 4c2dc012605..36198500ca1 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/ScalarFunctionImpl.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/ScalarFunctionImpl.java
@@ -151,11 +151,11 @@ public static ScalarFunction createUnsafe(Method method) {
     return new ScalarFunctionImpl(method, implementor);
   }
 
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return typeFactory.createJavaType(method.getReturnType());
   }
 
-  public CallImplementor getImplementor() {
+  @Override public CallImplementor getImplementor() {
     return implementor;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/StarTable.java b/core/src/main/java/org/apache/calcite/schema/impl/StarTable.java
index 71e4bdad4e2..1a0f03803fc 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/StarTable.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/StarTable.java
@@ -76,7 +76,7 @@ public static StarTable of(Lattice lattice, List<Table> tables) {
     return Schema.TableType.STAR;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     final List<RelDataType> typeList = new ArrayList<>();
     final List<Integer> fieldCounts = new ArrayList<>();
     for (Table table : tables) {
@@ -92,7 +92,7 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return typeFactory.createStructType(typeList, lattice.uniqueColumnNames());
   }
 
-  public RelNode toRel(RelOptTable.ToRelContext context, RelOptTable table) {
+  @Override public RelNode toRel(RelOptTable.ToRelContext context, RelOptTable table) {
     // Create a table scan of infinite cost.
     return new StarTableScan(context.getCluster(), table);
   }
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/TableFunctionImpl.java b/core/src/main/java/org/apache/calcite/schema/impl/TableFunctionImpl.java
index 295d690461b..0ecf9125382 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/TableFunctionImpl.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/TableFunctionImpl.java
@@ -92,12 +92,12 @@ public static TableFunction create(final Method method) {
     return new TableFunctionImpl(method, implementor);
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory,
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory,
       List<Object> arguments) {
     return apply(arguments).getRowType(typeFactory);
   }
 
-  public Type getElementType(List<Object> arguments) {
+  @Override public Type getElementType(List<Object> arguments) {
     final Table table = apply(arguments);
     if (table instanceof QueryableTable) {
       QueryableTable queryableTable = (QueryableTable) table;
@@ -109,14 +109,14 @@ public Type getElementType(List<Object> arguments) {
         + table.getClass());
   }
 
-  public CallImplementor getImplementor() {
+  @Override public CallImplementor getImplementor() {
     return implementor;
   }
 
   private static CallImplementor createImplementor(final Method method) {
     return RexImpTable.createImplementor(
         new ReflectiveCallNotNullImplementor(method) {
-          public Expression implement(RexToLixTranslator translator,
+          @Override public Expression implement(RexToLixTranslator translator,
               RexCall call, List<Expression> translatedOperands) {
             Expression expr = super.implement(translator, call,
                 translatedOperands);
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/TableMacroImpl.java b/core/src/main/java/org/apache/calcite/schema/impl/TableMacroImpl.java
index 91cdfc6265f..754eee0ab12 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/TableMacroImpl.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/TableMacroImpl.java
@@ -71,7 +71,7 @@ public static TableMacro create(final Method method) {
    * @param arguments Arguments
    * @return Table
    */
-  public TranslatableTable apply(List<Object> arguments) {
+  @Override public TranslatableTable apply(List<Object> arguments) {
     try {
       Object o = null;
       if (!Modifier.isStatic(method.getModifiers())) {
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/ViewTable.java b/core/src/main/java/org/apache/calcite/schema/impl/ViewTable.java
index 1e439d27e48..5ae67162b63 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/ViewTable.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/ViewTable.java
@@ -104,17 +104,17 @@ public List<String> getViewPath() {
     return Schema.TableType.VIEW;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return protoRowType.apply(typeFactory);
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return queryProvider.createQuery(
         getExpression(schema, tableName, Queryable.class), elementType);
   }
 
-  public RelNode toRel(
+  @Override public RelNode toRel(
       RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     return expandView(context, relOptTable.getRowType(), viewSql).rel;
diff --git a/core/src/main/java/org/apache/calcite/schema/impl/ViewTableMacro.java b/core/src/main/java/org/apache/calcite/schema/impl/ViewTableMacro.java
index 8bdbbccc5ee..83424a3df8c 100644
--- a/core/src/main/java/org/apache/calcite/schema/impl/ViewTableMacro.java
+++ b/core/src/main/java/org/apache/calcite/schema/impl/ViewTableMacro.java
@@ -63,11 +63,11 @@ public ViewTableMacro(CalciteSchema schema, String viewSql,
         schemaPath == null ? null : ImmutableList.copyOf(schemaPath);
   }
 
-  public List<FunctionParameter> getParameters() {
+  @Override public List<FunctionParameter> getParameters() {
     return Collections.emptyList();
   }
 
-  public TranslatableTable apply(List<Object> arguments) {
+  @Override public TranslatableTable apply(List<Object> arguments) {
     final CalciteConnection connection =
         MaterializedViewTable.MATERIALIZATION_CONNECTION;
     CalcitePrepare.AnalyzeViewResult parsed =
diff --git a/core/src/main/java/org/apache/calcite/sql/ExplicitOperatorBinding.java b/core/src/main/java/org/apache/calcite/sql/ExplicitOperatorBinding.java
index e42a461c0cc..cc8a0f8e414 100644
--- a/core/src/main/java/org/apache/calcite/sql/ExplicitOperatorBinding.java
+++ b/core/src/main/java/org/apache/calcite/sql/ExplicitOperatorBinding.java
@@ -67,16 +67,16 @@ private ExplicitOperatorBinding(
   //~ Methods ----------------------------------------------------------------
 
   // implement SqlOperatorBinding
-  public int getOperandCount() {
+  @Override public int getOperandCount() {
     return types.size();
   }
 
   // implement SqlOperatorBinding
-  public RelDataType getOperandType(int ordinal) {
+  @Override public RelDataType getOperandType(int ordinal) {
     return types.get(ordinal);
   }
 
-  public CalciteException newError(
+  @Override public CalciteException newError(
       Resources.ExInst<SqlValidatorException> e) {
     if (delegate != null) {
       return delegate.newError(e);
@@ -85,7 +85,7 @@ public CalciteException newError(
     }
   }
 
-  public boolean isOperandNull(int ordinal, boolean allowCast) {
+  @Override public boolean isOperandNull(int ordinal, boolean allowCast) {
     // NOTE jvs 1-May-2006:  This call is only relevant
     // for SQL validation, so anywhere else, just say
     // everything's OK.
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlAbstractDateTimeLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlAbstractDateTimeLiteral.java
index 65fa6bee212..cc7873a5ac6 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlAbstractDateTimeLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlAbstractDateTimeLiteral.java
@@ -65,20 +65,20 @@ public int getPrec() {
   /**
    * Returns e.g. <code>DATE '1969-07-21'</code>.
    */
-  public abstract String toString();
+  @Override public abstract String toString();
 
   /**
    * Returns e.g. <code>1969-07-21</code>.
    */
   public abstract String toFormattedString();
 
-  public RelDataType createSqlType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType createSqlType(RelDataTypeFactory typeFactory) {
     return typeFactory.createSqlType(
         getTypeName(),
         getPrec());
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlAccessType.java b/core/src/main/java/org/apache/calcite/sql/SqlAccessType.java
index 7f9ee24733e..d33a7e55575 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlAccessType.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlAccessType.java
@@ -50,7 +50,7 @@ public boolean allowsAccess(SqlAccessEnum access) {
     return accessEnums.contains(access);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return accessEnums.toString();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlAggFunction.java b/core/src/main/java/org/apache/calcite/sql/SqlAggFunction.java
index 9555a0b4e15..cdff6391fcc 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlAggFunction.java
@@ -111,7 +111,7 @@ protected SqlAggFunction(
 
   //~ Methods ----------------------------------------------------------------
 
-  public <T> T unwrap(Class<T> clazz) {
+  @Override public <T> T unwrap(Class<T> clazz) {
     return clazz.isInstance(this) ? clazz.cast(this) : null;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlAsOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlAsOperator.java
index 514c29aac67..5bb9e2256e5 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlAsOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlAsOperator.java
@@ -64,7 +64,7 @@ protected SqlAsOperator(String name, SqlKind kind, int prec,
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -93,7 +93,7 @@ public void unparse(
     writer.endList(frame);
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
@@ -111,7 +111,7 @@ public void validateCall(
     }
   }
 
-  public <R> void acceptCall(
+  @Override public <R> void acceptCall(
       SqlVisitor<R> visitor,
       SqlCall call,
       boolean onlyExpressions,
@@ -124,7 +124,7 @@ public <R> void acceptCall(
     }
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlBasicCall.java b/core/src/main/java/org/apache/calcite/sql/SqlBasicCall.java
index 0a141f70e40..b1d99d9760a 100755
--- a/core/src/main/java/org/apache/calcite/sql/SqlBasicCall.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlBasicCall.java
@@ -51,7 +51,7 @@ public SqlBasicCall(
     this.functionQuantifier = functionQualifier;
   }
 
-  public SqlKind getKind() {
+  @Override public SqlKind getKind() {
     return operator.getKind();
   }
 
@@ -67,7 +67,7 @@ public void setOperator(SqlOperator operator) {
     this.operator = Objects.requireNonNull(operator);
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return operator;
   }
 
@@ -75,7 +75,7 @@ public SqlNode[] getOperands() {
     return operands;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return UnmodifiableArrayList.of(operands); // not immutable, but quick
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlBinaryOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlBinaryOperator.java
index 287c3171453..eb7fcb19461 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlBinaryOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlBinaryOperator.java
@@ -70,11 +70,11 @@ public SqlBinaryOperator(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.BINARY;
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     Util.discard(operandsCount);
 
     // op0 opname op1
@@ -95,7 +95,7 @@ public String getSignatureTemplate(final int operandsCount) {
     return !getName().equals(".");
   }
 
-  protected RelDataType adjustType(
+  @Override protected RelDataType adjustType(
       SqlValidator validator,
       final SqlCall call,
       RelDataType type) {
@@ -141,7 +141,7 @@ private RelDataType convertType(SqlValidator validator, SqlCall call, RelDataTyp
     return type;
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlBinaryStringLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlBinaryStringLiteral.java
index 9c225da287b..eb7a7e3458b 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlBinaryStringLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlBinaryStringLiteral.java
@@ -54,7 +54,7 @@ public BitString getBitString() {
     return new SqlBinaryStringLiteral((BitString) value, pos);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
@@ -62,7 +62,7 @@ public void unparse(
     writer.literal("X'" + ((BitString) value).toHexString() + "'");
   }
 
-  protected SqlAbstractStringLiteral concat1(List<SqlLiteral> literals) {
+  @Override protected SqlAbstractStringLiteral concat1(List<SqlLiteral> literals) {
     return new SqlBinaryStringLiteral(
         BitString.concat(
             Util.transform(literals,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlCall.java b/core/src/main/java/org/apache/calcite/sql/SqlCall.java
index 8678c7e4e44..80cf8bfc8e8 100755
--- a/core/src/main/java/org/apache/calcite/sql/SqlCall.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlCall.java
@@ -88,7 +88,7 @@ public int operandCount() {
         operandList.toArray(new SqlNode[0]));
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
@@ -112,11 +112,11 @@ public void unparse(
    * {@link SqlOperator#validateCall}. Derived classes may override (as do,
    * for example {@link SqlSelect} and {@link SqlUpdate}).
    */
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateCall(this, scope);
   }
 
-  public void findValidOptions(
+  @Override public void findValidOptions(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlParserPos pos,
@@ -135,11 +135,11 @@ public void findValidOptions(
     // no valid options
   }
 
-  public <R> R accept(SqlVisitor<R> visitor) {
+  @Override public <R> R accept(SqlVisitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public boolean equalsDeep(SqlNode node, Litmus litmus) {
+  @Override public boolean equalsDeep(SqlNode node, Litmus litmus) {
     if (node == this) {
       return true;
     }
@@ -175,7 +175,7 @@ protected String getCallSignature(
     return SqlUtil.getOperatorSignature(getOperator(), signatureList);
   }
 
-  public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
+  @Override public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
     // Delegate to operator.
     final SqlCallBinding binding =
         new SqlCallBinding(scope.getValidator(), scope, this);
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlCallBinding.java b/core/src/main/java/org/apache/calcite/sql/SqlCallBinding.java
index c0bda8dd71e..8448ef4e338 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlCallBinding.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlCallBinding.java
@@ -227,7 +227,7 @@ public SqlCall permutedCall() {
     return call.getOperator().createCall(call.pos, operandList);
   }
 
-  public SqlMonotonicity getOperandMonotonicity(int ordinal) {
+  @Override public SqlMonotonicity getOperandMonotonicity(int ordinal) {
     return call.getOperandList().get(ordinal).getMonotonicity(scope);
   }
 
@@ -375,7 +375,7 @@ private <T> T valueAs(SqlNode node, Class<T> clazz) {
     return validator.getParentCursor(paramName);
   }
 
-  public CalciteException newError(
+  @Override public CalciteException newError(
       Resources.ExInst<SqlValidatorException> e) {
     return validator.newValidationError(call, e);
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlCharStringLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlCharStringLiteral.java
index 15c7c6d9793..bab807f53da 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlCharStringLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlCharStringLiteral.java
@@ -61,7 +61,7 @@ public SqlCollation getCollation() {
     return new SqlCharStringLiteral((NlsString) value, pos);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
@@ -76,7 +76,7 @@ public void unparse(
     writer.literal(nlsString.asSql(true, true, writer.getDialect()));
   }
 
-  protected SqlAbstractStringLiteral concat1(List<SqlLiteral> literals) {
+  @Override protected SqlAbstractStringLiteral concat1(List<SqlLiteral> literals) {
     return new SqlCharStringLiteral(
         NlsString.concat(
             Util.transform(literals,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlCollation.java b/core/src/main/java/org/apache/calcite/sql/SqlCollation.java
index cadc89e783c..36cb6312e82 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlCollation.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlCollation.java
@@ -274,7 +274,7 @@ protected static SqlCollation getCoercibilityDyadic(
     }
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "COLLATE " + collationName;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDataTypeSpec.java b/core/src/main/java/org/apache/calcite/sql/SqlDataTypeSpec.java
index 93bba29ab79..5d3c263f75b 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDataTypeSpec.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDataTypeSpec.java
@@ -122,11 +122,11 @@ public SqlDataTypeSpec(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode clone(SqlParserPos pos) {
+  @Override public SqlNode clone(SqlParserPos pos) {
     return new SqlDataTypeSpec(typeNameSpec, timeZone, pos);
   }
 
-  public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
+  @Override public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
     return SqlMonotonicity.CONSTANT;
   }
 
@@ -183,19 +183,19 @@ public SqlDataTypeSpec getComponentTypeSpec() {
     return new SqlDataTypeSpec(elementTypeName, timeZone, getParserPosition());
   }
 
-  public void unparse(SqlWriter writer, int leftPrec, int rightPrec) {
+  @Override public void unparse(SqlWriter writer, int leftPrec, int rightPrec) {
     typeNameSpec.unparse(writer, leftPrec, rightPrec);
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateDataType(this);
   }
 
-  public <R> R accept(SqlVisitor<R> visitor) {
+  @Override public <R> R accept(SqlVisitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public boolean equalsDeep(SqlNode node, Litmus litmus) {
+  @Override public boolean equalsDeep(SqlNode node, Litmus litmus) {
     if (!(node instanceof SqlDataTypeSpec)) {
       return litmus.fail("{} != {}", this, node);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDateLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlDateLiteral.java
index 62f862f712a..bc302a3c025 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDateLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDateLiteral.java
@@ -53,15 +53,15 @@ protected DateString getDate() {
   /**
    * Returns e.g. '1969-07-21'.
    */
-  public String toFormattedString() {
+  @Override public String toFormattedString() {
     return getDate().toString();
   }
 
-  public RelDataType createSqlType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType createSqlType(RelDataTypeFactory typeFactory) {
     return typeFactory.createSqlType(getTypeName());
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDdl.java b/core/src/main/java/org/apache/calcite/sql/SqlDdl.java
index 3abbcf8b45e..ae97be418e8 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDdl.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDdl.java
@@ -34,7 +34,7 @@ public SqlDdl(SqlOperator operator, SqlParserPos pos) {
     this.operator = Objects.requireNonNull(operator);
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return operator;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDelete.java b/core/src/main/java/org/apache/calcite/sql/SqlDelete.java
index e9772f1cbd2..a76c40c2e62 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDelete.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDelete.java
@@ -58,11 +58,11 @@ public SqlDelete(
     return SqlKind.DELETE;
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(targetTable, condition, alias);
   }
 
@@ -137,7 +137,7 @@ public SqlSelect getSourceSelect() {
     writer.endList(frame);
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateDelete(this);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
index 38c823cee6b..49726c2896c 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
@@ -1395,11 +1395,11 @@ private ContextImpl(DatabaseProduct databaseProduct,
       this.jethroInfo = Objects.requireNonNull(jethroInfo);
     }
 
-    @Nonnull public DatabaseProduct databaseProduct() {
+    @Override @Nonnull public DatabaseProduct databaseProduct() {
       return databaseProduct;
     }
 
-    public Context withDatabaseProduct(
+    @Override public Context withDatabaseProduct(
         @Nonnull DatabaseProduct databaseProduct) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
@@ -1408,11 +1408,11 @@ public Context withDatabaseProduct(
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public String databaseProductName() {
+    @Override public String databaseProductName() {
       return databaseProductName;
     }
 
-    public Context withDatabaseProductName(String databaseProductName) {
+    @Override public Context withDatabaseProductName(String databaseProductName) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1420,11 +1420,11 @@ public Context withDatabaseProductName(String databaseProductName) {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public String databaseVersion() {
+    @Override public String databaseVersion() {
       return databaseVersion;
     }
 
-    public Context withDatabaseVersion(String databaseVersion) {
+    @Override public Context withDatabaseVersion(String databaseVersion) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1432,11 +1432,11 @@ public Context withDatabaseVersion(String databaseVersion) {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public int databaseMajorVersion() {
+    @Override public int databaseMajorVersion() {
       return databaseMajorVersion;
     }
 
-    public Context withDatabaseMajorVersion(int databaseMajorVersion) {
+    @Override public Context withDatabaseMajorVersion(int databaseMajorVersion) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1444,11 +1444,11 @@ public Context withDatabaseMajorVersion(int databaseMajorVersion) {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public int databaseMinorVersion() {
+    @Override public int databaseMinorVersion() {
       return databaseMinorVersion;
     }
 
-    public Context withDatabaseMinorVersion(int databaseMinorVersion) {
+    @Override public Context withDatabaseMinorVersion(int databaseMinorVersion) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1456,11 +1456,11 @@ public Context withDatabaseMinorVersion(int databaseMinorVersion) {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public String literalQuoteString() {
+    @Override public String literalQuoteString() {
       return literalQuoteString;
     }
 
-    public Context withLiteralQuoteString(String literalQuoteString) {
+    @Override public Context withLiteralQuoteString(String literalQuoteString) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1468,11 +1468,11 @@ public Context withLiteralQuoteString(String literalQuoteString) {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public String literalEscapedQuoteString() {
+    @Override public String literalEscapedQuoteString() {
       return literalEscapedQuoteString;
     }
 
-    public Context withLiteralEscapedQuoteString(
+    @Override public Context withLiteralEscapedQuoteString(
         String literalEscapedQuoteString) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
@@ -1481,11 +1481,11 @@ public Context withLiteralEscapedQuoteString(
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public String identifierQuoteString() {
+    @Override public String identifierQuoteString() {
       return identifierQuoteString;
     }
 
-    @Nonnull public Context withIdentifierQuoteString(
+    @Override @Nonnull public Context withIdentifierQuoteString(
         String identifierQuoteString) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
@@ -1494,11 +1494,11 @@ public String identifierQuoteString() {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    @Nonnull public Casing unquotedCasing() {
+    @Override @Nonnull public Casing unquotedCasing() {
       return unquotedCasing;
     }
 
-    @Nonnull public Context withUnquotedCasing(Casing unquotedCasing) {
+    @Override @Nonnull public Context withUnquotedCasing(Casing unquotedCasing) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1506,11 +1506,11 @@ public String identifierQuoteString() {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    @Nonnull public Casing quotedCasing() {
+    @Override @Nonnull public Casing quotedCasing() {
       return quotedCasing;
     }
 
-    @Nonnull public Context withQuotedCasing(Casing quotedCasing) {
+    @Override @Nonnull public Context withQuotedCasing(Casing quotedCasing) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1518,11 +1518,11 @@ public String identifierQuoteString() {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    public boolean caseSensitive() {
+    @Override public boolean caseSensitive() {
       return caseSensitive;
     }
 
-    @Nonnull public Context withCaseSensitive(boolean caseSensitive) {
+    @Override @Nonnull public Context withCaseSensitive(boolean caseSensitive) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1530,11 +1530,11 @@ public boolean caseSensitive() {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    @Nonnull public SqlConformance conformance() {
+    @Override @Nonnull public SqlConformance conformance() {
       return conformance;
     }
 
-    @Nonnull public Context withConformance(SqlConformance conformance) {
+    @Override @Nonnull public Context withConformance(SqlConformance conformance) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1542,11 +1542,11 @@ public boolean caseSensitive() {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    @Nonnull public NullCollation nullCollation() {
+    @Override @Nonnull public NullCollation nullCollation() {
       return nullCollation;
     }
 
-    @Nonnull public Context withNullCollation(
+    @Override @Nonnull public Context withNullCollation(
         @Nonnull NullCollation nullCollation) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
@@ -1555,11 +1555,11 @@ public boolean caseSensitive() {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    @Nonnull public RelDataTypeSystem dataTypeSystem() {
+    @Override @Nonnull public RelDataTypeSystem dataTypeSystem() {
       return dataTypeSystem;
     }
 
-    public Context withDataTypeSystem(@Nonnull RelDataTypeSystem dataTypeSystem) {
+    @Override public Context withDataTypeSystem(@Nonnull RelDataTypeSystem dataTypeSystem) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
@@ -1567,11 +1567,11 @@ public Context withDataTypeSystem(@Nonnull RelDataTypeSystem dataTypeSystem) {
           conformance, nullCollation, dataTypeSystem, jethroInfo);
     }
 
-    @Nonnull public JethroDataSqlDialect.JethroInfo jethroInfo() {
+    @Override @Nonnull public JethroDataSqlDialect.JethroInfo jethroInfo() {
       return jethroInfo;
     }
 
-    public Context withJethroInfo(JethroDataSqlDialect.JethroInfo jethroInfo) {
+    @Override public Context withJethroInfo(JethroDataSqlDialect.JethroInfo jethroInfo) {
       return new ContextImpl(databaseProduct, databaseProductName,
           databaseVersion, databaseMajorVersion, databaseMinorVersion,
           literalQuoteString, literalEscapedQuoteString,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDialectFactoryImpl.java b/core/src/main/java/org/apache/calcite/sql/SqlDialectFactoryImpl.java
index d150794c912..11094273835 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDialectFactoryImpl.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDialectFactoryImpl.java
@@ -69,7 +69,7 @@ public class SqlDialectFactoryImpl implements SqlDialectFactory {
   private final JethroDataSqlDialect.JethroInfoCache jethroCache =
       JethroDataSqlDialect.createCache();
 
-  public SqlDialect create(DatabaseMetaData databaseMetaData) {
+  @Override public SqlDialect create(DatabaseMetaData databaseMetaData) {
     String databaseProductName;
     int databaseMajorVersion;
     int databaseMinorVersion;
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDynamicParam.java b/core/src/main/java/org/apache/calcite/sql/SqlDynamicParam.java
index 1e2a084bec9..0cdb794727a 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDynamicParam.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDynamicParam.java
@@ -45,11 +45,11 @@ public SqlDynamicParam(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode clone(SqlParserPos pos) {
+  @Override public SqlNode clone(SqlParserPos pos) {
     return new SqlDynamicParam(index, pos);
   }
 
-  public SqlKind getKind() {
+  @Override public SqlKind getKind() {
     return SqlKind.DYNAMIC_PARAM;
   }
 
@@ -57,26 +57,26 @@ public int getIndex() {
     return index;
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
     writer.dynamicParam(index);
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateDynamicParam(this);
   }
 
-  public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
+  @Override public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
     return SqlMonotonicity.CONSTANT;
   }
 
-  public <R> R accept(SqlVisitor<R> visitor) {
+  @Override public <R> R accept(SqlVisitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public boolean equalsDeep(SqlNode node, Litmus litmus) {
+  @Override public boolean equalsDeep(SqlNode node, Litmus litmus) {
     if (!(node instanceof SqlDynamicParam)) {
       return litmus.fail("{} != {}", this, node);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlExplain.java b/core/src/main/java/org/apache/calcite/sql/SqlExplain.java
index 79ccc5fbf17..7af8bd6fd54 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlExplain.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlExplain.java
@@ -74,11 +74,11 @@ public SqlExplain(SqlParserPos pos,
     return SqlKind.EXPLAIN;
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(explicandum, detailLevel, depth, format);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlFilterOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlFilterOperator.java
index a77280dbcbe..885be2090a8 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlFilterOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlFilterOperator.java
@@ -62,7 +62,7 @@ public SqlFilterOperator() {
     writer.endList(frame);
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
@@ -89,7 +89,7 @@ public void validateCall(
     }
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlFunction.java b/core/src/main/java/org/apache/calcite/sql/SqlFunction.java
index e2128e669ef..4000b0eacbc 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlFunction.java
@@ -134,7 +134,7 @@ protected SqlFunction(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.FUNCTION;
   }
 
@@ -167,7 +167,7 @@ public List<String> getParamNames() {
     return Functions.generate(getParamTypes().size(), i -> "arg" + i);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -191,7 +191,7 @@ public boolean isQuantifierAllowed() {
     return false;
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
@@ -219,7 +219,7 @@ protected void validateQuantifier(SqlValidator validator, SqlCall call) {
     }
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlFunctionalOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlFunctionalOperator.java
index ca26a1586a1..17ecc12fd90 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlFunctionalOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlFunctionalOperator.java
@@ -47,7 +47,7 @@ public SqlFunctionalOperator(
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlHint.java b/core/src/main/java/org/apache/calcite/sql/SqlHint.java
index bbdc0fee538..558afb5159f 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlHint.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlHint.java
@@ -84,11 +84,11 @@ public SqlHint(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableList.of(name, options);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlIdentifier.java b/core/src/main/java/org/apache/calcite/sql/SqlIdentifier.java
index d3380758f6e..3db2bad0419 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlIdentifier.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlIdentifier.java
@@ -127,7 +127,7 @@ public static SqlIdentifier star(List<String> names, SqlParserPos pos,
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlKind getKind() {
+  @Override public SqlKind getKind() {
     return SqlKind.IDENTIFIER;
   }
 
@@ -277,18 +277,18 @@ public SqlIdentifier skipLast(int n) {
     return getComponent(0, names.size() - n);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
     SqlUtil.unparseSqlIdentifierSyntax(writer, this, false);
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateIdentifier(this, scope);
   }
 
-  public void validateExpr(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validateExpr(SqlValidator validator, SqlValidatorScope scope) {
     // First check for builtin functions which don't have parentheses,
     // like "LOCALTIME".
     final SqlCall call = validator.makeNullaryCall(this);
@@ -300,7 +300,7 @@ public void validateExpr(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateIdentifier(this, scope);
   }
 
-  public boolean equalsDeep(SqlNode node, Litmus litmus) {
+  @Override public boolean equalsDeep(SqlNode node, Litmus litmus) {
     if (!(node instanceof SqlIdentifier)) {
       return litmus.fail("{} != {}", this, node);
     }
@@ -316,7 +316,7 @@ public boolean equalsDeep(SqlNode node, Litmus litmus) {
     return litmus.succeed();
   }
 
-  public <R> R accept(SqlVisitor<R> visitor) {
+  @Override public <R> R accept(SqlVisitor<R> visitor) {
     return visitor.visit(this);
   }
 
@@ -356,7 +356,7 @@ public boolean isComponentQuoted(int i) {
         && componentPositions.get(i).isQuoted();
   }
 
-  public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
+  @Override public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
     // for "star" column, whether it's static or dynamic return not_monotonic directly.
     if (Util.last(names).equals("") || DynamicRecordType.isDynamicStarColName(Util.last(names))) {
       return SqlMonotonicity.NOT_MONOTONIC;
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlInfixOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlInfixOperator.java
index 8d716f87b36..10489adb8a4 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlInfixOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlInfixOperator.java
@@ -56,7 +56,7 @@ protected SqlInfixOperator(
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlInsert.java b/core/src/main/java/org/apache/calcite/sql/SqlInsert.java
index b3dccd7008b..30f8cf24fca 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlInsert.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlInsert.java
@@ -67,11 +67,11 @@ public SqlInsert(SqlParserPos pos,
     return SqlKind.INSERT;
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(keywords, targetTable, source, columnList);
   }
 
@@ -154,7 +154,7 @@ public final SqlNode getModifierNode(SqlInsertKeyword modifier) {
     source.unparse(writer, 0, 0);
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateInsert(this);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlIntervalLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlIntervalLiteral.java
index d0d49bb3770..bbaae81fc17 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlIntervalLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlIntervalLiteral.java
@@ -68,7 +68,7 @@ private SqlIntervalLiteral(
     return new SqlIntervalLiteral((IntervalValue) value, getTypeName(), pos);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
@@ -76,7 +76,7 @@ public void unparse(
   }
 
   @SuppressWarnings("deprecation")
-  public int signum() {
+  @Override public int signum() {
     return ((IntervalValue) value).signum();
   }
 
@@ -109,7 +109,7 @@ public static class IntervalValue {
       this.intervalStr = intervalStr;
     }
 
-    public boolean equals(Object obj) {
+    @Override public boolean equals(Object obj) {
       if (!(obj instanceof IntervalValue)) {
         return false;
       }
@@ -120,7 +120,7 @@ public boolean equals(Object obj) {
               Litmus.IGNORE);
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       return Objects.hash(sign, intervalStr, intervalQualifier);
     }
 
@@ -147,7 +147,7 @@ public int signum() {
       return 0;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return intervalStr;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlIntervalQualifier.java b/core/src/main/java/org/apache/calcite/sql/SqlIntervalQualifier.java
index e0d0cd9f7e4..f67b9452177 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlIntervalQualifier.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlIntervalQualifier.java
@@ -178,17 +178,17 @@ public SqlTypeName typeName() {
     }
   }
 
-  public void validate(
+  @Override public void validate(
       SqlValidator validator,
       SqlValidatorScope scope) {
     validator.validateIntervalQualifier(this);
   }
 
-  public <R> R accept(SqlVisitor<R> visitor) {
+  @Override public <R> R accept(SqlVisitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public boolean equalsDeep(SqlNode node, Litmus litmus) {
+  @Override public boolean equalsDeep(SqlNode node, Litmus litmus) {
     final String thisString = this.toString();
     final String thatString = node.toString();
     if (!thisString.equals(thatString)) {
@@ -305,12 +305,12 @@ public TimeUnit getUnit() {
     return Util.first(timeUnitRange.endUnit, timeUnitRange.startUnit);
   }
 
-  public SqlNode clone(SqlParserPos pos) {
+  @Override public SqlNode clone(SqlParserPos pos) {
     return new SqlIntervalQualifier(timeUnitRange.startUnit, startPrecision,
         timeUnitRange.endUnit, fractionalSecondPrecision, pos);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlJdbcFunctionCall.java b/core/src/main/java/org/apache/calcite/sql/SqlJdbcFunctionCall.java
index c04babcd4e7..058ed591480 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlJdbcFunctionCall.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlJdbcFunctionCall.java
@@ -435,7 +435,7 @@ private static String constructFuncList(String... functionNames) {
     return sb.toString();
   }
 
-  public SqlCall createCall(
+  @Override public SqlCall createCall(
       SqlLiteral functionQualifier,
       SqlParserPos pos,
       SqlNode... operands) {
@@ -460,11 +460,11 @@ public SqlCall getLookupCall() {
     return lookupCall;
   }
 
-  public String getAllowedSignatures(String name) {
+  @Override public String getAllowedSignatures(String name) {
     return lookupMakeCallObj.getOperator().getAllowedSignatures(name);
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
@@ -480,7 +480,7 @@ public RelDataType deriveType(
     return validateOperands(validator, scope, call);
   }
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     // only expected to come here if validator called this method
     SqlCallBinding callBinding = (SqlCallBinding) opBinding;
@@ -511,7 +511,7 @@ public RelDataType inferReturnType(
         callBinding.getScope(), newCall);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -581,15 +581,15 @@ public SimpleMakeCall(SqlOperator operator) {
       this.operator = operator;
     }
 
-    public SqlOperator getOperator() {
+    @Override public SqlOperator getOperator() {
       return operator;
     }
 
-    public SqlCall createCall(SqlParserPos pos, SqlNode... operands) {
+    @Override public SqlCall createCall(SqlParserPos pos, SqlNode... operands) {
       return operator.createCall(pos, operands);
     }
 
-    public String isValidArgCount(SqlCallBinding binding) {
+    @Override public String isValidArgCount(SqlCallBinding binding) {
       return null; // any number of arguments is valid
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlJoin.java b/core/src/main/java/org/apache/calcite/sql/SqlJoin.java
index 21663e83e37..41342bc853b 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlJoin.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlJoin.java
@@ -74,7 +74,7 @@ public SqlJoin(SqlParserPos pos, SqlNode left, SqlLiteral natural,
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
@@ -82,7 +82,7 @@ public SqlOperator getOperator() {
     return SqlKind.JOIN;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(left, natural, joinType, right,
         conditionType, condition);
   }
@@ -175,11 +175,11 @@ private SqlJoinOperator() {
 
     //~ Methods ----------------------------------------------------------------
 
-    public SqlSyntax getSyntax() {
+    @Override public SqlSyntax getSyntax() {
       return SqlSyntax.SPECIAL;
     }
 
-    public SqlCall createCall(
+    @Override public SqlCall createCall(
         SqlLiteral functionQualifier,
         SqlParserPos pos,
         SqlNode... operands) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlLiteral.java
index c3b7981f093..809c7fde508 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlLiteral.java
@@ -232,11 +232,11 @@ public static boolean valueMatchesType(
     }
   }
 
-  public SqlLiteral clone(SqlParserPos pos) {
+  @Override public SqlLiteral clone(SqlParserPos pos) {
     return new SqlLiteral(value, typeName, pos);
   }
 
-  public @Nonnull SqlKind getKind() {
+  @Override public @Nonnull SqlKind getKind() {
     return SqlKind.LITERAL;
   }
 
@@ -550,15 +550,15 @@ public String toValue() {
     }
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateLiteral(this);
   }
 
-  public <R> R accept(SqlVisitor<R> visitor) {
+  @Override public <R> R accept(SqlVisitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public boolean equalsDeep(SqlNode node, Litmus litmus) {
+  @Override public boolean equalsDeep(SqlNode node, Litmus litmus) {
     if (!(node instanceof SqlLiteral)) {
       return litmus.fail("{} != {}", this, node);
     }
@@ -569,7 +569,7 @@ public boolean equalsDeep(SqlNode node, Litmus litmus) {
     return litmus.succeed();
   }
 
-  public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
+  @Override public SqlMonotonicity getMonotonicity(SqlValidatorScope scope) {
     return SqlMonotonicity.CONSTANT;
   }
 
@@ -618,7 +618,7 @@ public static SqlLiteral createSample(
     return new SqlLiteral(sampleSpec, SqlTypeName.SYMBOL, pos);
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (!(obj instanceof SqlLiteral)) {
       return false;
     }
@@ -626,7 +626,7 @@ public boolean equals(Object obj) {
     return Objects.equals(value, that.value);
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return (value == null) ? 0 : value.hashCode();
   }
 
@@ -715,7 +715,7 @@ public String getStringValue() {
     return ((NlsString) value).getValue();
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlMerge.java b/core/src/main/java/org/apache/calcite/sql/SqlMerge.java
index 665897e08dc..167aa8b0a2e 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlMerge.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlMerge.java
@@ -63,7 +63,7 @@ public SqlMerge(SqlParserPos pos,
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
@@ -71,7 +71,7 @@ public SqlOperator getOperator() {
     return SqlKind.MERGE;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(targetTable, condition, source, updateCall,
         insertCall, sourceSelect, alias);
   }
@@ -207,7 +207,7 @@ public void setSourceSelect(SqlSelect sourceSelect) {
     }
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateMerge(this);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlNode.java b/core/src/main/java/org/apache/calcite/sql/SqlNode.java
index 27af71439e2..d4cb3bcef93 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlNode.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlNode.java
@@ -71,7 +71,7 @@ public abstract class SqlNode implements Cloneable {
    * along too much baggage from early versions of Java */
   @Deprecated
   @SuppressWarnings("MethodDoesntCallSuperMethod")
-  public Object clone() {
+  @Override public Object clone() {
     return clone(getParserPosition());
   }
 
@@ -125,7 +125,7 @@ public static SqlNode[] cloneArray(SqlNode[] nodes) {
     return clones;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return toSqlString(c -> c.withDialect(AnsiSqlDialect.DEFAULT)
         .withAlwaysUseParentheses(false)
         .withSelectListItemsOnSeparateLines(false)
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlNodeList.java b/core/src/main/java/org/apache/calcite/sql/SqlNodeList.java
index 937945d5f2e..0d17ada3036 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlNodeList.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlNodeList.java
@@ -43,7 +43,7 @@ public class SqlNodeList extends SqlNode implements Iterable<SqlNode> {
    */
   public static final SqlNodeList EMPTY =
       new SqlNodeList(SqlParserPos.ZERO) {
-        public void add(SqlNode node) {
+        @Override public void add(SqlNode node) {
           throw new UnsupportedOperationException();
         }
       };
@@ -88,7 +88,7 @@ public SqlNodeList(
   //~ Methods ----------------------------------------------------------------
 
   // implement Iterable<SqlNode>
-  public Iterator<SqlNode> iterator() {
+  @Override public Iterator<SqlNode> iterator() {
     return list.iterator();
   }
 
@@ -100,7 +100,7 @@ public void add(SqlNode node) {
     list.add(node);
   }
 
-  public SqlNodeList clone(SqlParserPos pos) {
+  @Override public SqlNodeList clone(SqlParserPos pos) {
     return new SqlNodeList(list, pos);
   }
 
@@ -116,7 +116,7 @@ public int size() {
     return list.size();
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
@@ -137,17 +137,17 @@ void andOrList(SqlWriter writer, SqlBinaryOperator sepOp) {
     writer.list(SqlWriter.FrameTypeEnum.WHERE_LIST, sepOp, this);
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     for (SqlNode child : list) {
       child.validate(validator, scope);
     }
   }
 
-  public <R> R accept(SqlVisitor<R> visitor) {
+  @Override public <R> R accept(SqlVisitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public boolean equalsDeep(SqlNode node, Litmus litmus) {
+  @Override public boolean equalsDeep(SqlNode node, Litmus litmus) {
     if (!(node instanceof SqlNodeList)) {
       return litmus.fail("{} != {}", this, node);
     }
@@ -201,7 +201,7 @@ public static SqlNodeList of(SqlNode node1, SqlNode node2, SqlNode... nodes) {
     return list;
   }
 
-  public void validateExpr(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validateExpr(SqlValidator validator, SqlValidatorScope scope) {
     // While a SqlNodeList is not always a valid expression, this
     // implementation makes that assumption. It just validates the members
     // of the list.
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlNullTreatmentOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlNullTreatmentOperator.java
index 298ae2f09c6..2e1afd1c92d 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlNullTreatmentOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlNullTreatmentOperator.java
@@ -48,7 +48,7 @@ public SqlNullTreatmentOperator(SqlKind kind) {
     writer.keyword(getName());
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlNumericLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlNumericLiteral.java
index 40584f9b6bc..d1c0c7e14e0 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlNumericLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlNumericLiteral.java
@@ -70,14 +70,14 @@ public boolean isExact() {
         isExact, pos);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
     writer.literal(toValue());
   }
 
-  public String toValue() {
+  @Override public String toValue() {
     BigDecimal bd = (BigDecimal) value;
     if (isExact) {
       return value.toString();
@@ -85,7 +85,7 @@ public String toValue() {
     return Util.toScientificNotation(bd);
   }
 
-  public RelDataType createSqlType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType createSqlType(RelDataTypeFactory typeFactory) {
     if (isExact) {
       int scaleValue = scale.intValue();
       if (0 == scaleValue) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlOperator.java
index 310b325f65a..c69596bf157 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlOperator.java
@@ -213,7 +213,7 @@ public SqlKind getKind() {
     return kind;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return name;
   }
 
@@ -366,7 +366,7 @@ protected void unparseListClause(
   }
 
   // override Object
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (!(obj instanceof SqlOperator)) {
       return false;
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlOperatorBinding.java b/core/src/main/java/org/apache/calcite/sql/SqlOperatorBinding.java
index aabf09e8825..fce400a630f 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlOperatorBinding.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlOperatorBinding.java
@@ -205,11 +205,11 @@ public SqlMonotonicity getOperandMonotonicity(int ordinal) {
    */
   public List<RelDataType> collectOperandTypes() {
     return new AbstractList<RelDataType>() {
-      public RelDataType get(int index) {
+      @Override public RelDataType get(int index) {
         return getOperandType(index);
       }
 
-      public int size() {
+      @Override public int size() {
         return getOperandCount();
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlOrderBy.java b/core/src/main/java/org/apache/calcite/sql/SqlOrderBy.java
index e21fe4d4e5c..50a967051be 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlOrderBy.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlOrderBy.java
@@ -60,11 +60,11 @@ public SqlOrderBy(SqlParserPos pos, SqlNode query, SqlNodeList orderList,
     return SqlKind.ORDER_BY;
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(query, orderList, offset, fetch);
   }
 
@@ -75,11 +75,11 @@ private Operator() {
       super("ORDER BY", SqlKind.ORDER_BY, 0);
     }
 
-    public SqlSyntax getSyntax() {
+    @Override public SqlSyntax getSyntax() {
       return SqlSyntax.POSTFIX;
     }
 
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlCall call,
         int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlOverOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlOverOperator.java
index 99b7a63cb3b..68f46eee028 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlOverOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlOverOperator.java
@@ -57,7 +57,7 @@ public SqlOverOperator() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
@@ -78,7 +78,7 @@ public void validateCall(
     validator.validateWindow(window, scope, aggCall);
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
@@ -122,7 +122,7 @@ public RelDataType deriveType(
    *
    * @param visitor Visitor
    */
-  public <R> void acceptCall(
+  @Override public <R> void acceptCall(
       SqlVisitor<R> visitor,
       SqlCall call,
       boolean onlyExpressions,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlPostfixOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlPostfixOperator.java
index a4e0b7ef4b9..c55085ce0f8 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlPostfixOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlPostfixOperator.java
@@ -50,16 +50,16 @@ public SqlPostfixOperator(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.POSTFIX;
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     Util.discard(operandsCount);
     return "{1} {0}";
   }
 
-  protected RelDataType adjustType(
+  @Override protected RelDataType adjustType(
       SqlValidator validator,
       SqlCall call,
       RelDataType type) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlPrefixOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlPrefixOperator.java
index 9217d763c19..5c0bfe7d98b 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlPrefixOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlPrefixOperator.java
@@ -51,16 +51,16 @@ public SqlPrefixOperator(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.PREFIX;
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     Util.discard(operandsCount);
     return "{0}{1}";
   }
 
-  protected RelDataType adjustType(
+  @Override protected RelDataType adjustType(
       SqlValidator validator,
       SqlCall call,
       RelDataType type) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlProcedureCallOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlProcedureCallOperator.java
index f127f733349..d6575389224 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlProcedureCallOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlProcedureCallOperator.java
@@ -36,7 +36,7 @@ public SqlProcedureCallOperator() {
   //~ Methods ----------------------------------------------------------------
 
   // override SqlOperator
-  public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
+  @Override public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
     // for now, rewrite "CALL f(x)" to "SELECT f(x) FROM VALUES(0)"
     // TODO jvs 18-Jan-2005:  rewrite to SELECT * FROM TABLE f(x)
     // once we support function calls as tables
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlSampleSpec.java b/core/src/main/java/org/apache/calcite/sql/SqlSampleSpec.java
index 77e262411e5..7f4a6f0d496 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlSampleSpec.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlSampleSpec.java
@@ -94,7 +94,7 @@ public String getName() {
       return name;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "SUBSTITUTE("
           + CalciteSqlDialect.DEFAULT.quoteStringLiteral(name)
           + ")";
@@ -153,7 +153,7 @@ public int getRepeatableSeed() {
       return repeatableSeed;
     }
 
-    public String toString() {
+    @Override public String toString() {
       StringBuilder b = new StringBuilder();
       b.append(isBernoulli ? "BERNOULLI" : "SYSTEM");
       b.append('(');
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlSelect.java b/core/src/main/java/org/apache/calcite/sql/SqlSelect.java
index b05600d8d55..5b3a92502cf 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlSelect.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlSelect.java
@@ -82,7 +82,7 @@ public SqlSelect(SqlParserPos pos,
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return SqlSelectOperator.INSTANCE;
   }
 
@@ -228,7 +228,7 @@ public boolean hasHints() {
     return this.hints != null && this.hints.size() > 0;
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateQuery(this, scope, validator.getUnknownType());
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlSelectOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlSelectOperator.java
index 5d12b71ad48..56d75784066 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlSelectOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlSelectOperator.java
@@ -53,11 +53,11 @@ private SqlSelectOperator() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.SPECIAL;
   }
 
-  public SqlCall createCall(
+  @Override public SqlCall createCall(
       SqlLiteral functionQualifier,
       SqlParserPos pos,
       SqlNode... operands) {
@@ -123,7 +123,7 @@ public SqlSelect createCall(
         hints);
   }
 
-  public <R> void acceptCall(
+  @Override public <R> void acceptCall(
       SqlVisitor<R> visitor,
       SqlCall call,
       boolean onlyExpressions,
@@ -135,7 +135,7 @@ public <R> void acceptCall(
   }
 
   @SuppressWarnings("deprecation")
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -236,7 +236,7 @@ public void unparse(
     writer.endList(selectFrame);
   }
 
-  public boolean argumentMustBeScalar(int ordinal) {
+  @Override public boolean argumentMustBeScalar(int ordinal) {
     return ordinal == SqlSelect.WHERE_OPERAND;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlSetOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlSetOperator.java
index 2d19a9b3901..6d0f48c4f41 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlSetOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlSetOperator.java
@@ -82,7 +82,7 @@ public boolean isDistinct() {
     return !all;
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlSpecialOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlSpecialOperator.java
index e17ea19b8ed..3754952ec34 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlSpecialOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlSpecialOperator.java
@@ -64,7 +64,7 @@ public SqlSpecialOperator(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.SPECIAL;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlSplittableAggFunction.java b/core/src/main/java/org/apache/calcite/sql/SqlSplittableAggFunction.java
index 9e213bd8a2f..5ec772f084f 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlSplittableAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlSplittableAggFunction.java
@@ -126,18 +126,18 @@ interface Registry<E> {
   class CountSplitter implements SqlSplittableAggFunction {
     public static final CountSplitter INSTANCE = new CountSplitter();
 
-    public AggregateCall split(AggregateCall aggregateCall,
+    @Override public AggregateCall split(AggregateCall aggregateCall,
         Mappings.TargetMapping mapping) {
       return aggregateCall.transform(mapping);
     }
 
-    public AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e) {
+    @Override public AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e) {
       return AggregateCall.create(SqlStdOperatorTable.COUNT, false, false,
           false, ImmutableIntList.of(), -1, RelCollations.EMPTY,
           typeFactory.createSqlType(SqlTypeName.BIGINT), null);
     }
 
-    public AggregateCall topSplit(RexBuilder rexBuilder,
+    @Override public AggregateCall topSplit(RexBuilder rexBuilder,
         Registry<RexNode> extra, int offset, RelDataType inputRowType,
         AggregateCall aggregateCall, int leftSubTotal, int rightSubTotal) {
       final List<RexNode> merges = new ArrayList<>();
@@ -173,7 +173,7 @@ public AggregateCall topSplit(RexBuilder rexBuilder,
      * become {@code 1}; otherwise
      * {@code CASE WHEN arg0 IS NOT NULL THEN 1 ELSE 0 END}.
      */
-    public RexNode singleton(RexBuilder rexBuilder, RelDataType inputRowType,
+    @Override public RexNode singleton(RexBuilder rexBuilder, RelDataType inputRowType,
         AggregateCall aggregateCall) {
       final List<RexNode> predicates = new ArrayList<>();
       for (Integer arg : aggregateCall.getArgList()) {
@@ -196,7 +196,7 @@ public RexNode singleton(RexBuilder rexBuilder, RelDataType inputRowType,
       }
     }
 
-    public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
+    @Override public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
       if (bottom.getAggregation().getKind() == SqlKind.COUNT
           && (top.getAggregation().getKind() == SqlKind.SUM
               || top.getAggregation().getKind() == SqlKind.SUM0)) {
@@ -216,23 +216,23 @@ public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
   class SelfSplitter implements SqlSplittableAggFunction {
     public static final SelfSplitter INSTANCE = new SelfSplitter();
 
-    public RexNode singleton(RexBuilder rexBuilder,
+    @Override public RexNode singleton(RexBuilder rexBuilder,
         RelDataType inputRowType, AggregateCall aggregateCall) {
       final int arg = aggregateCall.getArgList().get(0);
       final RelDataTypeField field = inputRowType.getFieldList().get(arg);
       return rexBuilder.makeInputRef(field.getType(), arg);
     }
 
-    public AggregateCall split(AggregateCall aggregateCall,
+    @Override public AggregateCall split(AggregateCall aggregateCall,
         Mappings.TargetMapping mapping) {
       return aggregateCall.transform(mapping);
     }
 
-    public AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e) {
+    @Override public AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e) {
       return null; // no aggregate function required on other side
     }
 
-    public AggregateCall topSplit(RexBuilder rexBuilder,
+    @Override public AggregateCall topSplit(RexBuilder rexBuilder,
         Registry<RexNode> extra, int offset, RelDataType inputRowType,
         AggregateCall aggregateCall, int leftSubTotal, int rightSubTotal) {
       assert (leftSubTotal >= 0) != (rightSubTotal >= 0);
@@ -242,7 +242,7 @@ public AggregateCall topSplit(RexBuilder rexBuilder,
           RelCollations.EMPTY);
     }
 
-    public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
+    @Override public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
       if (top.getAggregation().getKind() == bottom.getAggregation().getKind()) {
         return AggregateCall.create(bottom.getAggregation(),
             bottom.isDistinct(), bottom.isApproximate(), false,
@@ -257,7 +257,7 @@ public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
   /** Common splitting strategy for {@code SUM} and {@code SUM0} functions. */
   abstract class AbstractSumSplitter implements SqlSplittableAggFunction {
 
-    public RexNode singleton(RexBuilder rexBuilder,
+    @Override public RexNode singleton(RexBuilder rexBuilder,
         RelDataType inputRowType, AggregateCall aggregateCall) {
       final int arg = aggregateCall.getArgList().get(0);
       final RelDataTypeField field = inputRowType.getFieldList().get(arg);
@@ -267,12 +267,12 @@ public RexNode singleton(RexBuilder rexBuilder,
       return rexBuilder.makeInputRef(type, arg);
     }
 
-    public AggregateCall split(AggregateCall aggregateCall,
+    @Override public AggregateCall split(AggregateCall aggregateCall,
         Mappings.TargetMapping mapping) {
       return aggregateCall.transform(mapping);
     }
 
-    public AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e) {
+    @Override public AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e) {
       return AggregateCall.create(SqlStdOperatorTable.COUNT, false, false,
           false,
           ImmutableIntList.of(), -1,
@@ -280,7 +280,7 @@ public AggregateCall other(RelDataTypeFactory typeFactory, AggregateCall e) {
           typeFactory.createSqlType(SqlTypeName.BIGINT), null);
     }
 
-    public AggregateCall topSplit(RexBuilder rexBuilder,
+    @Override public AggregateCall topSplit(RexBuilder rexBuilder,
         Registry<RexNode> extra, int offset, RelDataType inputRowType,
         AggregateCall aggregateCall, int leftSubTotal, int rightSubTotal) {
       final List<RexNode> merges = new ArrayList<>();
@@ -311,7 +311,7 @@ public AggregateCall topSplit(RexBuilder rexBuilder,
           aggregateCall.type, aggregateCall.name);
     }
 
-    public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
+    @Override public AggregateCall merge(AggregateCall top, AggregateCall bottom) {
       SqlKind topKind = top.getAggregation().getKind();
       if (topKind == bottom.getAggregation().getKind()
           && (topKind == SqlKind.SUM
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlSyntax.java b/core/src/main/java/org/apache/calcite/sql/SqlSyntax.java
index 0f53ee1693a..d43484d61f1 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlSyntax.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlSyntax.java
@@ -27,7 +27,7 @@ public enum SqlSyntax {
    * Function syntax, as in "Foo(x, y)".
    */
   FUNCTION {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
@@ -42,7 +42,7 @@ public void unparse(
    * for example "COUNT(*)".
    */
   FUNCTION_STAR {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
@@ -56,7 +56,7 @@ public void unparse(
    * Binary operator syntax, as in "x + y".
    */
   BINARY {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
@@ -70,7 +70,7 @@ public void unparse(
    * Prefix unary operator syntax, as in "- x".
    */
   PREFIX {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
@@ -87,7 +87,7 @@ public void unparse(
    * Postfix unary operator syntax, as in "x ++".
    */
   POSTFIX {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
@@ -105,7 +105,7 @@ public void unparse(
    * THEN 2 ELSE 3 END".
    */
   SPECIAL {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
@@ -124,7 +124,7 @@ public void unparse(
    * @see SqlConformance#allowNiladicParentheses()
    */
   FUNCTION_ID {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
@@ -138,7 +138,7 @@ public void unparse(
    * Syntax of an internal operator, which does not appear in the SQL.
    */
   INTERNAL {
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlOperator operator,
         SqlCall call,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlTableRef.java b/core/src/main/java/org/apache/calcite/sql/SqlTableRef.java
index 7c2386b3568..3d72c45a37e 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlTableRef.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlTableRef.java
@@ -50,11 +50,11 @@ public SqlTableRef(SqlParserPos pos, SqlIdentifier tableName, SqlNodeList hints)
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableList.of(tableName, hints);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlTimeLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlTimeLiteral.java
index 20ec2f50918..20944ffb964 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlTimeLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlTimeLiteral.java
@@ -48,18 +48,18 @@ protected TimeString getTime() {
     return new SqlTimeLiteral((TimeString) value, precision, hasTimeZone, pos);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "TIME '" + toFormattedString() + "'";
   }
 
   /**
    * Returns e.g. '03:05:67.456'.
    */
-  public String toFormattedString() {
+  @Override public String toFormattedString() {
     return getTime().toString(precision);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlTimestampLiteral.java b/core/src/main/java/org/apache/calcite/sql/SqlTimestampLiteral.java
index 47de667b5c4..8ee775a1e6c 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlTimestampLiteral.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlTimestampLiteral.java
@@ -44,14 +44,14 @@ public class SqlTimestampLiteral extends SqlAbstractDateTimeLiteral {
         hasTimeZone, pos);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "TIMESTAMP '" + toFormattedString() + "'";
   }
 
   /**
    * Returns e.g. '03:05:67.456'.
    */
-  public String toFormattedString() {
+  @Override public String toFormattedString() {
     TimestampString ts = getTimestamp();
     if (precision > 0) {
       ts = ts.round(precision);
@@ -59,7 +59,7 @@ public String toFormattedString() {
     return ts.toString(precision);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       int leftPrec,
       int rightPrec) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlUnnestOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlUnnestOperator.java
index 6e87a924d6a..eb1da8c5ea9 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlUnnestOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlUnnestOperator.java
@@ -121,7 +121,7 @@ private boolean allowAliasUnnestItems(SqlOperatorBinding operatorBinding) {
     }
   }
 
-  public boolean argumentMustBeScalar(int ordinal) {
+  @Override public boolean argumentMustBeScalar(int ordinal) {
     return false;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlUpdate.java b/core/src/main/java/org/apache/calcite/sql/SqlUpdate.java
index 611e181d0a8..1aef579bc50 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlUpdate.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlUpdate.java
@@ -65,11 +65,11 @@ public SqlUpdate(SqlParserPos pos,
     return SqlKind.UPDATE;
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return OPERATOR;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(targetTable, targetColumnList,
         sourceExpressionList, condition, alias);
   }
@@ -178,7 +178,7 @@ public void setSourceSelect(SqlSelect sourceSelect) {
     writer.endList(frame);
   }
 
-  public void validate(SqlValidator validator, SqlValidatorScope scope) {
+  @Override public void validate(SqlValidator validator, SqlValidatorScope scope) {
     validator.validateUpdate(this);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlValuesOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlValuesOperator.java
index 3e45ec1d1e4..0175f89a316 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlValuesOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlValuesOperator.java
@@ -28,7 +28,7 @@ public SqlValuesOperator() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlWindow.java b/core/src/main/java/org/apache/calcite/sql/SqlWindow.java
index ceba7e0f461..88223aaed5f 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlWindow.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlWindow.java
@@ -140,7 +140,7 @@ public static SqlWindow create(SqlIdentifier declName, SqlIdentifier refName,
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return SqlWindowOperator.INSTANCE;
   }
 
@@ -148,7 +148,7 @@ public SqlOperator getOperator() {
     return SqlKind.WINDOW;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(declName, refName, partitionList, orderList,
         isRows, lowerBound, upperBound, allowPartial);
   }
@@ -790,7 +790,7 @@ enum Bound implements Symbolizable {
       this.sql = sql;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return sql;
     }
   }
@@ -803,11 +803,11 @@ private SqlWindowOperator() {
       super("WINDOW", SqlKind.WINDOW, 2, true, null, null, null);
     }
 
-    public SqlSyntax getSyntax() {
+    @Override public SqlSyntax getSyntax() {
       return SqlSyntax.SPECIAL;
     }
 
-    public SqlCall createCall(
+    @Override public SqlCall createCall(
         SqlLiteral functionQualifier,
         SqlParserPos pos,
         SqlNode... operands) {
@@ -825,7 +825,7 @@ public SqlCall createCall(
           pos);
     }
 
-    public <R> void acceptCall(
+    @Override public <R> void acceptCall(
         SqlVisitor<R> visitor,
         SqlCall call,
         boolean onlyExpressions,
@@ -849,7 +849,7 @@ public <R> void acceptCall(
       }
     }
 
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlCall call,
         int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlWith.java b/core/src/main/java/org/apache/calcite/sql/SqlWith.java
index 9363e229141..e9fb1c801ee 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlWith.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlWith.java
@@ -49,7 +49,7 @@ public SqlWith(SqlParserPos pos, SqlNodeList withList, SqlNode body) {
     return SqlWithOperator.INSTANCE;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableList.of(withList, body);
   }
 
@@ -85,7 +85,7 @@ private SqlWithOperator() {
 
     //~ Methods ----------------------------------------------------------------
 
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlCall call,
         int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlWithItem.java b/core/src/main/java/org/apache/calcite/sql/SqlWithItem.java
index 686f772286b..b0c67be237f 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlWithItem.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlWithItem.java
@@ -44,7 +44,7 @@ public SqlWithItem(SqlParserPos pos, SqlIdentifier name,
     return SqlKind.WITH_ITEM;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(name, columnList, query);
   }
 
@@ -64,7 +64,7 @@ public List<SqlNode> getOperandList() {
     }
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return SqlWithItemOperator.INSTANCE;
   }
 
@@ -82,7 +82,7 @@ private static class SqlWithItemOperator extends SqlSpecialOperator {
 
     //~ Methods ----------------------------------------------------------------
 
-    public void unparse(
+    @Override public void unparse(
         SqlWriter writer,
         SqlCall call,
         int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlWithinGroupOperator.java b/core/src/main/java/org/apache/calcite/sql/SqlWithinGroupOperator.java
index d5402a6a18c..38da619e286 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlWithinGroupOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlWithinGroupOperator.java
@@ -52,7 +52,7 @@ public SqlWithinGroupOperator() {
     writer.endList(orderFrame);
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
@@ -73,7 +73,7 @@ public void validateCall(
     validator.validateAggregateParams(aggCall, null, orderList, scope);
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlWriter.java b/core/src/main/java/org/apache/calcite/sql/SqlWriter.java
index b26489ed2ae..1c5cb015e99 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlWriter.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlWriter.java
@@ -263,7 +263,7 @@ enum FrameTypeEnum implements FrameType {
       this.needsIndent = needsIndent;
     }
 
-    public boolean needsIndent() {
+    @Override public boolean needsIndent() {
       return needsIndent;
     }
 
@@ -275,17 +275,17 @@ public boolean needsIndent() {
      */
     public static FrameType create(final String name) {
       return new FrameType() {
-        public String getName() {
+        @Override public String getName() {
           return name;
         }
 
-        public boolean needsIndent() {
+        @Override public boolean needsIndent() {
           return true;
         }
       };
     }
 
-    public String getName() {
+    @Override public String getName() {
       return name();
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction.java b/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction.java
index e41d15a86a5..cbd2a1893a2 100644
--- a/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction.java
@@ -71,20 +71,20 @@ public class SqlAdvisorGetHintsFunction
           .add(int.class, "pos")
           .build();
 
-  public CallImplementor getImplementor() {
+  @Override public CallImplementor getImplementor() {
     return IMPLEMENTOR;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory,
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory,
       List<Object> arguments) {
     return typeFactory.createJavaType(SqlAdvisorHint.class);
   }
 
-  public Type getElementType(List<Object> arguments) {
+  @Override public Type getElementType(List<Object> arguments) {
     return SqlAdvisorHint.class;
   }
 
-  public List<FunctionParameter> getParameters() {
+  @Override public List<FunctionParameter> getParameters() {
     return PARAMETERS;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction2.java b/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction2.java
index 27562508eed..68b2924865d 100644
--- a/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction2.java
+++ b/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorGetHintsFunction2.java
@@ -73,20 +73,20 @@ public class SqlAdvisorGetHintsFunction2
           .add(int.class, "pos")
           .build();
 
-  public CallImplementor getImplementor() {
+  @Override public CallImplementor getImplementor() {
     return IMPLEMENTOR;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory,
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory,
       List<Object> arguments) {
     return typeFactory.createJavaType(SqlAdvisorHint2.class);
   }
 
-  public Type getElementType(List<Object> arguments) {
+  @Override public Type getElementType(List<Object> arguments) {
     return SqlAdvisorHint2.class;
   }
 
-  public List<FunctionParameter> getParameters() {
+  @Override public List<FunctionParameter> getParameters() {
     return PARAMETERS;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorValidator.java b/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorValidator.java
index 37ee866b6b4..a4d157fd7dd 100644
--- a/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorValidator.java
+++ b/core/src/main/java/org/apache/calcite/sql/advise/SqlAdvisorValidator.java
@@ -75,7 +75,7 @@ public SqlAdvisorValidator(
   /**
    * Registers the identifier and its scope into a map keyed by ParserPosition.
    */
-  public void validateIdentifier(SqlIdentifier id, SqlValidatorScope scope) {
+  @Override public void validateIdentifier(SqlIdentifier id, SqlValidatorScope scope) {
     registerId(id, scope);
     try {
       super.validateIdentifier(id, scope);
@@ -95,18 +95,18 @@ private void registerId(SqlIdentifier id, SqlValidatorScope scope) {
     }
   }
 
-  public SqlNode expand(SqlNode expr, SqlValidatorScope scope) {
+  @Override public SqlNode expand(SqlNode expr, SqlValidatorScope scope) {
     // Disable expansion. It doesn't help us come up with better hints.
     return expr;
   }
 
-  public SqlNode expandSelectExpr(SqlNode expr,
+  @Override public SqlNode expandSelectExpr(SqlNode expr,
       SelectScope scope, SqlSelect select) {
     // Disable expansion. It doesn't help us come up with better hints.
     return expr;
   }
 
-  public SqlNode expandOrderExpr(SqlSelect select, SqlNode orderExpr) {
+  @Override public SqlNode expandOrderExpr(SqlSelect select, SqlNode orderExpr) {
     // Disable expansion. It doesn't help us come up with better hints.
     return orderExpr;
   }
@@ -114,7 +114,7 @@ public SqlNode expandOrderExpr(SqlSelect select, SqlNode orderExpr) {
   /**
    * Calls the parent class method and mask Farrago exception thrown.
    */
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidatorScope scope,
       SqlNode operand) {
     // REVIEW Do not mask Error (indicates a serious system problem) or
@@ -134,7 +134,7 @@ public RelDataType deriveType(
   // we do not need to validate from clause for traversing the parse tree
   // because there is no SqlIdentifier in from clause that need to be
   // registered into {@link #idPositions} map
-  protected void validateFrom(
+  @Override protected void validateFrom(
       SqlNode node,
       RelDataType targetRowType,
       SqlValidatorScope scope) {
@@ -148,7 +148,7 @@ protected void validateFrom(
   /**
    * Calls the parent class method and masks Farrago exception thrown.
    */
-  protected void validateWhereClause(SqlSelect select) {
+  @Override protected void validateWhereClause(SqlSelect select) {
     try {
       super.validateWhereClause(select);
     } catch (CalciteException e) {
@@ -159,7 +159,7 @@ protected void validateWhereClause(SqlSelect select) {
   /**
    * Calls the parent class method and masks Farrago exception thrown.
    */
-  protected void validateHavingClause(SqlSelect select) {
+  @Override protected void validateHavingClause(SqlSelect select) {
     try {
       super.validateHavingClause(select);
     } catch (CalciteException e) {
@@ -167,7 +167,7 @@ protected void validateHavingClause(SqlSelect select) {
     }
   }
 
-  protected void validateOver(SqlCall call, SqlValidatorScope scope) {
+  @Override protected void validateOver(SqlCall call, SqlValidatorScope scope) {
     try {
       final OverScope overScope = (OverScope) getOverScope(call);
       final SqlNode relation = call.operand(0);
@@ -183,7 +183,7 @@ protected void validateOver(SqlCall call, SqlValidatorScope scope) {
     }
   }
 
-  protected void validateNamespace(final SqlValidatorNamespace namespace,
+  @Override protected void validateNamespace(final SqlValidatorNamespace namespace,
       RelDataType targetRowType) {
     // Only attempt to validate each namespace once. Otherwise if
     // validation fails, we may end up cycling.
@@ -199,7 +199,7 @@ protected void validateNamespace(final SqlValidatorNamespace namespace,
     return true;
   }
 
-  protected boolean shouldAllowOverRelation() {
+  @Override protected boolean shouldAllowOverRelation() {
     return true; // no reason not to be lenient
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/advise/SqlSimpleParser.java b/core/src/main/java/org/apache/calcite/sql/advise/SqlSimpleParser.java
index 7e98225f64d..f1d64f14679 100644
--- a/core/src/main/java/org/apache/calcite/sql/advise/SqlSimpleParser.java
+++ b/core/src/main/java/org/apache/calcite/sql/advise/SqlSimpleParser.java
@@ -43,14 +43,14 @@ enum TokenType {
 
     /** Left parenthesis. */
     LPAREN {
-      public String sql() {
+      @Override public String sql() {
         return "(";
       }
     },
 
     /** Right parenthesis. */
     RPAREN {
-      public String sql() {
+      @Override public String sql() {
         return ")";
       }
     },
@@ -68,7 +68,7 @@ public String sql() {
      */
     SQID, COMMENT,
     COMMA {
-      public String sql() {
+      @Override public String sql() {
         return ",";
       }
     },
@@ -454,7 +454,7 @@ public static class Token {
       this.s = s;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return (s == null) ? type.toString() : (type + "(" + s + ")");
     }
 
@@ -484,7 +484,7 @@ static class Query extends Token {
       this.tokenList = new ArrayList<>(tokenList);
     }
 
-    public void unparse(StringBuilder buf) {
+    @Override public void unparse(StringBuilder buf) {
       int k = -1;
       for (Token token : tokenList) {
         if (++k > 0) {
diff --git a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateForeignSchema.java b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateForeignSchema.java
index 9c6b667990b..a2c25586813 100644
--- a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateForeignSchema.java
+++ b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateForeignSchema.java
@@ -106,12 +106,12 @@ public List<Pair<SqlIdentifier, SqlNode>> options() {
   private static List<Pair<SqlIdentifier, SqlNode>> options(
       final SqlNodeList optionList) {
     return new AbstractList<Pair<SqlIdentifier, SqlNode>>() {
-      public Pair<SqlIdentifier, SqlNode> get(int index) {
+      @Override public Pair<SqlIdentifier, SqlNode> get(int index) {
         return Pair.of((SqlIdentifier) optionList.get(index * 2),
             optionList.get(index * 2 + 1));
       }
 
-      public int size() {
+      @Override public int size() {
         return optionList.size() / 2;
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateMaterializedView.java b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateMaterializedView.java
index 26fd93327ea..dbd93c1592e 100644
--- a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateMaterializedView.java
+++ b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateMaterializedView.java
@@ -52,7 +52,7 @@ public class SqlCreateMaterializedView extends SqlCreate {
     this.query = Objects.requireNonNull(query);
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(name, columnList, query);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateTable.java b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateTable.java
index 6e033180b6d..8f97b954ec4 100644
--- a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateTable.java
@@ -50,7 +50,7 @@ protected SqlCreateTable(SqlParserPos pos, boolean replace, boolean ifNotExists,
     this.query = query; // for "CREATE TABLE ... AS query"; may be null
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(name, columnList, query);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateView.java b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateView.java
index ab05ecf4919..7751f2b523b 100644
--- a/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateView.java
+++ b/core/src/main/java/org/apache/calcite/sql/ddl/SqlCreateView.java
@@ -50,7 +50,7 @@ public class SqlCreateView extends SqlCreate {
     this.query = Objects.requireNonNull(query);
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableNullableList.of(name, columnList, query);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropObject.java b/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropObject.java
index 8ca55853906..ccc4a2fa166 100644
--- a/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropObject.java
+++ b/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropObject.java
@@ -43,7 +43,7 @@ public abstract class SqlDropObject extends SqlDrop {
     this.name = name;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableList.of(name);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropSchema.java b/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropSchema.java
index 73c9493f0f6..b06022977b6 100644
--- a/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropSchema.java
+++ b/core/src/main/java/org/apache/calcite/sql/ddl/SqlDropSchema.java
@@ -48,7 +48,7 @@ public class SqlDropSchema extends SqlDrop {
     this.name = name;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return ImmutableList.of(
         SqlLiteral.createBoolean(foreign, SqlParserPos.ZERO), name);
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/JethroDataSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/JethroDataSqlDialect.java
index abd2c79bfae..8a6a9c7f8db 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/JethroDataSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/JethroDataSqlDialect.java
@@ -175,7 +175,7 @@ public interface JethroInfoCache {
   private static class JethroInfoCacheImpl implements JethroInfoCache {
     final Map<String, JethroInfo> map = new HashMap<>();
 
-    public JethroInfo get(final DatabaseMetaData metaData) {
+    @Override public JethroInfo get(final DatabaseMetaData metaData) {
       try {
         assert "JethroData".equals(metaData.getDatabaseProductName());
         String productVersion = metaData.getDatabaseProductVersion();
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
index 19ad82091df..469588d7294 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
@@ -101,7 +101,7 @@ public MysqlSqlDialect(Context context) {
     return true;
   }
 
-  public boolean supportsAliasedValues() {
+  @Override public boolean supportsAliasedValues() {
     // MySQL supports VALUES only in INSERT; not in a FROM clause
     return false;
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlAbstractTimeFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlAbstractTimeFunction.java
index 1ee37ab77c9..1c9caff0610 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlAbstractTimeFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlAbstractTimeFunction.java
@@ -54,11 +54,11 @@ protected SqlAbstractTimeFunction(String name, SqlTypeName typeName) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.FUNCTION_ID;
   }
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     // REVIEW jvs 20-Feb-2005: Need to take care of time zones.
     int precision = 0;
@@ -84,7 +84,7 @@ public RelDataType inferReturnType(
   }
 
   // Plans referencing context variables should never be cached
-  public boolean isDynamicFunction() {
+  @Override public boolean isDynamicFunction() {
     return true;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlBaseContextVariable.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlBaseContextVariable.java
index 5aa9c6837b1..8c0d9cf8abf 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlBaseContextVariable.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlBaseContextVariable.java
@@ -40,7 +40,7 @@ protected SqlBaseContextVariable(String name,
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.FUNCTION_ID;
   }
 
@@ -50,7 +50,7 @@ public SqlSyntax getSyntax() {
   }
 
   // Plans referencing context variables should never be cached
-  public boolean isDynamicFunction() {
+  @Override public boolean isDynamicFunction() {
     return true;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlBetweenOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlBetweenOperator.java
index 2da2a54d892..54b60cf08eb 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlBetweenOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlBetweenOperator.java
@@ -119,7 +119,7 @@ public boolean isNegated() {
     return negated;
   }
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     ExplicitOperatorBinding newOpBinding =
         new ExplicitOperatorBinding(
@@ -129,7 +129,7 @@ public RelDataType inferReturnType(
         newOpBinding);
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     Util.discard(operandsCount);
     return "{1} {0} {2} AND {3}";
   }
@@ -140,7 +140,7 @@ public String getSignatureTemplate(final int operandsCount) {
         + flag.name();
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -172,7 +172,7 @@ public void unparse(
     writer.endList(frame);
   }
 
-  public ReduceResult reduceExpr(int opOrdinal, TokenSequence list) {
+  @Override public ReduceResult reduceExpr(int opOrdinal, TokenSequence list) {
     SqlOperator op = list.op(opOrdinal);
     assert op == this;
 
@@ -233,7 +233,7 @@ public ReduceResult reduceExpr(int opOrdinal, TokenSequence list) {
    * Finds an AND operator in an expression.
    */
   private static class AndFinder extends SqlBasicVisitor<Void> {
-    public Void visit(SqlCall call) {
+    @Override public Void visit(SqlCall call) {
       final SqlOperator operator = call.getOperator();
       if (operator == SqlStdOperatorTable.AND) {
         throw Util.FoundOne.NULL;
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlCase.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlCase.java
index b2d737afa1a..2c7f5b2748c 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlCase.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlCase.java
@@ -97,11 +97,11 @@ public static SqlCase createSwitched(SqlParserPos pos, SqlNode value,
     return SqlKind.CASE;
   }
 
-  public SqlOperator getOperator() {
+  @Override public SqlOperator getOperator() {
     return SqlStdOperatorTable.CASE;
   }
 
-  public List<SqlNode> getOperandList() {
+  @Override public List<SqlNode> getOperandList() {
     return UnmodifiableArrayList.of(value, whenList, thenList, elseExpr);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlCaseOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlCaseOperator.java
index 73868aafc2a..bdbfb06aec2 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlCaseOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlCaseOperator.java
@@ -139,7 +139,7 @@ private SqlCaseOperator() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
@@ -159,7 +159,7 @@ public void validateCall(
     }
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
@@ -168,7 +168,7 @@ public RelDataType deriveType(
     return validateOperands(validator, scope, call);
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     SqlCase caseCall = (SqlCase) callBinding.getCall();
@@ -212,7 +212,7 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     // REVIEW jvs 4-June-2005:  can't these be unified?
     if (!(opBinding instanceof SqlCallBinding)) {
@@ -314,15 +314,15 @@ private RelDataType inferTypeFromOperands(SqlOperatorBinding opBinding) {
     return typeFactory.leastRestrictive(thenTypes);
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.any();
   }
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.SPECIAL;
   }
 
-  public SqlCall createCall(
+  @Override public SqlCall createCall(
       SqlLiteral functionQualifier,
       SqlParserPos pos,
       SqlNode... operands) {
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlCastFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlCastFunction.java
index 28d856e3e4d..5d6e49eee70 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlCastFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlCastFunction.java
@@ -94,7 +94,7 @@ public SqlCastFunction() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     assert opBinding.getOperandCount() == 2;
     RelDataType ret = opBinding.getOperandType(1);
@@ -120,12 +120,12 @@ public RelDataType inferReturnType(
     return ret;
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     assert operandsCount == 2;
     return "{0}({1} AS {2})";
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(2);
   }
 
@@ -134,7 +134,7 @@ public SqlOperandCountRange getOperandCountRange() {
    * Operators (such as "ROW" and "AS") which do not check their arguments can
    * override this method.
    */
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     final SqlNode left = callBinding.operand(0);
@@ -169,11 +169,11 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.SPECIAL;
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlCoalesceFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlCoalesceFunction.java
index 79f058e1b87..1dcfe477f9e 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlCoalesceFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlCoalesceFunction.java
@@ -54,7 +54,7 @@ public SqlCoalesceFunction() {
   //~ Methods ----------------------------------------------------------------
 
   // override SqlOperator
-  public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
+  @Override public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
     validateQuantifier(validator, call); // check DISTINCT/ALL
 
     List<SqlNode> operands = call.getOperandList();
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlColumnListConstructor.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlColumnListConstructor.java
index 55028e4e2a4..14c0321eb60 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlColumnListConstructor.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlColumnListConstructor.java
@@ -43,7 +43,7 @@ public SqlColumnListConstructor() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlConvertFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlConvertFunction.java
index eb4ff4a6a8c..2d10cc1d978 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlConvertFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlConvertFunction.java
@@ -41,7 +41,7 @@ protected SqlConvertFunction(String name) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -53,7 +53,7 @@ public void unparse(
     writer.endFunCall(frame);
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     switch (operandsCount) {
     case 2:
       return "{0}({1} USING {2})";
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlCountAggFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlCountAggFunction.java
index cd3c8a68d58..4a7c8d32658 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlCountAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlCountAggFunction.java
@@ -65,18 +65,18 @@ public SqlCountAggFunction(String name,
   }
 
   @SuppressWarnings("deprecation")
-  public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
+  @Override public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
     return ImmutableList.of(
         typeFactory.createTypeWithNullability(
             typeFactory.createSqlType(SqlTypeName.ANY), true));
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return typeFactory.createSqlType(SqlTypeName.BIGINT);
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlCurrentDateFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlCurrentDateFunction.java
index 6df32ac6d27..623377b821f 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlCurrentDateFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlCurrentDateFunction.java
@@ -43,7 +43,7 @@ public SqlCurrentDateFunction() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.FUNCTION_ID;
   }
 
@@ -52,7 +52,7 @@ public SqlSyntax getSyntax() {
   }
 
   // Plans referencing context variables should never be cached
-  public boolean isDynamicFunction() {
+  @Override public boolean isDynamicFunction() {
     return true;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlCursorConstructor.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlCursorConstructor.java
index c906a75e0ef..7d23c4123ea 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlCursorConstructor.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlCursorConstructor.java
@@ -46,7 +46,7 @@ public SqlCursorConstructor() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
@@ -56,7 +56,7 @@ public RelDataType deriveType(
     return super.deriveType(validator, scope, call);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -68,7 +68,7 @@ public void unparse(
     writer.endList(frame);
   }
 
-  public boolean argumentMustBeScalar(int ordinal) {
+  @Override public boolean argumentMustBeScalar(int ordinal) {
     return false;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlDatePartFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlDatePartFunction.java
index f43ee05fa1a..31fbc284e0e 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlDatePartFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlDatePartFunction.java
@@ -62,16 +62,16 @@ public SqlDatePartFunction(String name, TimeUnit timeUnit) {
         operands.get(0));
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(1);
   }
 
-  public String getSignatureTemplate(int operandsCount) {
+  @Override public String getSignatureTemplate(int operandsCount) {
     assert 1 == operandsCount;
     return "{0}({1})";
   }
 
-  public boolean checkOperandTypes(SqlCallBinding callBinding,
+  @Override public boolean checkOperandTypes(SqlCallBinding callBinding,
       boolean throwOnFailure) {
     // Use #checkOperandTypes instead of #checkSingleOperandType to enable implicit
     // type coercion. REVIEW Danny 2019-09-10, because we declare that the operand
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimePlusOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimePlusOperator.java
index 0827c59ed57..dd83c265518 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimePlusOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimePlusOperator.java
@@ -53,7 +53,7 @@ public class SqlDatetimePlusOperator extends SqlSpecialOperator {
         unitType, leftType);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimeSubtractionOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimeSubtractionOperator.java
index c08a0786fc7..e63303e02d8 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimeSubtractionOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlDatetimeSubtractionOperator.java
@@ -53,7 +53,7 @@ public SqlDatetimeSubtractionOperator() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlDotOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlDotOperator.java
index 874707c4632..72e164d76de 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlDotOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlDotOperator.java
@@ -123,7 +123,7 @@ public class SqlDotOperator extends SqlSpecialOperator {
     return type;
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlExtractFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlExtractFunction.java
index 375f30e6683..a580f5d0e4c 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlExtractFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlExtractFunction.java
@@ -47,12 +47,12 @@ public SqlExtractFunction() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public String getSignatureTemplate(int operandsCount) {
+  @Override public String getSignatureTemplate(int operandsCount) {
     Util.discard(operandsCount);
     return "{0}({1} FROM {2})";
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlFirstLastValueAggFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlFirstLastValueAggFunction.java
index 17828446fd7..100639ca4a4 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlFirstLastValueAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlFirstLastValueAggFunction.java
@@ -63,14 +63,14 @@ public SqlFirstLastValueAggFunction(boolean firstFlag) {
   //~ Methods ----------------------------------------------------------------
 
   @SuppressWarnings("deprecation")
-  public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
+  @Override public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
     return ImmutableList.of(
         typeFactory.createTypeWithNullability(
             typeFactory.createSqlType(SqlTypeName.ANY), true));
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return typeFactory.createTypeWithNullability(
         typeFactory.createSqlType(SqlTypeName.ANY), true);
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlGeoFunctions.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlGeoFunctions.java
index 7638d426424..dcd4baac58b 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlGeoFunctions.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlGeoFunctions.java
@@ -101,7 +101,7 @@ public static class GridTable implements ScannableTable {
           .build();
     }
 
-    public Enumerable<Object[]> scan(DataContext root) {
+    @Override public Enumerable<Object[]> scan(DataContext root) {
       if (geom != null && deltaX != null && deltaY != null) {
         final Geometry geometry = geom.g();
         final Envelope envelope = new Envelope();
@@ -115,19 +115,19 @@ public Enumerable<Object[]> scan(DataContext root) {
       return Linq4j.emptyEnumerable();
     }
 
-    public Statistic getStatistic() {
+    @Override public Statistic getStatistic() {
       return Statistics.of(100d, ImmutableList.of(ImmutableBitSet.of(0, 1)));
     }
 
-    public Schema.TableType getJdbcTableType() {
+    @Override public Schema.TableType getJdbcTableType() {
       return Schema.TableType.OTHER;
     }
 
-    public boolean isRolledUp(String column) {
+    @Override public boolean isRolledUp(String column) {
       return false;
     }
 
-    public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+    @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
         SqlNode parent, CalciteConnectionConfig config) {
       return false;
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlHistogramAggFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlHistogramAggFunction.java
index 6e200dcfa8a..e13ef20e390 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlHistogramAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlHistogramAggFunction.java
@@ -62,7 +62,7 @@ public SqlHistogramAggFunction(RelDataType type) {
   //~ Methods ----------------------------------------------------------------
 
   @SuppressWarnings("deprecation")
-  public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
+  @Override public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
     return ImmutableList.of(type);
   }
 
@@ -72,7 +72,7 @@ public RelDataType getType() {
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return type;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlInOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlInOperator.java
index 3851a14e539..d4d28190520 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlInOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlInOperator.java
@@ -87,7 +87,7 @@ public boolean isNotIn() {
     return litmus.succeed();
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
@@ -185,7 +185,7 @@ private static boolean anyNullable(List<RelDataTypeField> fieldList) {
     return false;
   }
 
-  public boolean argumentMustBeScalar(int ordinal) {
+  @Override public boolean argumentMustBeScalar(int ordinal) {
     // Argument #0 must be scalar, argument #1 can be a list (1, 2) or
     // a query (select deptno from emp). So, only coerce argument #0 into
     // a scalar sub-query. For example, in
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlLikeOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlLikeOperator.java
index 0e934c98642..89e889b1af8 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlLikeOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlLikeOperator.java
@@ -92,11 +92,11 @@ public boolean isNegated() {
     return negated;
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.between(2, 3);
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     switch (callBinding.getOperandCount()) {
@@ -128,7 +128,7 @@ public boolean checkOperandTypes(
         throwOnFailure);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -145,7 +145,7 @@ public void unparse(
     writer.endList(frame);
   }
 
-  public ReduceResult reduceExpr(
+  @Override public ReduceResult reduceExpr(
       final int opOrdinal,
       TokenSequence list) {
     // Example:
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlLiteralChainOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlLiteralChainOperator.java
index 8b2d96daf18..6cd82396278 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlLiteralChainOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlLiteralChainOperator.java
@@ -93,7 +93,7 @@ private boolean argTypesValid(SqlCallBinding callBinding) {
     return true;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     if (!argTypesValid(callBinding)) {
@@ -109,7 +109,7 @@ public boolean checkOperandTypes(
   // total size.
   // REVIEW mb 8/8/04: Possibly this can be achieved by combining
   // the strategy useFirstArgType with a new transformer.
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     // Here we know all the operands have the same type,
     // which has a size (precision), but not a scale.
@@ -126,11 +126,11 @@ public RelDataType inferReturnType(
     return opBinding.getTypeFactory().createSqlType(typeName, size);
   }
 
-  public String getAllowedSignatures(String opName) {
+  @Override public String getAllowedSignatures(String opName) {
     return opName + "(...)";
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidator validator,
       SqlValidatorScope scope,
@@ -148,7 +148,7 @@ public void validateCall(
     }
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlMapValueConstructor.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlMapValueConstructor.java
index 7fe4db7900e..61300d1b910 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlMapValueConstructor.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlMapValueConstructor.java
@@ -54,7 +54,7 @@ public SqlMapValueConstructor() {
         false);
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     final List<RelDataType> argTypes = SqlTypeUtil.deriveType(callBinding, callBinding.operands());
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlMinMaxAggFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlMinMaxAggFunction.java
index f6c3b2236d4..4fd9764a38c 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlMinMaxAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlMinMaxAggFunction.java
@@ -118,7 +118,7 @@ public int getMinMaxKind() {
   }
 
   @SuppressWarnings("deprecation")
-  public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
+  @Override public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
     switch (minMaxKind) {
     case MINMAX_PRIMITIVE:
     case MINMAX_COMPARABLE:
@@ -131,7 +131,7 @@ public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     switch (minMaxKind) {
     case MINMAX_PRIMITIVE:
     case MINMAX_COMPARABLE:
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetMemberOfOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetMemberOfOperator.java
index ebff588c652..1d51fb74719 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetMemberOfOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetMemberOfOperator.java
@@ -51,7 +51,7 @@ public SqlMultisetMemberOfOperator() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     if (!OperandTypes.MULTISET.checkSingleOperandType(
@@ -77,7 +77,7 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(2);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetQueryConstructor.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetQueryConstructor.java
index 72a76df26ec..2eaec975a9b 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetQueryConstructor.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetQueryConstructor.java
@@ -61,7 +61,7 @@ protected SqlMultisetQueryConstructor(String name, SqlKind kind) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     RelDataType type =
         getComponentType(
@@ -82,7 +82,7 @@ private RelDataType getComponentType(
     return typeFactory.leastRestrictive(argTypes);
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     final List<RelDataType> argTypes = SqlTypeUtil.deriveType(callBinding, callBinding.operands());
@@ -99,7 +99,7 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidator validator,
       SqlValidatorScope scope,
       SqlCall call) {
@@ -113,7 +113,7 @@ public RelDataType deriveType(
         false);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -125,7 +125,7 @@ public void unparse(
     writer.endList(frame);
   }
 
-  public boolean argumentMustBeScalar(int ordinal) {
+  @Override public boolean argumentMustBeScalar(int ordinal) {
     return false;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetValueConstructor.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetValueConstructor.java
index b4604b98c8a..d91f54e13f5 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetValueConstructor.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlMultisetValueConstructor.java
@@ -61,7 +61,7 @@ protected SqlMultisetValueConstructor(String name, SqlKind kind) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     RelDataType type =
         getComponentType(
@@ -82,7 +82,7 @@ protected RelDataType getComponentType(
     return typeFactory.leastRestrictive(argTypes);
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     final List<RelDataType> argTypes =
@@ -103,7 +103,7 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlNewOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlNewOperator.java
index 3370dd71851..f5e73849351 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlNewOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlNewOperator.java
@@ -39,14 +39,14 @@ public SqlNewOperator() {
   //~ Methods ----------------------------------------------------------------
 
   // override SqlOperator
-  public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
+  @Override public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
     // New specification is purely syntactic, so we rewrite it as a
     // direct call to the constructor method.
     return call.operand(0);
   }
 
   // override SqlOperator
-  public boolean requiresDecimalExpansion() {
+  @Override public boolean requiresDecimalExpansion() {
     return false;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlNullifFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlNullifFunction.java
index ec7380a2da9..b34e7d15866 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlNullifFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlNullifFunction.java
@@ -53,7 +53,7 @@ public SqlNullifFunction() {
   //~ Methods ----------------------------------------------------------------
 
   // override SqlOperator
-  public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
+  @Override public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
     List<SqlNode> operands = call.getOperandList();
     SqlParserPos pos = call.getParserPosition();
 
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlapsOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlapsOperator.java
index e45d2c2be7d..355f5c2ad5c 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlapsOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlapsOperator.java
@@ -73,11 +73,11 @@ void arg(SqlWriter writer, SqlCall call, int leftPrec, int rightPrec, int i) {
     }
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(2);
   }
 
-  public String getAllowedSignatures(String opName) {
+  @Override public String getAllowedSignatures(String opName) {
     final String d = "DATETIME";
     final String i = "INTERVAL";
     String[] typeNames = {
@@ -99,7 +99,7 @@ public String getAllowedSignatures(String opName) {
     return ret.toString();
   }
 
-  public boolean checkOperandTypes(SqlCallBinding callBinding,
+  @Override public boolean checkOperandTypes(SqlCallBinding callBinding,
       boolean throwOnFailure) {
     if (!OperandTypes.PERIOD.checkSingleOperandType(callBinding,
         callBinding.operand(0), 0, throwOnFailure)) {
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlayFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlayFunction.java
index 05d77c87c6e..9d991c196c1 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlayFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlOverlayFunction.java
@@ -50,7 +50,7 @@ public SqlOverlayFunction() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -68,7 +68,7 @@ public void unparse(
     writer.endFunCall(frame);
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     switch (operandsCount) {
     case 3:
       return "{0}({1} PLACING {2} FROM {3})";
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlPositionFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlPositionFunction.java
index a133bffd714..349715a1767 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlPositionFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlPositionFunction.java
@@ -52,7 +52,7 @@ public SqlPositionFunction() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -68,7 +68,7 @@ public void unparse(
     writer.endFunCall(frame);
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     switch (operandsCount) {
     case 2:
       return "{0}({1} IN {2})";
@@ -79,7 +79,7 @@ public String getSignatureTemplate(final int operandsCount) {
     }
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     // check that the two operands are of same type.
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlPosixRegexOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlPosixRegexOperator.java
index 232f94f0107..2e45a1c153a 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlPosixRegexOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlPosixRegexOperator.java
@@ -74,11 +74,11 @@ public class SqlPosixRegexOperator extends SqlBinaryOperator {
 
   // ~ Methods ----------------------------------------------------------------
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.between(2, 3);
   }
 
-  public SqlCall createCall(
+  @Override public SqlCall createCall(
       SqlLiteral functionQualifier,
       SqlParserPos pos,
       SqlNode... operands) {
@@ -88,7 +88,7 @@ public SqlCall createCall(
     return new SqlBasicCall(this, operands, pos, false, functionQualifier);
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     int operandCount = callBinding.getOperandCount();
@@ -111,7 +111,7 @@ public boolean checkOperandTypes(
         throwOnFailure);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlRandFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlRandFunction.java
index fe96d19845d..e8319e31a53 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlRandFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlRandFunction.java
@@ -46,12 +46,12 @@ public SqlRandFunction() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.FUNCTION;
   }
 
   // Plans referencing context variables should never be cached
-  public boolean isDynamicFunction() {
+  @Override public boolean isDynamicFunction() {
     return true;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlRandIntegerFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlRandIntegerFunction.java
index 384fb463f6f..1b27a17999e 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlRandIntegerFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlRandIntegerFunction.java
@@ -46,12 +46,12 @@ public SqlRandIntegerFunction() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlSyntax getSyntax() {
+  @Override public SqlSyntax getSyntax() {
     return SqlSyntax.FUNCTION;
   }
 
   // Plans referencing context variables should never be cached
-  public boolean isDynamicFunction() {
+  @Override public boolean isDynamicFunction() {
     return true;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlRowOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlRowOperator.java
index d48b03c1d4d..e83728c48f0 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlRowOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlRowOperator.java
@@ -51,26 +51,26 @@ public SqlRowOperator(String name) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       final SqlOperatorBinding opBinding) {
     // The type of a ROW(e1,e2) expression is a record with the types
     // {e1type,e2type}.  According to the standard, field names are
     // implementation-defined.
     return opBinding.getTypeFactory().createStructType(
         new AbstractList<Map.Entry<String, RelDataType>>() {
-          public Map.Entry<String, RelDataType> get(int index) {
+          @Override public Map.Entry<String, RelDataType> get(int index) {
             return Pair.of(
                 SqlUtil.deriveAliasFromOrdinal(index),
                 opBinding.getOperandType(index));
           }
 
-          public int size() {
+          @Override public int size() {
             return opBinding.getOperandCount();
           }
         });
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -79,7 +79,7 @@ public void unparse(
   }
 
   // override SqlOperator
-  public boolean requiresDecimalExpansion() {
+  @Override public boolean requiresDecimalExpansion() {
     return false;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlSingleValueAggFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlSingleValueAggFunction.java
index 85218260706..e234bd4841c 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlSingleValueAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlSingleValueAggFunction.java
@@ -64,12 +64,12 @@ public SqlSingleValueAggFunction(
   }
 
   @SuppressWarnings("deprecation")
-  public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
+  @Override public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
     return ImmutableList.of(type);
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return type;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
index c178607b78b..96fa7bfaa86 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
@@ -839,7 +839,7 @@ public class SqlStdOperatorTable extends ReflectiveSqlOperatorTable {
           ReturnTypes.BOOLEAN,
           null,
           OperandTypes.ANY) {
-        public boolean argumentMustBeScalar(int ordinal) {
+        @Override public boolean argumentMustBeScalar(int ordinal) {
           return false;
         }
 
@@ -1454,7 +1454,7 @@ public boolean argumentMustBeScalar(int ordinal) {
    */
   public static final SqlSpecialOperator REINTERPRET =
       new SqlSpecialOperator("Reinterpret", SqlKind.REINTERPRET) {
-        public SqlOperandCountRange getOperandCountRange() {
+        @Override public SqlOperandCountRange getOperandCountRange() {
           return SqlOperandCountRanges.between(1, 2);
         }
       };
@@ -1764,7 +1764,7 @@ public SqlOperandCountRange getOperandCountRange() {
           null,
           OperandTypes.NILADIC,
           SqlFunctionCategory.NUMERIC) {
-        public SqlSyntax getSyntax() {
+        @Override public SqlSyntax getSyntax() {
           return SqlSyntax.FUNCTION_ID;
         }
       };
@@ -2133,7 +2133,7 @@ public SqlSyntax getSyntax() {
           ReturnTypes.MULTISET_RECORD,
           null,
           OperandTypes.MULTISET) {
-        public void unparse(
+        @Override public void unparse(
             SqlWriter writer,
             SqlCall call,
             int leftPrec,
@@ -2158,7 +2158,7 @@ public void unparse(
           ReturnTypes.RECORD_TO_SCALAR,
           null,
           OperandTypes.RECORD_TO_SCALAR) {
-        public void unparse(
+        @Override public void unparse(
             SqlWriter writer,
             SqlCall call,
             int leftPrec,
@@ -2168,7 +2168,7 @@ public void unparse(
           writer.endList(frame);
         }
 
-        public boolean argumentMustBeScalar(int ordinal) {
+        @Override public boolean argumentMustBeScalar(int ordinal) {
           // Obvious, really.
           return false;
         }
@@ -2289,7 +2289,7 @@ public boolean argumentMustBeScalar(int ordinal) {
           ReturnTypes.ARG0,
           null,
           OperandTypes.VARIADIC) {
-        public void unparse(
+        @Override public void unparse(
             SqlWriter writer,
             SqlCall call,
             int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlSubstringFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlSubstringFunction.java
index 952c3e9af7f..9d3db136180 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlSubstringFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlSubstringFunction.java
@@ -63,7 +63,7 @@ public class SqlSubstringFunction extends SqlFunction {
 
   //~ Methods ----------------------------------------------------------------
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     switch (operandsCount) {
     case 2:
       return "{0}({1} FROM {2})";
@@ -74,7 +74,7 @@ public String getSignatureTemplate(final int operandsCount) {
     }
   }
 
-  public String getAllowedSignatures(String opName) {
+  @Override public String getAllowedSignatures(String opName) {
     StringBuilder ret = new StringBuilder();
     for (Ord<SqlTypeName> typeName : Ord.zip(SqlTypeName.STRING_TYPES)) {
       if (typeName.i > 0) {
@@ -92,7 +92,7 @@ public String getAllowedSignatures(String opName) {
     return ret.toString();
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     List<SqlNode> operands = callBinding.operands();
@@ -134,11 +134,11 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.between(2, 3);
   }
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlSumAggFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlSumAggFunction.java
index b6a9df67337..e02f4ac4aa3 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlSumAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlSumAggFunction.java
@@ -63,7 +63,7 @@ public SqlSumAggFunction(RelDataType type) {
   //~ Methods ----------------------------------------------------------------
 
   @SuppressWarnings("deprecation")
-  public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
+  @Override public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
     return ImmutableList.of(type);
   }
 
@@ -73,7 +73,7 @@ public RelDataType getType() {
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return type;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlSumEmptyIsZeroAggFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlSumEmptyIsZeroAggFunction.java
index 206303bc820..277e22a5048 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlSumEmptyIsZeroAggFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlSumEmptyIsZeroAggFunction.java
@@ -56,14 +56,14 @@ public SqlSumEmptyIsZeroAggFunction() {
   //~ Methods ----------------------------------------------------------------
 
   @SuppressWarnings("deprecation")
-  public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
+  @Override public List<RelDataType> getParameterTypes(RelDataTypeFactory typeFactory) {
     return ImmutableList.of(
         typeFactory.createTypeWithNullability(
             typeFactory.createSqlType(SqlTypeName.ANY), true));
   }
 
   @SuppressWarnings("deprecation")
-  public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
     return typeFactory.createTypeWithNullability(
         typeFactory.createSqlType(SqlTypeName.ANY), true);
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlThrowOperator.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlThrowOperator.java
index fac830bd2aa..61c90b0b838 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlThrowOperator.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlThrowOperator.java
@@ -53,7 +53,7 @@ public SqlThrowOperator() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlTrimFunction.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlTrimFunction.java
index aff3235e09e..0594dfe92df 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlTrimFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlTrimFunction.java
@@ -95,7 +95,7 @@ public SqlTrimFunction(String name, SqlKind kind,
 
   //~ Methods ----------------------------------------------------------------
 
-  public void unparse(
+  @Override public void unparse(
       SqlWriter writer,
       SqlCall call,
       int leftPrec,
@@ -109,7 +109,7 @@ public void unparse(
     writer.endFunCall(frame);
   }
 
-  public String getSignatureTemplate(final int operandsCount) {
+  @Override public String getSignatureTemplate(final int operandsCount) {
     switch (operandsCount) {
     case 3:
       return "{0}([BOTH|LEADING|TRAILING] {1} FROM {2})";
@@ -118,7 +118,7 @@ public String getSignatureTemplate(final int operandsCount) {
     }
   }
 
-  public SqlCall createCall(
+  @Override public SqlCall createCall(
       SqlLiteral functionQualifier,
       SqlParserPos pos,
       SqlNode... operands) {
@@ -147,7 +147,7 @@ public SqlCall createCall(
     return super.createCall(functionQualifier, pos, operands);
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     if (!super.checkOperandTypes(callBinding, throwOnFailure)) {
diff --git a/core/src/main/java/org/apache/calcite/sql/parser/SqlAbstractParserImpl.java b/core/src/main/java/org/apache/calcite/sql/parser/SqlAbstractParserImpl.java
index 4350bdd6e9b..aa8c65d5a01 100644
--- a/core/src/main/java/org/apache/calcite/sql/parser/SqlAbstractParserImpl.java
+++ b/core/src/main/java/org/apache/calcite/sql/parser/SqlAbstractParserImpl.java
@@ -745,18 +745,22 @@ private String constructSql92ReservedWordList() {
       return sb.toString();
     }
 
+    @Override
     public List<String> getTokens() {
       return tokenList;
     }
 
+    @Override
     public boolean isSql92ReservedWord(String token) {
       return SQL_92_RESERVED_WORD_SET.contains(token);
     }
 
+    @Override
     public String getJdbcKeywords() {
       return sql92ReservedWords;
     }
 
+    @Override
     public boolean isKeyword(String token) {
       return isNonReservedKeyword(token)
           || isReservedFunctionName(token)
@@ -764,18 +768,22 @@ public boolean isKeyword(String token) {
           || isReservedWord(token);
     }
 
+    @Override
     public boolean isNonReservedKeyword(String token) {
       return nonReservedKeyWordSet.contains(token);
     }
 
+    @Override
     public boolean isReservedFunctionName(String token) {
       return reservedFunctionNames.contains(token);
     }
 
+    @Override
     public boolean isContextVariableName(String token) {
       return contextVariableNames.contains(token);
     }
 
+    @Override
     public boolean isReservedWord(String token) {
       return reservedWords.contains(token);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/parser/SqlParseException.java b/core/src/main/java/org/apache/calcite/sql/parser/SqlParseException.java
index cb5d562a6ad..bba8b93d5d5 100644
--- a/core/src/main/java/org/apache/calcite/sql/parser/SqlParseException.java
+++ b/core/src/main/java/org/apache/calcite/sql/parser/SqlParseException.java
@@ -154,7 +154,7 @@ public int[][] getExpectedTokenSequences() {
   }
 
   // override Exception
-  public Throwable getCause() {
+  @Override public Throwable getCause() {
     return parserException;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/parser/SqlParserPos.java b/core/src/main/java/org/apache/calcite/sql/parser/SqlParserPos.java
index e5e94eb8164..d2eacec767f 100644
--- a/core/src/main/java/org/apache/calcite/sql/parser/SqlParserPos.java
+++ b/core/src/main/java/org/apache/calcite/sql/parser/SqlParserPos.java
@@ -85,11 +85,11 @@ public SqlParserPos(
 
   //~ Methods ----------------------------------------------------------------
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return Objects.hash(lineNumber, columnNumber, endLineNumber, endColumnNumber);
   }
 
-  public boolean equals(Object o) {
+  @Override public boolean equals(Object o) {
     return o == this
         || o instanceof SqlParserPos
         && this.lineNumber == ((SqlParserPos) o).lineNumber
@@ -185,10 +185,10 @@ public static SqlParserPos sum(final SqlNode[] nodes) {
 
   private static List<SqlParserPos> toPos(final SqlNode[] nodes) {
     return new AbstractList<SqlParserPos>() {
-      public SqlParserPos get(int index) {
+      @Override public SqlParserPos get(int index) {
         return nodes[index].getParserPosition();
       }
-      public int size() {
+      @Override public int size() {
         return nodes.length;
       }
     };
@@ -230,10 +230,10 @@ private static SqlParserPos sum_(final List<SqlParserPos> positions) {
       return positions.get(0);
     default:
       final List<SqlParserPos> poses = new AbstractList<SqlParserPos>() {
-        public SqlParserPos get(int index) {
+        @Override public SqlParserPos get(int index) {
           return positions.get(index + 1);
         }
-        public int size() {
+        @Override public int size() {
           return positions.size() - 1;
         }
       };
diff --git a/core/src/main/java/org/apache/calcite/sql/parser/SqlParserUtil.java b/core/src/main/java/org/apache/calcite/sql/parser/SqlParserUtil.java
index 8208bc035b9..6d6393338ff 100644
--- a/core/src/main/java/org/apache/calcite/sql/parser/SqlParserUtil.java
+++ b/core/src/main/java/org/apache/calcite/sql/parser/SqlParserUtil.java
@@ -771,7 +771,7 @@ public ToTreeListItem(
       this.pos = pos;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return op.toString();
     }
 
@@ -797,16 +797,16 @@ private TokenSequenceImpl(PrecedenceClimbingParser parser) {
       this.list = parser.all();
     }
 
-    public PrecedenceClimbingParser parser(int start,
+    @Override public PrecedenceClimbingParser parser(int start,
         Predicate<PrecedenceClimbingParser.Token> predicate) {
       return parser.copy(start, predicate);
     }
 
-    public int size() {
+    @Override public int size() {
       return list.size();
     }
 
-    public SqlOperator op(int i) {
+    @Override public SqlOperator op(int i) {
       return ((ToTreeListItem) list.get(i).o).getOperator();
     }
 
@@ -827,19 +827,19 @@ private static SqlParserPos pos(PrecedenceClimbingParser.Token token) {
       }
     }
 
-    public SqlParserPos pos(int i) {
+    @Override public SqlParserPos pos(int i) {
       return pos(list.get(i));
     }
 
-    public boolean isOp(int i) {
+    @Override public boolean isOp(int i) {
       return list.get(i).o instanceof ToTreeListItem;
     }
 
-    public SqlNode node(int i) {
+    @Override public SqlNode node(int i) {
       return convert(list.get(i));
     }
 
-    public void replaceSublist(int start, int end, SqlNode e) {
+    @Override public void replaceSublist(int start, int end, SqlNode e) {
       SqlParserUtil.replaceSublist(list, start, end, parser.atom(e));
     }
   }
@@ -894,30 +894,30 @@ private OldTokenSequenceImpl(List<Object> list) {
       return builder.build();
     }
 
-    public int size() {
+    @Override public int size() {
       return list.size();
     }
 
-    public SqlOperator op(int i) {
+    @Override public SqlOperator op(int i) {
       return ((ToTreeListItem) list.get(i)).op;
     }
 
-    public SqlParserPos pos(int i) {
+    @Override public SqlParserPos pos(int i) {
       final Object o = list.get(i);
       return o instanceof ToTreeListItem
           ? ((ToTreeListItem) o).pos
           : ((SqlNode) o).getParserPosition();
     }
 
-    public boolean isOp(int i) {
+    @Override public boolean isOp(int i) {
       return list.get(i) instanceof ToTreeListItem;
     }
 
-    public SqlNode node(int i) {
+    @Override public SqlNode node(int i) {
       return (SqlNode) list.get(i);
     }
 
-    public void replaceSublist(int start, int end, SqlNode e) {
+    @Override public void replaceSublist(int start, int end, SqlNode e) {
       SqlParserUtil.replaceSublist(list, start, end, e);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/pretty/SqlPrettyWriter.java b/core/src/main/java/org/apache/calcite/sql/pretty/SqlPrettyWriter.java
index 8d04713bb9b..5297d57ff8f 100644
--- a/core/src/main/java/org/apache/calcite/sql/pretty/SqlPrettyWriter.java
+++ b/core/src/main/java/org/apache/calcite/sql/pretty/SqlPrettyWriter.java
@@ -377,16 +377,16 @@ public void setWindowDeclListNewline(boolean windowDeclListNewline) {
   }
 
   @Deprecated
-  public int getIndentation() {
+  @Override public int getIndentation() {
     return config.indentation();
   }
 
   @Deprecated
-  public boolean isAlwaysUseParentheses() {
+  @Override public boolean isAlwaysUseParentheses() {
     return config.alwaysUseParentheses();
   }
 
-  public boolean inQuery() {
+  @Override public boolean inQuery() {
     return (frame == null)
         || (frame.frameType == FrameTypeEnum.ORDER_BY)
         || (frame.frameType == FrameTypeEnum.WITH)
@@ -394,17 +394,17 @@ public boolean inQuery() {
   }
 
   @Deprecated
-  public boolean isQuoteAllIdentifiers() {
+  @Override public boolean isQuoteAllIdentifiers() {
     return config.quoteAllIdentifiers();
   }
 
   @Deprecated
-  public boolean isClauseStartsLine() {
+  @Override public boolean isClauseStartsLine() {
     return config.clauseStartsLine();
   }
 
   @Deprecated
-  public boolean isSelectListItemsOnSeparateLines() {
+  @Override public boolean isSelectListItemsOnSeparateLines() {
     return config.selectListItemsOnSeparateLines();
   }
 
@@ -419,7 +419,7 @@ public boolean isSelectListExtraIndentFlag() {
   }
 
   @Deprecated
-  public boolean isKeywordsLowerCase() {
+  @Override public boolean isKeywordsLowerCase() {
     return config.keywordsLowerCase();
   }
 
@@ -428,12 +428,12 @@ public int getLineLength() {
     return config.lineLength();
   }
 
-  public void resetSettings() {
+  @Override public void resetSettings() {
     reset();
     config = config();
   }
 
-  public void reset() {
+  @Override public void reset() {
     buf.setLength(0);
     lineStart = 0;
     dynamicParameters = null;
@@ -528,7 +528,7 @@ public void setAlwaysUseParentheses(boolean alwaysUseParentheses) {
     this.config = config.withAlwaysUseParentheses(alwaysUseParentheses);
   }
 
-  public void newlineAndIndent() {
+  @Override public void newlineAndIndent() {
     newlineAndIndent(currentIndent);
   }
 
@@ -749,7 +749,7 @@ protected void _before() {
       return new FrameImpl(frameType, keyword, open, close, left,
           indentation, chopColumn, lineFolding, newlineAfterOpen,
           newlineBeforeSep, sepIndent, newlineAfterSep, false, false) {
-        protected void sep(boolean printFirst, String sep) {
+        @Override protected void sep(boolean printFirst, String sep) {
           final boolean newlineBeforeSep;
           final boolean newlineAfterSep;
           if (sep.equals(",")) {
@@ -866,7 +866,7 @@ protected Frame startList(
     return frame;
   }
 
-  public void endList(Frame frame) {
+  @Override public void endList(Frame frame) {
     FrameImpl endedFrame = (FrameImpl) frame;
     Preconditions.checkArgument(frame == this.frame,
         "Frame does not match current frame");
@@ -903,26 +903,26 @@ public String format(SqlNode node) {
     return toString();
   }
 
-  public String toString() {
+  @Override public String toString() {
     return buf.toString();
   }
 
-  public SqlString toSqlString() {
+  @Override public SqlString toSqlString() {
     ImmutableList<Integer> dynamicParameters =
         this.dynamicParameters == null ? null : this.dynamicParameters.build();
     return new SqlString(dialect, toString(), dynamicParameters);
   }
 
-  public SqlDialect getDialect() {
+  @Override public SqlDialect getDialect() {
     return dialect;
   }
 
-  public void literal(String s) {
+  @Override public void literal(String s) {
     print(s);
     setNeedWhitespace(true);
   }
 
-  public void keyword(String s) {
+  @Override public void keyword(String s) {
     maybeWhitespace(s);
     buf.append(
         isKeywordsLowerCase()
@@ -984,17 +984,17 @@ protected boolean tooLong(String s) {
     return result;
   }
 
-  public void print(String s) {
+  @Override public void print(String s) {
     maybeWhitespace(s);
     buf.append(s);
   }
 
-  public void print(int x) {
+  @Override public void print(int x) {
     maybeWhitespace("0");
     buf.append(x);
   }
 
-  public void identifier(String name, boolean quoted) {
+  @Override public void identifier(String name, boolean quoted) {
     // If configured globally or the original identifier is quoted,
     // then quotes the identifier.
     maybeWhitespace(name);
@@ -1015,45 +1015,45 @@ public void identifier(String name, boolean quoted) {
     setNeedWhitespace(true);
   }
 
-  public void fetchOffset(SqlNode fetch, SqlNode offset) {
+  @Override public void fetchOffset(SqlNode fetch, SqlNode offset) {
     if (fetch == null && offset == null) {
       return;
     }
     dialect.unparseOffsetFetch(this, offset, fetch);
   }
 
-  public void topN(SqlNode fetch, SqlNode offset) {
+  @Override public void topN(SqlNode fetch, SqlNode offset) {
     if (fetch == null && offset == null) {
       return;
     }
     dialect.unparseTopN(this, offset, fetch);
   }
 
-  public Frame startFunCall(String funName) {
+  @Override public Frame startFunCall(String funName) {
     keyword(funName);
     setNeedWhitespace(false);
     return startList(FrameTypeEnum.FUN_CALL, "(", ")");
   }
 
-  public void endFunCall(Frame frame) {
+  @Override public void endFunCall(Frame frame) {
     endList(this.frame);
   }
 
-  public Frame startList(String open, String close) {
+  @Override public Frame startList(String open, String close) {
     return startList(FrameTypeEnum.SIMPLE, null, open, close);
   }
 
-  public Frame startList(FrameTypeEnum frameType) {
+  @Override public Frame startList(FrameTypeEnum frameType) {
     assert frameType != null;
     return startList(frameType, null, "", "");
   }
 
-  public Frame startList(FrameType frameType, String open, String close) {
+  @Override public Frame startList(FrameType frameType, String open, String close) {
     assert frameType != null;
     return startList(frameType, null, open, close);
   }
 
-  public SqlWriter list(FrameTypeEnum frameType, Consumer<SqlWriter> action) {
+  @Override public SqlWriter list(FrameTypeEnum frameType, Consumer<SqlWriter> action) {
     final SqlWriter.Frame selectListFrame =
         startList(SqlWriter.FrameTypeEnum.SELECT_LIST);
     final SqlWriter w = this;
@@ -1062,7 +1062,7 @@ public SqlWriter list(FrameTypeEnum frameType, Consumer<SqlWriter> action) {
     return this;
   }
 
-  public SqlWriter list(FrameTypeEnum frameType, SqlBinaryOperator sepOp,
+  @Override public SqlWriter list(FrameTypeEnum frameType, SqlBinaryOperator sepOp,
       SqlNodeList list) {
     final SqlWriter.Frame frame = startList(frameType);
     ((FrameImpl) frame).list(list, sepOp);
@@ -1070,11 +1070,11 @@ public SqlWriter list(FrameTypeEnum frameType, SqlBinaryOperator sepOp,
     return this;
   }
 
-  public void sep(String sep) {
+  @Override public void sep(String sep) {
     sep(sep, !(sep.equals(",") || sep.equals(".")));
   }
 
-  public void sep(String sep, boolean printFirst) {
+  @Override public void sep(String sep, boolean printFirst) {
     if (frame == null) {
       throw new RuntimeException("No list started");
     }
@@ -1084,7 +1084,7 @@ public void sep(String sep, boolean printFirst) {
     frame.sep(printFirst, sep);
   }
 
-  public void setNeedWhitespace(boolean needWhitespace) {
+  @Override public void setNeedWhitespace(boolean needWhitespace) {
     this.needWhitespace = needWhitespace;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/type/ArraySqlType.java b/core/src/main/java/org/apache/calcite/sql/type/ArraySqlType.java
index a749c8c4775..c1bb983ec06 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/ArraySqlType.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/ArraySqlType.java
@@ -45,7 +45,7 @@ public ArraySqlType(RelDataType elementType, boolean isNullable) {
   //~ Methods ----------------------------------------------------------------
 
   // implement RelDataTypeImpl
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     if (withDetail) {
       sb.append(elementType.getFullTypeString());
     } else {
@@ -55,25 +55,25 @@ protected void generateTypeString(StringBuilder sb, boolean withDetail) {
   }
 
   // implement RelDataType
-  public RelDataType getComponentType() {
+  @Override public RelDataType getComponentType() {
     return elementType;
   }
 
   // implement RelDataType
-  public RelDataTypeFamily getFamily() {
+  @Override public RelDataTypeFamily getFamily() {
     return this;
   }
 
   @Override public RelDataTypePrecedenceList getPrecedenceList() {
     return new RelDataTypePrecedenceList() {
-      public boolean containsType(RelDataType type) {
+      @Override public boolean containsType(RelDataType type) {
         return type.getSqlTypeName() == getSqlTypeName()
             && type.getComponentType() != null
             && getComponentType().getPrecedenceList().containsType(
                 type.getComponentType());
       }
 
-      public int compareTypePrecedence(RelDataType type1, RelDataType type2) {
+      @Override public int compareTypePrecedence(RelDataType type1, RelDataType type2) {
         if (!containsType(type1)) {
           throw new IllegalArgumentException("must contain type: " + type1);
         }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/AssignableOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/AssignableOperandTypeChecker.java
index 5db711fb8f9..b00ad7ffa76 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/AssignableOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/AssignableOperandTypeChecker.java
@@ -57,15 +57,15 @@ public AssignableOperandTypeChecker(List<RelDataType> paramTypes,
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     return false;
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(paramTypes.size());
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     // Do not use callBinding.operands(). We have not resolved to a function
@@ -85,7 +85,7 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     StringBuilder sb = new StringBuilder();
     sb.append(opName);
     sb.append("(");
@@ -105,7 +105,7 @@ public String getAllowedSignatures(SqlOperator op, String opName) {
     return sb.toString();
   }
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/BasicSqlType.java b/core/src/main/java/org/apache/calcite/sql/type/BasicSqlType.java
index bea494ecb86..90b41cf7ea7 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/BasicSqlType.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/BasicSqlType.java
@@ -171,7 +171,7 @@ BasicSqlType createWithCharsetAndCollation(Charset charset,
   }
 
   // implement RelDataTypeImpl
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     // Called to make the digest, which equals() compares;
     // so equivalent data types must produce identical type strings.
 
diff --git a/core/src/main/java/org/apache/calcite/sql/type/ComparableOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/ComparableOperandTypeChecker.java
index a3a2b22a629..4983feb48d7 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/ComparableOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/ComparableOperandTypeChecker.java
@@ -51,7 +51,7 @@ public ComparableOperandTypeChecker(int nOperands,
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     boolean b = true;
@@ -98,7 +98,7 @@ private boolean checkType(
    * {@link #checkOperandTypes(SqlCallBinding, boolean)}, but not part of the
    * interface, and cannot throw an error.
    */
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlOperatorBinding operatorBinding, SqlCallBinding callBinding) {
     boolean b = true;
     for (int i = 0; i < nOperands; ++i) {
diff --git a/core/src/main/java/org/apache/calcite/sql/type/CompositeOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/CompositeOperandTypeChecker.java
index 4981ce98a2b..96dd97af50f 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/CompositeOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/CompositeOperandTypeChecker.java
@@ -108,7 +108,7 @@ public enum Composition {
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     for (SqlOperandTypeChecker allowedRule : allowedRules) {
       if (allowedRule.isOptional(i)) {
         return true;
@@ -121,11 +121,11 @@ public ImmutableList<? extends SqlOperandTypeChecker> getRules() {
     return allowedRules;
   }
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     if (allowedSignatures != null) {
       return allowedSignatures;
     }
@@ -147,7 +147,7 @@ public String getAllowedSignatures(SqlOperator op, String opName) {
     return ret.toString();
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     switch (composition) {
     case REPEAT:
       return range;
@@ -158,11 +158,11 @@ public SqlOperandCountRange getOperandCountRange() {
     default:
       final List<SqlOperandCountRange> ranges =
           new AbstractList<SqlOperandCountRange>() {
-            public SqlOperandCountRange get(int index) {
+            @Override public SqlOperandCountRange get(int index) {
               return allowedRules.get(index).getOperandCountRange();
             }
 
-            public int size() {
+            @Override public int size() {
               return allowedRules.size();
             }
           };
@@ -170,7 +170,7 @@ public int size() {
       final int max = maxMax(ranges);
       SqlOperandCountRange composite =
           new SqlOperandCountRange() {
-            public boolean isValidCount(int count) {
+            @Override public boolean isValidCount(int count) {
               switch (composition) {
               case AND:
                 for (SqlOperandCountRange range : ranges) {
@@ -190,11 +190,11 @@ public boolean isValidCount(int count) {
               }
             }
 
-            public int getMin() {
+            @Override public int getMin() {
               return min;
             }
 
-            public int getMax() {
+            @Override public int getMax() {
               return max;
             }
           };
@@ -235,7 +235,7 @@ private int maxMax(List<SqlOperandCountRange> ranges) {
     return max;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     // 1. Check eagerly for binary arithmetic expressions.
diff --git a/core/src/main/java/org/apache/calcite/sql/type/CompositeSingleOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/CompositeSingleOperandTypeChecker.java
index 8d03d00a085..d6748c6cbb9 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/CompositeSingleOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/CompositeSingleOperandTypeChecker.java
@@ -52,7 +52,7 @@ public class CompositeSingleOperandTypeChecker
     return (ImmutableList<? extends SqlSingleOperandTypeChecker>) allowedRules;
   }
 
-  public boolean checkSingleOperandType(
+  @Override public boolean checkSingleOperandType(
       SqlCallBinding callBinding,
       SqlNode node,
       int iFormalOperand,
diff --git a/core/src/main/java/org/apache/calcite/sql/type/CursorReturnTypeInference.java b/core/src/main/java/org/apache/calcite/sql/type/CursorReturnTypeInference.java
index f965ad376ed..69f92148089 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/CursorReturnTypeInference.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/CursorReturnTypeInference.java
@@ -38,7 +38,7 @@ public CursorReturnTypeInference(int ordinal) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     return opBinding.getCursorOperand(ordinal);
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeChecker.java
index f817724e9c3..14b247de71b 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeChecker.java
@@ -38,11 +38,11 @@ public ExplicitOperandTypeChecker(RelDataType type) {
     this.type = Objects.requireNonNull(type);
   }
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     return false;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     List<SqlTypeFamily> families = new ArrayList<>();
@@ -62,15 +62,15 @@ public boolean checkOperandTypes(
     return OperandTypes.family(families).checkOperandTypes(callBinding, throwOnFailure);
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(type.getFieldCount());
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     return "<TYPE> " + opName + " <TYPE>";
   }
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeInference.java b/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeInference.java
index 08d0ab6b275..c0bad4bdd52 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeInference.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/ExplicitOperandTypeInference.java
@@ -40,7 +40,7 @@ public class ExplicitOperandTypeInference implements SqlOperandTypeInference {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void inferOperandTypes(
+  @Override public void inferOperandTypes(
       SqlCallBinding callBinding,
       RelDataType returnType,
       RelDataType[] operandTypes) {
diff --git a/core/src/main/java/org/apache/calcite/sql/type/ExplicitReturnTypeInference.java b/core/src/main/java/org/apache/calcite/sql/type/ExplicitReturnTypeInference.java
index e64b1a324f4..f3b6392e50b 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/ExplicitReturnTypeInference.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/ExplicitReturnTypeInference.java
@@ -51,7 +51,7 @@ protected ExplicitReturnTypeInference(RelProtoDataType protoType) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(SqlOperatorBinding opBinding) {
+  @Override public RelDataType inferReturnType(SqlOperatorBinding opBinding) {
     return protoType.apply(opBinding.getTypeFactory());
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/FamilyOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/FamilyOperandTypeChecker.java
index 3910e307497..c8fe147e29d 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/FamilyOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/FamilyOperandTypeChecker.java
@@ -56,11 +56,11 @@ public class FamilyOperandTypeChecker implements SqlSingleOperandTypeChecker,
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     return optional.test(i);
   }
 
-  public boolean checkSingleOperandType(
+  @Override public boolean checkSingleOperandType(
       SqlCallBinding callBinding,
       SqlNode node,
       int iFormalOperand,
@@ -110,7 +110,7 @@ public boolean checkSingleOperandType(
     return true;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     if (families.size() != callBinding.getOperandCount()) {
@@ -175,7 +175,7 @@ public boolean checkOperandTypes(
     return families.get(iFormalOperand);
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     final int max = families.size();
     int min = max;
     while (min > 0 && optional.test(min - 1)) {
@@ -184,11 +184,11 @@ public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.between(min, max);
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     return SqlUtil.getAliasedSignature(op, opName, families);
   }
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/IntervalSqlType.java b/core/src/main/java/org/apache/calcite/sql/type/IntervalSqlType.java
index c58240c3b27..203db2f6413 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/IntervalSqlType.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/IntervalSqlType.java
@@ -56,7 +56,7 @@ public IntervalSqlType(RelDataTypeSystem typeSystem,
 
   //~ Methods ----------------------------------------------------------------
 
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     sb.append("INTERVAL ");
     final SqlDialect dialect = AnsiSqlDialect.DEFAULT;
     final SqlWriterConfig config = SqlPrettyWriter.config()
diff --git a/core/src/main/java/org/apache/calcite/sql/type/LiteralOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/LiteralOperandTypeChecker.java
index 47265441845..771714965ae 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/LiteralOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/LiteralOperandTypeChecker.java
@@ -44,11 +44,11 @@ public LiteralOperandTypeChecker(boolean allowNull) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     return false;
   }
 
-  public boolean checkSingleOperandType(
+  @Override public boolean checkSingleOperandType(
       SqlCallBinding callBinding,
       SqlNode node,
       int iFormalOperand,
@@ -78,7 +78,7 @@ public boolean checkSingleOperandType(
     return true;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     return checkSingleOperandType(
@@ -88,15 +88,15 @@ public boolean checkOperandTypes(
         throwOnFailure);
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(1);
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     return "<LITERAL>";
   }
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/MapSqlType.java b/core/src/main/java/org/apache/calcite/sql/type/MapSqlType.java
index 551940577ba..7ca3b1343a6 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/MapSqlType.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/MapSqlType.java
@@ -55,7 +55,7 @@ public MapSqlType(
   }
 
   // implement RelDataTypeImpl
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     sb.append("(")
         .append(
             withDetail
@@ -70,7 +70,7 @@ protected void generateTypeString(StringBuilder sb, boolean withDetail) {
   }
 
   // implement RelDataType
-  public RelDataTypeFamily getFamily() {
+  @Override public RelDataTypeFamily getFamily() {
     return this;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/MatchReturnTypeInference.java b/core/src/main/java/org/apache/calcite/sql/type/MatchReturnTypeInference.java
index 832ba2bf944..a8465506fbe 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/MatchReturnTypeInference.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/MatchReturnTypeInference.java
@@ -59,7 +59,7 @@ public MatchReturnTypeInference(int start, Iterable<SqlTypeName> typeNames) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     for (int i = start; i < opBinding.getOperandCount(); i++) {
       RelDataType argType = opBinding.getOperandType(i);
diff --git a/core/src/main/java/org/apache/calcite/sql/type/MultisetOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/MultisetOperandTypeChecker.java
index 0e728c888dd..57c3ffe6d4e 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/MultisetOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/MultisetOperandTypeChecker.java
@@ -35,11 +35,11 @@
 public class MultisetOperandTypeChecker implements SqlOperandTypeChecker {
   //~ Methods ----------------------------------------------------------------
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     return false;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     final SqlNode op0 = callBinding.operand(0);
@@ -82,15 +82,15 @@ public boolean checkOperandTypes(
     return true;
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(2);
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     return "<MULTISET> " + opName + " <MULTISET>";
   }
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/MultisetSqlType.java b/core/src/main/java/org/apache/calcite/sql/type/MultisetSqlType.java
index b43971cfc10..1bb70eef390 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/MultisetSqlType.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/MultisetSqlType.java
@@ -44,7 +44,7 @@ public MultisetSqlType(RelDataType elementType, boolean isNullable) {
   //~ Methods ----------------------------------------------------------------
 
   // implement RelDataTypeImpl
-  protected void generateTypeString(StringBuilder sb, boolean withDetail) {
+  @Override protected void generateTypeString(StringBuilder sb, boolean withDetail) {
     if (withDetail) {
       sb.append(elementType.getFullTypeString());
     } else {
@@ -54,12 +54,12 @@ protected void generateTypeString(StringBuilder sb, boolean withDetail) {
   }
 
   // implement RelDataType
-  public RelDataType getComponentType() {
+  @Override public RelDataType getComponentType() {
     return elementType;
   }
 
   // implement RelDataType
-  public RelDataTypeFamily getFamily() {
+  @Override public RelDataTypeFamily getFamily() {
     // TODO jvs 2-Dec-2004:  This gives each multiset type its
     // own family.  But that's not quite correct; the family should
     // be based on the element type for proper comparability
@@ -72,14 +72,14 @@ public RelDataTypeFamily getFamily() {
 
   @Override public RelDataTypePrecedenceList getPrecedenceList() {
     return new RelDataTypePrecedenceList() {
-      public boolean containsType(RelDataType type) {
+      @Override public boolean containsType(RelDataType type) {
         return type.getSqlTypeName() == getSqlTypeName()
             && type.getComponentType() != null
             && getComponentType().getPrecedenceList().containsType(
                 type.getComponentType());
       }
 
-      public int compareTypePrecedence(RelDataType type1, RelDataType type2) {
+      @Override public int compareTypePrecedence(RelDataType type1, RelDataType type2) {
         if (!containsType(type1)) {
           throw new IllegalArgumentException("must contain type: " + type1);
         }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/OperandTypes.java b/core/src/main/java/org/apache/calcite/sql/type/OperandTypes.java
index abb6fb87868..e0e1353147b 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/OperandTypes.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/OperandTypes.java
@@ -186,25 +186,25 @@ public static SqlOperandTypeChecker repeat(SqlOperandCountRange range,
   public static SqlOperandTypeChecker variadic(
       final SqlOperandCountRange range) {
     return new SqlOperandTypeChecker() {
-      public boolean checkOperandTypes(
+      @Override public boolean checkOperandTypes(
           SqlCallBinding callBinding,
           boolean throwOnFailure) {
         return range.isValidCount(callBinding.getOperandCount());
       }
 
-      public SqlOperandCountRange getOperandCountRange() {
+      @Override public SqlOperandCountRange getOperandCountRange() {
         return range;
       }
 
-      public String getAllowedSignatures(SqlOperator op, String opName) {
+      @Override public String getAllowedSignatures(SqlOperator op, String opName) {
         return opName + "(...)";
       }
 
-      public boolean isOptional(int i) {
+      @Override public boolean isOptional(int i) {
         return false;
       }
 
-      public Consistency getConsistency() {
+      @Override public Consistency getConsistency() {
         return Consistency.NONE;
       }
     };
@@ -319,7 +319,7 @@ public Consistency getConsistency() {
   public static final SqlSingleOperandTypeChecker POSITIVE_INTEGER_LITERAL =
       new FamilyOperandTypeChecker(ImmutableList.of(SqlTypeFamily.INTEGER),
           i -> false) {
-        public boolean checkSingleOperandType(
+        @Override public boolean checkSingleOperandType(
             SqlCallBinding callBinding,
             SqlNode node,
             int iFormalOperand,
@@ -532,7 +532,7 @@ private boolean hasFractionalPart(BigDecimal bd) {
           ImmutableList.of(SqlTypeFamily.DATETIME, SqlTypeFamily.DATETIME,
               SqlTypeFamily.DATETIME_INTERVAL),
           i -> false) {
-        public boolean checkOperandTypes(
+        @Override public boolean checkOperandTypes(
             SqlCallBinding callBinding,
             boolean throwOnFailure) {
           if (!super.checkOperandTypes(callBinding, throwOnFailure)) {
@@ -575,7 +575,7 @@ private RecordTypeWithOneFieldChecker(Predicate<SqlTypeName> predicate) {
       this.typeNamePredicate = predicate;
     }
 
-    public boolean checkSingleOperandType(
+    @Override public boolean checkSingleOperandType(
         SqlCallBinding callBinding,
         SqlNode node,
         int iFormalOperand,
@@ -601,7 +601,7 @@ public boolean checkSingleOperandType(
       return !validationError;
     }
 
-    public boolean checkOperandTypes(
+    @Override public boolean checkOperandTypes(
         SqlCallBinding callBinding,
         boolean throwOnFailure) {
       return checkSingleOperandType(
@@ -611,15 +611,15 @@ public boolean checkOperandTypes(
           throwOnFailure);
     }
 
-    public SqlOperandCountRange getOperandCountRange() {
+    @Override public SqlOperandCountRange getOperandCountRange() {
       return SqlOperandCountRanges.of(1);
     }
 
-    public boolean isOptional(int i) {
+    @Override public boolean isOptional(int i) {
       return false;
     }
 
-    public Consistency getConsistency() {
+    @Override public Consistency getConsistency() {
       return Consistency.NONE;
     }
   }
@@ -654,7 +654,7 @@ public Consistency getConsistency() {
 
   public static final SqlOperandTypeChecker RECORD_TO_SCALAR =
       new SqlSingleOperandTypeChecker() {
-        public boolean checkSingleOperandType(
+        @Override public boolean checkSingleOperandType(
             SqlCallBinding callBinding,
             SqlNode node,
             int iFormalOperand,
@@ -674,7 +674,7 @@ public boolean checkSingleOperandType(
           return !validationError;
         }
 
-        public boolean checkOperandTypes(
+        @Override public boolean checkOperandTypes(
             SqlCallBinding callBinding,
             boolean throwOnFailure) {
           return checkSingleOperandType(
@@ -684,20 +684,20 @@ public boolean checkOperandTypes(
               throwOnFailure);
         }
 
-        public SqlOperandCountRange getOperandCountRange() {
+        @Override public SqlOperandCountRange getOperandCountRange() {
           return SqlOperandCountRanges.of(1);
         }
 
-        public String getAllowedSignatures(SqlOperator op, String opName) {
+        @Override public String getAllowedSignatures(SqlOperator op, String opName) {
           return SqlUtil.getAliasedSignature(op, opName,
               ImmutableList.of("RECORDTYPE(SINGLE FIELD)"));
         }
 
-        public boolean isOptional(int i) {
+        @Override public boolean isOptional(int i) {
           return false;
         }
 
-        public Consistency getConsistency() {
+        @Override public Consistency getConsistency() {
           return Consistency.NONE;
         }
       };
@@ -712,7 +712,7 @@ public Consistency getConsistency() {
    * </ul> */
   private static class PeriodOperandTypeChecker
       implements SqlSingleOperandTypeChecker {
-    public boolean checkSingleOperandType(SqlCallBinding callBinding,
+    @Override public boolean checkSingleOperandType(SqlCallBinding callBinding,
         SqlNode node, int iFormalOperand, boolean throwOnFailure) {
       assert 0 == iFormalOperand;
       RelDataType type = SqlTypeUtil.deriveType(callBinding, node);
@@ -738,27 +738,27 @@ public boolean checkSingleOperandType(SqlCallBinding callBinding,
       return valid;
     }
 
-    public boolean checkOperandTypes(SqlCallBinding callBinding,
+    @Override public boolean checkOperandTypes(SqlCallBinding callBinding,
         boolean throwOnFailure) {
       return checkSingleOperandType(callBinding, callBinding.operand(0), 0,
           throwOnFailure);
     }
 
-    public SqlOperandCountRange getOperandCountRange() {
+    @Override public SqlOperandCountRange getOperandCountRange() {
       return SqlOperandCountRanges.of(1);
     }
 
-    public String getAllowedSignatures(SqlOperator op, String opName) {
+    @Override public String getAllowedSignatures(SqlOperator op, String opName) {
       return SqlUtil.getAliasedSignature(op, opName,
           ImmutableList.of("PERIOD (DATETIME, INTERVAL)",
               "PERIOD (DATETIME, DATETIME)"));
     }
 
-    public boolean isOptional(int i) {
+    @Override public boolean isOptional(int i) {
       return false;
     }
 
-    public Consistency getConsistency() {
+    @Override public Consistency getConsistency() {
       return Consistency.NONE;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/OrdinalReturnTypeInference.java b/core/src/main/java/org/apache/calcite/sql/type/OrdinalReturnTypeInference.java
index 7c6c53fe550..8ef2670de02 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/OrdinalReturnTypeInference.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/OrdinalReturnTypeInference.java
@@ -35,7 +35,7 @@ public OrdinalReturnTypeInference(int ordinal) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     return opBinding.getOperandType(ordinal);
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java b/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java
index 98bfcb33fee..44ede214a6c 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java
@@ -384,7 +384,7 @@ public static ExplicitReturnTypeInference explicit(SqlTypeName typeName,
             opBinding,
             new AbstractList<RelDataType>() {
               // CHECKSTYLE: IGNORE 12
-              public RelDataType get(int index) {
+              @Override public RelDataType get(int index) {
                 RelDataType type =
                     opBinding.getOperandType(index)
                         .getComponentType();
@@ -392,7 +392,7 @@ public RelDataType get(int index) {
                 return type;
               }
 
-              public int size() {
+              @Override public int size() {
                 return opBinding.getOperandCount();
               }
             });
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeChecker.java
index fadd960e7cd..4087102d9fe 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeChecker.java
@@ -49,15 +49,15 @@ public SameOperandTypeChecker(
 
   //~ Methods ----------------------------------------------------------------
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     return false;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     return checkOperandTypesImpl(
@@ -118,7 +118,7 @@ public boolean checkOperandTypes(
   }
 
   // implement SqlOperandTypeChecker
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     if (nOperands == -1) {
       return SqlOperandCountRanges.any();
     } else {
@@ -126,7 +126,7 @@ public SqlOperandCountRange getOperandCountRange() {
     }
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     final String typeName = getTypeName();
     return SqlUtil.getAliasedSignature(op, opName,
         nOperands == -1
@@ -140,7 +140,7 @@ protected String getTypeName() {
     return "EQUIVALENT_TYPE";
   }
 
-  public boolean checkSingleOperandType(
+  @Override public boolean checkSingleOperandType(
       SqlCallBinding callBinding,
       SqlNode operand,
       int iFormalOperand,
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeExceptLastOperandChecker.java b/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeExceptLastOperandChecker.java
index 8896a0a4015..7c34c1e4a36 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeExceptLastOperandChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeExceptLastOperandChecker.java
@@ -47,7 +47,7 @@ public SameOperandTypeExceptLastOperandChecker(
 
   //~ Methods ----------------------------------------------------------------
 
-  protected boolean checkOperandTypesImpl(
+  @Override protected boolean checkOperandTypesImpl(
       SqlOperatorBinding operatorBinding,
       boolean throwOnFailure,
       SqlCallBinding callBinding) {
@@ -94,7 +94,7 @@ protected boolean checkOperandTypesImpl(
     return true;
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     final String typeName = getTypeName();
     if (nOperands == -1) {
       return SqlUtil.getAliasedSignature(op, opName,
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SetopOperandTypeChecker.java b/core/src/main/java/org/apache/calcite/sql/type/SetopOperandTypeChecker.java
index cc27d9bd878..05a11170466 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SetopOperandTypeChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SetopOperandTypeChecker.java
@@ -42,11 +42,11 @@
 public class SetopOperandTypeChecker implements SqlOperandTypeChecker {
   //~ Methods ----------------------------------------------------------------
 
-  public boolean isOptional(int i) {
+  @Override public boolean isOptional(int i) {
     return false;
   }
 
-  public boolean checkOperandTypes(
+  @Override public boolean checkOperandTypes(
       SqlCallBinding callBinding,
       boolean throwOnFailure) {
     assert callBinding.getOperandCount() == 2
@@ -100,12 +100,12 @@ public boolean checkOperandTypes(
       // and record type (f3: VARCHAR, f4: DECIMAL, f5: INT),
       // the list would be [[INT, VARCHAR], [BIGINT, DECIMAL], [VARCHAR, INT]].
       final List<RelDataType> columnIthTypes = new AbstractList<RelDataType>() {
-        public RelDataType get(int index) {
+        @Override public RelDataType get(int index) {
           return argTypes[index].getFieldList().get(i2)
               .getType();
         }
 
-        public int size() {
+        @Override public int size() {
           return argTypes.length;
         }
       };
@@ -143,15 +143,15 @@ public int size() {
     return true;
   }
 
-  public SqlOperandCountRange getOperandCountRange() {
+  @Override public SqlOperandCountRange getOperandCountRange() {
     return SqlOperandCountRanges.of(2);
   }
 
-  public String getAllowedSignatures(SqlOperator op, String opName) {
+  @Override public String getAllowedSignatures(SqlOperator op, String opName) {
     return "{0} " + opName + " {1}";
   }
 
-  public Consistency getConsistency() {
+  @Override public Consistency getConsistency() {
     return Consistency.NONE;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SqlOperandCountRanges.java b/core/src/main/java/org/apache/calcite/sql/type/SqlOperandCountRanges.java
index 63a7b615e4c..f8494e95f3f 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SqlOperandCountRanges.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SqlOperandCountRanges.java
@@ -52,15 +52,15 @@ private static class RangeImpl implements SqlOperandCountRange {
       Preconditions.checkArgument(min >= 0);
     }
 
-    public boolean isValidCount(int count) {
+    @Override public boolean isValidCount(int count) {
       return count >= min && (max == -1 || count <= max);
     }
 
-    public int getMin() {
+    @Override public int getMin() {
       return min;
     }
 
-    public int getMax() {
+    @Override public int getMax() {
       return max;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SqlReturnTypeInferenceChain.java b/core/src/main/java/org/apache/calcite/sql/type/SqlReturnTypeInferenceChain.java
index 67163d95187..213eba9f9ff 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SqlReturnTypeInferenceChain.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SqlReturnTypeInferenceChain.java
@@ -48,7 +48,7 @@ public class SqlReturnTypeInferenceChain implements SqlReturnTypeInference {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(SqlOperatorBinding opBinding) {
+  @Override public RelDataType inferReturnType(SqlOperatorBinding opBinding) {
     for (SqlReturnTypeInference rule : rules) {
       RelDataType ret = rule.inferReturnType(opBinding);
       if (ret != null) {
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeExplicitPrecedenceList.java b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeExplicitPrecedenceList.java
index bd4fee33984..45309971a3a 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeExplicitPrecedenceList.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeExplicitPrecedenceList.java
@@ -129,13 +129,13 @@ private static SqlTypeExplicitPrecedenceList numeric(SqlTypeName typeName) {
   }
 
   // implement RelDataTypePrecedenceList
-  public boolean containsType(RelDataType type) {
+  @Override public boolean containsType(RelDataType type) {
     SqlTypeName typeName = type.getSqlTypeName();
     return typeName != null && typeNames.contains(typeName);
   }
 
   // implement RelDataTypePrecedenceList
-  public int compareTypePrecedence(RelDataType type1, RelDataType type2) {
+  @Override public int compareTypePrecedence(RelDataType type1, RelDataType type2) {
     assert containsType(type1) : type1;
     assert containsType(type2) : type2;
 
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeFactoryImpl.java b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeFactoryImpl.java
index 7709985dbad..fecf939c9c0 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeFactoryImpl.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeFactoryImpl.java
@@ -41,7 +41,7 @@ public SqlTypeFactoryImpl(RelDataTypeSystem typeSystem) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType createSqlType(SqlTypeName typeName) {
+  @Override public RelDataType createSqlType(SqlTypeName typeName) {
     if (typeName.allowsPrec()) {
       return createSqlType(typeName, typeSystem.getDefaultPrecision(typeName));
     }
@@ -50,7 +50,7 @@ public RelDataType createSqlType(SqlTypeName typeName) {
     return canonize(newType);
   }
 
-  public RelDataType createSqlType(
+  @Override public RelDataType createSqlType(
       SqlTypeName typeName,
       int precision) {
     final int maxPrecision = typeSystem.getMaxPrecision(typeName);
@@ -71,7 +71,7 @@ public RelDataType createSqlType(
     return canonize(newType);
   }
 
-  public RelDataType createSqlType(
+  @Override public RelDataType createSqlType(
       SqlTypeName typeName,
       int precision,
       int scale) {
@@ -88,11 +88,11 @@ public RelDataType createSqlType(
     return canonize(newType);
   }
 
-  public RelDataType createUnknownType() {
+  @Override public RelDataType createUnknownType() {
     return canonize(new UnknownSqlType(this));
   }
 
-  public RelDataType createMultisetType(
+  @Override public RelDataType createMultisetType(
       RelDataType type,
       long maxCardinality) {
     assert maxCardinality == -1;
@@ -100,7 +100,7 @@ public RelDataType createMultisetType(
     return canonize(newType);
   }
 
-  public RelDataType createArrayType(
+  @Override public RelDataType createArrayType(
       RelDataType elementType,
       long maxCardinality) {
     assert maxCardinality == -1;
@@ -108,21 +108,21 @@ public RelDataType createArrayType(
     return canonize(newType);
   }
 
-  public RelDataType createMapType(
+  @Override public RelDataType createMapType(
       RelDataType keyType,
       RelDataType valueType) {
     MapSqlType newType = new MapSqlType(keyType, valueType, false);
     return canonize(newType);
   }
 
-  public RelDataType createSqlIntervalType(
+  @Override public RelDataType createSqlIntervalType(
       SqlIntervalQualifier intervalQualifier) {
     RelDataType newType =
         new IntervalSqlType(typeSystem, intervalQualifier, false);
     return canonize(newType);
   }
 
-  public RelDataType createTypeWithCharsetAndCollation(
+  @Override public RelDataType createTypeWithCharsetAndCollation(
       RelDataType type,
       Charset charset,
       SqlCollation collation) {
@@ -538,7 +538,7 @@ private RelDataType copyMapType(RelDataType type, boolean nullable) {
   }
 
   // override RelDataTypeFactoryImpl
-  protected RelDataType canonize(RelDataType type) {
+  @Override protected RelDataType canonize(RelDataType type) {
     type = super.canonize(type);
     if (!(type instanceof ObjectSqlType)) {
       return type;
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransformCascade.java b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransformCascade.java
index 474a0f0980f..2916cacb4a2 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransformCascade.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransformCascade.java
@@ -51,7 +51,7 @@ public SqlTypeTransformCascade(
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     RelDataType ret = rule.inferReturnType(opBinding);
     if (ret == null) {
diff --git a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransforms.java b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransforms.java
index 59125142eb3..4f3247fb237 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransforms.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/SqlTypeTransforms.java
@@ -100,7 +100,7 @@ public abstract class SqlTypeTransforms {
    */
   public static final SqlTypeTransform TO_VARYING =
       new SqlTypeTransform() {
-        public RelDataType transformType(
+        @Override public RelDataType transformType(
             SqlOperatorBinding opBinding,
             RelDataType typeToTransform) {
           switch (typeToTransform.getSqlTypeName()) {
diff --git a/core/src/main/java/org/apache/calcite/sql/type/TableFunctionReturnTypeInference.java b/core/src/main/java/org/apache/calcite/sql/type/TableFunctionReturnTypeInference.java
index 248a0e3afa2..ffe396e2fe4 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/TableFunctionReturnTypeInference.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/TableFunctionReturnTypeInference.java
@@ -61,7 +61,7 @@ public Set<RelColumnMapping> getColumnMappings() {
     return columnMappings;
   }
 
-  public RelDataType inferReturnType(
+  @Override public RelDataType inferReturnType(
       SqlOperatorBinding opBinding) {
     columnMappings = new HashSet<>();
     RelDataType unexpandedOutputType =
diff --git a/core/src/main/java/org/apache/calcite/sql/util/ChainedSqlOperatorTable.java b/core/src/main/java/org/apache/calcite/sql/util/ChainedSqlOperatorTable.java
index a85d025d543..4f8b4509bb1 100644
--- a/core/src/main/java/org/apache/calcite/sql/util/ChainedSqlOperatorTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/util/ChainedSqlOperatorTable.java
@@ -60,7 +60,7 @@ public void add(SqlOperatorTable table) {
     }
   }
 
-  public void lookupOperatorOverloads(SqlIdentifier opName,
+  @Override public void lookupOperatorOverloads(SqlIdentifier opName,
       SqlFunctionCategory category, SqlSyntax syntax,
       List<SqlOperator> operatorList, SqlNameMatcher nameMatcher) {
     for (SqlOperatorTable table : tableList) {
@@ -69,7 +69,7 @@ public void lookupOperatorOverloads(SqlIdentifier opName,
     }
   }
 
-  public List<SqlOperator> getOperatorList() {
+  @Override public List<SqlOperator> getOperatorList() {
     List<SqlOperator> list = new ArrayList<>();
     for (SqlOperatorTable table : tableList) {
       list.addAll(table.getOperatorList());
diff --git a/core/src/main/java/org/apache/calcite/sql/util/ListSqlOperatorTable.java b/core/src/main/java/org/apache/calcite/sql/util/ListSqlOperatorTable.java
index f9a9c31a6fc..f752565b3b4 100644
--- a/core/src/main/java/org/apache/calcite/sql/util/ListSqlOperatorTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/util/ListSqlOperatorTable.java
@@ -52,7 +52,7 @@ public void add(SqlOperator op) {
     operatorList.add(op);
   }
 
-  public void lookupOperatorOverloads(SqlIdentifier opName,
+  @Override public void lookupOperatorOverloads(SqlIdentifier opName,
       SqlFunctionCategory category,
       SqlSyntax syntax,
       List<SqlOperator> operatorList,
@@ -82,7 +82,7 @@ protected static SqlFunctionCategory category(SqlOperator operator) {
     }
   }
 
-  public List<SqlOperator> getOperatorList() {
+  @Override public List<SqlOperator> getOperatorList() {
     return operatorList;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/util/ReflectiveSqlOperatorTable.java b/core/src/main/java/org/apache/calcite/sql/util/ReflectiveSqlOperatorTable.java
index 158075a8aaf..246bc587e94 100644
--- a/core/src/main/java/org/apache/calcite/sql/util/ReflectiveSqlOperatorTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/util/ReflectiveSqlOperatorTable.java
@@ -84,7 +84,7 @@ public final void init() {
   }
 
   // implement SqlOperatorTable
-  public void lookupOperatorOverloads(SqlIdentifier opName,
+  @Override public void lookupOperatorOverloads(SqlIdentifier opName,
       SqlFunctionCategory category, SqlSyntax syntax,
       List<SqlOperator> operatorList, SqlNameMatcher nameMatcher) {
     // NOTE jvs 3-Mar-2005:  ignore category until someone cares
@@ -159,7 +159,7 @@ public void register(SqlOperator op) {
     caseInsensitiveOperators.put(new CaseInsensitiveKey(op.getName(), op.getSyntax()), op);
   }
 
-  public List<SqlOperator> getOperatorList() {
+  @Override public List<SqlOperator> getOperatorList() {
     return ImmutableList.copyOf(caseSensitiveOperators.values());
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/util/SqlBasicVisitor.java b/core/src/main/java/org/apache/calcite/sql/util/SqlBasicVisitor.java
index eac3b7e07ba..a0f04f8b5d5 100644
--- a/core/src/main/java/org/apache/calcite/sql/util/SqlBasicVisitor.java
+++ b/core/src/main/java/org/apache/calcite/sql/util/SqlBasicVisitor.java
@@ -37,15 +37,15 @@
 public class SqlBasicVisitor<R> implements SqlVisitor<R> {
   //~ Methods ----------------------------------------------------------------
 
-  public R visit(SqlLiteral literal) {
+  @Override public R visit(SqlLiteral literal) {
     return null;
   }
 
-  public R visit(SqlCall call) {
+  @Override public R visit(SqlCall call) {
     return call.getOperator().acceptCall(this, call);
   }
 
-  public R visit(SqlNodeList nodeList) {
+  @Override public R visit(SqlNodeList nodeList) {
     R result = null;
     for (int i = 0; i < nodeList.size(); i++) {
       SqlNode node = nodeList.get(i);
@@ -54,19 +54,19 @@ public R visit(SqlNodeList nodeList) {
     return result;
   }
 
-  public R visit(SqlIdentifier id) {
+  @Override public R visit(SqlIdentifier id) {
     return null;
   }
 
-  public R visit(SqlDataTypeSpec type) {
+  @Override public R visit(SqlDataTypeSpec type) {
     return null;
   }
 
-  public R visit(SqlDynamicParam param) {
+  @Override public R visit(SqlDynamicParam param) {
     return null;
   }
 
-  public R visit(SqlIntervalQualifier intervalQualifier) {
+  @Override public R visit(SqlIntervalQualifier intervalQualifier) {
     return null;
   }
 
@@ -108,11 +108,11 @@ public static <R> ArgHandler<R> instance() {
       return INSTANCE;
     }
 
-    public R result() {
+    @Override public R result() {
       return null;
     }
 
-    public R visitChild(
+    @Override public R visitChild(
         SqlVisitor<R> visitor,
         SqlNode expr,
         int i,
diff --git a/core/src/main/java/org/apache/calcite/sql/util/SqlShuttle.java b/core/src/main/java/org/apache/calcite/sql/util/SqlShuttle.java
index f9352e54ce3..a38d1b635e7 100644
--- a/core/src/main/java/org/apache/calcite/sql/util/SqlShuttle.java
+++ b/core/src/main/java/org/apache/calcite/sql/util/SqlShuttle.java
@@ -39,27 +39,27 @@
 public class SqlShuttle extends SqlBasicVisitor<SqlNode> {
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode visit(SqlLiteral literal) {
+  @Override public SqlNode visit(SqlLiteral literal) {
     return literal;
   }
 
-  public SqlNode visit(SqlIdentifier id) {
+  @Override public SqlNode visit(SqlIdentifier id) {
     return id;
   }
 
-  public SqlNode visit(SqlDataTypeSpec type) {
+  @Override public SqlNode visit(SqlDataTypeSpec type) {
     return type;
   }
 
-  public SqlNode visit(SqlDynamicParam param) {
+  @Override public SqlNode visit(SqlDynamicParam param) {
     return param;
   }
 
-  public SqlNode visit(SqlIntervalQualifier intervalQualifier) {
+  @Override public SqlNode visit(SqlIntervalQualifier intervalQualifier) {
     return intervalQualifier;
   }
 
-  public SqlNode visit(final SqlCall call) {
+  @Override public SqlNode visit(final SqlCall call) {
     // Handler creates a new copy of 'call' only if one or more operands
     // change.
     ArgHandler<SqlNode> argHandler = new CallCopyingArgHandler(call, false);
@@ -67,7 +67,7 @@ public SqlNode visit(final SqlCall call) {
     return argHandler.result();
   }
 
-  public SqlNode visit(SqlNodeList nodeList) {
+  @Override public SqlNode visit(SqlNodeList nodeList) {
     boolean update = false;
     List<SqlNode> exprs = nodeList.getList();
     int exprCount = exprs.size();
@@ -112,7 +112,7 @@ public CallCopyingArgHandler(SqlCall call, boolean alwaysCopy) {
       this.alwaysCopy = alwaysCopy;
     }
 
-    public SqlNode result() {
+    @Override public SqlNode result() {
       if (update || alwaysCopy) {
         return call.getOperator().createCall(
             call.getFunctionQuantifier(),
@@ -123,7 +123,7 @@ public SqlNode result() {
       }
     }
 
-    public SqlNode visitChild(
+    @Override public SqlNode visitChild(
         SqlVisitor<SqlNode> visitor,
         SqlNode expr,
         int i,
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/AbstractNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/AbstractNamespace.java
index 7a2a85b5af4..5b8d5c989c5 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/AbstractNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/AbstractNamespace.java
@@ -70,11 +70,11 @@ abstract class AbstractNamespace implements SqlValidatorNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlValidator getValidator() {
+  @Override public SqlValidator getValidator() {
     return validator;
   }
 
-  public final void validate(RelDataType targetRowType) {
+  @Override public final void validate(RelDataType targetRowType) {
     switch (status) {
     case UNVALIDATED:
       try {
@@ -110,7 +110,7 @@ public final void validate(RelDataType targetRowType) {
    */
   protected abstract RelDataType validateImpl(RelDataType targetRowType);
 
-  public RelDataType getRowType() {
+  @Override public RelDataType getRowType() {
     if (rowType == null) {
       validator.validateNamespace(this, validator.unknownType);
       Preconditions.checkArgument(rowType != null, "validate must set rowType");
@@ -118,68 +118,68 @@ public RelDataType getRowType() {
     return rowType;
   }
 
-  public RelDataType getRowTypeSansSystemColumns() {
+  @Override public RelDataType getRowTypeSansSystemColumns() {
     return getRowType();
   }
 
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     Util.discard(getRowType());
     return type;
   }
 
-  public void setType(RelDataType type) {
+  @Override public void setType(RelDataType type) {
     this.type = type;
     this.rowType = convertToStruct(type);
   }
 
-  public SqlNode getEnclosingNode() {
+  @Override public SqlNode getEnclosingNode() {
     return enclosingNode;
   }
 
-  public SqlValidatorTable getTable() {
+  @Override public SqlValidatorTable getTable() {
     return null;
   }
 
-  public SqlValidatorNamespace lookupChild(String name) {
+  @Override public SqlValidatorNamespace lookupChild(String name) {
     return validator.lookupFieldNamespace(
         getRowType(),
         name);
   }
 
-  public boolean fieldExists(String name) {
+  @Override public boolean fieldExists(String name) {
     final RelDataType rowType = getRowType();
     return validator.catalogReader.nameMatcher().field(rowType, name) != null;
   }
 
-  public List<Pair<SqlNode, SqlMonotonicity>> getMonotonicExprs() {
+  @Override public List<Pair<SqlNode, SqlMonotonicity>> getMonotonicExprs() {
     return ImmutableList.of();
   }
 
-  public SqlMonotonicity getMonotonicity(String columnName) {
+  @Override public SqlMonotonicity getMonotonicity(String columnName) {
     return SqlMonotonicity.NOT_MONOTONIC;
   }
 
   @SuppressWarnings("deprecation")
-  public void makeNullable() {
+  @Override public void makeNullable() {
   }
 
   public String translate(String name) {
     return name;
   }
 
-  public SqlValidatorNamespace resolve() {
+  @Override public SqlValidatorNamespace resolve() {
     return this;
   }
 
-  public boolean supportsModality(SqlModality modality) {
+  @Override public boolean supportsModality(SqlModality modality) {
     return true;
   }
 
-  public <T> T unwrap(Class<T> clazz) {
+  @Override public <T> T unwrap(Class<T> clazz) {
     return clazz.cast(this);
   }
 
-  public boolean isWrapperFor(Class<?> clazz) {
+  @Override public boolean isWrapperFor(Class<?> clazz) {
     return clazz.isInstance(this);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/AggChecker.java b/core/src/main/java/org/apache/calcite/sql/validate/AggChecker.java
index b0e901a70f6..7f7c9aa51a6 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/AggChecker.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/AggChecker.java
@@ -88,7 +88,7 @@ boolean isGroupExpr(SqlNode expr) {
     return false;
   }
 
-  public Void visit(SqlIdentifier id) {
+  @Override public Void visit(SqlIdentifier id) {
     if (isGroupExpr(id) || id.isStar()) {
       // Star may validly occur in "SELECT COUNT(*) OVER w"
       return null;
@@ -116,7 +116,7 @@ public Void visit(SqlIdentifier id) {
             : RESOURCE.notGroupExpr(exprString));
   }
 
-  public Void visit(SqlCall call) {
+  @Override public Void visit(SqlCall call) {
     final SqlValidatorScope scope = scopes.peek();
     if (call.getOperator().isAggregator()) {
       if (distinct) {
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/AggFinder.java b/core/src/main/java/org/apache/calcite/sql/validate/AggFinder.java
index 4dc9fabe7a6..3a4ca99e014 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/AggFinder.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/AggFinder.java
@@ -76,7 +76,7 @@ public SqlCall findAgg(List<SqlNode> nodes) {
     }
   }
 
-  protected Void found(SqlCall call) {
+  @Override protected Void found(SqlCall call) {
     throw new Util.FoundOne(call);
   }
 
@@ -105,7 +105,7 @@ static class AggIterable extends AggVisitor implements Iterable<SqlCall> {
       return null;
     }
 
-    @Nonnull public Iterator<SqlCall> iterator() {
+    @Override @Nonnull public Iterator<SqlCall> iterator() {
       return calls.iterator();
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/AggVisitor.java b/core/src/main/java/org/apache/calcite/sql/validate/AggVisitor.java
index 3f63e346759..ab8c5d91597 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/AggVisitor.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/AggVisitor.java
@@ -67,7 +67,7 @@ abstract class AggVisitor extends SqlBasicVisitor<Void> {
     this.nameMatcher = Objects.requireNonNull(nameMatcher);
   }
 
-  public Void visit(SqlCall call) {
+  @Override public Void visit(SqlCall call) {
     final SqlOperator operator = call.getOperator();
     // If nested aggregates disallowed or found an aggregate at invalid level
     if (operator.isAggregator()
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/AggregatingSelectScope.java b/core/src/main/java/org/apache/calcite/sql/validate/AggregatingSelectScope.java
index 279772d523a..2e4e3597ad4 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/AggregatingSelectScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/AggregatingSelectScope.java
@@ -151,7 +151,7 @@ private Pair<ImmutableList<SqlNode>, ImmutableList<SqlNode>> getGroupExprs() {
     }
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return select;
   }
 
@@ -168,7 +168,7 @@ public SqlNode getNode() {
     return type;
   }
 
-  public SqlValidatorScope getOperandScope(SqlCall call) {
+  @Override public SqlValidatorScope getOperandScope(SqlCall call) {
     if (call.getOperator().isAggregator()) {
       // If we're the 'SUM' node in 'select a + sum(b + c) from t
       // group by a', then we should validate our arguments in
@@ -195,7 +195,7 @@ public SqlValidatorScope getOperandScope(SqlCall call) {
     return super.getOperandScope(call);
   }
 
-  public boolean checkAggregateExpr(SqlNode expr, boolean deep) {
+  @Override public boolean checkAggregateExpr(SqlNode expr, boolean deep) {
     // Fully-qualify any identifiers in expr.
     if (deep) {
       expr = validator.expand(expr, this);
@@ -214,7 +214,7 @@ public boolean checkAggregateExpr(SqlNode expr, boolean deep) {
     return aggChecker.isGroupExpr(expr);
   }
 
-  public void validateExpr(SqlNode expr) {
+  @Override public void validateExpr(SqlNode expr) {
     checkAggregateExpr(expr, true);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/AliasNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/AliasNamespace.java
index 4abd72edbf8..38222d7d1ba 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/AliasNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/AliasNamespace.java
@@ -64,7 +64,7 @@ protected AliasNamespace(
 
   //~ Methods ----------------------------------------------------------------
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     final List<String> nameList = new ArrayList<>();
     final List<SqlNode> operands = call.getOperandList();
     final SqlValidatorNamespace childNs =
@@ -121,11 +121,11 @@ private String getString(RelDataType rowType) {
     return buf.toString();
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return call;
   }
 
-  public String translate(String name) {
+  @Override public String translate(String name) {
     final RelDataType underlyingRowType =
         validator.getValidatedNodeType(call.operand(0));
     int i = 0;
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/CatalogScope.java b/core/src/main/java/org/apache/calcite/sql/validate/CatalogScope.java
index 3bf59341fa4..3a8bfe27725 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/CatalogScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/CatalogScope.java
@@ -46,7 +46,7 @@ class CatalogScope extends DelegatingScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     throw new UnsupportedOperationException();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/CollectNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/CollectNamespace.java
index 1d48e87862b..ce6b6edbb76 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/CollectNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/CollectNamespace.java
@@ -64,11 +64,11 @@ public class CollectNamespace extends AbstractNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     return child.getOperator().deriveType(validator, scope, child);
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return child;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/CollectScope.java b/core/src/main/java/org/apache/calcite/sql/validate/CollectScope.java
index 6dc60edaf95..2e3a2975af1 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/CollectScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/CollectScope.java
@@ -45,7 +45,7 @@ class CollectScope extends ListScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return child;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingNamespace.java
index 4b00eef4834..b7b5f608147 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingNamespace.java
@@ -44,64 +44,64 @@ protected DelegatingNamespace(SqlValidatorNamespace namespace) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlValidator getValidator() {
+  @Override public SqlValidator getValidator() {
     return namespace.getValidator();
   }
 
-  public SqlValidatorTable getTable() {
+  @Override public SqlValidatorTable getTable() {
     return namespace.getTable();
   }
 
-  public RelDataType getRowType() {
+  @Override public RelDataType getRowType() {
     return namespace.getRowType();
   }
 
-  public void setType(RelDataType type) {
+  @Override public void setType(RelDataType type) {
     namespace.setType(type);
   }
 
-  public RelDataType getRowTypeSansSystemColumns() {
+  @Override public RelDataType getRowTypeSansSystemColumns() {
     return namespace.getRowTypeSansSystemColumns();
   }
 
-  public RelDataType getType() {
+  @Override public RelDataType getType() {
     return namespace.getType();
   }
 
-  public void validate(RelDataType targetRowType) {
+  @Override public void validate(RelDataType targetRowType) {
     namespace.validate(targetRowType);
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return namespace.getNode();
   }
 
-  public SqlNode getEnclosingNode() {
+  @Override public SqlNode getEnclosingNode() {
     return namespace.getEnclosingNode();
   }
 
-  public SqlValidatorNamespace lookupChild(
+  @Override public SqlValidatorNamespace lookupChild(
       String name) {
     return namespace.lookupChild(name);
   }
 
-  public boolean fieldExists(String name) {
+  @Override public boolean fieldExists(String name) {
     return namespace.fieldExists(name);
   }
 
-  public List<Pair<SqlNode, SqlMonotonicity>> getMonotonicExprs() {
+  @Override public List<Pair<SqlNode, SqlMonotonicity>> getMonotonicExprs() {
     return namespace.getMonotonicExprs();
   }
 
-  public SqlMonotonicity getMonotonicity(String columnName) {
+  @Override public SqlMonotonicity getMonotonicity(String columnName) {
     return namespace.getMonotonicity(columnName);
   }
 
   @SuppressWarnings("deprecation")
-  public void makeNullable() {
+  @Override public void makeNullable() {
   }
 
-  public <T> T unwrap(Class<T> clazz) {
+  @Override public <T> T unwrap(Class<T> clazz) {
     if (clazz.isInstance(this)) {
       return clazz.cast(this);
     } else {
@@ -109,7 +109,7 @@ public <T> T unwrap(Class<T> clazz) {
     }
   }
 
-  public boolean isWrapperFor(Class<?> clazz) {
+  @Override public boolean isWrapperFor(Class<?> clazz) {
     return clazz.isInstance(this)
         || namespace.isWrapperFor(clazz);
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingScope.java b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingScope.java
index a630a926507..ae746b83dce 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingScope.java
@@ -84,7 +84,7 @@ public abstract class DelegatingScope implements SqlValidatorScope {
     throw new UnsupportedOperationException();
   }
 
-  public void resolve(List<String> names, SqlNameMatcher nameMatcher,
+  @Override public void resolve(List<String> names, SqlNameMatcher nameMatcher,
       boolean deep, Resolved resolved) {
     parent.resolve(names, nameMatcher, deep, resolved);
   }
@@ -165,52 +165,52 @@ protected void addColumnNames(
     }
   }
 
-  public void findAllColumnNames(List<SqlMoniker> result) {
+  @Override public void findAllColumnNames(List<SqlMoniker> result) {
     parent.findAllColumnNames(result);
   }
 
-  public void findAliases(Collection<SqlMoniker> result) {
+  @Override public void findAliases(Collection<SqlMoniker> result) {
     parent.findAliases(result);
   }
 
   @SuppressWarnings("deprecation")
-  public Pair<String, SqlValidatorNamespace> findQualifyingTableName(
+  @Override public Pair<String, SqlValidatorNamespace> findQualifyingTableName(
       String columnName, SqlNode ctx) {
     //noinspection deprecation
     return parent.findQualifyingTableName(columnName, ctx);
   }
 
-  public Map<String, ScopeChild> findQualifyingTableNames(String columnName,
+  @Override public Map<String, ScopeChild> findQualifyingTableNames(String columnName,
       SqlNode ctx, SqlNameMatcher nameMatcher) {
     return parent.findQualifyingTableNames(columnName, ctx, nameMatcher);
   }
 
-  public RelDataType resolveColumn(String name, SqlNode ctx) {
+  @Override public RelDataType resolveColumn(String name, SqlNode ctx) {
     return parent.resolveColumn(name, ctx);
   }
 
-  public RelDataType nullifyType(SqlNode node, RelDataType type) {
+  @Override public RelDataType nullifyType(SqlNode node, RelDataType type) {
     return parent.nullifyType(node, type);
   }
 
-  @SuppressWarnings("deprecation")
+  @Override @SuppressWarnings("deprecation")
   public SqlValidatorNamespace getTableNamespace(List<String> names) {
     return parent.getTableNamespace(names);
   }
 
-  public void resolveTable(List<String> names, SqlNameMatcher nameMatcher,
+  @Override public void resolveTable(List<String> names, SqlNameMatcher nameMatcher,
       Path path, Resolved resolved) {
     parent.resolveTable(names, nameMatcher, path, resolved);
   }
 
-  public SqlValidatorScope getOperandScope(SqlCall call) {
+  @Override public SqlValidatorScope getOperandScope(SqlCall call) {
     if (call instanceof SqlSelect) {
       return validator.getSelectScope((SqlSelect) call);
     }
     return this;
   }
 
-  public SqlValidator getValidator() {
+  @Override public SqlValidator getValidator() {
     return validator;
   }
 
@@ -221,7 +221,7 @@ public SqlValidator getValidator() {
    *
    * <p>If the identifier cannot be resolved, throws. Never returns null.
    */
-  public SqlQualified fullyQualify(SqlIdentifier identifier) {
+  @Override public SqlQualified fullyQualify(SqlIdentifier identifier) {
     if (identifier.isStar()) {
       return SqlQualified.create(this, 1, null, identifier);
     }
@@ -444,7 +444,7 @@ public SqlQualified fullyQualify(SqlIdentifier identifier) {
       default:
         final Comparator<Resolve> c =
             new Comparator<Resolve>() {
-              public int compare(Resolve o1, Resolve o2) {
+              @Override public int compare(Resolve o1, Resolve o2) {
                 // Name resolution that uses fewer implicit steps wins.
                 int c = Integer.compare(worstKind(o1.path), worstKind(o2.path));
                 if (c != 0) {
@@ -525,20 +525,20 @@ private int worstKind(Path path) {
     }
   }
 
-  public void validateExpr(SqlNode expr) {
+  @Override public void validateExpr(SqlNode expr) {
     // Do not delegate to parent. An expression valid in this scope may not
     // be valid in the parent scope.
   }
 
-  public SqlWindow lookupWindow(String name) {
+  @Override public SqlWindow lookupWindow(String name) {
     return parent.lookupWindow(name);
   }
 
-  public SqlMonotonicity getMonotonicity(SqlNode expr) {
+  @Override public SqlMonotonicity getMonotonicity(SqlNode expr) {
     return parent.getMonotonicity(expr);
   }
 
-  public SqlNodeList getOrderList() {
+  @Override public SqlNodeList getOrderList() {
     return parent.getOrderList();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorCatalogReader.java b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorCatalogReader.java
index 0aff0f064b3..4c398cbb964 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorCatalogReader.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorCatalogReader.java
@@ -40,19 +40,19 @@ public DelegatingSqlValidatorCatalogReader(
     this.catalogReader = catalogReader;
   }
 
-  public SqlValidatorTable getTable(List<String> names) {
+  @Override public SqlValidatorTable getTable(List<String> names) {
     return catalogReader.getTable(names);
   }
 
-  public RelDataType getNamedType(SqlIdentifier typeName) {
+  @Override public RelDataType getNamedType(SqlIdentifier typeName) {
     return catalogReader.getNamedType(typeName);
   }
 
-  public List<SqlMoniker> getAllSchemaObjectNames(List<String> names) {
+  @Override public List<SqlMoniker> getAllSchemaObjectNames(List<String> names) {
     return catalogReader.getAllSchemaObjectNames(names);
   }
 
-  public List<List<String>> getSchemaPaths() {
+  @Override public List<List<String>> getSchemaPaths() {
     return catalogReader.getSchemaPaths();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorTable.java b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorTable.java
index 6527c7bb567..c9c62174a54 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/DelegatingSqlValidatorTable.java
@@ -37,19 +37,19 @@ public DelegatingSqlValidatorTable(SqlValidatorTable table) {
     this.table = table;
   }
 
-  public RelDataType getRowType() {
+  @Override public RelDataType getRowType() {
     return table.getRowType();
   }
 
-  public List<String> getQualifiedName() {
+  @Override public List<String> getQualifiedName() {
     return table.getQualifiedName();
   }
 
-  public SqlMonotonicity getMonotonicity(String columnName) {
+  @Override public SqlMonotonicity getMonotonicity(String columnName) {
     return table.getMonotonicity(columnName);
   }
 
-  public SqlAccessType getAllowedAccess() {
+  @Override public SqlAccessType getAllowedAccess() {
     return table.getAllowedAccess();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/EmptyScope.java b/core/src/main/java/org/apache/calcite/sql/validate/EmptyScope.java
index 42636d54aa6..dde9205e678 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/EmptyScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/EmptyScope.java
@@ -65,23 +65,23 @@ class EmptyScope implements SqlValidatorScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlValidator getValidator() {
+  @Override public SqlValidator getValidator() {
     return validator;
   }
 
-  public SqlQualified fullyQualify(SqlIdentifier identifier) {
+  @Override public SqlQualified fullyQualify(SqlIdentifier identifier) {
     return SqlQualified.create(this, 1, null, identifier);
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     throw new UnsupportedOperationException();
   }
 
-  public void resolve(List<String> names, SqlNameMatcher nameMatcher,
+  @Override public void resolve(List<String> names, SqlNameMatcher nameMatcher,
       boolean deep, Resolved resolved) {
   }
 
-  @SuppressWarnings("deprecation")
+  @Override @SuppressWarnings("deprecation")
   public SqlValidatorNamespace getTableNamespace(List<String> names) {
     SqlValidatorTable table = validator.catalogReader.getTable(names);
     return table != null
@@ -89,7 +89,7 @@ public SqlValidatorNamespace getTableNamespace(List<String> names) {
         : null;
   }
 
-  public void resolveTable(List<String> names, SqlNameMatcher nameMatcher,
+  @Override public void resolveTable(List<String> names, SqlNameMatcher nameMatcher,
       Path path, Resolved resolved) {
     final List<Resolve> imperfectResolves = new ArrayList<>();
     final List<Resolve> resolves = ((ResolvedImpl) resolved).resolves;
@@ -172,55 +172,55 @@ private void resolve_(final CalciteSchema rootSchema, List<String> names,
     }
   }
 
-  public RelDataType nullifyType(SqlNode node, RelDataType type) {
+  @Override public RelDataType nullifyType(SqlNode node, RelDataType type) {
     return type;
   }
 
-  public void findAllColumnNames(List<SqlMoniker> result) {
+  @Override public void findAllColumnNames(List<SqlMoniker> result) {
   }
 
   public void findAllTableNames(List<SqlMoniker> result) {
   }
 
-  public void findAliases(Collection<SqlMoniker> result) {
+  @Override public void findAliases(Collection<SqlMoniker> result) {
   }
 
-  public RelDataType resolveColumn(String name, SqlNode ctx) {
+  @Override public RelDataType resolveColumn(String name, SqlNode ctx) {
     return null;
   }
 
-  public SqlValidatorScope getOperandScope(SqlCall call) {
+  @Override public SqlValidatorScope getOperandScope(SqlCall call) {
     return this;
   }
 
-  public void validateExpr(SqlNode expr) {
+  @Override public void validateExpr(SqlNode expr) {
     // valid
   }
 
   @SuppressWarnings("deprecation")
-  public Pair<String, SqlValidatorNamespace> findQualifyingTableName(
+  @Override public Pair<String, SqlValidatorNamespace> findQualifyingTableName(
       String columnName, SqlNode ctx) {
     throw validator.newValidationError(ctx,
         RESOURCE.columnNotFound(columnName));
   }
 
-  public Map<String, ScopeChild> findQualifyingTableNames(String columnName,
+  @Override public Map<String, ScopeChild> findQualifyingTableNames(String columnName,
       SqlNode ctx, SqlNameMatcher nameMatcher) {
     return ImmutableMap.of();
   }
 
-  public void addChild(SqlValidatorNamespace ns, String alias,
+  @Override public void addChild(SqlValidatorNamespace ns, String alias,
       boolean nullable) {
     // cannot add to the empty scope
     throw new UnsupportedOperationException();
   }
 
-  public SqlWindow lookupWindow(String name) {
+  @Override public SqlWindow lookupWindow(String name) {
     // No windows defined in this scope.
     return null;
   }
 
-  public SqlMonotonicity getMonotonicity(SqlNode expr) {
+  @Override public SqlMonotonicity getMonotonicity(SqlNode expr) {
     return
         ((expr instanceof SqlLiteral)
             || (expr instanceof SqlDynamicParam)
@@ -228,7 +228,7 @@ public SqlMonotonicity getMonotonicity(SqlNode expr) {
             : SqlMonotonicity.NOT_MONOTONIC;
   }
 
-  public SqlNodeList getOrderList() {
+  @Override public SqlNodeList getOrderList() {
     // scope is not ordered
     return null;
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/FieldNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/FieldNamespace.java
index 74c87de59c6..a60f629ac75 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/FieldNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/FieldNamespace.java
@@ -45,19 +45,19 @@ class FieldNamespace extends AbstractNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  public void setType(RelDataType type) {
+  @Override public void setType(RelDataType type) {
     throw new UnsupportedOperationException();
   }
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     return rowType;
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return null;
   }
 
-  public SqlValidatorNamespace lookupChild(String name) {
+  @Override public SqlValidatorNamespace lookupChild(String name) {
     if (rowType.isStruct()) {
       return validator.lookupFieldNamespace(
           rowType,
@@ -66,7 +66,7 @@ public SqlValidatorNamespace lookupChild(String name) {
     return null;
   }
 
-  public boolean fieldExists(String name) {
+  @Override public boolean fieldExists(String name) {
     return false;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/GroupByScope.java b/core/src/main/java/org/apache/calcite/sql/validate/GroupByScope.java
index 1f43086cda9..d7c5d208094 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/GroupByScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/GroupByScope.java
@@ -51,11 +51,11 @@ public class GroupByScope extends DelegatingScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return groupByList;
   }
 
-  public void validateExpr(SqlNode expr) {
+  @Override public void validateExpr(SqlNode expr) {
     SqlNode expanded = validator.expandGroupByOrHavingExpr(expr, this, select, false);
 
     // expression needs to be valid in parent scope too
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/IdentifierNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/IdentifierNamespace.java
index 8da8756c6f1..f37cc5adf55 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/IdentifierNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/IdentifierNamespace.java
@@ -180,7 +180,7 @@ private SqlValidatorNamespace resolveImpl(SqlIdentifier id) {
         RESOURCE.objectNotFound(id.getComponent(0).toString()));
   }
 
-  public RelDataType validateImpl(RelDataType targetRowType) {
+  @Override public RelDataType validateImpl(RelDataType targetRowType) {
     resolvedNamespace = Objects.requireNonNull(resolveImpl(id));
     if (resolvedNamespace instanceof TableNamespace) {
       SqlValidatorTable table = resolvedNamespace.getTable();
@@ -244,7 +244,7 @@ public SqlIdentifier getId() {
     return id;
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return id;
   }
 
@@ -257,7 +257,7 @@ public SqlNode getNode() {
     return resolvedNamespace == null ? null : resolve().getTable();
   }
 
-  public List<Pair<SqlNode, SqlMonotonicity>> getMonotonicExprs() {
+  @Override public List<Pair<SqlNode, SqlMonotonicity>> getMonotonicExprs() {
     return monotonicExprs;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/JoinNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/JoinNamespace.java
index 2197a40e770..2bb9989bcf7 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/JoinNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/JoinNamespace.java
@@ -38,7 +38,7 @@ class JoinNamespace extends AbstractNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     RelDataType leftType =
         validator.getNamespace(join.getLeft()).getRowType();
     RelDataType rightType =
@@ -59,7 +59,7 @@ protected RelDataType validateImpl(RelDataType targetRowType) {
     return typeFactory.createJoinType(leftType, rightType);
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return join;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/JoinScope.java b/core/src/main/java/org/apache/calcite/sql/validate/JoinScope.java
index 406ffb2c97a..6cdd48afb0a 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/JoinScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/JoinScope.java
@@ -55,11 +55,11 @@ public class JoinScope extends ListScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return join;
   }
 
-  public void addChild(SqlValidatorNamespace ns, String alias,
+  @Override public void addChild(SqlValidatorNamespace ns, String alias,
       boolean nullable) {
     super.addChild(ns, alias, nullable);
     if ((usingScope != null) && (usingScope != parent)) {
@@ -77,7 +77,7 @@ public void addChild(SqlValidatorNamespace ns, String alias,
     }
   }
 
-  public SqlWindow lookupWindow(String name) {
+  @Override public SqlWindow lookupWindow(String name) {
     // Lookup window in enclosing select.
     if (usingScope != null) {
       return usingScope.lookupWindow(name);
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/ListScope.java b/core/src/main/java/org/apache/calcite/sql/validate/ListScope.java
index 3ac85111a53..6354b4875ac 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/ListScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/ListScope.java
@@ -112,14 +112,14 @@ private ScopeChild findChild(List<String> names,
     return null;
   }
 
-  public void findAllColumnNames(List<SqlMoniker> result) {
+  @Override public void findAllColumnNames(List<SqlMoniker> result) {
     for (ScopeChild child : children) {
       addColumnNames(child.namespace, result);
     }
     parent.findAllColumnNames(result);
   }
 
-  public void findAliases(Collection<SqlMoniker> result) {
+  @Override public void findAliases(Collection<SqlMoniker> result) {
     for (ScopeChild child : children) {
       result.add(new SqlMonikerImpl(child.name, SqlMonikerType.TABLE));
     }
@@ -200,7 +200,7 @@ public void findAliases(Collection<SqlMoniker> result) {
     super.resolve(names, nameMatcher, deep, resolved);
   }
 
-  public RelDataType resolveColumn(String columnName, SqlNode ctx) {
+  @Override public RelDataType resolveColumn(String columnName, SqlNode ctx) {
     final SqlNameMatcher nameMatcher = validator.catalogReader.nameMatcher();
     int found = 0;
     RelDataType type = null;
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/OrderByScope.java b/core/src/main/java/org/apache/calcite/sql/validate/OrderByScope.java
index 222fd0effc2..c1288019a53 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/OrderByScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/OrderByScope.java
@@ -58,16 +58,16 @@ public class OrderByScope extends DelegatingScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return orderList;
   }
 
-  public void findAllColumnNames(List<SqlMoniker> result) {
+  @Override public void findAllColumnNames(List<SqlMoniker> result) {
     final SqlValidatorNamespace ns = validator.getNamespace(select);
     addColumnNames(ns, result);
   }
 
-  public SqlQualified fullyQualify(SqlIdentifier identifier) {
+  @Override public SqlQualified fullyQualify(SqlIdentifier identifier) {
     // If it's a simple identifier, look for an alias.
     if (identifier.isSimple()
         && validator.config().sqlConformance().isSortByAlias()) {
@@ -106,7 +106,7 @@ private int aliasCount(SqlNameMatcher nameMatcher, String name) {
     return n;
   }
 
-  public RelDataType resolveColumn(String name, SqlNode ctx) {
+  @Override public RelDataType resolveColumn(String name, SqlNode ctx) {
     final SqlValidatorNamespace selectNs = validator.getNamespace(select);
     final RelDataType rowType = selectNs.getRowType();
     final SqlNameMatcher nameMatcher = validator.catalogReader.nameMatcher();
@@ -118,7 +118,7 @@ public RelDataType resolveColumn(String name, SqlNode ctx) {
     return selectScope.resolveColumn(name, ctx);
   }
 
-  public void validateExpr(SqlNode expr) {
+  @Override public void validateExpr(SqlNode expr) {
     SqlNode expanded = validator.expandOrderExpr(select, expr);
 
     // expression needs to be valid in parent scope too
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/OverScope.java b/core/src/main/java/org/apache/calcite/sql/validate/OverScope.java
index b1350e76786..25bad3b3155 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/OverScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/OverScope.java
@@ -64,11 +64,11 @@ public class OverScope extends ListScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return overCall;
   }
 
-  public SqlMonotonicity getMonotonicity(SqlNode expr) {
+  @Override public SqlMonotonicity getMonotonicity(SqlNode expr) {
     SqlMonotonicity monotonicity = expr.getMonotonicity(this);
     if (monotonicity != SqlMonotonicity.NOT_MONOTONIC) {
       return monotonicity;
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/ParameterNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/ParameterNamespace.java
index de21ac843f6..b57fdf85cb1 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/ParameterNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/ParameterNamespace.java
@@ -38,15 +38,15 @@ class ParameterNamespace extends AbstractNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return null;
   }
 
-  public RelDataType validateImpl(RelDataType targetRowType) {
+  @Override public RelDataType validateImpl(RelDataType targetRowType) {
     return type;
   }
 
-  public RelDataType getRowType() {
+  @Override public RelDataType getRowType() {
     return type;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/ParameterScope.java b/core/src/main/java/org/apache/calcite/sql/validate/ParameterScope.java
index 66bbba7ea22..e5ff5cae062 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/ParameterScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/ParameterScope.java
@@ -49,11 +49,11 @@ public ParameterScope(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlQualified fullyQualify(SqlIdentifier identifier) {
+  @Override public SqlQualified fullyQualify(SqlIdentifier identifier) {
     return SqlQualified.create(this, 1, null, identifier);
   }
 
-  public SqlValidatorScope getOperandScope(SqlCall call) {
+  @Override public SqlValidatorScope getOperandScope(SqlCall call) {
     return this;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/ProcedureNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/ProcedureNamespace.java
index c4ffb6de14f..25ed7058660 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/ProcedureNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/ProcedureNamespace.java
@@ -50,7 +50,7 @@ public class ProcedureNamespace extends AbstractNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RelDataType validateImpl(RelDataType targetRowType) {
+  @Override public RelDataType validateImpl(RelDataType targetRowType) {
     validator.inferUnknownTypes(validator.unknownType, scope, call);
     final RelDataType type = validator.deriveTypeImpl(scope, call);
     final SqlOperator operator = call.getOperator();
@@ -70,7 +70,7 @@ public RelDataType validateImpl(RelDataType targetRowType) {
     return rowTypeInference.inferReturnType(callBinding);
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return call;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SchemaNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/SchemaNamespace.java
index a73ee494771..1f9c98fae99 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SchemaNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SchemaNamespace.java
@@ -40,7 +40,7 @@ class SchemaNamespace extends AbstractNamespace {
     this.names = Objects.requireNonNull(names);
   }
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     final RelDataTypeFactory.Builder builder =
         validator.getTypeFactory().builder();
     for (SqlMoniker moniker
@@ -52,7 +52,7 @@ protected RelDataType validateImpl(RelDataType targetRowType) {
     return builder.build();
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return null;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SelectNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/SelectNamespace.java
index 5f05946f9d4..6dd4f69d725 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SelectNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SelectNamespace.java
@@ -56,7 +56,7 @@ public SelectNamespace(
     return select;
   }
 
-  public RelDataType validateImpl(RelDataType targetRowType) {
+  @Override public RelDataType validateImpl(RelDataType targetRowType) {
     validator.validateSelect(select, targetRowType);
     return rowType;
   }
@@ -65,7 +65,7 @@ public RelDataType validateImpl(RelDataType targetRowType) {
     return validator.validateModality(select, modality, false);
   }
 
-  public SqlMonotonicity getMonotonicity(String columnName) {
+  @Override public SqlMonotonicity getMonotonicity(String columnName) {
     final RelDataType rowType = this.getRowTypeSansSystemColumns();
     final int field = SqlTypeUtil.findField(rowType, columnName);
     final SqlNode selectItem =
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SelectScope.java b/core/src/main/java/org/apache/calcite/sql/validate/SelectScope.java
index 2649d59e918..d118db12d41 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SelectScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SelectScope.java
@@ -126,11 +126,11 @@ public SqlValidatorTable getTable() {
     return null;
   }
 
-  public SqlSelect getNode() {
+  @Override public SqlSelect getNode() {
     return select;
   }
 
-  public SqlWindow lookupWindow(String name) {
+  @Override public SqlWindow lookupWindow(String name) {
     final SqlNodeList windowList = select.getWindowList();
     for (int i = 0; i < windowList.size(); i++) {
       SqlWindow window = (SqlWindow) windowList.get(i);
@@ -149,7 +149,7 @@ public SqlWindow lookupWindow(String name) {
     }
   }
 
-  public SqlMonotonicity getMonotonicity(SqlNode expr) {
+  @Override public SqlMonotonicity getMonotonicity(SqlNode expr) {
     SqlMonotonicity monotonicity = expr.getMonotonicity(this);
     if (monotonicity != SqlMonotonicity.NOT_MONOTONIC) {
       return monotonicity;
@@ -174,7 +174,7 @@ public SqlMonotonicity getMonotonicity(SqlNode expr) {
     return SqlMonotonicity.NOT_MONOTONIC;
   }
 
-  public SqlNodeList getOrderList() {
+  @Override public SqlNodeList getOrderList() {
     if (orderList == null) {
       // Compute on demand first call.
       orderList = new SqlNodeList(SqlParserPos.ZERO);
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SetopNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/SetopNamespace.java
index cb444b789d4..5dac9b082bd 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SetopNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SetopNamespace.java
@@ -50,7 +50,7 @@ protected SetopNamespace(
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return call;
   }
 
@@ -88,7 +88,7 @@ private SqlMonotonicity combine(SqlMonotonicity m0, SqlMonotonicity m1) {
     return SqlMonotonicity.NOT_MONOTONIC;
   }
 
-  public RelDataType validateImpl(RelDataType targetRowType) {
+  @Override public RelDataType validateImpl(RelDataType targetRowType) {
     switch (call.getKind()) {
     case UNION:
     case INTERSECT:
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlAbstractConformance.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlAbstractConformance.java
index f49fe67c542..11c7691ef1c 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlAbstractConformance.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlAbstractConformance.java
@@ -23,107 +23,107 @@
  * and behaves the same as in {@link SqlConformanceEnum#DEFAULT}.
  */
 public abstract class SqlAbstractConformance implements SqlConformance {
-  public boolean isLiberal() {
+  @Override public boolean isLiberal() {
     return SqlConformanceEnum.DEFAULT.isLiberal();
   }
 
-  public boolean allowCharLiteralAlias() {
+  @Override public boolean allowCharLiteralAlias() {
     return SqlConformanceEnum.DEFAULT.allowCharLiteralAlias();
   }
 
-  public boolean isGroupByAlias() {
+  @Override public boolean isGroupByAlias() {
     return SqlConformanceEnum.DEFAULT.isGroupByAlias();
   }
 
-  public boolean isGroupByOrdinal() {
+  @Override public boolean isGroupByOrdinal() {
     return SqlConformanceEnum.DEFAULT.isGroupByOrdinal();
   }
 
-  public boolean isHavingAlias() {
+  @Override public boolean isHavingAlias() {
     return SqlConformanceEnum.DEFAULT.isHavingAlias();
   }
 
-  public boolean isSortByOrdinal() {
+  @Override public boolean isSortByOrdinal() {
     return SqlConformanceEnum.DEFAULT.isSortByOrdinal();
   }
 
-  public boolean isSortByAlias() {
+  @Override public boolean isSortByAlias() {
     return SqlConformanceEnum.DEFAULT.isSortByAlias();
   }
 
-  public boolean isSortByAliasObscures() {
+  @Override public boolean isSortByAliasObscures() {
     return SqlConformanceEnum.DEFAULT.isSortByAliasObscures();
   }
 
-  public boolean isFromRequired() {
+  @Override public boolean isFromRequired() {
     return SqlConformanceEnum.DEFAULT.isFromRequired();
   }
 
-  public boolean splitQuotedTableName() {
+  @Override public boolean splitQuotedTableName() {
     return SqlConformanceEnum.DEFAULT.splitQuotedTableName();
   }
 
-  public boolean allowHyphenInUnquotedTableName() {
+  @Override public boolean allowHyphenInUnquotedTableName() {
     return SqlConformanceEnum.DEFAULT.allowHyphenInUnquotedTableName();
   }
 
-  public boolean isBangEqualAllowed() {
+  @Override public boolean isBangEqualAllowed() {
     return SqlConformanceEnum.DEFAULT.isBangEqualAllowed();
   }
 
-  public boolean isMinusAllowed() {
+  @Override public boolean isMinusAllowed() {
     return SqlConformanceEnum.DEFAULT.isMinusAllowed();
   }
 
-  public boolean isApplyAllowed() {
+  @Override public boolean isApplyAllowed() {
     return SqlConformanceEnum.DEFAULT.isApplyAllowed();
   }
 
-  public boolean isInsertSubsetColumnsAllowed() {
+  @Override public boolean isInsertSubsetColumnsAllowed() {
     return SqlConformanceEnum.DEFAULT.isInsertSubsetColumnsAllowed();
   }
 
-  public boolean allowNiladicParentheses() {
+  @Override public boolean allowNiladicParentheses() {
     return SqlConformanceEnum.DEFAULT.allowNiladicParentheses();
   }
 
-  public boolean allowExplicitRowValueConstructor() {
+  @Override public boolean allowExplicitRowValueConstructor() {
     return SqlConformanceEnum.DEFAULT.allowExplicitRowValueConstructor();
   }
 
-  public boolean allowExtend() {
+  @Override public boolean allowExtend() {
     return SqlConformanceEnum.DEFAULT.allowExtend();
   }
 
-  public boolean isLimitStartCountAllowed() {
+  @Override public boolean isLimitStartCountAllowed() {
     return SqlConformanceEnum.DEFAULT.isLimitStartCountAllowed();
   }
 
-  public boolean isPercentRemainderAllowed() {
+  @Override public boolean isPercentRemainderAllowed() {
     return SqlConformanceEnum.DEFAULT.isPercentRemainderAllowed();
   }
 
-  public boolean allowGeometry() {
+  @Override public boolean allowGeometry() {
     return SqlConformanceEnum.DEFAULT.allowGeometry();
   }
 
-  public boolean shouldConvertRaggedUnionTypesToVarying() {
+  @Override public boolean shouldConvertRaggedUnionTypesToVarying() {
     return SqlConformanceEnum.DEFAULT.shouldConvertRaggedUnionTypesToVarying();
   }
 
-  public boolean allowExtendedTrim() {
+  @Override public boolean allowExtendedTrim() {
     return SqlConformanceEnum.DEFAULT.allowExtendedTrim();
   }
 
-  public boolean allowPluralTimeUnits() {
+  @Override public boolean allowPluralTimeUnits() {
     return SqlConformanceEnum.DEFAULT.allowPluralTimeUnits();
   }
 
-  public boolean allowQualifyingCommonColumn() {
+  @Override public boolean allowQualifyingCommonColumn() {
     return SqlConformanceEnum.DEFAULT.allowQualifyingCommonColumn();
   }
 
-  public boolean allowAliasUnnestItems() {
+  @Override public boolean allowAliasUnnestItems() {
     return SqlConformanceEnum.DEFAULT.allowAliasUnnestItems();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlConformanceEnum.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlConformanceEnum.java
index 97a1608aebf..0bd37b9e256 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlConformanceEnum.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlConformanceEnum.java
@@ -79,7 +79,7 @@ public enum SqlConformanceEnum implements SqlConformance {
    * consistent with Microsoft SQL Server version 2008. */
   SQL_SERVER_2008;
 
-  public boolean isLiberal() {
+  @Override public boolean isLiberal() {
     switch (this) {
     case BABEL:
       return true;
@@ -88,7 +88,7 @@ public boolean isLiberal() {
     }
   }
 
-  public boolean allowCharLiteralAlias() {
+  @Override public boolean allowCharLiteralAlias() {
     switch (this) {
     case BABEL:
     case BIG_QUERY:
@@ -102,7 +102,7 @@ public boolean allowCharLiteralAlias() {
   }
 
 
-  public boolean isGroupByAlias() {
+  @Override public boolean isGroupByAlias() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -114,7 +114,7 @@ public boolean isGroupByAlias() {
     }
   }
 
-  public boolean isGroupByOrdinal() {
+  @Override public boolean isGroupByOrdinal() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -126,7 +126,7 @@ public boolean isGroupByOrdinal() {
     }
   }
 
-  public boolean isHavingAlias() {
+  @Override public boolean isHavingAlias() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -138,7 +138,7 @@ public boolean isHavingAlias() {
     }
   }
 
-  public boolean isSortByOrdinal() {
+  @Override public boolean isSortByOrdinal() {
     switch (this) {
     case DEFAULT:
     case BABEL:
@@ -158,7 +158,7 @@ public boolean isSortByOrdinal() {
     }
   }
 
-  public boolean isSortByAlias() {
+  @Override public boolean isSortByAlias() {
     switch (this) {
     case DEFAULT:
     case BABEL:
@@ -174,11 +174,11 @@ public boolean isSortByAlias() {
     }
   }
 
-  public boolean isSortByAliasObscures() {
+  @Override public boolean isSortByAliasObscures() {
     return this == SqlConformanceEnum.STRICT_92;
   }
 
-  public boolean isFromRequired() {
+  @Override public boolean isFromRequired() {
     switch (this) {
     case ORACLE_10:
     case ORACLE_12:
@@ -191,7 +191,7 @@ public boolean isFromRequired() {
     }
   }
 
-  public boolean splitQuotedTableName() {
+  @Override public boolean splitQuotedTableName() {
     switch (this) {
     case BIG_QUERY:
       return true;
@@ -200,7 +200,7 @@ public boolean splitQuotedTableName() {
     }
   }
 
-  public boolean allowHyphenInUnquotedTableName() {
+  @Override public boolean allowHyphenInUnquotedTableName() {
     switch (this) {
     case BIG_QUERY:
       return true;
@@ -209,7 +209,7 @@ public boolean allowHyphenInUnquotedTableName() {
     }
   }
 
-  public boolean isBangEqualAllowed() {
+  @Override public boolean isBangEqualAllowed() {
     switch (this) {
     case LENIENT:
     case BABEL:
@@ -247,7 +247,7 @@ public boolean isBangEqualAllowed() {
     }
   }
 
-  public boolean isApplyAllowed() {
+  @Override public boolean isApplyAllowed() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -259,7 +259,7 @@ public boolean isApplyAllowed() {
     }
   }
 
-  public boolean isInsertSubsetColumnsAllowed() {
+  @Override public boolean isInsertSubsetColumnsAllowed() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -272,7 +272,7 @@ public boolean isInsertSubsetColumnsAllowed() {
     }
   }
 
-  public boolean allowNiladicParentheses() {
+  @Override public boolean allowNiladicParentheses() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -283,7 +283,7 @@ public boolean allowNiladicParentheses() {
     }
   }
 
-  public boolean allowExplicitRowValueConstructor() {
+  @Override public boolean allowExplicitRowValueConstructor() {
     switch (this) {
     case DEFAULT:
     case LENIENT:
@@ -294,7 +294,7 @@ public boolean allowExplicitRowValueConstructor() {
     }
   }
 
-  public boolean allowExtend() {
+  @Override public boolean allowExtend() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -304,7 +304,7 @@ public boolean allowExtend() {
     }
   }
 
-  public boolean isLimitStartCountAllowed() {
+  @Override public boolean isLimitStartCountAllowed() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -315,7 +315,7 @@ public boolean isLimitStartCountAllowed() {
     }
   }
 
-  public boolean allowGeometry() {
+  @Override public boolean allowGeometry() {
     switch (this) {
     case BABEL:
     case LENIENT:
@@ -328,7 +328,7 @@ public boolean allowGeometry() {
     }
   }
 
-  public boolean shouldConvertRaggedUnionTypesToVarying() {
+  @Override public boolean shouldConvertRaggedUnionTypesToVarying() {
     switch (this) {
     case PRAGMATIC_99:
     case PRAGMATIC_2003:
@@ -344,7 +344,7 @@ public boolean shouldConvertRaggedUnionTypesToVarying() {
     }
   }
 
-  public boolean allowExtendedTrim() {
+  @Override public boolean allowExtendedTrim() {
     switch (this) {
     case BABEL:
     case LENIENT:
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlIdentifierMoniker.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlIdentifierMoniker.java
index aa9a68ac53d..14e609dfae7 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlIdentifierMoniker.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlIdentifierMoniker.java
@@ -41,23 +41,23 @@ public SqlIdentifierMoniker(SqlIdentifier id) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlMonikerType getType() {
+  @Override public SqlMonikerType getType() {
     return SqlMonikerType.COLUMN;
   }
 
-  public List<String> getFullyQualifiedNames() {
+  @Override public List<String> getFullyQualifiedNames() {
     return id.names;
   }
 
-  public SqlIdentifier toIdentifier() {
+  @Override public SqlIdentifier toIdentifier() {
     return id;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return id.toString();
   }
 
-  public String id() {
+  @Override public String id() {
     return id.toString();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlMoniker.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlMoniker.java
index 8b8069ea57f..3f3b385a59c 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlMoniker.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlMoniker.java
@@ -32,7 +32,7 @@ public interface SqlMoniker {
         final Ordering<Iterable<String>> listOrdering =
             Ordering.<String>natural().lexicographical();
 
-        public int compare(SqlMoniker o1, SqlMoniker o2) {
+        @Override public int compare(SqlMoniker o1, SqlMoniker o2) {
           int c = o1.getType().compareTo(o2.getType());
           if (c == 0) {
             c = listOrdering.compare(o1.getFullyQualifiedNames(),
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlMonikerImpl.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlMonikerImpl.java
index 8b504284634..27fe51fb56a 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlMonikerImpl.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlMonikerImpl.java
@@ -64,23 +64,23 @@ public SqlMonikerImpl(String name, SqlMonikerType type) {
     return Objects.hash(type, names);
   }
 
-  public SqlMonikerType getType() {
+  @Override public SqlMonikerType getType() {
     return type;
   }
 
-  public List<String> getFullyQualifiedNames() {
+  @Override public List<String> getFullyQualifiedNames() {
     return names;
   }
 
-  public SqlIdentifier toIdentifier() {
+  @Override public SqlIdentifier toIdentifier() {
     return new SqlIdentifier(names, SqlParserPos.ZERO);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return Util.sepList(names, ".");
   }
 
-  public String id() {
+  @Override public String id() {
     return type + "(" + this + ")";
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlNameMatchers.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlNameMatchers.java
index 458e50b6872..966485707f3 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlNameMatchers.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlNameMatchers.java
@@ -59,11 +59,11 @@ private static class BaseMatcher implements SqlNameMatcher {
       this.caseSensitive = caseSensitive;
     }
 
-    public boolean isCaseSensitive() {
+    @Override public boolean isCaseSensitive() {
       return caseSensitive;
     }
 
-    public boolean matches(String string, String name) {
+    @Override public boolean matches(String string, String name) {
       return caseSensitive ? string.equals(name)
           : string.equalsIgnoreCase(name);
     }
@@ -82,7 +82,7 @@ protected boolean listMatches(List<String> list0, List<String> list1) {
       return true;
     }
 
-    public <K extends List<String>, V> V get(Map<K, V> map,
+    @Override public <K extends List<String>, V> V get(Map<K, V> map,
         List<String> prefixNames, List<String> names) {
       final List<String> key = concat(prefixNames, names);
       if (caseSensitive) {
@@ -114,15 +114,15 @@ protected List<String> bestMatch() {
       throw new UnsupportedOperationException();
     }
 
-    public String bestString() {
+    @Override public String bestString() {
       return SqlIdentifier.getString(bestMatch());
     }
 
-    public RelDataTypeField field(RelDataType rowType, String fieldName) {
+    @Override public RelDataTypeField field(RelDataType rowType, String fieldName) {
       return rowType.getField(fieldName, caseSensitive, false);
     }
 
-    public int frequency(Iterable<String> names, String name) {
+    @Override public int frequency(Iterable<String> names, String name) {
       int n = 0;
       for (String s : names) {
         if (matches(s, name)) {
@@ -132,7 +132,7 @@ public int frequency(Iterable<String> names, String name) {
       return n;
     }
 
-    public Set<String> createSet() {
+    @Override public Set<String> createSet() {
       return isCaseSensitive()
           ? new LinkedHashSet<>()
           : new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlScopedShuttle.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlScopedShuttle.java
index 4388aefd41a..1006374e1e8 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlScopedShuttle.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlScopedShuttle.java
@@ -43,7 +43,7 @@ protected SqlScopedShuttle(SqlValidatorScope initialScope) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public final SqlNode visit(SqlCall call) {
+  @Override public final SqlNode visit(SqlCall call) {
     SqlValidatorScope oldScope = scopes.peek();
     SqlValidatorScope newScope = oldScope.getOperandScope(call);
     scopes.push(newScope);
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlUserDefinedTableFunction.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlUserDefinedTableFunction.java
index 440019dea1d..1afd7fc8a55 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlUserDefinedTableFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlUserDefinedTableFunction.java
@@ -69,7 +69,7 @@ public SqlUserDefinedTableFunction(SqlIdentifier opName, SqlKind kind,
    * Returns function that implements given operator call.
    * @return function that implements given operator call
    */
-  public TableFunction getFunction() {
+  @Override public TableFunction getFunction() {
     return (TableFunction) super.getFunction();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorImpl.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorImpl.java
index 9302c480238..1de2f640194 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorImpl.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorImpl.java
@@ -301,23 +301,23 @@ public SqlConformance getConformance() {
     return config.sqlConformance();
   }
 
-  public SqlValidatorCatalogReader getCatalogReader() {
+  @Override public SqlValidatorCatalogReader getCatalogReader() {
     return catalogReader;
   }
 
-  public SqlOperatorTable getOperatorTable() {
+  @Override public SqlOperatorTable getOperatorTable() {
     return opTab;
   }
 
-  public RelDataTypeFactory getTypeFactory() {
+  @Override public RelDataTypeFactory getTypeFactory() {
     return typeFactory;
   }
 
-  public RelDataType getUnknownType() {
+  @Override public RelDataType getUnknownType() {
     return unknownType;
   }
 
-  public SqlNodeList expandStar(
+  @Override public SqlNodeList expandStar(
       SqlNodeList selectList,
       SqlSelect select,
       boolean includeSystemVars) {
@@ -340,7 +340,7 @@ public SqlNodeList expandStar(
   }
 
   // implement SqlValidator
-  public void declareCursor(SqlSelect select, SqlValidatorScope parentScope) {
+  @Override public void declareCursor(SqlSelect select, SqlValidatorScope parentScope) {
     cursorSet.add(select);
 
     // add the cursor to a map that maps the cursor to its select based on
@@ -361,18 +361,18 @@ public void declareCursor(SqlSelect select, SqlValidatorScope parentScope) {
   }
 
   // implement SqlValidator
-  public void pushFunctionCall() {
+  @Override public void pushFunctionCall() {
     FunctionParamInfo funcInfo = new FunctionParamInfo();
     functionCallStack.push(funcInfo);
   }
 
   // implement SqlValidator
-  public void popFunctionCall() {
+  @Override public void popFunctionCall() {
     functionCallStack.pop();
   }
 
   // implement SqlValidator
-  public String getParentCursor(String columnListParamName) {
+  @Override public String getParentCursor(String columnListParamName) {
     FunctionParamInfo funcParamInfo = functionCallStack.peek();
     Map<String, String> parentCursorMap =
         funcParamInfo.columnListParamToParentCursorMap;
@@ -718,7 +718,7 @@ private boolean addOrExpandField(List<SqlNode> selectItems, Set<String> aliases,
     return false;
   }
 
-  public SqlNode validate(SqlNode topNode) {
+  @Override public SqlNode validate(SqlNode topNode) {
     SqlValidatorScope scope = new EmptyScope(this);
     scope = new CatalogScope(scope, ImmutableList.of("CATALOG"));
     final SqlNode topNode2 = validateScopedExpression(topNode, scope);
@@ -727,7 +727,7 @@ public SqlNode validate(SqlNode topNode) {
     return topNode2;
   }
 
-  public List<SqlMoniker> lookupHints(SqlNode topNode, SqlParserPos pos) {
+  @Override public List<SqlMoniker> lookupHints(SqlNode topNode, SqlParserPos pos) {
     SqlValidatorScope scope = new EmptyScope(this);
     SqlNode outermostNode = performUnconditionalRewrites(topNode, false);
     cursorSet.add(outermostNode);
@@ -749,7 +749,7 @@ public List<SqlMoniker> lookupHints(SqlNode topNode, SqlParserPos pos) {
     return ImmutableList.copyOf(hintList);
   }
 
-  public SqlMoniker lookupQualifiedName(SqlNode topNode, SqlParserPos pos) {
+  @Override public SqlMoniker lookupQualifiedName(SqlNode topNode, SqlParserPos pos) {
     final String posString = pos.toString();
     IdInfo info = idPositions.get(posString);
     if (info != null) {
@@ -996,7 +996,7 @@ private static void findAllValidFunctionNames(
     }
   }
 
-  public SqlNode validateParameterizedExpression(
+  @Override public SqlNode validateParameterizedExpression(
       SqlNode topNode,
       final Map<String, RelDataType> nameToTypeMap) {
     SqlValidatorScope scope = new ParameterScope(this, nameToTypeMap);
@@ -1023,7 +1023,7 @@ private SqlNode validateScopedExpression(
     return outermostNode;
   }
 
-  public void validateQuery(SqlNode node, SqlValidatorScope scope,
+  @Override public void validateQuery(SqlNode node, SqlValidatorScope scope,
       RelDataType targetRowType) {
     final SqlValidatorNamespace ns = getNamespace(node, scope);
     if (node.getKind() == SqlKind.TABLESAMPLE) {
@@ -1079,15 +1079,15 @@ public SqlValidatorScope getCursorScope(SqlSelect select) {
     return clauseScopes.get(IdPair.of(select, Clause.CURSOR));
   }
 
-  public SqlValidatorScope getWhereScope(SqlSelect select) {
+  @Override public SqlValidatorScope getWhereScope(SqlSelect select) {
     return clauseScopes.get(IdPair.of(select, Clause.WHERE));
   }
 
-  public SqlValidatorScope getSelectScope(SqlSelect select) {
+  @Override public SqlValidatorScope getSelectScope(SqlSelect select) {
     return clauseScopes.get(IdPair.of(select, Clause.SELECT));
   }
 
-  public SelectScope getRawSelectScope(SqlSelect select) {
+  @Override public SelectScope getRawSelectScope(SqlSelect select) {
     SqlValidatorScope scope = getSelectScope(select);
     if (scope instanceof AggregatingSelectScope) {
       scope = ((AggregatingSelectScope) scope).getParent();
@@ -1095,33 +1095,33 @@ public SelectScope getRawSelectScope(SqlSelect select) {
     return (SelectScope) scope;
   }
 
-  public SqlValidatorScope getHavingScope(SqlSelect select) {
+  @Override public SqlValidatorScope getHavingScope(SqlSelect select) {
     // Yes, it's the same as getSelectScope
     return clauseScopes.get(IdPair.of(select, Clause.SELECT));
   }
 
-  public SqlValidatorScope getGroupScope(SqlSelect select) {
+  @Override public SqlValidatorScope getGroupScope(SqlSelect select) {
     // Yes, it's the same as getWhereScope
     return clauseScopes.get(IdPair.of(select, Clause.GROUP_BY));
   }
 
-  public SqlValidatorScope getFromScope(SqlSelect select) {
+  @Override public SqlValidatorScope getFromScope(SqlSelect select) {
     return scopes.get(select);
   }
 
-  public SqlValidatorScope getOrderScope(SqlSelect select) {
+  @Override public SqlValidatorScope getOrderScope(SqlSelect select) {
     return clauseScopes.get(IdPair.of(select, Clause.ORDER));
   }
 
-  public SqlValidatorScope getMatchRecognizeScope(SqlMatchRecognize node) {
+  @Override public SqlValidatorScope getMatchRecognizeScope(SqlMatchRecognize node) {
     return scopes.get(node);
   }
 
-  public SqlValidatorScope getJoinScope(SqlNode node) {
+  @Override public SqlValidatorScope getJoinScope(SqlNode node) {
     return scopes.get(stripAs(node));
   }
 
-  public SqlValidatorScope getOverScope(SqlNode node) {
+  @Override public SqlValidatorScope getOverScope(SqlNode node) {
     return scopes.get(node);
   }
 
@@ -1170,7 +1170,7 @@ private SqlValidatorNamespace getNamespace(SqlIdentifier id, DelegatingScope sco
     return getNamespace(id);
   }
 
-  public SqlValidatorNamespace getNamespace(SqlNode node) {
+  @Override public SqlValidatorNamespace getNamespace(SqlNode node) {
     switch (node.getKind()) {
     case AS:
 
@@ -1652,7 +1652,7 @@ RelDataType getTableConstructorRowType(
     return typeFactory.leastRestrictive(rowTypes);
   }
 
-  public RelDataType getValidatedNodeType(SqlNode node) {
+  @Override public RelDataType getValidatedNodeType(SqlNode node) {
     RelDataType type = getValidatedNodeTypeIfKnown(node);
     if (type == null) {
       throw Util.needToImplement(node);
@@ -1661,7 +1661,7 @@ public RelDataType getValidatedNodeType(SqlNode node) {
     }
   }
 
-  public RelDataType getValidatedNodeTypeIfKnown(SqlNode node) {
+  @Override public RelDataType getValidatedNodeTypeIfKnown(SqlNode node) {
     final RelDataType type = nodeToTypeMap.get(node);
     if (type != null) {
       return type;
@@ -1689,7 +1689,7 @@ public RelDataType getValidatedNodeTypeIfKnown(SqlNode node) {
    * @param node A SQL parse tree node, never null
    * @param type Its type; must not be null
    */
-  public final void setValidatedNodeType(SqlNode node, RelDataType type) {
+  @Override public final void setValidatedNodeType(SqlNode node, RelDataType type) {
     Objects.requireNonNull(type);
     Objects.requireNonNull(node);
     if (type.equals(unknownType)) {
@@ -1700,11 +1700,11 @@ public final void setValidatedNodeType(SqlNode node, RelDataType type) {
     nodeToTypeMap.put(node, type);
   }
 
-  public void removeValidatedNodeType(SqlNode node) {
+  @Override public void removeValidatedNodeType(SqlNode node) {
     nodeToTypeMap.remove(node);
   }
 
-  @Nullable public SqlCall makeNullaryCall(SqlIdentifier id) {
+  @Override @Nullable public SqlCall makeNullaryCall(SqlIdentifier id) {
     if (id.names.size() == 1 && !id.isComponentQuoted(0)) {
       final List<SqlOperator> list = new ArrayList<>();
       opTab.lookupOperatorOverloads(id, null, SqlSyntax.FUNCTION, list,
@@ -1723,7 +1723,7 @@ public void removeValidatedNodeType(SqlNode node) {
     return null;
   }
 
-  public RelDataType deriveType(
+  @Override public RelDataType deriveType(
       SqlValidatorScope scope,
       SqlNode expr) {
     Objects.requireNonNull(scope);
@@ -1757,7 +1757,7 @@ RelDataType deriveTypeImpl(
     return Objects.requireNonNull(scope.nullifyType(operand, type));
   }
 
-  public RelDataType deriveConstructorType(
+  @Override public RelDataType deriveConstructorType(
       SqlValidatorScope scope,
       SqlCall call,
       SqlFunction unresolvedConstructor,
@@ -1810,7 +1810,7 @@ public RelDataType deriveConstructorType(
     return type;
   }
 
-  public CalciteException handleUnresolvedFunction(SqlCall call,
+  @Override public CalciteException handleUnresolvedFunction(SqlCall call,
       SqlFunction unresolvedFunction, List<RelDataType> argTypes,
       List<String> argNames) {
     // For builtins, we can give a better error message
@@ -1969,7 +1969,7 @@ protected void addToSelectList(
     list.add(exp);
   }
 
-  public String deriveAlias(
+  @Override public String deriveAlias(
       SqlNode node,
       int ordinal) {
     return SqlValidatorUtil.getAlias(node, ordinal);
@@ -2898,7 +2898,7 @@ private void registerWith(
         checkUpdate);
   }
 
-  public boolean isAggregate(SqlSelect select) {
+  @Override public boolean isAggregate(SqlSelect select) {
     if (getAggregate(select) != null) {
       return true;
     }
@@ -3032,7 +3032,7 @@ private void registerOperandSubQueries(
     registerSubQueries(parentScope, operand);
   }
 
-  public void validateIdentifier(SqlIdentifier id, SqlValidatorScope scope) {
+  @Override public void validateIdentifier(SqlIdentifier id, SqlValidatorScope scope) {
     final SqlQualified fqId = scope.fullyQualify(id);
     if (this.config.columnReferenceExpansion()) {
       // NOTE jvs 9-Apr-2007: this doesn't cover ORDER BY, which has its
@@ -3043,7 +3043,7 @@ public void validateIdentifier(SqlIdentifier id, SqlValidatorScope scope) {
     }
   }
 
-  public void validateLiteral(SqlLiteral literal) {
+  @Override public void validateLiteral(SqlLiteral literal) {
     switch (literal.getTypeName()) {
     case DECIMAL:
       // Decimal and long have the same precision (as 64-bit integers), so
@@ -3133,7 +3133,7 @@ private void validateLiteralAsDouble(SqlLiteral literal) {
     // REVIEW jvs 4-Aug-2004:  what about underflow?
   }
 
-  public void validateIntervalQualifier(SqlIntervalQualifier qualifier) {
+  @Override public void validateIntervalQualifier(SqlIntervalQualifier qualifier) {
     assert qualifier != null;
     boolean startPrecisionOutOfRange = false;
     boolean fractionalSecondPrecisionOutOfRange = false;
@@ -3696,7 +3696,7 @@ private SqlModality deduceModality(SqlNode query) {
     }
   }
 
-  public boolean validateModality(SqlSelect select, SqlModality modality,
+  @Override public boolean validateModality(SqlSelect select, SqlModality modality,
       boolean fail) {
     final SelectScope scope = getRawSelectScope(select);
 
@@ -3860,12 +3860,12 @@ protected void validateWindowClause(SqlSelect select) {
     windowList.validate(this, windowScope);
   }
 
-  public void validateWith(SqlWith with, SqlValidatorScope scope) {
+  @Override public void validateWith(SqlWith with, SqlValidatorScope scope) {
     final SqlValidatorNamespace namespace = getNamespace(with);
     validateNamespace(namespace, unknownType);
   }
 
-  public void validateWithItem(SqlWithItem withItem) {
+  @Override public void validateWithItem(SqlWithItem withItem) {
     if (withItem.columnList != null) {
       final RelDataType rowType = getValidatedNodeType(withItem.query);
       final int fieldCount = rowType.getFieldCount();
@@ -3887,7 +3887,7 @@ public void validateWithItem(SqlWithItem withItem) {
     }
   }
 
-  public void validateSequenceValue(SqlValidatorScope scope, SqlIdentifier id) {
+  @Override public void validateSequenceValue(SqlValidatorScope scope, SqlIdentifier id) {
     // Resolve identifier as a table.
     final SqlValidatorScope.ResolvedImpl resolved =
         new SqlValidatorScope.ResolvedImpl();
@@ -3909,21 +3909,21 @@ public void validateSequenceValue(SqlValidatorScope scope, SqlIdentifier id) {
     throw newValidationError(id, RESOURCE.notASequence(id.toString()));
   }
 
-  public SqlValidatorScope getWithScope(SqlNode withItem) {
+  @Override public SqlValidatorScope getWithScope(SqlNode withItem) {
     assert withItem.getKind() == SqlKind.WITH_ITEM;
     return scopes.get(withItem);
   }
 
-  public TypeCoercion getTypeCoercion() {
+  @Override public TypeCoercion getTypeCoercion() {
     assert config.typeCoercionEnabled();
     return this.typeCoercion;
   }
 
-  public Config config() {
+  @Override public Config config() {
     return this.config;
   }
 
-  public SqlValidator transform(UnaryOperator<Config> transform) {
+  @Override public SqlValidator transform(UnaryOperator<Config> transform) {
     this.config = transform.apply(this.config);
     return this;
   }
@@ -4013,7 +4013,7 @@ private void validateOrderItem(SqlSelect select, SqlNode orderItem) {
     validateExpr(orderItem, orderScope);
   }
 
-  public SqlNode expandOrderExpr(SqlSelect select, SqlNode orderExpr) {
+  @Override public SqlNode expandOrderExpr(SqlSelect select, SqlNode orderExpr) {
     final SqlNode newSqlNode =
         new OrderExpressionExpander(select, orderExpr).go();
     if (newSqlNode != orderExpr) {
@@ -4358,7 +4358,7 @@ protected RelDataType createTargetRowType(
     return typeFactory.createStructType(fields);
   }
 
-  public void validateInsert(SqlInsert insert) {
+  @Override public void validateInsert(SqlInsert insert) {
     final SqlValidatorNamespace targetNamespace = getNamespace(insert);
     validateNamespace(targetNamespace, unknownType);
     final RelOptTable relOptTable = SqlValidatorUtil.getRelOptTable(
@@ -4760,7 +4760,7 @@ private SqlNode getNthExpr(SqlNode query, int ordinal, int sourceCount) {
     }
   }
 
-  public void validateDelete(SqlDelete call) {
+  @Override public void validateDelete(SqlDelete call) {
     final SqlSelect sqlSelect = call.getSourceSelect();
     validateSelect(sqlSelect, unknownType);
 
@@ -4771,7 +4771,7 @@ public void validateDelete(SqlDelete call) {
     validateAccess(call.getTargetTable(), table, SqlAccessEnum.DELETE);
   }
 
-  public void validateUpdate(SqlUpdate call) {
+  @Override public void validateUpdate(SqlUpdate call) {
     final SqlValidatorNamespace targetNamespace = getNamespace(call);
     validateNamespace(targetNamespace, unknownType);
     final RelOptTable relOptTable = SqlValidatorUtil.getRelOptTable(
@@ -4801,7 +4801,7 @@ public void validateUpdate(SqlUpdate call) {
     validateAccess(call.getTargetTable(), table, SqlAccessEnum.UPDATE);
   }
 
-  public void validateMerge(SqlMerge call) {
+  @Override public void validateMerge(SqlMerge call) {
     SqlSelect sqlSelect = call.getSourceSelect();
     // REVIEW zfong 5/25/06 - Does an actual type have to be passed into
     // validateSelect()?
@@ -4975,12 +4975,12 @@ protected void validateValues(
         final RelDataType type =
             typeFactory.leastRestrictive(
                 new AbstractList<RelDataType>() {
-                  public RelDataType get(int row) {
+                  @Override public RelDataType get(int row) {
                     SqlCall thisRow = (SqlCall) operands.get(row);
                     return deriveType(scope, thisRow.operand(c));
                   }
 
-                  public int size() {
+                  @Override public int size() {
                     return rowCount;
                   }
                 });
@@ -4994,10 +4994,10 @@ public int size() {
     }
   }
 
-  public void validateDataType(SqlDataTypeSpec dataType) {
+  @Override public void validateDataType(SqlDataTypeSpec dataType) {
   }
 
-  public void validateDynamicParam(SqlDynamicParam dynamicParam) {
+  @Override public void validateDynamicParam(SqlDynamicParam dynamicParam) {
   }
 
   /**
@@ -5014,7 +5014,7 @@ private class ValidationError implements Supplier<CalciteContextException> {
       this.validatorException = validatorException;
     }
 
-    public CalciteContextException get() {
+    @Override public CalciteContextException get() {
       return newValidationError(sqlNode, validatorException);
     }
   }
@@ -5036,7 +5036,7 @@ public ValidationErrorFunction getValidationErrorFunction() {
     return validationErrorFunction;
   }
 
-  public CalciteContextException newValidationError(SqlNode node,
+  @Override public CalciteContextException newValidationError(SqlNode node,
       Resources.ExInst<SqlValidatorException> e) {
     assert node != null;
     final SqlParserPos pos = node.getParserPosition();
@@ -5057,7 +5057,7 @@ protected SqlWindow getWindowByName(
     return window;
   }
 
-  public SqlWindow resolveWindow(
+  @Override public SqlWindow resolveWindow(
       SqlNode windowOrRef,
       SqlValidatorScope scope) {
     SqlWindow window;
@@ -5104,7 +5104,7 @@ SqlValidatorNamespace lookupFieldNamespace(RelDataType rowType, String name) {
     return new FieldNamespace(this, field.getType());
   }
 
-  public void validateWindow(
+  @Override public void validateWindow(
       SqlNode windowOrId,
       SqlValidatorScope scope,
       SqlCall call) {
@@ -5479,7 +5479,7 @@ private SqlNode navigationInDefine(SqlNode node, String alpha) {
     return node;
   }
 
-  public void validateAggregateParams(SqlCall aggCall, SqlNode filter,
+  @Override public void validateAggregateParams(SqlCall aggCall, SqlNode filter,
       SqlNodeList orderList, SqlValidatorScope scope) {
     // For "agg(expr)", expr cannot itself contain aggregate function
     // invocations.  For example, "SUM(2 * MAX(x))" is illegal; when
@@ -5550,7 +5550,7 @@ public void validateAggregateParams(SqlCall aggCall, SqlNode filter,
     }
   }
 
-  public void validateCall(
+  @Override public void validateCall(
       SqlCall call,
       SqlValidatorScope scope) {
     final SqlOperator operator = call.getOperator();
@@ -5604,7 +5604,7 @@ public SqlNode expandSelectExpr(SqlNode expr,
     return newExpr;
   }
 
-  public SqlNode expand(SqlNode expr, SqlValidatorScope scope) {
+  @Override public SqlNode expand(SqlNode expr, SqlValidatorScope scope) {
     final Expander expander = new Expander(this, scope);
     SqlNode newExpr = expr.accept(expander);
     if (expr != newExpr) {
@@ -5624,11 +5624,11 @@ public SqlNode expandGroupByOrHavingExpr(SqlNode expr,
     return newExpr;
   }
 
-  public boolean isSystemField(RelDataTypeField field) {
+  @Override public boolean isSystemField(RelDataTypeField field) {
     return false;
   }
 
-  public List<List<String>> getFieldOrigins(SqlNode sqlQuery) {
+  @Override public List<List<String>> getFieldOrigins(SqlNode sqlQuery) {
     if (sqlQuery instanceof SqlExplain) {
       return Collections.emptyList();
     }
@@ -5677,7 +5677,7 @@ private List<String> getFieldOrigin(SqlNode sqlQuery, int i) {
     }
   }
 
-  public RelDataType getParameterRowType(SqlNode sqlQuery) {
+  @Override public RelDataType getParameterRowType(SqlNode sqlQuery) {
     // NOTE: We assume that bind variables occur in depth-first tree
     // traversal in the same order that they occurred in the SQL text.
     final List<RelDataType> types = new ArrayList<>();
@@ -5708,7 +5708,7 @@ public RelDataType getParameterRowType(SqlNode sqlQuery) {
         });
   }
 
-  public void validateColumnListParams(
+  @Override public void validateColumnListParams(
       SqlFunction function,
       List<RelDataType> argTypes,
       List<SqlNode> operands) {
@@ -5763,7 +5763,7 @@ private static class InsertNamespace extends DmlNamespace {
       this.node = Objects.requireNonNull(node);
     }
 
-    public SqlInsert getNode() {
+    @Override public SqlInsert getNode() {
       return node;
     }
   }
@@ -5780,7 +5780,7 @@ private static class UpdateNamespace extends DmlNamespace {
       this.node = Objects.requireNonNull(node);
     }
 
-    public SqlUpdate getNode() {
+    @Override public SqlUpdate getNode() {
       return node;
     }
   }
@@ -5797,7 +5797,7 @@ private static class DeleteNamespace extends DmlNamespace {
       this.node = Objects.requireNonNull(node);
     }
 
-    public SqlDelete getNode() {
+    @Override public SqlDelete getNode() {
       return node;
     }
   }
@@ -5814,7 +5814,7 @@ private static class MergeNamespace extends DmlNamespace {
       this.node = Objects.requireNonNull(node);
     }
 
-    public SqlMerge getNode() {
+    @Override public SqlMerge getNode() {
       return node;
     }
   }
@@ -5873,16 +5873,16 @@ private class DeriveTypeVisitor implements SqlVisitor<RelDataType> {
       this.scope = scope;
     }
 
-    public RelDataType visit(SqlLiteral literal) {
+    @Override public RelDataType visit(SqlLiteral literal) {
       return literal.createSqlType(typeFactory);
     }
 
-    public RelDataType visit(SqlCall call) {
+    @Override public RelDataType visit(SqlCall call) {
       final SqlOperator operator = call.getOperator();
       return operator.deriveType(SqlValidatorImpl.this, scope, call);
     }
 
-    public RelDataType visit(SqlNodeList nodeList) {
+    @Override public RelDataType visit(SqlNodeList nodeList) {
       // Operand is of a type that we can't derive a type for. If the
       // operand is of a peculiar type, such as a SqlNodeList, then you
       // should override the operator's validateCall() method so that it
@@ -5890,7 +5890,7 @@ public RelDataType visit(SqlNodeList nodeList) {
       throw Util.needToImplement(nodeList);
     }
 
-    public RelDataType visit(SqlIdentifier id) {
+    @Override public RelDataType visit(SqlIdentifier id) {
       // First check for builtin functions which don't have parentheses,
       // like "LOCALTIME".
       final SqlCall call = makeNullaryCall(id);
@@ -5976,7 +5976,7 @@ public RelDataType visit(SqlIdentifier id) {
       return type;
     }
 
-    public RelDataType visit(SqlDataTypeSpec dataType) {
+    @Override public RelDataType visit(SqlDataTypeSpec dataType) {
       // Q. How can a data type have a type?
       // A. When it appears in an expression. (Say as the 2nd arg to the
       //    CAST operator.)
@@ -5984,11 +5984,11 @@ public RelDataType visit(SqlDataTypeSpec dataType) {
       return dataType.deriveType(SqlValidatorImpl.this);
     }
 
-    public RelDataType visit(SqlDynamicParam param) {
+    @Override public RelDataType visit(SqlDynamicParam param) {
       return unknownType;
     }
 
-    public RelDataType visit(SqlIntervalQualifier intervalQualifier) {
+    @Override public RelDataType visit(SqlIntervalQualifier intervalQualifier) {
       return typeFactory.createSqlIntervalType(intervalQualifier);
     }
   }
@@ -6075,7 +6075,7 @@ public SqlNode go() {
       return root.accept(this);
     }
 
-    public SqlNode visit(SqlLiteral literal) {
+    @Override public SqlNode visit(SqlLiteral literal) {
       // Ordinal markers, e.g. 'select a, b from t order by 2'.
       // Only recognize them if they are the whole expression,
       // and if the dialect permits.
@@ -6125,7 +6125,7 @@ private SqlNode nthSelectItem(int ordinal, final SqlParserPos pos) {
       return expr.clone(pos);
     }
 
-    public SqlNode visit(SqlIdentifier id) {
+    @Override public SqlNode visit(SqlIdentifier id) {
       // Aliases, e.g. 'select a as x, b from t order by x'.
       if (id.isSimple()
           && config.sqlConformance().isSortByAlias()) {
@@ -6146,7 +6146,7 @@ public SqlNode visit(SqlIdentifier id) {
       return getScope().fullyQualify(id).identifier;
     }
 
-    protected SqlNode visitScoped(SqlCall call) {
+    @Override protected SqlNode visitScoped(SqlCall call) {
       // Don't attempt to expand sub-queries. We haven't implemented
       // these yet.
       if (call instanceof SqlSelect) {
@@ -6242,7 +6242,7 @@ static class ExtendedExpander extends Expander {
       return super.visit(id);
     }
 
-    public SqlNode visit(SqlLiteral literal) {
+    @Override public SqlNode visit(SqlLiteral literal) {
       if (havingExpr || !validator.config().sqlConformance().isGroupByOrdinal()) {
         return super.visit(literal);
       }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorScope.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorScope.java
index cc58c163bc4..fcdd9acf3cb 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorScope.java
@@ -278,7 +278,7 @@ class Step extends Path {
       return 1 + parent.stepCount();
     }
 
-    protected void build(ImmutableList.Builder<Step> paths) {
+    @Override protected void build(ImmutableList.Builder<Step> paths) {
       parent.build(paths);
       paths.add(this);
     }
@@ -289,7 +289,7 @@ protected void build(ImmutableList.Builder<Step> paths) {
   class ResolvedImpl implements Resolved {
     final List<Resolve> resolves = new ArrayList<>();
 
-    public void found(SqlValidatorNamespace namespace, boolean nullable,
+    @Override public void found(SqlValidatorNamespace namespace, boolean nullable,
         SqlValidatorScope scope, Path path, List<String> remainingNames) {
       if (scope instanceof TableScope) {
         scope = scope.getValidator().getSelectScope((SqlSelect) scope.getNode());
@@ -302,7 +302,7 @@ public void found(SqlValidatorNamespace namespace, boolean nullable,
           new Resolve(namespace, nullable, scope, path, remainingNames));
     }
 
-    public int count() {
+    @Override public int count() {
       return resolves.size();
     }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorUtil.java b/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorUtil.java
index 83644722c09..dcd20bd5f36 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorUtil.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorUtil.java
@@ -1227,7 +1227,7 @@ public static SqlNodeList copy(SqlValidatorScope scope, SqlNodeList list) {
       return (SqlNodeList) list.accept(new DeepCopier(scope));
     }
 
-    public SqlNode visit(SqlNodeList list) {
+    @Override public SqlNode visit(SqlNodeList list) {
       SqlNodeList copy = new SqlNodeList(list.getParserPosition());
       for (SqlNode node : list) {
         copy.add(node.accept(this));
@@ -1237,18 +1237,18 @@ public SqlNode visit(SqlNodeList list) {
 
     // Override to copy all arguments regardless of whether visitor changes
     // them.
-    protected SqlNode visitScoped(SqlCall call) {
+    @Override protected SqlNode visitScoped(SqlCall call) {
       ArgHandler<SqlNode> argHandler =
           new CallCopyingArgHandler(call, true);
       call.getOperator().acceptCall(this, call, false, argHandler);
       return argHandler.result();
     }
 
-    public SqlNode visit(SqlLiteral literal) {
+    @Override public SqlNode visit(SqlLiteral literal) {
       return SqlNode.clone(literal);
     }
 
-    public SqlNode visit(SqlIdentifier id) {
+    @Override public SqlNode visit(SqlIdentifier id) {
       // First check for builtin functions which don't have parentheses,
       // like "LOCALTIME".
       SqlValidator validator = getScope().getValidator();
@@ -1260,15 +1260,15 @@ public SqlNode visit(SqlIdentifier id) {
       return getScope().fullyQualify(id).identifier;
     }
 
-    public SqlNode visit(SqlDataTypeSpec type) {
+    @Override public SqlNode visit(SqlDataTypeSpec type) {
       return SqlNode.clone(type);
     }
 
-    public SqlNode visit(SqlDynamicParam param) {
+    @Override public SqlNode visit(SqlDynamicParam param) {
       return SqlNode.clone(param);
     }
 
-    public SqlNode visit(SqlIntervalQualifier intervalQualifier) {
+    @Override public SqlNode visit(SqlIntervalQualifier intervalQualifier) {
       return SqlNode.clone(intervalQualifier);
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/TableConstructorNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/TableConstructorNamespace.java
index 4dcf36efcb0..0ca3ae77e06 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/TableConstructorNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/TableConstructorNamespace.java
@@ -53,7 +53,7 @@ public class TableConstructorNamespace extends AbstractNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     // First, validate the VALUES. If VALUES is inside INSERT, infers
     // the type of NULL values based on the types of target columns.
     validator.validateValues(values, targetRowType, scope);
@@ -65,7 +65,7 @@ protected RelDataType validateImpl(RelDataType targetRowType) {
     return tableConstructorRowType;
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return values;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/TableNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/TableNamespace.java
index 8a8c59a7345..3ff1ed667c5 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/TableNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/TableNamespace.java
@@ -54,7 +54,7 @@ private TableNamespace(SqlValidatorImpl validator, SqlValidatorTable table,
     this(validator, table, ImmutableList.of());
   }
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     if (extendedFields.isEmpty()) {
       return table.getRowType();
     }
@@ -65,7 +65,7 @@ protected RelDataType validateImpl(RelDataType targetRowType) {
     return builder.build();
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     // This is the only kind of namespace not based on a node in the parse tree.
     return null;
   }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/TableScope.java b/core/src/main/java/org/apache/calcite/sql/validate/TableScope.java
index a412edf6587..c8eb339834e 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/TableScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/TableScope.java
@@ -46,7 +46,7 @@ class TableScope extends ListScope {
 
   //~ Methods ----------------------------------------------------------------
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return node;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/UnnestNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/UnnestNamespace.java
index 06d5a517459..bb80bf6998c 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/UnnestNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/UnnestNamespace.java
@@ -59,7 +59,7 @@ class UnnestNamespace extends AbstractNamespace {
     return null;
   }
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     // Validate the call and its arguments, and infer the return type.
     validator.validateCall(unnest, scope);
     RelDataType type =
@@ -68,7 +68,7 @@ protected RelDataType validateImpl(RelDataType targetRowType) {
     return toStruct(type, unnest);
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return unnest;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/WithItemNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/WithItemNamespace.java
index f7449abacd9..cd3fc4c8808 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/WithItemNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/WithItemNamespace.java
@@ -51,7 +51,7 @@ class WithItemNamespace extends AbstractNamespace {
     return builder.build();
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return withItem;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/WithNamespace.java b/core/src/main/java/org/apache/calcite/sql/validate/WithNamespace.java
index f1e8914a845..364116a4e5c 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/WithNamespace.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/WithNamespace.java
@@ -48,7 +48,7 @@ public class WithNamespace extends AbstractNamespace {
 
   //~ Methods ----------------------------------------------------------------
 
-  protected RelDataType validateImpl(RelDataType targetRowType) {
+  @Override protected RelDataType validateImpl(RelDataType targetRowType) {
     for (SqlNode withItem : with.withList) {
       validator.validateWithItem((SqlWithItem) withItem);
     }
@@ -60,7 +60,7 @@ protected RelDataType validateImpl(RelDataType targetRowType) {
     return rowType;
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return with;
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/WithScope.java b/core/src/main/java/org/apache/calcite/sql/validate/WithScope.java
index 3bfa8474657..35cc98a3a91 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/WithScope.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/WithScope.java
@@ -43,7 +43,7 @@ class WithScope extends ListScope {
     this.withItem = withItem;
   }
 
-  public SqlNode getNode() {
+  @Override public SqlNode getNode() {
     return withItem;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/implicit/AbstractTypeCoercion.java b/core/src/main/java/org/apache/calcite/sql/validate/implicit/AbstractTypeCoercion.java
index fcb424ee32b..858bb3c5091 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/implicit/AbstractTypeCoercion.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/implicit/AbstractTypeCoercion.java
@@ -324,7 +324,7 @@ protected void updateInferredColumnType(
    *
    * @return tightest common type, i.e. INTEGER + DECIMAL(10, 2) returns DECIMAL(10, 2)
    */
-  public RelDataType getTightestCommonType(RelDataType type1, RelDataType type2) {
+  @Override public RelDataType getTightestCommonType(RelDataType type1, RelDataType type2) {
     if (type1 == null || type2 == null) {
       return null;
     }
@@ -430,7 +430,7 @@ private RelDataType promoteToVarChar(RelDataType type1, RelDataType type2) {
    * other is not. For date + timestamp operands, use timestamp as common type,
    * i.e. Timestamp(2017-01-01 00:00 ...) &gt; Date(2018) evaluates to be false.
    */
-  public RelDataType commonTypeForBinaryComparison(RelDataType type1, RelDataType type2) {
+  @Override public RelDataType commonTypeForBinaryComparison(RelDataType type1, RelDataType type2) {
     SqlTypeName typeName1 = type1.getSqlTypeName();
     SqlTypeName typeName2 = type2.getSqlTypeName();
 
@@ -508,7 +508,7 @@ public RelDataType commonTypeForBinaryComparison(RelDataType type1, RelDataType
    * is that we allow some precision loss when widening decimal to fractional,
    * or promote fractional to string type.
    */
-  public RelDataType getWiderTypeForTwo(
+  @Override public RelDataType getWiderTypeForTwo(
       RelDataType type1,
       RelDataType type2,
       boolean stringPromotion) {
@@ -542,7 +542,7 @@ public RelDataType getWiderTypeForTwo(
    * you can override it based on the specific system requirement in
    * {@link org.apache.calcite.rel.type.RelDataTypeSystem}.
    */
-  public RelDataType getWiderTypeForDecimal(RelDataType type1, RelDataType type2) {
+  @Override public RelDataType getWiderTypeForDecimal(RelDataType type1, RelDataType type2) {
     if (!SqlTypeUtil.isDecimal(type1) && !SqlTypeUtil.isDecimal(type2)) {
       return null;
     }
@@ -564,7 +564,8 @@ public RelDataType getWiderTypeForDecimal(RelDataType type1, RelDataType type2)
    * {@link #getWiderTypeForTwo} satisfies the associative law. For instance,
    * (DATE, INTEGER, VARCHAR) should have VARCHAR as the wider common type.
    */
-  public RelDataType getWiderTypeFor(List<RelDataType> typeList, boolean stringPromotion) {
+  @Override public RelDataType getWiderTypeFor(List<RelDataType> typeList,
+      boolean stringPromotion) {
     assert typeList.size() > 1;
     RelDataType resultType = typeList.get(0);
 
diff --git a/core/src/main/java/org/apache/calcite/sql/validate/implicit/TypeCoercionImpl.java b/core/src/main/java/org/apache/calcite/sql/validate/implicit/TypeCoercionImpl.java
index 66ed010d240..a602337fe99 100644
--- a/core/src/main/java/org/apache/calcite/sql/validate/implicit/TypeCoercionImpl.java
+++ b/core/src/main/java/org/apache/calcite/sql/validate/implicit/TypeCoercionImpl.java
@@ -79,7 +79,7 @@ public TypeCoercionImpl(RelDataTypeFactory typeFactory, SqlValidator validator)
    * @param columnIndex Target column index
    * @param targetType  Target type to cast to
    */
-  public boolean rowTypeCoercion(
+  @Override public boolean rowTypeCoercion(
       SqlValidatorScope scope,
       SqlNode query,
       int columnIndex,
@@ -132,7 +132,7 @@ public boolean rowTypeCoercion(
    * If the other operand is DECIMAL,
    * coerce the STRING operand to max precision/scale DECIMAL.
    */
-  public boolean binaryArithmeticCoercion(SqlCallBinding binding) {
+  @Override public boolean binaryArithmeticCoercion(SqlCallBinding binding) {
     // Assume the operator has NUMERIC family operand type checker.
     SqlOperator operator = binding.getOperator();
     SqlKind kind = operator.getKind();
@@ -204,7 +204,7 @@ protected boolean binaryArithmeticWithStrings(
    *   then common comparison type E between D and C as the final common type.</li>
    * </ul>
    */
-  public boolean binaryComparisonCoercion(SqlCallBinding binding) {
+  @Override public boolean binaryComparisonCoercion(SqlCallBinding binding) {
     SqlOperator operator = binding.getOperator();
     SqlKind kind = operator.getKind();
     int operandCnt = binding.getOperandCount();
@@ -376,7 +376,7 @@ protected boolean booleanEquality(SqlCallBinding binding,
    * operands and else operands to find a common type, then cast the operands to the common type
    * when needed.
    */
-  public boolean caseWhenCoercion(SqlCallBinding callBinding) {
+  @Override public boolean caseWhenCoercion(SqlCallBinding callBinding) {
     // For sql statement like:
     // `case when ... then (a, b, c) when ... then (d, e, f) else (g, h, i)`
     // an exception throws when entering this method.
@@ -449,7 +449,7 @@ public boolean caseWhenCoercion(SqlCallBinding callBinding) {
    *   find the common type of LHS and RHS nodes.
    * </ul>
    */
-  public boolean inOperationCoercion(SqlCallBinding binding) {
+  @Override public boolean inOperationCoercion(SqlCallBinding binding) {
     SqlOperator operator = binding.getOperator();
     if (operator.getKind() == SqlKind.IN || operator.getKind() == SqlKind.NOT_IN) {
       assert binding.getOperandCount() == 2;
@@ -472,13 +472,13 @@ public boolean inOperationCoercion(SqlCallBinding binding) {
       for (int i = 0; i < colCount; i++) {
         final int i2 = i;
         List<RelDataType> columnIthTypes = new AbstractList<RelDataType>() {
-          public RelDataType get(int index) {
+          @Override public RelDataType get(int index) {
             return argTypes[index].isStruct()
                 ? argTypes[index].getFieldList().get(i2).getType()
                 : argTypes[index];
           }
 
-          public int size() {
+          @Override public int size() {
             return argTypes.length;
           }
         };
@@ -542,7 +542,7 @@ public int size() {
     return false;
   }
 
-  public boolean builtinFunctionCoercion(
+  @Override public boolean builtinFunctionCoercion(
       SqlCallBinding binding,
       List<RelDataType> operandTypes,
       List<SqlTypeFamily> expectedFamilies) {
@@ -564,7 +564,7 @@ && coerceOperandType(binding.getScope(), binding.getCall(), i, implicitType)
   /**
    * Type coercion for user-defined functions (UDFs).
    */
-  public boolean userDefinedFunctionCoercion(SqlValidatorScope scope,
+  @Override public boolean userDefinedFunctionCoercion(SqlValidatorScope scope,
       SqlCall call, SqlFunction function) {
     final SqlOperandMetadata operandMetadata =
         (SqlOperandMetadata) function.getOperandTypeChecker();
@@ -591,7 +591,7 @@ public boolean userDefinedFunctionCoercion(SqlValidatorScope scope,
     return coerced;
   }
 
-  public boolean querySourceCoercion(SqlValidatorScope scope,
+  @Override public boolean querySourceCoercion(SqlValidatorScope scope,
       RelDataType sourceRowType, RelDataType targetRowType, SqlNode query) {
     final List<RelDataTypeField> sourceFields = sourceRowType.getFieldList();
     final List<RelDataTypeField> targetFields = targetRowType.getFieldList();
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/AuxiliaryConverter.java b/core/src/main/java/org/apache/calcite/sql2rel/AuxiliaryConverter.java
index c0bc1a1a418..c58ad997f75 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/AuxiliaryConverter.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/AuxiliaryConverter.java
@@ -47,7 +47,7 @@ public Impl(SqlFunction f) {
       this.f = f;
     }
 
-    public RexNode convert(RexBuilder rexBuilder, RexNode groupCall,
+    @Override public RexNode convert(RexBuilder rexBuilder, RexNode groupCall,
         RexNode e) {
       switch (f.getKind()) {
       case TUMBLE_START:
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/NullInitializerExpressionFactory.java b/core/src/main/java/org/apache/calcite/sql2rel/NullInitializerExpressionFactory.java
index fe85b749850..8992f04890d 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/NullInitializerExpressionFactory.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/NullInitializerExpressionFactory.java
@@ -38,7 +38,7 @@ public NullInitializerExpressionFactory() {
   }
 
   @SuppressWarnings("deprecation")
-  public boolean isGeneratedAlways(RelOptTable table, int iColumn) {
+  @Override public boolean isGeneratedAlways(RelOptTable table, int iColumn) {
     switch (generationStrategy(table, iColumn)) {
     case VIRTUAL:
     case STORED:
@@ -48,24 +48,24 @@ public boolean isGeneratedAlways(RelOptTable table, int iColumn) {
     }
   }
 
-  public ColumnStrategy generationStrategy(RelOptTable table, int iColumn) {
+  @Override public ColumnStrategy generationStrategy(RelOptTable table, int iColumn) {
     return table.getRowType().getFieldList().get(iColumn).getType().isNullable()
         ? ColumnStrategy.NULLABLE
         : ColumnStrategy.NOT_NULLABLE;
   }
 
-  public RexNode newColumnDefaultValue(RelOptTable table, int iColumn,
+  @Override public RexNode newColumnDefaultValue(RelOptTable table, int iColumn,
       InitializerContext context) {
     final RelDataType fieldType =
         table.getRowType().getFieldList().get(iColumn).getType();
     return context.getRexBuilder().makeNullLiteral(fieldType);
   }
 
-  public BiFunction<InitializerContext, RelNode, RelNode> postExpressionConversionHook() {
+  @Override public BiFunction<InitializerContext, RelNode, RelNode> postExpressionConversionHook() {
     return null;
   }
 
-  public RexNode newAttributeInitializer(RelDataType type,
+  @Override public RexNode newAttributeInitializer(RelDataType type,
       SqlFunction constructor, int iAttribute, List<RexNode> constructorArgs,
       InitializerContext context) {
     final RelDataType fieldType =
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/ReflectiveConvertletTable.java b/core/src/main/java/org/apache/calcite/sql2rel/ReflectiveConvertletTable.java
index ffa05f006cc..47d977882d2 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/ReflectiveConvertletTable.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/ReflectiveConvertletTable.java
@@ -129,7 +129,7 @@ private void registerOpTypeMethod(final Method method) {
     });
   }
 
-  public SqlRexConvertlet get(SqlCall call) {
+  @Override public SqlRexConvertlet get(SqlCall call) {
     SqlRexConvertlet convertlet;
     final SqlOperator op = call.getOperator();
 
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/RelDecorrelator.java b/core/src/main/java/org/apache/calcite/sql2rel/RelDecorrelator.java
index 5ea0f9d1f3c..b4689195171 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/RelDecorrelator.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/RelDecorrelator.java
@@ -2687,7 +2687,7 @@ static class CorRef implements Comparable<CorRef> {
           && field == ((CorRef) o).field;
     }
 
-    public int compareTo(@Nonnull CorRef o) {
+    @Override public int compareTo(@Nonnull CorRef o) {
       int c = corr.compareTo(o.corr);
       if (c != 0) {
         return c;
@@ -2729,7 +2729,7 @@ static class CorDef implements Comparable<CorDef> {
           && field == ((CorDef) o).field;
     }
 
-    public int compareTo(@Nonnull CorDef o) {
+    @Override public int compareTo(@Nonnull CorDef o) {
       int c = corr.compareTo(o.corr);
       if (c != 0) {
         return c;
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/RelFieldTrimmer.java b/core/src/main/java/org/apache/calcite/sql2rel/RelFieldTrimmer.java
index 1f9e0136012..c32c0a6c968 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/RelFieldTrimmer.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/RelFieldTrimmer.java
@@ -208,7 +208,7 @@ protected TrimResult trimChild(
     for (final CorrelationId correlation : rel.getVariablesSet()) {
       rel.accept(
           new CorrelationReferenceFinder() {
-            protected RexNode handle(RexFieldAccess fieldAccess) {
+            @Override protected RexNode handle(RexFieldAccess fieldAccess) {
               final RexCorrelVariable v =
                   (RexCorrelVariable) fieldAccess.getReferenceExpr();
               if (v.id.equals(correlation)) {
@@ -303,7 +303,7 @@ protected TrimResult result(RelNode r, final Mapping mapping) {
     for (final CorrelationId correlation : r.getVariablesSet()) {
       r = r.accept(
           new CorrelationReferenceFinder() {
-            protected RexNode handle(RexFieldAccess fieldAccess) {
+            @Override protected RexNode handle(RexFieldAccess fieldAccess) {
               final RexCorrelVariable v =
                   (RexCorrelVariable) fieldAccess.getReferenceExpr();
               if (v.id.equals(correlation)
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/SqlNodeToRexConverterImpl.java b/core/src/main/java/org/apache/calcite/sql2rel/SqlNodeToRexConverterImpl.java
index c6104c46bf2..0c329741611 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/SqlNodeToRexConverterImpl.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/SqlNodeToRexConverterImpl.java
@@ -56,7 +56,7 @@ public class SqlNodeToRexConverterImpl implements SqlNodeToRexConverter {
 
   //~ Methods ----------------------------------------------------------------
 
-  public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+  @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
     final SqlRexConvertlet convertlet = convertletTable.get(call);
     if (convertlet != null) {
       return convertlet.convertCall(cx, call);
@@ -67,7 +67,7 @@ public RexNode convertCall(SqlRexContext cx, SqlCall call) {
     throw Util.needToImplement(call);
   }
 
-  public RexLiteral convertInterval(
+  @Override public RexLiteral convertInterval(
       SqlRexContext cx,
       SqlIntervalQualifier intervalQualifier) {
     RexBuilder rexBuilder = cx.getRexBuilder();
@@ -75,7 +75,7 @@ public RexLiteral convertInterval(
     return rexBuilder.makeIntervalLiteral(intervalQualifier);
   }
 
-  public RexNode convertLiteral(
+  @Override public RexNode convertLiteral(
       SqlRexContext cx,
       SqlLiteral literal) {
     RexBuilder rexBuilder = cx.getRexBuilder();
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java b/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java
index 2a1c49e2114..2ccbf3d1097 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java
@@ -892,7 +892,7 @@ private static boolean containsInOperator(
     try {
       SqlVisitor<Void> visitor =
           new SqlBasicVisitor<Void>() {
-            public Void visit(SqlCall call) {
+            @Override public Void visit(SqlCall call) {
               if (call.getOperator() instanceof SqlInOperator) {
                 throw new Util.FoundOne(call);
               }
@@ -4094,7 +4094,7 @@ private RelNode convertMultisets(final List<SqlNode> operands,
         } else {
           usedBb =
               createBlackboard(new ListScope(bb.scope) {
-                public SqlNode getNode() {
+                @Override public SqlNode getNode() {
                   return call;
                 }
               }, null, false);
@@ -4542,13 +4542,13 @@ public RexNode register(
         RelDataType returnType =
             typeFactory.createStructType(
                 new AbstractList<Map.Entry<String, RelDataType>>() {
-                  public Map.Entry<String, RelDataType> get(
+                  @Override public Map.Entry<String, RelDataType> get(
                       int index) {
                     return join.getRowType().getFieldList()
                         .get(origLeftInputCount + index);
                   }
 
-                  public int size() {
+                  @Override public int size() {
                     return rexRangeRefLength;
                   }
                 });
@@ -4804,7 +4804,7 @@ ImmutableList<RelNode> retrieveCursors() {
       }
     }
 
-    public RexNode convertExpression(SqlNode expr) {
+    @Override public RexNode convertExpression(SqlNode expr) {
       // If we're in aggregation mode and this is an expression in the
       // GROUP BY clause, return a reference to the field.
       if (agg != null) {
@@ -5035,7 +5035,7 @@ private boolean isConvertedSubq(RexNode rex) {
       return false;
     }
 
-    public int getGroupCount() {
+    @Override public int getGroupCount() {
       if (agg != null) {
         return agg.groupExprs.size();
       }
@@ -5045,35 +5045,35 @@ public int getGroupCount() {
       return -1;
     }
 
-    public RexBuilder getRexBuilder() {
+    @Override public RexBuilder getRexBuilder() {
       return rexBuilder;
     }
 
-    public SqlNode validateExpression(RelDataType rowType, SqlNode expr) {
+    @Override public SqlNode validateExpression(RelDataType rowType, SqlNode expr) {
       return SqlValidatorUtil.validateExprWithRowType(
           catalogReader.nameMatcher().isCaseSensitive(), opTab,
           typeFactory, rowType, expr).left;
     }
 
-    public RexRangeRef getSubQueryExpr(SqlCall call) {
+    @Override public RexRangeRef getSubQueryExpr(SqlCall call) {
       final SubQuery subQuery = getSubQuery(call);
       assert subQuery != null;
       return (RexRangeRef) subQuery.expr;
     }
 
-    public RelDataTypeFactory getTypeFactory() {
+    @Override public RelDataTypeFactory getTypeFactory() {
       return typeFactory;
     }
 
-    public InitializerExpressionFactory getInitializerExpressionFactory() {
+    @Override public InitializerExpressionFactory getInitializerExpressionFactory() {
       return initializerExpressionFactory;
     }
 
-    public SqlValidator getValidator() {
+    @Override public SqlValidator getValidator() {
       return validator;
     }
 
-    public RexNode convertLiteral(SqlLiteral literal) {
+    @Override public RexNode convertLiteral(SqlLiteral literal) {
       return exprConverter.convertLiteral(this, literal);
     }
 
@@ -5081,11 +5081,11 @@ public RexNode convertInterval(SqlIntervalQualifier intervalQualifier) {
       return exprConverter.convertInterval(this, intervalQualifier);
     }
 
-    public RexNode visit(SqlLiteral literal) {
+    @Override public RexNode visit(SqlLiteral literal) {
       return exprConverter.convertLiteral(this, literal);
     }
 
-    public RexNode visit(SqlCall call) {
+    @Override public RexNode visit(SqlCall call) {
       if (agg != null) {
         final SqlOperator op = call.getOperator();
         if (window == null
@@ -5099,23 +5099,23 @@ public RexNode visit(SqlCall call) {
           new SqlCallBinding(validator, scope, call).permutedCall());
     }
 
-    public RexNode visit(SqlNodeList nodeList) {
+    @Override public RexNode visit(SqlNodeList nodeList) {
       throw new UnsupportedOperationException();
     }
 
-    public RexNode visit(SqlIdentifier id) {
+    @Override public RexNode visit(SqlIdentifier id) {
       return convertIdentifier(this, id);
     }
 
-    public RexNode visit(SqlDataTypeSpec type) {
+    @Override public RexNode visit(SqlDataTypeSpec type) {
       throw new UnsupportedOperationException();
     }
 
-    public RexNode visit(SqlDynamicParam param) {
+    @Override public RexNode visit(SqlDynamicParam param) {
       return convertDynamicParam(param);
     }
 
-    public RexNode visit(SqlIntervalQualifier intervalQualifier) {
+    @Override public RexNode visit(SqlIntervalQualifier intervalQualifier) {
       return convertInterval(intervalQualifier);
     }
 
@@ -5155,11 +5155,11 @@ public String getOriginalRelName() {
    * A default implementation of SubQueryConverter that does no conversion.
    */
   private class NoOpSubQueryConverter implements SubQueryConverter {
-    public boolean canConvertSubQuery() {
+    @Override public boolean canConvertSubQuery() {
       return false;
     }
 
-    public RexNode convertSubQuery(
+    @Override public RexNode convertSubQuery(
         SqlCall subQuery,
         SqlToRelConverter parentConverter,
         boolean isExists,
@@ -5316,34 +5316,34 @@ private void addExpr(RexNode expr, String name) {
       convertedInputExprs.add(Pair.of(expr, name));
     }
 
-    public Void visit(SqlIdentifier id) {
+    @Override public Void visit(SqlIdentifier id) {
       return null;
     }
 
-    public Void visit(SqlNodeList nodeList) {
+    @Override public Void visit(SqlNodeList nodeList) {
       for (int i = 0; i < nodeList.size(); i++) {
         nodeList.get(i).accept(this);
       }
       return null;
     }
 
-    public Void visit(SqlLiteral lit) {
+    @Override public Void visit(SqlLiteral lit) {
       return null;
     }
 
-    public Void visit(SqlDataTypeSpec type) {
+    @Override public Void visit(SqlDataTypeSpec type) {
       return null;
     }
 
-    public Void visit(SqlDynamicParam param) {
+    @Override public Void visit(SqlDynamicParam param) {
       return null;
     }
 
-    public Void visit(SqlIntervalQualifier intervalQualifier) {
+    @Override public Void visit(SqlIntervalQualifier intervalQualifier) {
       return null;
     }
 
-    public Void visit(SqlCall call) {
+    @Override public Void visit(SqlCall call) {
       switch (call.getKind()) {
       case FILTER:
       case WITHIN_GROUP:
@@ -5675,7 +5675,7 @@ private class HistogramShuttle extends RexShuttle {
       this.ignoreNulls = ignoreNulls;
     }
 
-    public RexNode visitCall(RexCall call) {
+    @Override public RexNode visitCall(RexCall call) {
       final SqlOperator op = call.getOperator();
       if (!(op instanceof SqlAggFunction)) {
         return super.visitCall(call);
diff --git a/core/src/main/java/org/apache/calcite/sql2rel/StandardConvertletTable.java b/core/src/main/java/org/apache/calcite/sql2rel/StandardConvertletTable.java
index d1c9bd9cd2d..cda75ec1013 100644
--- a/core/src/main/java/org/apache/calcite/sql2rel/StandardConvertletTable.java
+++ b/core/src/main/java/org/apache/calcite/sql2rel/StandardConvertletTable.java
@@ -759,15 +759,15 @@ private static RexNode makeConstructorCall(
     ImmutableList.Builder<RexNode> initializationExprs =
         ImmutableList.builder();
     final InitializerContext initializerContext = new InitializerContext() {
-      public RexBuilder getRexBuilder() {
+      @Override public RexBuilder getRexBuilder() {
         return rexBuilder;
       }
 
-      public SqlNode validateExpression(RelDataType rowType, SqlNode expr) {
+      @Override public SqlNode validateExpression(RelDataType rowType, SqlNode expr) {
         throw new UnsupportedOperationException();
       }
 
-      public RexNode convertExpression(SqlNode e) {
+      @Override public RexNode convertExpression(SqlNode e) {
         throw new UnsupportedOperationException();
       }
     };
@@ -1143,7 +1143,7 @@ private static class RegrCovarianceConvertlet implements SqlRexConvertlet {
       this.kind = kind;
     }
 
-    public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+    @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
       assert call.operandCount() == 2;
       final SqlNode arg1 = call.operand(0);
       final SqlNode arg2 = call.operand(1);
@@ -1269,7 +1269,7 @@ private static class AvgVarianceConvertlet implements SqlRexConvertlet {
       this.kind = kind;
     }
 
-    public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+    @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
       assert call.operandCount() == 1;
       final SqlNode arg = call.operand(0);
       final SqlNode expr;
@@ -1410,7 +1410,7 @@ private static class TrimConvertlet implements SqlRexConvertlet {
       this.flag = flag;
     }
 
-    public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+    @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
       final RexBuilder rexBuilder = cx.getRexBuilder();
       final RexNode operand =
           cx.convertExpression(call.getOperandList().get(0));
@@ -1421,7 +1421,7 @@ public RexNode convertCall(SqlRexContext cx, SqlCall call) {
 
   /** Convertlet that converts {@code GREATEST} and {@code LEAST}. */
   private static class GreatestConvertlet implements SqlRexConvertlet {
-    public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+    @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
       // Translate
       //   GREATEST(a, b, c, d)
       // to
@@ -1476,14 +1476,14 @@ public RexNode convertCall(SqlRexContext cx, SqlCall call) {
 
   /** Convertlet that handles {@code FLOOR} and {@code CEIL} functions. */
   private class FloorCeilConvertlet implements SqlRexConvertlet {
-    public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+    @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
       return convertFloorCeil(cx, call);
     }
   }
 
   /** Convertlet that handles the {@code TIMESTAMPADD} function. */
   private static class TimestampAddConvertlet implements SqlRexConvertlet {
-    public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+    @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
       // TIMESTAMPADD(unit, count, timestamp)
       //  => timestamp + count * INTERVAL '1' UNIT
       final RexBuilder rexBuilder = cx.getRexBuilder();
@@ -1515,7 +1515,7 @@ public RexNode convertCall(SqlRexContext cx, SqlCall call) {
 
   /** Convertlet that handles the {@code TIMESTAMPDIFF} function. */
   private static class TimestampDiffConvertlet implements SqlRexConvertlet {
-    public RexNode convertCall(SqlRexContext cx, SqlCall call) {
+    @Override public RexNode convertCall(SqlRexContext cx, SqlCall call) {
       // TIMESTAMPDIFF(unit, t1, t2)
       //    => (t2 - t1) UNIT
       final RexBuilder rexBuilder = cx.getRexBuilder();
diff --git a/core/src/main/java/org/apache/calcite/statistic/CachingSqlStatisticProvider.java b/core/src/main/java/org/apache/calcite/statistic/CachingSqlStatisticProvider.java
index 37715c9153b..f68e48d2072 100644
--- a/core/src/main/java/org/apache/calcite/statistic/CachingSqlStatisticProvider.java
+++ b/core/src/main/java/org/apache/calcite/statistic/CachingSqlStatisticProvider.java
@@ -43,7 +43,7 @@ public CachingSqlStatisticProvider(SqlStatisticProvider provider,
     this.cache = cache;
   }
 
-  public double tableCardinality(RelOptTable table) {
+  @Override public double tableCardinality(RelOptTable table) {
     try {
       final ImmutableList<Object> key =
           ImmutableList.of("tableCardinality",
@@ -55,7 +55,7 @@ public double tableCardinality(RelOptTable table) {
     }
   }
 
-  public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
+  @Override public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
       RelOptTable toTable, List<Integer> toColumns) {
     try {
       final ImmutableList<Object> key =
@@ -72,7 +72,7 @@ public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
     }
   }
 
-  public boolean isKey(RelOptTable table, List<Integer> columns) {
+  @Override public boolean isKey(RelOptTable table, List<Integer> columns) {
     try {
       final ImmutableList<Object> key =
           ImmutableList.of("isKey", table.getQualifiedName(),
diff --git a/core/src/main/java/org/apache/calcite/statistic/MapSqlStatisticProvider.java b/core/src/main/java/org/apache/calcite/statistic/MapSqlStatisticProvider.java
index 70bbccf6b70..40d0f45d829 100644
--- a/core/src/main/java/org/apache/calcite/statistic/MapSqlStatisticProvider.java
+++ b/core/src/main/java/org/apache/calcite/statistic/MapSqlStatisticProvider.java
@@ -98,7 +98,7 @@ public enum MapSqlStatisticProvider implements SqlStatisticProvider {
     keyMap = initializer.keyMapBuilder.build();
   }
 
-  public double tableCardinality(RelOptTable table) {
+  @Override public double tableCardinality(RelOptTable table) {
     final JdbcTable jdbcTable = table.unwrap(JdbcTable.class);
     final List<String> qualifiedName;
     if (jdbcTable != null) {
@@ -110,7 +110,7 @@ public double tableCardinality(RelOptTable table) {
     return cardinalityMap.get(qualifiedName.toString());
   }
 
-  public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
+  @Override public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
       RelOptTable toTable, List<Integer> toColumns) {
     // Assume that anything that references a primary key is a foreign key.
     // It's wrong but it's enough for our current test cases.
@@ -122,7 +122,7 @@ public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
                 + columnNames(fromTable, fromColumns));
   }
 
-  public boolean isKey(RelOptTable table, List<Integer> columns) {
+  @Override public boolean isKey(RelOptTable table, List<Integer> columns) {
     // In order to match, all column ordinals must be in range 0 .. columnCount
     return columns.stream().allMatch(columnOrdinal ->
         (columnOrdinal >= 0)
diff --git a/core/src/main/java/org/apache/calcite/statistic/QuerySqlStatisticProvider.java b/core/src/main/java/org/apache/calcite/statistic/QuerySqlStatisticProvider.java
index 6529ea011b9..6f510811d40 100644
--- a/core/src/main/java/org/apache/calcite/statistic/QuerySqlStatisticProvider.java
+++ b/core/src/main/java/org/apache/calcite/statistic/QuerySqlStatisticProvider.java
@@ -79,7 +79,7 @@ public QuerySqlStatisticProvider(Consumer<String> sqlConsumer) {
     this.sqlConsumer = Objects.requireNonNull(sqlConsumer);
   }
 
-  public double tableCardinality(RelOptTable table) {
+  @Override public double tableCardinality(RelOptTable table) {
     final SqlDialect dialect = table.unwrap(SqlDialect.class);
     final DataSource dataSource = table.unwrap(DataSource.class);
     return withBuilder(
@@ -107,7 +107,7 @@ public double tableCardinality(RelOptTable table) {
         });
   }
 
-  public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
+  @Override public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
       RelOptTable toTable, List<Integer> toColumns) {
     final SqlDialect dialect = fromTable.unwrap(SqlDialect.class);
     final DataSource dataSource = fromTable.unwrap(DataSource.class);
@@ -152,7 +152,7 @@ public boolean isForeignKey(RelOptTable fromTable, List<Integer> fromColumns,
         });
   }
 
-  public boolean isKey(RelOptTable table, List<Integer> columns) {
+  @Override public boolean isKey(RelOptTable table, List<Integer> columns) {
     final SqlDialect dialect = table.unwrap(SqlDialect.class);
     final DataSource dataSource = table.unwrap(DataSource.class);
     return withBuilder(
diff --git a/core/src/main/java/org/apache/calcite/tools/Frameworks.java b/core/src/main/java/org/apache/calcite/tools/Frameworks.java
index 9a9f9aa633b..111e78c62a4 100644
--- a/core/src/main/java/org/apache/calcite/tools/Frameworks.java
+++ b/core/src/main/java/org/apache/calcite/tools/Frameworks.java
@@ -423,63 +423,63 @@ static class StdFrameworkConfig implements FrameworkConfig {
       this.viewExpander = viewExpander;
     }
 
-    public SqlParser.Config getParserConfig() {
+    @Override public SqlParser.Config getParserConfig() {
       return parserConfig;
     }
 
-    public SqlValidator.Config getSqlValidatorConfig() {
+    @Override public SqlValidator.Config getSqlValidatorConfig() {
       return sqlValidatorConfig;
     }
 
-    public SqlToRelConverter.Config getSqlToRelConverterConfig() {
+    @Override public SqlToRelConverter.Config getSqlToRelConverterConfig() {
       return sqlToRelConverterConfig;
     }
 
-    public SchemaPlus getDefaultSchema() {
+    @Override public SchemaPlus getDefaultSchema() {
       return defaultSchema;
     }
 
-    public RexExecutor getExecutor() {
+    @Override public RexExecutor getExecutor() {
       return executor;
     }
 
-    public ImmutableList<Program> getPrograms() {
+    @Override public ImmutableList<Program> getPrograms() {
       return programs;
     }
 
-    public RelOptCostFactory getCostFactory() {
+    @Override public RelOptCostFactory getCostFactory() {
       return costFactory;
     }
 
-    public ImmutableList<RelTraitDef> getTraitDefs() {
+    @Override public ImmutableList<RelTraitDef> getTraitDefs() {
       return traitDefs;
     }
 
-    public SqlRexConvertletTable getConvertletTable() {
+    @Override public SqlRexConvertletTable getConvertletTable() {
       return convertletTable;
     }
 
-    public Context getContext() {
+    @Override public Context getContext() {
       return context;
     }
 
-    public SqlOperatorTable getOperatorTable() {
+    @Override public SqlOperatorTable getOperatorTable() {
       return operatorTable;
     }
 
-    public RelDataTypeSystem getTypeSystem() {
+    @Override public RelDataTypeSystem getTypeSystem() {
       return typeSystem;
     }
 
-    public boolean isEvolveLattice() {
+    @Override public boolean isEvolveLattice() {
       return evolveLattice;
     }
 
-    public SqlStatisticProvider getStatisticProvider() {
+    @Override public SqlStatisticProvider getStatisticProvider() {
       return statisticProvider;
     }
 
-    public RelOptTable.ViewExpander getViewExpander() {
+    @Override public RelOptTable.ViewExpander getViewExpander() {
       return viewExpander;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/tools/Planner.java b/core/src/main/java/org/apache/calcite/tools/Planner.java
index dccd41473b1..11de3da0d85 100644
--- a/core/src/main/java/org/apache/calcite/tools/Planner.java
+++ b/core/src/main/java/org/apache/calcite/tools/Planner.java
@@ -127,7 +127,7 @@ RelNode transform(int ruleSetIndex,
    * Releases all internal resources utilized while this {@code Planner}
    * exists.  Once called, this Planner object is no longer valid.
    */
-  void close();
+  @Override void close();
 
   RelTraitSet getEmptyTraitSet();
 }
diff --git a/core/src/main/java/org/apache/calcite/tools/Programs.java b/core/src/main/java/org/apache/calcite/tools/Programs.java
index edbfe0c7f32..48d06380b1b 100644
--- a/core/src/main/java/org/apache/calcite/tools/Programs.java
+++ b/core/src/main/java/org/apache/calcite/tools/Programs.java
@@ -291,7 +291,7 @@ private RuleSetProgram(RuleSet ruleSet) {
       this.ruleSet = ruleSet;
     }
 
-    public RelNode run(RelOptPlanner planner, RelNode rel,
+    @Override public RelNode run(RelOptPlanner planner, RelNode rel,
         RelTraitSet requiredOutputTraits,
         List<RelOptMaterialization> materializations,
         List<RelOptLattice> lattices) {
@@ -323,7 +323,7 @@ private static class SequenceProgram implements Program {
       this.programs = programs;
     }
 
-    public RelNode run(RelOptPlanner planner, RelNode rel,
+    @Override public RelNode run(RelOptPlanner planner, RelNode rel,
         RelTraitSet requiredOutputTraits,
         List<RelOptMaterialization> materializations,
         List<RelOptLattice> lattices) {
@@ -343,7 +343,7 @@ public RelNode run(RelOptPlanner planner, RelNode rel,
    * disable field-trimming in {@link SqlToRelConverter}, and run
    * {@link TrimFieldsProgram} after this program. */
   private static class DecorrelateProgram implements Program {
-    public RelNode run(RelOptPlanner planner, RelNode rel,
+    @Override public RelNode run(RelOptPlanner planner, RelNode rel,
         RelTraitSet requiredOutputTraits,
         List<RelOptMaterialization> materializations,
         List<RelOptLattice> lattices) {
@@ -361,7 +361,7 @@ public RelNode run(RelOptPlanner planner, RelNode rel,
 
   /** Program that trims fields. */
   private static class TrimFieldsProgram implements Program {
-    public RelNode run(RelOptPlanner planner, RelNode rel,
+    @Override public RelNode run(RelOptPlanner planner, RelNode rel,
         RelTraitSet requiredOutputTraits,
         List<RelOptMaterialization> materializations,
         List<RelOptLattice> lattices) {
diff --git a/core/src/main/java/org/apache/calcite/tools/RelBuilder.java b/core/src/main/java/org/apache/calcite/tools/RelBuilder.java
index 4f9bb06085d..50477f74ccd 100644
--- a/core/src/main/java/org/apache/calcite/tools/RelBuilder.java
+++ b/core/src/main/java/org/apache/calcite/tools/RelBuilder.java
@@ -2430,11 +2430,11 @@ public RelBuilder values(String[] fieldNames, Object... values) {
           fieldName.e != null ? fieldName.e : "expr$" + fieldName.i;
       final RelDataType type = typeFactory.leastRestrictive(
           new AbstractList<RelDataType>() {
-            public RelDataType get(int index) {
+            @Override public RelDataType get(int index) {
               return tupleList.get(index).get(fieldName.i).getType();
             }
 
-            public int size() {
+            @Override public int size() {
               return rowCount;
             }
           });
@@ -3011,7 +3011,7 @@ static class GroupKeyImpl implements GroupKey {
       return nodes.size();
     }
 
-    public GroupKey alias(String alias) {
+    @Override public GroupKey alias(String alias) {
       return Objects.equals(this.alias, alias)
           ? this
           : new GroupKeyImpl(nodes, nodeLists, alias);
@@ -3124,7 +3124,7 @@ private class AggCallImpl implements AggCallPlus {
       }
     }
 
-    public AggCall sort(Iterable<RexNode> orderKeys) {
+    @Override public AggCall sort(Iterable<RexNode> orderKeys) {
       final ImmutableList<RexNode> orderKeyList =
           ImmutableList.copyOf(orderKeys);
       return orderKeyList.equals(this.orderKeys)
@@ -3133,43 +3133,43 @@ public AggCall sort(Iterable<RexNode> orderKeys) {
               filter, alias, operands, orderKeyList);
     }
 
-    public AggCall sort(RexNode... orderKeys) {
+    @Override public AggCall sort(RexNode... orderKeys) {
       return sort(ImmutableList.copyOf(orderKeys));
     }
 
-    public AggCall approximate(boolean approximate) {
+    @Override public AggCall approximate(boolean approximate) {
       return approximate == this.approximate
           ? this
           : new AggCallImpl(aggFunction, distinct, approximate, ignoreNulls,
               filter, alias, operands, orderKeys);
     }
 
-    public AggCall filter(RexNode condition) {
+    @Override public AggCall filter(RexNode condition) {
       return Objects.equals(condition, this.filter)
           ? this
           : new AggCallImpl(aggFunction, distinct, approximate, ignoreNulls,
               condition, alias, operands, orderKeys);
     }
 
-    public AggCall as(String alias) {
+    @Override public AggCall as(String alias) {
       return Objects.equals(alias, this.alias)
           ? this
           : new AggCallImpl(aggFunction, distinct, approximate, ignoreNulls,
               filter, alias, operands, orderKeys);
     }
 
-    public AggCall distinct(boolean distinct) {
+    @Override public AggCall distinct(boolean distinct) {
       return distinct == this.distinct
           ? this
           : new AggCallImpl(aggFunction, distinct, approximate, ignoreNulls,
               filter, alias, operands, orderKeys);
     }
 
-    public AggCall distinct() {
+    @Override public AggCall distinct() {
       return distinct(true);
     }
 
-    public AggCall ignoreNulls(boolean ignoreNulls) {
+    @Override public AggCall ignoreNulls(boolean ignoreNulls) {
       return ignoreNulls == this.ignoreNulls
           ? this
           : new AggCallImpl(aggFunction, distinct, approximate, ignoreNulls,
@@ -3211,35 +3211,35 @@ private static class AggCallImpl2 implements AggCallPlus {
       // nothing to do
     }
 
-    public AggCall sort(Iterable<RexNode> orderKeys) {
+    @Override public AggCall sort(Iterable<RexNode> orderKeys) {
       throw new UnsupportedOperationException();
     }
 
-    public AggCall sort(RexNode... orderKeys) {
+    @Override public AggCall sort(RexNode... orderKeys) {
       throw new UnsupportedOperationException();
     }
 
-    public AggCall approximate(boolean approximate) {
+    @Override public AggCall approximate(boolean approximate) {
       throw new UnsupportedOperationException();
     }
 
-    public AggCall filter(RexNode condition) {
+    @Override public AggCall filter(RexNode condition) {
       throw new UnsupportedOperationException();
     }
 
-    public AggCall as(String alias) {
+    @Override public AggCall as(String alias) {
       throw new UnsupportedOperationException();
     }
 
-    public AggCall distinct(boolean distinct) {
+    @Override public AggCall distinct(boolean distinct) {
       throw new UnsupportedOperationException();
     }
 
-    public AggCall distinct() {
+    @Override public AggCall distinct() {
       throw new UnsupportedOperationException();
     }
 
-    public AggCall ignoreNulls(boolean ignoreNulls) {
+    @Override public AggCall ignoreNulls(boolean ignoreNulls) {
       throw new UnsupportedOperationException();
     }
   }
@@ -3386,7 +3386,7 @@ private class Shifter extends RexShuttle {
       this.right = right;
     }
 
-    public RexNode visitInputRef(RexInputRef inputRef) {
+    @Override public RexNode visitInputRef(RexInputRef inputRef) {
       final RelDataType leftRowType = left.getRowType();
       final RexBuilder rexBuilder = getRexBuilder();
       final int leftCount = leftRowType.getFieldCount();
diff --git a/core/src/main/java/org/apache/calcite/tools/RuleSets.java b/core/src/main/java/org/apache/calcite/tools/RuleSets.java
index e158ad8dd15..73aff87ad0b 100644
--- a/core/src/main/java/org/apache/calcite/tools/RuleSets.java
+++ b/core/src/main/java/org/apache/calcite/tools/RuleSets.java
@@ -59,7 +59,7 @@ private static class ListRuleSet implements RuleSet {
           && rules.equals(((ListRuleSet) obj).rules);
     }
 
-    public Iterator<RelOptRule> iterator() {
+    @Override public Iterator<RelOptRule> iterator() {
       return rules.iterator();
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/util/BarfingInvocationHandler.java b/core/src/main/java/org/apache/calcite/util/BarfingInvocationHandler.java
index 2ac503086c9..636bc5f1c4c 100644
--- a/core/src/main/java/org/apache/calcite/util/BarfingInvocationHandler.java
+++ b/core/src/main/java/org/apache/calcite/util/BarfingInvocationHandler.java
@@ -39,7 +39,7 @@ protected BarfingInvocationHandler() {
 
   //~ Methods ----------------------------------------------------------------
 
-  public Object invoke(
+  @Override public Object invoke(
       Object proxy,
       Method method,
       Object[] args) throws Throwable {
diff --git a/core/src/main/java/org/apache/calcite/util/BitSets.java b/core/src/main/java/org/apache/calcite/util/BitSets.java
index b592b387af2..559954d4a6e 100644
--- a/core/src/main/java/org/apache/calcite/util/BitSets.java
+++ b/core/src/main/java/org/apache/calcite/util/BitSets.java
@@ -88,17 +88,17 @@ public static Iterable<Integer> toIter(final BitSet bitSet) {
     return () -> new Iterator<Integer>() {
       int i = bitSet.nextSetBit(0);
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return i >= 0;
       }
 
-      public Integer next() {
+      @Override public Integer next() {
         int prev = i;
         i = bitSet.nextSetBit(i + 1);
         return prev;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException();
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/util/BitString.java b/core/src/main/java/org/apache/calcite/util/BitString.java
index eb0caf74267..6cbced8d39e 100644
--- a/core/src/main/java/org/apache/calcite/util/BitString.java
+++ b/core/src/main/java/org/apache/calcite/util/BitString.java
@@ -87,7 +87,7 @@ public static BitString createFromBitString(String s) {
     return new BitString(s, n);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return toBitString();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/util/CastingList.java b/core/src/main/java/org/apache/calcite/util/CastingList.java
index 5329a6bded6..3e52ac9a95e 100644
--- a/core/src/main/java/org/apache/calcite/util/CastingList.java
+++ b/core/src/main/java/org/apache/calcite/util/CastingList.java
@@ -47,24 +47,24 @@ protected CastingList(List<? super E> list, Class<E> clazz) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public E get(int index) {
+  @Override public E get(int index) {
     return clazz.cast(list.get(index));
   }
 
-  public int size() {
+  @Override public int size() {
     return list.size();
   }
 
-  public E set(int index, E element) {
+  @Override public E set(int index, E element) {
     final Object o = list.set(index, element);
     return clazz.cast(o);
   }
 
-  public E remove(int index) {
+  @Override public E remove(int index) {
     return clazz.cast(list.remove(index));
   }
 
-  public void add(int pos, E o) {
+  @Override public void add(int pos, E o) {
     list.add(pos, o);
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/util/ChunkList.java b/core/src/main/java/org/apache/calcite/util/ChunkList.java
index 406e899e521..66d9f6b4671 100644
--- a/core/src/main/java/org/apache/calcite/util/ChunkList.java
+++ b/core/src/main/java/org/apache/calcite/util/ChunkList.java
@@ -218,11 +218,11 @@ private class ChunkListIterator implements ListIterator<E> {
       this.end = end;
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return cursor < size;
     }
 
-    public E next() {
+    @Override public E next() {
       if (cursor >= size) {
         throw new NoSuchElementException();
       }
@@ -245,11 +245,11 @@ public E next() {
       return element;
     }
 
-    public boolean hasPrevious() {
+    @Override public boolean hasPrevious() {
       return cursor > 0;
     }
 
-    public E previous() {
+    @Override public E previous() {
       lastRet = cursor--;
       if (cursor < start) {
         chunk = chunk == null ? last : ChunkList.prev(chunk);
@@ -265,15 +265,15 @@ public E previous() {
       return (E) element(chunk, cursor - start);
     }
 
-    public int nextIndex() {
+    @Override public int nextIndex() {
       return cursor;
     }
 
-    public int previousIndex() {
+    @Override public int previousIndex() {
       return cursor - 1;
     }
 
-    public void remove() {
+    @Override public void remove() {
       if (lastRet < 0) {
         throw new IllegalStateException();
       }
@@ -348,7 +348,7 @@ public void remove() {
       }
     }
 
-    public void set(E e) {
+    @Override public void set(E e) {
       if (lastRet < 0) {
         throw new IllegalStateException();
       }
@@ -363,7 +363,7 @@ public void set(E e) {
       setElement(c, HEADER_SIZE + p - s, e);
     }
 
-    public void add(E e) {
+    @Override public void add(E e) {
       if (chunk == null) {
         Object[] newChunk = new Object[CHUNK_SIZE + HEADER_SIZE];
         if (first != null) {
diff --git a/core/src/main/java/org/apache/calcite/util/Closer.java b/core/src/main/java/org/apache/calcite/util/Closer.java
index 2b3c7bbfea0..39213928721 100644
--- a/core/src/main/java/org/apache/calcite/util/Closer.java
+++ b/core/src/main/java/org/apache/calcite/util/Closer.java
@@ -34,7 +34,7 @@ public <E extends AutoCloseable> E add(E e) {
     return e;
   }
 
-  public void close() {
+  @Override public void close() {
     for (AutoCloseable closeable : list) {
       try {
         closeable.close();
diff --git a/core/src/main/java/org/apache/calcite/util/CompositeList.java b/core/src/main/java/org/apache/calcite/util/CompositeList.java
index f58986c6bc9..a79a90ff2b0 100644
--- a/core/src/main/java/org/apache/calcite/util/CompositeList.java
+++ b/core/src/main/java/org/apache/calcite/util/CompositeList.java
@@ -123,7 +123,7 @@ public static <T> CompositeList<T> of(List<? extends T> list0,
     return new CompositeList<T>((ImmutableList) ImmutableList.of(list0, list1, list2));
   }
 
-  public T get(int index) {
+  @Override public T get(int index) {
     for (List<? extends T> list : lists) {
       int nextIndex = index - list.size();
       if (nextIndex < 0) {
@@ -134,7 +134,7 @@ public T get(int index) {
     throw new IndexOutOfBoundsException();
   }
 
-  public int size() {
+  @Override public int size() {
     int n = 0;
     for (List<? extends T> list : lists) {
       n += list.size();
diff --git a/core/src/main/java/org/apache/calcite/util/CompositeMap.java b/core/src/main/java/org/apache/calcite/util/CompositeMap.java
index 264e9628f2b..6f0d5c36d23 100644
--- a/core/src/main/java/org/apache/calcite/util/CompositeMap.java
+++ b/core/src/main/java/org/apache/calcite/util/CompositeMap.java
@@ -54,11 +54,11 @@ private static <E> ImmutableList<E> list(E e, E[] es) {
     return builder.build();
   }
 
-  public int size() {
+  @Override public int size() {
     return keySet().size();
   }
 
-  public boolean isEmpty() {
+  @Override public boolean isEmpty() {
     // Empty iff all maps are empty.
     for (Map<K, V> map : maps) {
       if (!map.isEmpty()) {
@@ -68,7 +68,7 @@ public boolean isEmpty() {
     return true;
   }
 
-  public boolean containsKey(Object key) {
+  @Override public boolean containsKey(Object key) {
     for (Map<K, V> map : maps) {
       if (map.containsKey(key)) {
         return true;
@@ -77,7 +77,7 @@ public boolean containsKey(Object key) {
     return false;
   }
 
-  public boolean containsValue(Object value) {
+  @Override public boolean containsValue(Object value) {
     for (Map<K, V> map : maps) {
       if (map.containsValue(value)) {
         return true;
@@ -86,7 +86,7 @@ public boolean containsValue(Object value) {
     return false;
   }
 
-  public V get(Object key) {
+  @Override public V get(Object key) {
     for (Map<K, V> map : maps) {
       //noinspection SuspiciousMethodCalls
       if (map.containsKey(key)) {
@@ -96,27 +96,27 @@ public V get(Object key) {
     return null;
   }
 
-  public V put(K key, V value) {
+  @Override public V put(K key, V value) {
     // we are an unmodifiable view on the maps
     throw new UnsupportedOperationException();
   }
 
-  public V remove(Object key) {
+  @Override public V remove(Object key) {
     // we are an unmodifiable view on the maps
     throw new UnsupportedOperationException();
   }
 
-  public void putAll(Map<? extends K, ? extends V> m) {
+  @Override public void putAll(Map<? extends K, ? extends V> m) {
     // we are an unmodifiable view on the maps
     throw new UnsupportedOperationException();
   }
 
-  public void clear() {
+  @Override public void clear() {
     // we are an unmodifiable view on the maps
     throw new UnsupportedOperationException();
   }
 
-  public Set<K> keySet() {
+  @Override public Set<K> keySet() {
     final Set<K> keys = new LinkedHashSet<>();
     for (Map<K, V> map : maps) {
       keys.addAll(map.keySet());
@@ -137,11 +137,11 @@ private Map<K, V> combinedMap() {
     return builder.build();
   }
 
-  public Collection<V> values() {
+  @Override public Collection<V> values() {
     return combinedMap().values();
   }
 
-  public Set<Entry<K, V>> entrySet() {
+  @Override public Set<Entry<K, V>> entrySet() {
     return combinedMap().entrySet();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/util/DelegatingInvocationHandler.java b/core/src/main/java/org/apache/calcite/util/DelegatingInvocationHandler.java
index 26898bb11af..b957698ef2a 100644
--- a/core/src/main/java/org/apache/calcite/util/DelegatingInvocationHandler.java
+++ b/core/src/main/java/org/apache/calcite/util/DelegatingInvocationHandler.java
@@ -51,7 +51,7 @@
 public abstract class DelegatingInvocationHandler implements InvocationHandler {
   //~ Methods ----------------------------------------------------------------
 
-  public Object invoke(
+  @Override public Object invoke(
       Object proxy,
       Method method,
       Object[] args) throws Throwable {
diff --git a/core/src/main/java/org/apache/calcite/util/Filterator.java b/core/src/main/java/org/apache/calcite/util/Filterator.java
index c365733e90d..c2a4fdf4af8 100644
--- a/core/src/main/java/org/apache/calcite/util/Filterator.java
+++ b/core/src/main/java/org/apache/calcite/util/Filterator.java
@@ -47,7 +47,7 @@ public Filterator(Iterator<?> iterator, Class<E> includeFilter) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean hasNext() {
+  @Override public boolean hasNext() {
     if (ready) {
       // Allow hasNext() to be called repeatedly.
       return true;
@@ -64,7 +64,7 @@ public boolean hasNext() {
     }
   }
 
-  public E next() {
+  @Override public E next() {
     if (ready) {
       E o = lookAhead;
       ready = false;
@@ -80,7 +80,7 @@ public E next() {
     throw new NoSuchElementException();
   }
 
-  public void remove() {
+  @Override public void remove() {
     iterator.remove();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/util/ImmutableBeans.java b/core/src/main/java/org/apache/calcite/util/ImmutableBeans.java
index bf38e14c332..a2309cd80fa 100644
--- a/core/src/main/java/org/apache/calcite/util/ImmutableBeans.java
+++ b/core/src/main/java/org/apache/calcite/util/ImmutableBeans.java
@@ -59,7 +59,7 @@ public class ImmutableBeans {
           .weakKeys()
           .softValues()
           .build(new CacheLoader<Class, Def>() {
-            public Def load(@Nonnull Class key) {
+            @Override public Def load(@Nonnull Class key) {
               //noinspection unchecked
               return makeDef(key);
             }
@@ -473,7 +473,7 @@ private static class BeanImpl<T> implements InvocationHandler {
       this.map = Objects.requireNonNull(map);
     }
 
-    public Object invoke(Object proxy, Method method, Object[] args) {
+    @Override public Object invoke(Object proxy, Method method, Object[] args) {
       final Handler handler = def.handlers.get(method);
       if (handler == null) {
         throw new IllegalArgumentException("no handler for method " + method);
diff --git a/core/src/main/java/org/apache/calcite/util/ImmutableBitSet.java b/core/src/main/java/org/apache/calcite/util/ImmutableBitSet.java
index 81cfacc7d9e..a0546275b63 100644
--- a/core/src/main/java/org/apache/calcite/util/ImmutableBitSet.java
+++ b/core/src/main/java/org/apache/calcite/util/ImmutableBitSet.java
@@ -356,7 +356,7 @@ private static void checkRange(int fromIndex, int toIndex) {
    *
    * @return a string representation of this bit set
    */
-  public String toString() {
+  @Override public String toString() {
     int numBits = words.length * BITS_PER_WORD;
     StringBuilder b = new StringBuilder(6 * numBits + 2);
     b.append('{');
@@ -420,7 +420,7 @@ private static int countBits(long[] words) {
    *
    * @return the hash code value for this bit set
    */
-  public int hashCode() {
+  @Override public int hashCode() {
     long h = 1234;
     for (int i = words.length; --i >= 0;) {
       h ^= words[i] * (i + 1);
@@ -453,7 +453,7 @@ public int size() {
    *         {@code false} otherwise
    * @see    #size()
    */
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (this == obj) {
       return true;
     }
@@ -470,7 +470,7 @@ public boolean equals(Object obj) {
    * <p>Bit sets {@code (), (0), (0, 1), (0, 1, 3), (1), (2, 3)} are in sorted
    * order.</p>
    */
-  public int compareTo(@Nonnull ImmutableBitSet o) {
+  @Override public int compareTo(@Nonnull ImmutableBitSet o) {
     int i = 0;
     for (;;) {
       int n0 = nextSetBit(i);
@@ -582,21 +582,21 @@ public int previousClearBit(int fromIndex) {
     }
   }
 
-  public Iterator<Integer> iterator() {
+  @Override public Iterator<Integer> iterator() {
     return new Iterator<Integer>() {
       int i = nextSetBit(0);
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return i >= 0;
       }
 
-      public Integer next() {
+      @Override public Integer next() {
         int prev = i;
         i = nextSetBit(i + 1);
         return prev;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException();
       }
     };
@@ -638,11 +638,11 @@ public List<Integer> asList() {
    * iterator is efficient. */
   public Set<Integer> asSet() {
     return new AbstractSet<Integer>() {
-      @Nonnull public Iterator<Integer> iterator() {
+      @Override @Nonnull public Iterator<Integer> iterator() {
         return ImmutableBitSet.this.iterator();
       }
 
-      public int size() {
+      @Override public int size() {
         return cardinality();
       }
 
diff --git a/core/src/main/java/org/apache/calcite/util/ImmutableIntList.java b/core/src/main/java/org/apache/calcite/util/ImmutableIntList.java
index e0f8e4cad88..81e4dac421c 100644
--- a/core/src/main/java/org/apache/calcite/util/ImmutableIntList.java
+++ b/core/src/main/java/org/apache/calcite/util/ImmutableIntList.java
@@ -128,11 +128,11 @@ private static ImmutableIntList copyFromCollection(
     return ints.length == 0;
   }
 
-  public int size() {
+  @Override public int size() {
     return ints.length;
   }
 
-  public Object[] toArray() {
+  @Override public Object[] toArray() {
     final Object[] objects = new Object[ints.length];
     for (int i = 0; i < objects.length; i++) {
       objects[i] = ints[i];
@@ -140,7 +140,7 @@ public Object[] toArray() {
     return objects;
   }
 
-  public <T> T[] toArray(T[] a) {
+  @Override public <T> T[] toArray(T[] a) {
     final int size = ints.length;
     if (a.length < size) {
       // Make a new array of a's runtime type, but my contents:
@@ -177,7 +177,7 @@ public List<Integer> toIntegerList() {
     return arrayList;
   }
 
-  public Integer get(int index) {
+  @Override public Integer get(int index) {
     return ints[index];
   }
 
@@ -195,13 +195,13 @@ public int getInt(int index) {
 
   @Override public ListIterator<Integer> listIterator(int index) {
     return new AbstractIndexedListIterator<Integer>(size(), index) {
-      protected Integer get(int index) {
+      @Override protected Integer get(int index) {
         return ImmutableIntList.this.get(index);
       }
     };
   }
 
-  public int indexOf(Object o) {
+  @Override public int indexOf(Object o) {
     if (o instanceof Integer) {
       return indexOf((int) (Integer) o);
     }
@@ -217,7 +217,7 @@ public int indexOf(int seek) {
     return -1;
   }
 
-  public int lastIndexOf(Object o) {
+  @Override public int lastIndexOf(Object o) {
     if (o instanceof Integer) {
       return lastIndexOf((int) (Integer) o);
     }
@@ -326,33 +326,33 @@ protected AbstractIndexedListIterator(int size, int position) {
       this.position = position;
     }
 
-    public final boolean hasNext() {
+    @Override public final boolean hasNext() {
       return position < size;
     }
 
-    public final E next() {
+    @Override public final E next() {
       if (!hasNext()) {
         throw new NoSuchElementException();
       }
       return get(position++);
     }
 
-    public final int nextIndex() {
+    @Override public final int nextIndex() {
       return position;
     }
 
-    public final boolean hasPrevious() {
+    @Override public final boolean hasPrevious() {
       return position > 0;
     }
 
-    public final E previous() {
+    @Override public final E previous() {
       if (!hasPrevious()) {
         throw new NoSuchElementException();
       }
       return get(--position);
     }
 
-    public final int previousIndex() {
+    @Override public final int previousIndex() {
       return position - 1;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/util/IntegerIntervalSet.java b/core/src/main/java/org/apache/calcite/util/IntegerIntervalSet.java
index 8fbd7b2ef97..0bdf1324a86 100644
--- a/core/src/main/java/org/apache/calcite/util/IntegerIntervalSet.java
+++ b/core/src/main/java/org/apache/calcite/util/IntegerIntervalSet.java
@@ -100,11 +100,11 @@ private Enumerator<Integer> enumerator() {
     return new Enumerator<Integer>() {
       int i = bounds[0] - 1;
 
-      public Integer current() {
+      @Override public Integer current() {
         return i;
       }
 
-      public boolean moveNext() {
+      @Override public boolean moveNext() {
         for (;;) {
           if (++i > bounds[1]) {
             return false;
@@ -115,11 +115,11 @@ public boolean moveNext() {
         }
       }
 
-      public void reset() {
+      @Override public void reset() {
         i = bounds[0] - 1;
       }
 
-      public void close() {
+      @Override public void close() {
         // no resources
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/util/Litmus.java b/core/src/main/java/org/apache/calcite/util/Litmus.java
index 04773815246..fc19049473d 100644
--- a/core/src/main/java/org/apache/calcite/util/Litmus.java
+++ b/core/src/main/java/org/apache/calcite/util/Litmus.java
@@ -25,17 +25,17 @@ public interface Litmus {
   /** Implementation of {@link org.apache.calcite.util.Litmus} that throws
    * an {@link java.lang.AssertionError} on failure. */
   Litmus THROW = new Litmus() {
-    public boolean fail(String message, Object... args) {
+    @Override public boolean fail(String message, Object... args) {
       final String s = message == null
           ? null : MessageFormatter.arrayFormat(message, args).getMessage();
       throw new AssertionError(s);
     }
 
-    public boolean succeed() {
+    @Override public boolean succeed() {
       return true;
     }
 
-    public boolean check(boolean condition, String message, Object... args) {
+    @Override public boolean check(boolean condition, String message, Object... args) {
       if (condition) {
         return succeed();
       } else {
@@ -47,15 +47,15 @@ public boolean check(boolean condition, String message, Object... args) {
   /** Implementation of {@link org.apache.calcite.util.Litmus} that returns
    * a status code but does not throw. */
   Litmus IGNORE = new Litmus() {
-    public boolean fail(String message, Object... args) {
+    @Override public boolean fail(String message, Object... args) {
       return false;
     }
 
-    public boolean succeed() {
+    @Override public boolean succeed() {
       return true;
     }
 
-    public boolean check(boolean condition, String message, Object... args) {
+    @Override public boolean check(boolean condition, String message, Object... args) {
       return condition;
     }
   };
diff --git a/core/src/main/java/org/apache/calcite/util/NlsString.java b/core/src/main/java/org/apache/calcite/util/NlsString.java
index 8c682563d05..ee7bbd346b2 100644
--- a/core/src/main/java/org/apache/calcite/util/NlsString.java
+++ b/core/src/main/java/org/apache/calcite/util/NlsString.java
@@ -53,7 +53,7 @@ public class NlsString implements Comparable<NlsString>, Cloneable {
           .softValues()
           .build(
               new CacheLoader<Pair<ByteString, Charset>, String>() {
-                public String load(@Nonnull Pair<ByteString, Charset> key) {
+                @Override public String load(@Nonnull Pair<ByteString, Charset> key) {
                   final Charset charset = key.right;
                   final CharsetDecoder decoder = charset.newDecoder();
                   final byte[] bytes = key.left.getBytes();
@@ -149,7 +149,7 @@ private NlsString(String stringValue, ByteString bytesValue,
 
   //~ Methods ----------------------------------------------------------------
 
-  public Object clone() {
+  @Override public Object clone() {
     try {
       return super.clone();
     } catch (CloneNotSupportedException e) {
@@ -157,11 +157,11 @@ public Object clone() {
     }
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return Objects.hash(stringValue, bytesValue, charsetName, collation);
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     return this == obj
         || obj instanceof NlsString
         && Objects.equals(stringValue, ((NlsString) obj).stringValue)
@@ -245,7 +245,7 @@ public String asSql(
    * Returns the string quoted for SQL, for example <code>_ISO-8859-1'is it a
    * plane? no it''s superman!'</code>.
    */
-  public String toString() {
+  @Override public String toString() {
     return asSql(true, true);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/util/Pair.java b/core/src/main/java/org/apache/calcite/util/Pair.java
index c0486475be6..c98f2033f36 100644
--- a/core/src/main/java/org/apache/calcite/util/Pair.java
+++ b/core/src/main/java/org/apache/calcite/util/Pair.java
@@ -87,7 +87,7 @@ public static <K, V> Pair<K, V> of(Map.Entry<K, V> entry) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     return this == obj
         || (obj instanceof Pair)
         && Objects.equals(this.left, ((Pair) obj).left)
@@ -104,7 +104,7 @@ public boolean equals(Object obj) {
     return keyHash ^ valueHash;
   }
 
-  public int compareTo(@Nonnull Pair<T1, T2> that) {
+  @Override public int compareTo(@Nonnull Pair<T1, T2> that) {
     //noinspection unchecked
     int c = NULLS_FIRST_COMPARATOR.compare(this.left, that.left);
     if (c == 0) {
@@ -114,19 +114,19 @@ public int compareTo(@Nonnull Pair<T1, T2> that) {
     return c;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "<" + left + ", " + right + ">";
   }
 
-  public T1 getKey() {
+  @Override public T1 getKey() {
     return left;
   }
 
-  public T2 getValue() {
+  @Override public T2 getValue() {
     return right;
   }
 
-  public T2 setValue(T2 value) {
+  @Override public T2 setValue(T2 value) {
     throw new UnsupportedOperationException();
   }
 
@@ -228,11 +228,11 @@ public static <K, V> List<Pair<K, V>> zip(
       final K[] ks,
       final V[] vs) {
     return new AbstractList<Pair<K, V>>() {
-      public Pair<K, V> get(int index) {
+      @Override public Pair<K, V> get(int index) {
         return Pair.of(ks[index], vs[index]);
       }
 
-      public int size() {
+      @Override public int size() {
         return Math.min(ks.length, vs.length);
       }
     };
@@ -384,15 +384,15 @@ private static class FirstAndIterator<E> implements Iterator<Pair<E, E>> {
       this.first = first;
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return iterator.hasNext();
     }
 
-    public Pair<E, E> next() {
+    @Override public Pair<E, E> next() {
       return of(first, iterator.next());
     }
 
-    public void remove() {
+    @Override public void remove() {
       throw new UnsupportedOperationException("remove");
     }
   }
@@ -411,15 +411,15 @@ private static class ZipIterator<L, R> implements Iterator<Pair<L, R>> {
       this.rightIterator = Objects.requireNonNull(rightIterator);
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return leftIterator.hasNext() && rightIterator.hasNext();
     }
 
-    public Pair<L, R> next() {
+    @Override public Pair<L, R> next() {
       return Pair.of(leftIterator.next(), rightIterator.next());
     }
 
-    public void remove() {
+    @Override public void remove() {
       leftIterator.remove();
       rightIterator.remove();
     }
@@ -440,18 +440,18 @@ private static class AdjacentIterator<E> implements Iterator<Pair<E, E>> {
       previous = first;
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return iterator.hasNext();
     }
 
-    public Pair<E, E> next() {
+    @Override public Pair<E, E> next() {
       final E current = iterator.next();
       final Pair<E, E> pair = of(previous, current);
       previous = current;
       return pair;
     }
 
-    public void remove() {
+    @Override public void remove() {
       throw new UnsupportedOperationException("remove");
     }
   }
@@ -477,11 +477,11 @@ private static class ZipList<K, V> extends AbstractList<Pair<K, V>> {
       this.size = size;
     }
 
-    public Pair<K, V> get(int index) {
+    @Override public Pair<K, V> get(int index) {
       return Pair.of(ks.get(index), vs.get(index));
     }
 
-    public int size() {
+    @Override public int size() {
       return size;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/util/PartiallyOrderedSet.java b/core/src/main/java/org/apache/calcite/util/PartiallyOrderedSet.java
index c63e900bc27..ba5d98f93bd 100644
--- a/core/src/main/java/org/apache/calcite/util/PartiallyOrderedSet.java
+++ b/core/src/main/java/org/apache/calcite/util/PartiallyOrderedSet.java
@@ -154,15 +154,15 @@ private PartiallyOrderedSet(Ordering<E> ordering, Map<E, Node<E>> map,
     return new Iterator<E>() {
       E previous;
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return iterator.hasNext();
       }
 
-      public E next() {
+      @Override public E next() {
         return previous = iterator.next();
       }
 
-      public void remove() {
+      @Override public void remove() {
         if (!PartiallyOrderedSet.this.remove(previous)) {
           // Object was not present.
           // Maybe they have never called 'next'?
diff --git a/core/src/main/java/org/apache/calcite/util/Permutation.java b/core/src/main/java/org/apache/calcite/util/Permutation.java
index 5c4148f8ff3..1a126f15dad 100644
--- a/core/src/main/java/org/apache/calcite/util/Permutation.java
+++ b/core/src/main/java/org/apache/calcite/util/Permutation.java
@@ -89,7 +89,7 @@ private Permutation(int[] targets, int[] sources) {
 
   //~ Methods ----------------------------------------------------------------
 
-  public Object clone() {
+  @Override public Object clone() {
     return new Permutation(
         targets.clone(),
         sources.clone());
@@ -107,11 +107,11 @@ public void identity() {
   /**
    * Returns the number of elements in this permutation.
    */
-  public final int size() {
+  @Override public final int size() {
     return targets.length;
   }
 
-  public void clear() {
+  @Override public void clear() {
     throw new UnsupportedOperationException(
         "Cannot clear: permutation must always contain one mapping per element");
   }
@@ -147,7 +147,7 @@ public void clear() {
    *
    * <p>is represented by the string "[2, 0, 1, 3]".
    */
-  public String toString() {
+  @Override public String toString() {
     StringBuilder buf = new StringBuilder();
     buf.append("[");
     for (int i = 0; i < targets.length; i++) {
@@ -192,7 +192,7 @@ public String toString() {
    *                                        greater than or equal to the size of
    *                                        the permuation
    */
-  public void set(int source, int target) {
+  @Override public void set(int source, int target) {
     set(source, target, false);
   }
 
@@ -393,7 +393,7 @@ private void setInternal(int source, int target) {
   /**
    * Returns the inverse permutation.
    */
-  public Permutation inverse() {
+  @Override public Permutation inverse() {
     return new Permutation(
         sources.clone(),
         targets.clone());
@@ -402,7 +402,7 @@ public Permutation inverse() {
   /**
    * Returns whether this is the identity permutation.
    */
-  public boolean isIdentity() {
+  @Override public boolean isIdentity() {
     for (int i = 0; i < targets.length; i++) {
       if (targets[i] != i) {
         return false;
@@ -414,14 +414,14 @@ public boolean isIdentity() {
   /**
    * Returns the position that <code>source</code> is mapped to.
    */
-  public int getTarget(int source) {
+  @Override public int getTarget(int source) {
     return targets[source];
   }
 
   /**
    * Returns the position which maps to <code>target</code>.
    */
-  public int getSource(int target) {
+  @Override public int getSource(int target) {
     return sources[target];
   }
 
@@ -468,55 +468,55 @@ private boolean isValid(boolean fail) {
     return true;
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     // not very efficient
     return toString().hashCode();
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     // not very efficient
     return (obj instanceof Permutation)
         && toString().equals(obj.toString());
   }
 
   // implement Mapping
-  public Iterator<IntPair> iterator() {
+  @Override public Iterator<IntPair> iterator() {
     return new Iterator<IntPair>() {
       private int i = 0;
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return i < targets.length;
       }
 
-      public IntPair next() {
+      @Override public IntPair next() {
         final IntPair pair = new IntPair(i, targets[i]);
         ++i;
         return pair;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException();
       }
     };
   }
 
-  public int getSourceCount() {
+  @Override public int getSourceCount() {
     return targets.length;
   }
 
-  public int getTargetCount() {
+  @Override public int getTargetCount() {
     return targets.length;
   }
 
-  public MappingType getMappingType() {
+  @Override public MappingType getMappingType() {
     return MappingType.BIJECTION;
   }
 
-  public int getTargetOpt(int source) {
+  @Override public int getTargetOpt(int source) {
     return getTarget(source);
   }
 
-  public int getSourceOpt(int target) {
+  @Override public int getSourceOpt(int target) {
     return getSource(target);
   }
 
diff --git a/core/src/main/java/org/apache/calcite/util/PrecedenceClimbingParser.java b/core/src/main/java/org/apache/calcite/util/PrecedenceClimbingParser.java
index a2a2879655a..940ab155aaf 100644
--- a/core/src/main/java/org/apache/calcite/util/PrecedenceClimbingParser.java
+++ b/core/src/main/java/org/apache/calcite/util/PrecedenceClimbingParser.java
@@ -281,7 +281,7 @@ public static class Call extends Token {
       return print(new StringBuilder()).toString();
     }
 
-    protected StringBuilder print(StringBuilder b) {
+    @Override protected StringBuilder print(StringBuilder b) {
       switch (op.type) {
       case PREFIX:
         b.append('(');
diff --git a/core/src/main/java/org/apache/calcite/util/ReflectUtil.java b/core/src/main/java/org/apache/calcite/util/ReflectUtil.java
index 3609b7545ac..09cf6cebccd 100644
--- a/core/src/main/java/org/apache/calcite/util/ReflectUtil.java
+++ b/core/src/main/java/org/apache/calcite/util/ReflectUtil.java
@@ -419,7 +419,7 @@ public static <R extends ReflectiveVisitor, E> ReflectiveVisitDispatcher<R, E> c
     return new ReflectiveVisitDispatcher<R, E>() {
       final Map<List<Object>, Method> map = new HashMap<>();
 
-      public Method lookupVisitMethod(
+      @Override public Method lookupVisitMethod(
           Class<? extends R> visitorClass,
           Class<? extends E> visiteeClass,
           String visitMethodName) {
@@ -430,7 +430,7 @@ public Method lookupVisitMethod(
             Collections.emptyList());
       }
 
-      public Method lookupVisitMethod(
+      @Override public Method lookupVisitMethod(
           Class<? extends R> visitorClass,
           Class<? extends E> visiteeClass,
           String visitMethodName,
@@ -458,7 +458,7 @@ public Method lookupVisitMethod(
         return method;
       }
 
-      public boolean invokeVisitor(
+      @Override public boolean invokeVisitor(
           R visitor,
           E visitee,
           String visitMethodName) {
@@ -519,7 +519,7 @@ public static <E, T> MethodDispatcher<T> createMethodDispatcher(
         createDispatcher(
             (Class<ReflectiveVisitor>) visitor.getClass(), arg0Clazz);
     return new MethodDispatcher<T>() {
-      public T invoke(Object... args) {
+      @Override public T invoke(Object... args) {
         Method method = lookupMethod(args[0]);
         try {
           final Object o = method.invoke(visitor, args);
diff --git a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
index 98f4bf74083..4ba7edc3e5c 100644
--- a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
+++ b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
@@ -142,7 +142,7 @@ private static String escapeSpecialChar(String inputString) {
    * unparse override. */
   public static SqlSpecialOperator specialOperatorByName(String opName) {
     return new SqlSpecialOperator(opName, SqlKind.OTHER_FUNCTION) {
-      public void unparse(
+      @Override public void unparse(
           SqlWriter writer,
           SqlCall call,
           int leftPrec,
diff --git a/core/src/main/java/org/apache/calcite/util/Sources.java b/core/src/main/java/org/apache/calcite/util/Sources.java
index 4a8c514de05..98713e55731 100644
--- a/core/src/main/java/org/apache/calcite/util/Sources.java
+++ b/core/src/main/java/org/apache/calcite/util/Sources.java
@@ -234,7 +234,7 @@ private static URL fileToUrl(File file) {
       return url;
     }
 
-    public File file() {
+    @Override public File file() {
       if (file == null) {
         throw new UnsupportedOperationException();
       }
diff --git a/core/src/main/java/org/apache/calcite/util/StackWriter.java b/core/src/main/java/org/apache/calcite/util/StackWriter.java
index 9c6676214fd..40da99093a3 100644
--- a/core/src/main/java/org/apache/calcite/util/StackWriter.java
+++ b/core/src/main/java/org/apache/calcite/util/StackWriter.java
@@ -159,7 +159,7 @@ private void popQuote(Character quoteChar) throws IOException {
   }
 
   // implement Writer
-  public void write(int c) throws IOException {
+  @Override public void write(int c) throws IOException {
     switch (c) {
     case INDENT:
       indentationDepth++;
@@ -203,7 +203,7 @@ public void write(int c) throws IOException {
   }
 
   // implement Writer
-  public void write(char[] cbuf, int off, int len) throws IOException {
+  @Override public void write(char[] cbuf, int off, int len) throws IOException {
     // TODO: something more efficient using searches for
     // special characters
     for (int i = off; i < (off + len); i++) {
@@ -212,7 +212,7 @@ public void write(char[] cbuf, int off, int len) throws IOException {
   }
 
   // implement Writer
-  public void write(String str, int off, int len) throws IOException {
+  @Override public void write(String str, int off, int len) throws IOException {
     // TODO: something more efficient using searches for
     // special characters
     for (int i = off; i < (off + len); i++) {
diff --git a/core/src/main/java/org/apache/calcite/util/Util.java b/core/src/main/java/org/apache/calcite/util/Util.java
index 7e045a6e3d9..1f4c49bddcf 100644
--- a/core/src/main/java/org/apache/calcite/util/Util.java
+++ b/core/src/main/java/org/apache/calcite/util/Util.java
@@ -1378,17 +1378,17 @@ public static String lines(Iterable<String> strings) {
   public static Iterable<String> tokenize(final String s, final String delim) {
     return new Iterable<String>() {
       final StringTokenizer t = new StringTokenizer(s, delim);
-      public Iterator<String> iterator() {
+      @Override public Iterator<String> iterator() {
         return new Iterator<String>() {
-          public boolean hasNext() {
+          @Override public boolean hasNext() {
             return t.hasMoreTokens();
           }
 
-          public String next() {
+          @Override public String next() {
             return t.nextToken();
           }
 
-          public void remove() {
+          @Override public void remove() {
             throw new UnsupportedOperationException("remove");
           }
         };
@@ -1782,11 +1782,11 @@ public static <E> Collection<E> filter(
     return new AbstractCollection<E>() {
       private int size = -1;
 
-      public Iterator<E> iterator() {
+      @Override public Iterator<E> iterator() {
         return new Filterator<>(collection.iterator(), includeFilter);
       }
 
-      public int size() {
+      @Override public int size() {
         if (size == -1) {
           // Compute size.  This is expensive, but the value
           // collection.size() is not correct since we're
@@ -1966,11 +1966,11 @@ public static <E> List<E> quotientList(
     }
     final int size = (list.size() + n - k - 1) / n;
     return new AbstractList<E>() {
-      public E get(int index) {
+      @Override public E get(int index) {
         return list.get(index * n + k);
       }
 
-      public int size() {
+      @Override public int size() {
         return size;
       }
     };
@@ -2098,11 +2098,11 @@ public static <E> List<E> skip(List<E> list, int fromIndex) {
 
   public static List<Integer> range(final int end) {
     return new AbstractList<Integer>() {
-      public int size() {
+      @Override public int size() {
         return end;
       }
 
-      public Integer get(int index) {
+      @Override public Integer get(int index) {
         return index;
       }
     };
@@ -2110,11 +2110,11 @@ public Integer get(int index) {
 
   public static List<Integer> range(final int start, final int end) {
     return new AbstractList<Integer>() {
-      public int size() {
+      @Override public int size() {
         return end - start;
       }
 
-      public Integer get(int index) {
+      @Override public Integer get(int index) {
         return start + index;
       }
     };
@@ -2387,16 +2387,16 @@ public static <K, V> Map<K, V> asIndexMapJ(
         Collections2.transform(values, v -> Pair.of(function.apply(v), v));
     final Set<Map.Entry<K, V>> entrySet =
         new AbstractSet<Map.Entry<K, V>>() {
-          public Iterator<Map.Entry<K, V>> iterator() {
+          @Override public Iterator<Map.Entry<K, V>> iterator() {
             return entries.iterator();
           }
 
-          public int size() {
+          @Override public int size() {
             return entries.size();
           }
         };
     return new AbstractMap<K, V>() {
-      public Set<Entry<K, V>> entrySet() {
+      @Override public Set<Entry<K, V>> entrySet() {
         return entrySet;
       }
     };
@@ -2728,11 +2728,11 @@ private static class TransformingList<F, T> extends AbstractList<T> {
       this.list = list;
     }
 
-    public T get(int i) {
+    @Override public T get(int i) {
       return function.apply(list.get(i));
     }
 
-    public int size() {
+    @Override public int size() {
       return list.size();
     }
 
@@ -2771,11 +2771,11 @@ private static class FilteringIterator<T> implements Iterator<T> {
       current = moveNext();
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return current != DUMMY;
     }
 
-    public T next() {
+    @Override public T next() {
       final T t = this.current;
       current = moveNext();
       return t;
diff --git a/core/src/main/java/org/apache/calcite/util/XmlOutput.java b/core/src/main/java/org/apache/calcite/util/XmlOutput.java
index debda9dfc6f..bdf85407b7f 100644
--- a/core/src/main/java/org/apache/calcite/util/XmlOutput.java
+++ b/core/src/main/java/org/apache/calcite/util/XmlOutput.java
@@ -611,7 +611,7 @@ public String escapeString(String s) {
       }
     }
 
-    protected StringEscaper clone() {
+    @Override protected StringEscaper clone() {
       StringEscaper clone = new StringEscaper();
       if (translationVector != null) {
         clone.translationVector = new ArrayList<>(translationVector);
diff --git a/core/src/main/java/org/apache/calcite/util/graph/AttributedDirectedGraph.java b/core/src/main/java/org/apache/calcite/util/graph/AttributedDirectedGraph.java
index 2bae5b7697c..51f93f2e0d8 100644
--- a/core/src/main/java/org/apache/calcite/util/graph/AttributedDirectedGraph.java
+++ b/core/src/main/java/org/apache/calcite/util/graph/AttributedDirectedGraph.java
@@ -52,7 +52,7 @@ public static <V, E extends DefaultEdge> AttributedDirectedGraph<V, E> create(
 
   // CHECKSTYLE: IGNORE 1
   /** @deprecated Use {@link #addEdge(Object, Object, Object...)}. */
-  @Deprecated
+  @Override @Deprecated
   public E addEdge(V vertex, V targetVertex) {
     return super.addEdge(vertex, targetVertex);
   }
@@ -87,7 +87,7 @@ public Iterable<E> getEdges(V source, final V target) {
 
   /** Removes all edges from a given vertex to another.
    * Returns whether any were removed. */
-  public boolean removeEdge(V source, V target) {
+  @Override public boolean removeEdge(V source, V target) {
     // remove out edges
     final List<E> outEdges = vertexMap.get(source).outEdges;
     int removeOutCount = 0;
diff --git a/core/src/main/java/org/apache/calcite/util/graph/BreadthFirstIterator.java b/core/src/main/java/org/apache/calcite/util/graph/BreadthFirstIterator.java
index e6b1067586e..1b150766ce1 100644
--- a/core/src/main/java/org/apache/calcite/util/graph/BreadthFirstIterator.java
+++ b/core/src/main/java/org/apache/calcite/util/graph/BreadthFirstIterator.java
@@ -61,11 +61,11 @@ public static <V, E extends DefaultEdge> void reachable(Set<V> set,
     }
   }
 
-  public boolean hasNext() {
+  @Override public boolean hasNext() {
     return !deque.isEmpty();
   }
 
-  public V next() {
+  @Override public V next() {
     V v = deque.removeFirst();
     for (E e : graph.getOutwardEdges(v)) {
       @SuppressWarnings("unchecked") V target = (V) e.target;
@@ -76,7 +76,7 @@ public V next() {
     return v;
   }
 
-  public void remove() {
+  @Override public void remove() {
     throw new UnsupportedOperationException();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/util/graph/DefaultDirectedGraph.java b/core/src/main/java/org/apache/calcite/util/graph/DefaultDirectedGraph.java
index cae5b4bbce4..3f3bc153eba 100644
--- a/core/src/main/java/org/apache/calcite/util/graph/DefaultDirectedGraph.java
+++ b/core/src/main/java/org/apache/calcite/util/graph/DefaultDirectedGraph.java
@@ -78,7 +78,7 @@ private String toString(Ordering<V> vertexOrdering,
         + ", edges: " + edgeOrdering.sortedCopy(edges) + ")";
   }
 
-  public boolean addVertex(V vertex) {
+  @Override public boolean addVertex(V vertex) {
     if (vertexMap.containsKey(vertex)) {
       return false;
     } else {
@@ -87,11 +87,11 @@ public boolean addVertex(V vertex) {
     }
   }
 
-  public Set<E> edgeSet() {
+  @Override public Set<E> edgeSet() {
     return Collections.unmodifiableSet(edges);
   }
 
-  public E addEdge(V vertex, V targetVertex) {
+  @Override public E addEdge(V vertex, V targetVertex) {
     final VertexInfo<V, E> info = vertexMap.get(vertex);
     if (info == null) {
       throw new IllegalArgumentException("no vertex " + vertex);
@@ -110,7 +110,7 @@ public E addEdge(V vertex, V targetVertex) {
     }
   }
 
-  public E getEdge(V source, V target) {
+  @Override public E getEdge(V source, V target) {
     // REVIEW: could instead use edges.get(new DefaultEdge(source, target))
     final VertexInfo<V, E> info = vertexMap.get(source);
     for (E outEdge : info.outEdges) {
@@ -121,7 +121,7 @@ public E getEdge(V source, V target) {
     return null;
   }
 
-  public boolean removeEdge(V source, V target) {
+  @Override public boolean removeEdge(V source, V target) {
     // remove out edges
     final List<E> outEdges = vertexMap.get(source).outEdges;
     boolean outRemoved = false;
@@ -150,11 +150,11 @@ public boolean removeEdge(V source, V target) {
     return outRemoved;
   }
 
-  public Set<V> vertexSet() {
+  @Override public Set<V> vertexSet() {
     return vertexMap.keySet();
   }
 
-  public void removeAllVertices(Collection<V> collection) {
+  @Override public void removeAllVertices(Collection<V> collection) {
     // The point at which collection is large enough to make the 'majority'
     // algorithm more efficient.
     final float threshold = 0.35f;
@@ -208,11 +208,11 @@ private void removeMajorityVertices(Set<V> vertexSet) {
     }
   }
 
-  public List<E> getOutwardEdges(V source) {
+  @Override public List<E> getOutwardEdges(V source) {
     return vertexMap.get(source).outEdges;
   }
 
-  public List<E> getInwardEdges(V target) {
+  @Override public List<E> getInwardEdges(V target) {
     return vertexMap.get(target).inEdges;
   }
 
diff --git a/core/src/main/java/org/apache/calcite/util/graph/DepthFirstIterator.java b/core/src/main/java/org/apache/calcite/util/graph/DepthFirstIterator.java
index 3fbbaa29257..466a98079d3 100644
--- a/core/src/main/java/org/apache/calcite/util/graph/DepthFirstIterator.java
+++ b/core/src/main/java/org/apache/calcite/util/graph/DepthFirstIterator.java
@@ -75,15 +75,15 @@ private static <V, E extends DefaultEdge> void buildListRecurse(
     activeVertices.remove(start);
   }
 
-  public boolean hasNext() {
+  @Override public boolean hasNext() {
     return iterator.hasNext();
   }
 
-  public V next() {
+  @Override public V next() {
     return iterator.next();
   }
 
-  public void remove() {
+  @Override public void remove() {
     throw new UnsupportedOperationException();
   }
 }
diff --git a/core/src/main/java/org/apache/calcite/util/graph/Graphs.java b/core/src/main/java/org/apache/calcite/util/graph/Graphs.java
index e731e173e7e..3e2230d23c0 100644
--- a/core/src/main/java/org/apache/calcite/util/graph/Graphs.java
+++ b/core/src/main/java/org/apache/calcite/util/graph/Graphs.java
@@ -40,12 +40,12 @@ public static <V, E extends DefaultEdge> List<V> predecessorListOf(
       DirectedGraph<V, E> graph, V vertex) {
     final List<E> edges = graph.getInwardEdges(vertex);
     return new AbstractList<V>() {
-      public V get(int index) {
+      @Override public V get(int index) {
         //noinspection unchecked
         return (V) edges.get(index).source;
       }
 
-      public int size() {
+      @Override public int size() {
         return edges.size();
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/util/graph/TopologicalOrderIterator.java b/core/src/main/java/org/apache/calcite/util/graph/TopologicalOrderIterator.java
index ebbbc4ea452..9ea1c1dc270 100644
--- a/core/src/main/java/org/apache/calcite/util/graph/TopologicalOrderIterator.java
+++ b/core/src/main/java/org/apache/calcite/util/graph/TopologicalOrderIterator.java
@@ -65,11 +65,11 @@ private void populate(Map<V, int[]> countMap, List<V> empties) {
     countMap.keySet().removeAll(empties);
   }
 
-  public boolean hasNext() {
+  @Override public boolean hasNext() {
     return !empties.isEmpty();
   }
 
-  public V next() {
+  @Override public V next() {
     V v = empties.remove(0);
     for (E o : graph.vertexMap.get(v).outEdges) {
       //noinspection unchecked
@@ -82,7 +82,7 @@ public V next() {
     return v;
   }
 
-  public void remove() {
+  @Override public void remove() {
     throw new UnsupportedOperationException();
   }
 
diff --git a/core/src/main/java/org/apache/calcite/util/javac/JaninoCompiler.java b/core/src/main/java/org/apache/calcite/util/javac/JaninoCompiler.java
index 23b430c293e..47508616423 100644
--- a/core/src/main/java/org/apache/calcite/util/javac/JaninoCompiler.java
+++ b/core/src/main/java/org/apache/calcite/util/javac/JaninoCompiler.java
@@ -50,7 +50,7 @@ public JaninoCompiler() {
   //~ Methods ----------------------------------------------------------------
 
   // implement JavaCompiler
-  public void compile() {
+  @Override public void compile() {
     // REVIEW: SWZ: 3/12/2006: When this method is invoked multiple times,
     // it creates a series of AccountingClassLoader objects, each with
     // the previous as its parent ClassLoader.  If we refactored this
@@ -90,17 +90,17 @@ public void compile() {
   }
 
   // implement JavaCompiler
-  public JavaCompilerArgs getArgs() {
+  @Override public JavaCompilerArgs getArgs() {
     return args;
   }
 
   // implement JavaCompiler
-  public ClassLoader getClassLoader() {
+  @Override public ClassLoader getClassLoader() {
     return classLoader;
   }
 
   // implement JavaCompiler
-  public int getTotalByteCodeSize() {
+  @Override public int getTotalByteCodeSize() {
     return classLoader.getTotalByteCodeSize();
   }
 
@@ -117,21 +117,21 @@ public static class JaninoCompilerArgs extends JavaCompilerArgs {
     public JaninoCompilerArgs() {
     }
 
-    public boolean supportsSetSource() {
+    @Override public boolean supportsSetSource() {
       return true;
     }
 
-    public void setDestdir(String destdir) {
+    @Override public void setDestdir(String destdir) {
       super.setDestdir(destdir);
       this.destdir = destdir;
     }
 
-    public void setSource(String source, String fileName) {
+    @Override public void setSource(String source, String fileName) {
       this.source = source;
       addFile(fileName);
     }
 
-    public void setFullClassName(String fullClassName) {
+    @Override public void setFullClassName(String fullClassName) {
       this.fullClassName = fullClassName;
     }
   }
diff --git a/core/src/main/java/org/apache/calcite/util/mapping/AbstractSourceMapping.java b/core/src/main/java/org/apache/calcite/util/mapping/AbstractSourceMapping.java
index c4329e32ed7..3bf8abbac00 100644
--- a/core/src/main/java/org/apache/calcite/util/mapping/AbstractSourceMapping.java
+++ b/core/src/main/java/org/apache/calcite/util/mapping/AbstractSourceMapping.java
@@ -43,23 +43,23 @@ public AbstractSourceMapping(int sourceCount, int targetCount) {
     return targetCount;
   }
 
-  public Mapping inverse() {
+  @Override public Mapping inverse() {
     return Mappings.invert(this);
   }
 
-  public int size() {
+  @Override public int size() {
     return targetCount;
   }
 
-  public void clear() {
+  @Override public void clear() {
     throw new UnsupportedOperationException();
   }
 
-  public MappingType getMappingType() {
+  @Override public MappingType getMappingType() {
     return MappingType.INVERSE_PARTIAL_FUNCTION;
   }
 
-  public Iterator<IntPair> iterator() {
+  @Override public Iterator<IntPair> iterator() {
     return new Iterator<IntPair>() {
       int source;
       int target = -1;
@@ -77,21 +77,21 @@ private void moveToNext() {
         }
       }
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return target < targetCount;
       }
 
-      public IntPair next() {
+      @Override public IntPair next() {
         IntPair p = new IntPair(source, target);
         moveToNext();
         return p;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException("remove");
       }
     };
   }
 
-  public abstract int getSourceOpt(int source);
+  @Override public abstract int getSourceOpt(int source);
 }
diff --git a/core/src/main/java/org/apache/calcite/util/mapping/AbstractTargetMapping.java b/core/src/main/java/org/apache/calcite/util/mapping/AbstractTargetMapping.java
index cd4db08aae7..22fa0166a22 100644
--- a/core/src/main/java/org/apache/calcite/util/mapping/AbstractTargetMapping.java
+++ b/core/src/main/java/org/apache/calcite/util/mapping/AbstractTargetMapping.java
@@ -43,23 +43,23 @@ public AbstractTargetMapping(int sourceCount, int targetCount) {
     return targetCount;
   }
 
-  public Mapping inverse() {
+  @Override public Mapping inverse() {
     return Mappings.invert(this);
   }
 
-  public int size() {
+  @Override public int size() {
     return sourceCount;
   }
 
-  public void clear() {
+  @Override public void clear() {
     throw new UnsupportedOperationException();
   }
 
-  public MappingType getMappingType() {
+  @Override public MappingType getMappingType() {
     return MappingType.PARTIAL_FUNCTION;
   }
 
-  public Iterator<IntPair> iterator() {
+  @Override public Iterator<IntPair> iterator() {
     return new Iterator<IntPair>() {
       int source = -1;
       int target;
@@ -77,21 +77,21 @@ private void moveToNext() {
         }
       }
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return source < sourceCount;
       }
 
-      public IntPair next() {
+      @Override public IntPair next() {
         IntPair p = new IntPair(source, target);
         moveToNext();
         return p;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException("remove");
       }
     };
   }
 
-  public abstract int getTargetOpt(int source);
+  @Override public abstract int getTargetOpt(int source);
 }
diff --git a/core/src/main/java/org/apache/calcite/util/mapping/IntPair.java b/core/src/main/java/org/apache/calcite/util/mapping/IntPair.java
index 2b2a4c06895..4abf84f2a49 100644
--- a/core/src/main/java/org/apache/calcite/util/mapping/IntPair.java
+++ b/core/src/main/java/org/apache/calcite/util/mapping/IntPair.java
@@ -36,7 +36,7 @@ public class IntPair {
   @Deprecated
   public static final Function<IntPair, IntPair> SWAP =
       new Function<IntPair, IntPair>() {
-        public IntPair apply(IntPair pair) {
+        @Override public IntPair apply(IntPair pair) {
           return of(pair.target, pair.source);
         }
       };
@@ -46,7 +46,7 @@ public IntPair apply(IntPair pair) {
   public static final Ordering<IntPair> ORDERING =
       Ordering.from(
           new Comparator<IntPair>() {
-            public int compare(IntPair o1, IntPair o2) {
+            @Override public int compare(IntPair o1, IntPair o2) {
               int c = Integer.compare(o1.source, o2.source);
               if (c == 0) {
                 c = Integer.compare(o1.target, o2.target);
@@ -59,7 +59,7 @@ public int compare(IntPair o1, IntPair o2) {
   @Deprecated
   public static final Function<IntPair, Integer> LEFT =
       new Function<IntPair, Integer>() {
-        public Integer apply(IntPair pair) {
+        @Override public Integer apply(IntPair pair) {
           return pair.source;
         }
       };
@@ -68,7 +68,7 @@ public Integer apply(IntPair pair) {
   @Deprecated
   public static final Function<IntPair, Integer> RIGHT =
       new Function<IntPair, Integer>() {
-        public Integer apply(IntPair pair) {
+        @Override public Integer apply(IntPair pair) {
           return pair.target;
         }
       };
@@ -91,11 +91,11 @@ public static IntPair of(int left, int right) {
     return new IntPair(left, right);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return source + "-" + target;
   }
 
-  public boolean equals(Object obj) {
+  @Override public boolean equals(Object obj) {
     if (obj instanceof IntPair) {
       IntPair that = (IntPair) obj;
       return (this.source == that.source) && (this.target == that.target);
@@ -103,7 +103,7 @@ public boolean equals(Object obj) {
     return false;
   }
 
-  public int hashCode() {
+  @Override public int hashCode() {
     return Utilities.hash(source, target);
   }
 
@@ -146,12 +146,12 @@ public static List<IntPair> zip(
       size = Math.min(lefts.size(), rights.size());
     }
     return new AbstractList<IntPair>() {
-      public IntPair get(int index) {
+      @Override public IntPair get(int index) {
         return IntPair.of(lefts.get(index).intValue(),
             rights.get(index).intValue());
       }
 
-      public int size() {
+      @Override public int size() {
         return size;
       }
     };
diff --git a/core/src/main/java/org/apache/calcite/util/mapping/Mapping.java b/core/src/main/java/org/apache/calcite/util/mapping/Mapping.java
index f3c20d77eee..ddf528b2724 100644
--- a/core/src/main/java/org/apache/calcite/util/mapping/Mapping.java
+++ b/core/src/main/java/org/apache/calcite/util/mapping/Mapping.java
@@ -48,26 +48,26 @@ public interface Mapping
    * <p>This method is optional; implementations may throw
    * {@link UnsupportedOperationException}.
    */
-  Iterator<IntPair> iterator();
+  @Override Iterator<IntPair> iterator();
 
   /**
    * Returns the number of sources. Valid sources will be in the range 0 ..
    * sourceCount.
    */
-  int getSourceCount();
+  @Override int getSourceCount();
 
   /**
    * Returns the number of targets. Valid targets will be in the range 0 ..
    * targetCount.
    */
-  int getTargetCount();
+  @Override int getTargetCount();
 
-  MappingType getMappingType();
+  @Override MappingType getMappingType();
 
   /**
    * Returns whether this mapping is the identity.
    */
-  boolean isIdentity();
+  @Override boolean isIdentity();
 
   /**
    * Removes all elements in the mapping.
@@ -77,5 +77,5 @@ public interface Mapping
   /**
    * Returns the number of elements in the mapping.
    */
-  int size();
+  @Override int size();
 }
diff --git a/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java b/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java
index aa88d1135fc..d0d70b812d6 100644
--- a/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java
+++ b/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java
@@ -250,12 +250,12 @@ public static List<Integer> apply2(
       final Mapping mapping,
       final List<Integer> list) {
     return new AbstractList<Integer>() {
-      public Integer get(int index) {
+      @Override public Integer get(int index) {
         final int source = list.get(index);
         return mapping.getTarget(source);
       }
 
-      public int size() {
+      @Override public int size() {
         return list.size();
       }
     };
@@ -294,11 +294,11 @@ public static <T> List<T> apply3(
   public static <T> List<T> permute(final List<T> list,
       final TargetMapping mapping) {
     return new AbstractList<T>() {
-      public T get(int index) {
+      @Override public T get(int index) {
         return list.get(mapping.getTarget(index));
       }
 
-      public int size() {
+      @Override public int size() {
         return mapping.getSourceCount();
       }
     };
@@ -313,12 +313,12 @@ public int size() {
    */
   public static List<Integer> asList(final TargetMapping mapping) {
     return new AbstractList<Integer>() {
-      public Integer get(int source) {
+      @Override public Integer get(int source) {
         int target = mapping.getTargetOpt(source);
         return target < 0 ? null : target;
       }
 
-      public int size() {
+      @Override public int size() {
         return mapping.getSourceCount();
       }
     };
@@ -336,7 +336,7 @@ public int size() {
    */
   public static List<Integer> asListNonNull(final TargetMapping mapping) {
     return new AbstractList<Integer>() {
-      public Integer get(int source) {
+      @Override public Integer get(int source) {
         int target = mapping.getTargetOpt(source);
         if (target < 0) {
           throw new IllegalArgumentException("Element " + source + " is not found in mapping "
@@ -345,7 +345,7 @@ public Integer get(int source) {
         return target;
       }
 
-      public int size() {
+      @Override public int size() {
         return mapping.getSourceCount();
       }
     };
@@ -764,16 +764,16 @@ public static Iterable<IntPair> invert(final Iterable<IntPair> pairs) {
    * {@link org.apache.calcite.util.mapping.IntPair}s. */
   public static Iterator<IntPair> invert(final Iterator<IntPair> pairs) {
     return new Iterator<IntPair>() {
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return pairs.hasNext();
       }
 
-      public IntPair next() {
+      @Override public IntPair next() {
         final IntPair pair = pairs.next();
         return IntPair.of(pair.target, pair.source);
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException("remove");
       }
     };
@@ -827,7 +827,7 @@ public interface FunctionMapping extends CoreMapping {
      */
     int getTarget(int source);
 
-    MappingType getMappingType();
+    @Override MappingType getMappingType();
 
     int getSourceCount();
   }
@@ -869,7 +869,7 @@ public interface SourceMapping extends CoreMapping {
      */
     int getTargetOpt(int source);
 
-    MappingType getMappingType();
+    @Override MappingType getMappingType();
 
     boolean isIdentity();
 
@@ -890,7 +890,7 @@ public interface SourceMapping extends CoreMapping {
    * <p>TODO: figure out which interfaces this should extend
    */
   public interface TargetMapping extends FunctionMapping {
-    int getSourceCount();
+    @Override int getSourceCount();
 
     /**
      * Returns the source that a target maps to, or -1 if it is not mapped.
@@ -906,12 +906,12 @@ public interface TargetMapping extends FunctionMapping {
      * @return target
      * @throws NoElementException if source is not mapped
      */
-    int getTarget(int source);
+    @Override int getTarget(int source);
 
     /**
      * Returns the target that a source maps to, or -1 if it is not mapped.
      */
-    int getTargetOpt(int source);
+    @Override int getTargetOpt(int source);
 
     void set(int source, int target);
 
@@ -922,15 +922,15 @@ public interface TargetMapping extends FunctionMapping {
 
   /** Abstract implementation of {@link Mapping}. */
   public abstract static class AbstractMapping implements Mapping {
-    public void set(int source, int target) {
+    @Override public void set(int source, int target) {
       throw new UnsupportedOperationException();
     }
 
-    public int getTargetOpt(int source) {
+    @Override public int getTargetOpt(int source) {
       throw new UnsupportedOperationException();
     }
 
-    public int getTarget(int source) {
+    @Override public int getTarget(int source) {
       int target = getTargetOpt(source);
       if (target == -1) {
         throw new NoElementException(
@@ -939,11 +939,11 @@ public int getTarget(int source) {
       return target;
     }
 
-    public int getSourceOpt(int target) {
+    @Override public int getSourceOpt(int target) {
       throw new UnsupportedOperationException();
     }
 
-    public int getSource(int target) {
+    @Override public int getSource(int target) {
       int source = getSourceOpt(target);
       if (source == -1) {
         throw new NoElementException(
@@ -952,15 +952,15 @@ public int getSource(int target) {
       return source;
     }
 
-    public int getSourceCount() {
+    @Override public int getSourceCount() {
       throw new UnsupportedOperationException();
     }
 
-    public int getTargetCount() {
+    @Override public int getTargetCount() {
       throw new UnsupportedOperationException();
     }
 
-    public boolean isIdentity() {
+    @Override public boolean isIdentity() {
       int sourceCount = getSourceCount();
       int targetCount = getTargetCount();
       if (sourceCount != targetCount) {
@@ -1017,7 +1017,7 @@ public boolean isIdentity() {
      *
      * <p>This method relies upon the optional method {@link #iterator()}.
      */
-    public String toString() {
+    @Override public String toString() {
       StringBuilder buf = new StringBuilder();
       buf.append("[size=").append(size())
           .append(", sourceCount=").append(getSourceCount())
@@ -1038,16 +1038,16 @@ public String toString() {
   /** Abstract implementation of mapping where both source and target
    * domains are finite. */
   public abstract static class FiniteAbstractMapping extends AbstractMapping {
-    public Iterator<IntPair> iterator() {
+    @Override public Iterator<IntPair> iterator() {
       return new FunctionMappingIter(this);
     }
 
-    public int hashCode() {
+    @Override public int hashCode() {
       // not very efficient
       return toString().hashCode();
     }
 
-    public boolean equals(Object obj) {
+    @Override public boolean equals(Object obj) {
       // not very efficient
       return (obj instanceof Mapping)
           && toString().equals(obj.toString());
@@ -1064,19 +1064,19 @@ static class FunctionMappingIter implements Iterator<IntPair> {
       this.mapping = mapping;
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return (i < mapping.getSourceCount())
           || (mapping.getSourceCount() == -1);
     }
 
-    public IntPair next() {
+    @Override public IntPair next() {
       int x = i++;
       return new IntPair(
           x,
           mapping.getTarget(x));
     }
 
-    public void remove() {
+    @Override public void remove() {
       throw new UnsupportedOperationException();
     }
   }
@@ -1232,24 +1232,24 @@ private PartialMapping(
       this.mappingType = mappingType;
     }
 
-    public MappingType getMappingType() {
+    @Override public MappingType getMappingType() {
       return mappingType;
     }
 
-    public int getSourceCount() {
+    @Override public int getSourceCount() {
       return targets.length;
     }
 
-    public int getTargetCount() {
+    @Override public int getTargetCount() {
       return sources.length;
     }
 
-    public void clear() {
+    @Override public void clear() {
       Arrays.fill(sources, -1);
       Arrays.fill(targets, -1);
     }
 
-    public int size() {
+    @Override public int size() {
       int size = 0;
       int[] a = sources.length < targets.length ? sources : targets;
       for (int i1 : a) {
@@ -1260,14 +1260,14 @@ public int size() {
       return size;
     }
 
-    public Mapping inverse() {
+    @Override public Mapping inverse() {
       return new PartialMapping(
           targets.clone(),
           sources.clone(),
           mappingType.inverse());
     }
 
-    public Iterator<IntPair> iterator() {
+    @Override public Iterator<IntPair> iterator() {
       return new MappingItr();
     }
 
@@ -1286,7 +1286,7 @@ private static void assertPartialValid(int[] sources, int[] targets) {
       }
     }
 
-    public void set(int source, int target) {
+    @Override public void set(int source, int target) {
       assert isValid();
       final int prevTarget = targets[source];
       targets[source] = target;
@@ -1304,18 +1304,18 @@ public void set(int source, int target) {
     /**
      * Returns the source that a target maps to, or -1 if it is not mapped.
      */
-    public int getSourceOpt(int target) {
+    @Override public int getSourceOpt(int target) {
       return sources[target];
     }
 
     /**
      * Returns the target that a source maps to, or -1 if it is not mapped.
      */
-    public int getTargetOpt(int source) {
+    @Override public int getTargetOpt(int source) {
       return targets[source];
     }
 
-    public boolean isIdentity() {
+    @Override public boolean isIdentity() {
       if (sources.length != targets.length) {
         return false;
       }
@@ -1336,7 +1336,7 @@ private class MappingItr implements Iterator<IntPair> {
         advance();
       }
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return i < targets.length;
       }
 
@@ -1346,13 +1346,13 @@ private void advance() {
         } while (i < targets.length && targets[i] == -1);
       }
 
-      public IntPair next() {
+      @Override public IntPair next() {
         final IntPair pair = new IntPair(i, targets[i]);
         advance();
         return pair;
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException();
       }
     }
@@ -1383,7 +1383,7 @@ static class SurjectionWithInverse extends PartialMapping {
      * @param source source
      * @param target target
      */
-    public void set(int source, int target) {
+    @Override public void set(int source, int target) {
       assert isValid();
       final int prevTarget = targets[source];
       if (prevTarget != -1) {
@@ -1394,7 +1394,7 @@ public void set(int source, int target) {
       sources[target] = source;
     }
 
-    public int getSource(int target) {
+    @Override public int getSource(int target) {
       return sources[target];
     }
   }
@@ -1413,35 +1413,35 @@ public IdentityMapping(int size) {
       this.size = size;
     }
 
-    public void clear() {
+    @Override public void clear() {
       throw new UnsupportedOperationException("Mapping is read-only");
     }
 
-    public int size() {
+    @Override public int size() {
       return size;
     }
 
-    public Mapping inverse() {
+    @Override public Mapping inverse() {
       return this;
     }
 
-    public boolean isIdentity() {
+    @Override public boolean isIdentity() {
       return true;
     }
 
-    public void set(int source, int target) {
+    @Override public void set(int source, int target) {
       throw new UnsupportedOperationException();
     }
 
-    public MappingType getMappingType() {
+    @Override public MappingType getMappingType() {
       return MappingType.BIJECTION;
     }
 
-    public int getSourceCount() {
+    @Override public int getSourceCount() {
       return size;
     }
 
-    public int getTargetCount() {
+    @Override public int getTargetCount() {
       return size;
     }
 
@@ -1451,7 +1451,7 @@ public int getTargetCount() {
      * @param source source
      * @return target
      */
-    public int getTarget(int source) {
+    @Override public int getTarget(int source) {
       if (source < 0 || (size != -1 && source >= size)) {
         throw new IndexOutOfBoundsException("source #" + source
             + " has no target in identity mapping of size " + size);
@@ -1465,7 +1465,7 @@ public int getTarget(int source) {
      * @param source source
      * @return target
      */
-    public int getTargetOpt(int source) {
+    @Override public int getTargetOpt(int source) {
       if (source < 0 || (size != -1 && source >= size)) {
         throw new IndexOutOfBoundsException("source #" + source
             + " has no target in identity mapping of size " + size);
@@ -1479,7 +1479,7 @@ public int getTargetOpt(int source) {
      * @param target target
      * @return source
      */
-    public int getSource(int target) {
+    @Override public int getSource(int target) {
       if (target < 0 || (size != -1 && target >= size)) {
         throw new IndexOutOfBoundsException("target #" + target
             + " has no source in identity mapping of size " + size);
@@ -1493,7 +1493,7 @@ public int getSource(int target) {
      * @param target target
      * @return source
      */
-    public int getSourceOpt(int target) {
+    @Override public int getSourceOpt(int target) {
       if (target < 0 || (size != -1 && target >= size)) {
         throw new IndexOutOfBoundsException("target #" + target
             + " has no source in identity mapping of size " + size);
@@ -1501,20 +1501,20 @@ public int getSourceOpt(int target) {
       return target;
     }
 
-    public Iterator<IntPair> iterator() {
+    @Override public Iterator<IntPair> iterator() {
       return new Iterator<IntPair>() {
         int i = 0;
 
-        public boolean hasNext() {
+        @Override public boolean hasNext() {
           return (size < 0) || (i < size);
         }
 
-        public IntPair next() {
+        @Override public IntPair next() {
           int x = i++;
           return new IntPair(x, x);
         }
 
-        public void remove() {
+        @Override public void remove() {
           throw new UnsupportedOperationException();
         }
       };
@@ -1538,29 +1538,29 @@ public OverridingSourceMapping(
       this.target = target;
     }
 
-    public void clear() {
+    @Override public void clear() {
       throw new UnsupportedOperationException("Mapping is read-only");
     }
 
-    public int size() {
+    @Override public int size() {
       return parent.getSourceOpt(target) >= 0
           ? parent.size()
           : parent.size() + 1;
     }
 
-    public Mapping inverse() {
+    @Override public Mapping inverse() {
       return new OverridingTargetMapping(
           (TargetMapping) parent.inverse(),
           target,
           source);
     }
 
-    public MappingType getMappingType() {
+    @Override public MappingType getMappingType() {
       // FIXME: Mapping type might be weaker than parent.
       return parent.getMappingType();
     }
 
-    public int getSource(int target) {
+    @Override public int getSource(int target) {
       if (target == this.target) {
         return this.source;
       } else {
@@ -1568,14 +1568,14 @@ public int getSource(int target) {
       }
     }
 
-    public boolean isIdentity() {
+    @Override public boolean isIdentity() {
       // FIXME: It's possible that parent was not the identity but that
       // this overriding fixed it.
       return (source == target)
           && parent.isIdentity();
     }
 
-    public Iterator<IntPair> iterator() {
+    @Override public Iterator<IntPair> iterator() {
       throw Util.needToImplement(this);
     }
   }
@@ -1597,40 +1597,40 @@ public OverridingTargetMapping(
       this.source = source;
     }
 
-    public void clear() {
+    @Override public void clear() {
       throw new UnsupportedOperationException("Mapping is read-only");
     }
 
-    public int size() {
+    @Override public int size() {
       return parent.getTargetOpt(source) >= 0
           ? parent.size()
           : parent.size() + 1;
     }
 
-    public void set(int source, int target) {
+    @Override public void set(int source, int target) {
       parent.set(source, target);
     }
 
-    public Mapping inverse() {
+    @Override public Mapping inverse() {
       return new OverridingSourceMapping(
           parent.inverse(),
           source,
           target);
     }
 
-    public MappingType getMappingType() {
+    @Override public MappingType getMappingType() {
       // FIXME: Mapping type might be weaker than parent.
       return parent.getMappingType();
     }
 
-    public boolean isIdentity() {
+    @Override public boolean isIdentity() {
       // FIXME: Possible that parent is not identity but this overriding
       // fixes it.
       return (source == target)
           && ((Mapping) parent).isIdentity();
     }
 
-    public int getTarget(int source) {
+    @Override public int getTarget(int source) {
       if (source == this.source) {
         return this.target;
       } else {
@@ -1638,7 +1638,7 @@ public int getTarget(int source) {
       }
     }
 
-    public Iterator<IntPair> iterator() {
+    @Override public Iterator<IntPair> iterator() {
       throw Util.needToImplement(this);
     }
   }
@@ -1677,19 +1677,19 @@ private static class PartialFunctionImpl extends AbstractMapping
       Arrays.fill(targets, -1);
     }
 
-    public int getSourceCount() {
+    @Override public int getSourceCount() {
       return sourceCount;
     }
 
-    public int getTargetCount() {
+    @Override public int getTargetCount() {
       return targetCount;
     }
 
-    public void clear() {
+    @Override public void clear() {
       Arrays.fill(targets, -1);
     }
 
-    public int size() {
+    @Override public int size() {
       int size = 0;
       for (int target : targets) {
         if (target >= 0) {
@@ -1699,7 +1699,7 @@ public int size() {
       return size;
     }
 
-    public Iterator<IntPair> iterator() {
+    @Override public Iterator<IntPair> iterator() {
       return new Iterator<IntPair>() {
         int i = -1;
 
@@ -1719,31 +1719,31 @@ private void advance() {
           }
         }
 
-        public boolean hasNext() {
+        @Override public boolean hasNext() {
           return i < sourceCount;
         }
 
-        public IntPair next() {
+        @Override public IntPair next() {
           final IntPair pair = new IntPair(i, targets[i]);
           advance();
           return pair;
         }
 
-        public void remove() {
+        @Override public void remove() {
           throw new UnsupportedOperationException();
         }
       };
     }
 
-    public MappingType getMappingType() {
+    @Override public MappingType getMappingType() {
       return mappingType;
     }
 
-    public Mapping inverse() {
+    @Override public Mapping inverse() {
       return target(invert(this), targetCount, sourceCount);
     }
 
-    public void set(int source, int target) {
+    @Override public void set(int source, int target) {
       if ((target < 0) && mappingType.isMandatorySource()) {
         throw new IllegalArgumentException("Target is required");
       }
@@ -1765,7 +1765,7 @@ public void setAll(Mapping mapping) {
      *
      * @return target
      */
-    public int getTargetOpt(int source) {
+    @Override public int getTargetOpt(int source) {
       return targets[source];
     }
   }
@@ -1784,69 +1784,69 @@ private static class InverseMapping implements Mapping {
       this.parent = parent;
     }
 
-    public Iterator<IntPair> iterator() {
+    @Override public Iterator<IntPair> iterator() {
       final Iterator<IntPair> parentIter = parent.iterator();
       return new Iterator<IntPair>() {
-        public boolean hasNext() {
+        @Override public boolean hasNext() {
           return parentIter.hasNext();
         }
 
-        public IntPair next() {
+        @Override public IntPair next() {
           IntPair parentPair = parentIter.next();
           return new IntPair(parentPair.target, parentPair.source);
         }
 
-        public void remove() {
+        @Override public void remove() {
           parentIter.remove();
         }
       };
     }
 
-    public void clear() {
+    @Override public void clear() {
       parent.clear();
     }
 
-    public int size() {
+    @Override public int size() {
       return parent.size();
     }
 
-    public int getSourceCount() {
+    @Override public int getSourceCount() {
       return parent.getTargetCount();
     }
 
-    public int getTargetCount() {
+    @Override public int getTargetCount() {
       return parent.getSourceCount();
     }
 
-    public MappingType getMappingType() {
+    @Override public MappingType getMappingType() {
       return parent.getMappingType().inverse();
     }
 
-    public boolean isIdentity() {
+    @Override public boolean isIdentity() {
       return parent.isIdentity();
     }
 
-    public int getTargetOpt(int source) {
+    @Override public int getTargetOpt(int source) {
       return parent.getSourceOpt(source);
     }
 
-    public int getTarget(int source) {
+    @Override public int getTarget(int source) {
       return parent.getSource(source);
     }
 
-    public int getSource(int target) {
+    @Override public int getSource(int target) {
       return parent.getTarget(target);
     }
 
-    public int getSourceOpt(int target) {
+    @Override public int getSourceOpt(int target) {
       return parent.getTargetOpt(target);
     }
 
-    public Mapping inverse() {
+    @Override public Mapping inverse() {
       return parent;
     }
 
-    public void set(int source, int target) {
+    @Override public void set(int source, int target) {
       parent.set(target, source);
     }
   }
diff --git a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidConnectionImpl.java b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidConnectionImpl.java
index 0ac6619d82e..8e66404a8df 100644
--- a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidConnectionImpl.java
+++ b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidConnectionImpl.java
@@ -513,20 +513,20 @@ public Enumerable<Row> enumerable(final QueryType queryType,
       final ExecutorService service)
       throws IOException {
     return new AbstractEnumerable<Row>() {
-      public Enumerator<Row> enumerator() {
+      @Override public Enumerator<Row> enumerator() {
         final BlockingQueueEnumerator<Row> enumerator =
             new BlockingQueueEnumerator<>();
         final RunnableQueueSink sink = new RunnableQueueSink() {
-          public void send(Row row) throws InterruptedException {
+          @Override public void send(Row row) throws InterruptedException {
             enumerator.queue.put(row);
           }
 
-          public void end() {
+          @Override public void end() {
             enumerator.done.set(true);
           }
 
           @SuppressWarnings("deprecation")
-          public void setSourceEnumerable(Enumerable<Row> enumerable)
+          @Override public void setSourceEnumerable(Enumerable<Row> enumerable)
               throws InterruptedException {
             for (Row row : enumerable) {
               send(row);
@@ -534,7 +534,7 @@ public void setSourceEnumerable(Enumerable<Row> enumerable)
             end();
           }
 
-          public void run() {
+          @Override public void run() {
             try {
               final Page page = new Page();
               final List<ColumnMetaData.Rep> fieldTypes =
@@ -667,14 +667,14 @@ private static class BlockingQueueEnumerator<E> implements Enumerator<E> {
 
     E next;
 
-    public E current() {
+    @Override public E current() {
       if (next == null) {
         throw new NoSuchElementException();
       }
       return next;
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       for (;;) {
         next = queue.poll();
         if (next != null) {
@@ -687,9 +687,9 @@ public boolean moveNext() {
       }
     }
 
-    public void reset() {}
+    @Override public void reset() {}
 
-    public void close() {
+    @Override public void close() {
       final Throwable e = throwableHolder.get();
       if (e != null) {
         throwableHolder.set(null);
diff --git a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidJsonFilter.java b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidJsonFilter.java
index 98822547cce..4dd6b8c4f05 100644
--- a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidJsonFilter.java
+++ b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidJsonFilter.java
@@ -509,7 +509,7 @@ private JsonSelector(String dimension, String value,
       this.extractionFunction = extractionFunction;
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type.lowercase());
       generator.writeStringField("dimension", dimension);
@@ -551,7 +551,7 @@ protected JsonBound(String dimension, String lower,
       this.extractionFunction = extractionFunction;
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type.lowercase());
       generator.writeStringField("dimension", dimension);
@@ -589,7 +589,7 @@ private JsonCompositeFilter(Type type, DruidJsonFilter... fields) {
       this(type, ImmutableList.copyOf(fields));
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type.lowercase());
       switch (type) {
@@ -621,7 +621,7 @@ protected JsonInFilter(String dimension, List<String> values,
       this.extractionFunction = extractionFunction;
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type.lowercase());
       generator.writeStringField("dimension", dimension);
diff --git a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidQuery.java b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidQuery.java
index bc30cfc606c..bf17b8055ed 100644
--- a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidQuery.java
+++ b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidQuery.java
@@ -1597,7 +1597,7 @@ private static class DruidQueryNode implements Node {
       Hook.QUERY_PLAN.run(querySpec);
     }
 
-    public void run() throws InterruptedException {
+    @Override public void run() throws InterruptedException {
       final List<ColumnMetaData.Rep> fieldTypes = new ArrayList<>();
       for (RelDataTypeField field : query.getRowType().getFieldList()) {
         fieldTypes.add(getPrimitive(field));
@@ -1660,7 +1660,7 @@ private JsonAggregation(String type, String name, String fieldName, String expre
       this.expression = expression;
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type);
       generator.writeStringField("name", name);
@@ -1703,7 +1703,7 @@ private JsonLimit(String type, Integer limit, List<JsonCollation> collations) {
       this.collations = collations;
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type);
       writeFieldIf(generator, "limit", limit);
@@ -1724,7 +1724,7 @@ private JsonCollation(String dimension, String direction, String dimensionOrder)
       this.dimensionOrder = dimensionOrder;
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("dimension", dimension);
       writeFieldIf(generator, "direction", direction);
@@ -1743,7 +1743,7 @@ private JsonCardinalityAggregation(String type, String name,
       this.fieldNames = fieldNames;
     }
 
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type);
       generator.writeStringField("name", name);
@@ -1785,7 +1785,7 @@ private JsonPostAggregation(String name, String type) {
     }
 
     // Expects all subclasses to write the EndObject item
-    public void write(JsonGenerator generator) throws IOException {
+    @Override public void write(JsonGenerator generator) throws IOException {
       generator.writeStartObject();
       generator.writeStringField("type", type);
       generator.writeStringField("name", name);
diff --git a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidSchemaFactory.java b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidSchemaFactory.java
index 4501b251067..d1dcbded87c 100644
--- a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidSchemaFactory.java
+++ b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidSchemaFactory.java
@@ -52,7 +52,7 @@ public class DruidSchemaFactory implements SchemaFactory {
   /** Default Druid URL. */
   public static final String DEFAULT_URL = "http://localhost:8082";
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     final String url = operand.get("url") instanceof String
         ? (String) operand.get("url")
diff --git a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTable.java b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTable.java
index 307d1544aa4..0c8c7d6b051 100644
--- a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTable.java
+++ b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTable.java
@@ -228,7 +228,7 @@ public boolean isComplexMetric(String alias) {
     return complexMetrics.get(alias) != null;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     final RelDataType rowType = protoRowType.apply(typeFactory);
     final List<String> fieldNames = rowType.getFieldNames();
     Preconditions.checkArgument(fieldNames.contains(timestampFieldName));
@@ -236,7 +236,7 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return rowType;
   }
 
-  public RelNode toRel(RelOptTable.ToRelContext context,
+  @Override public RelNode toRel(RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     final RelOptCluster cluster = context.getCluster();
     final TableScan scan = LogicalTableScan.create(cluster, relOptTable, ImmutableList.of());
@@ -265,7 +265,7 @@ private static class MapRelProtoDataType implements RelProtoDataType {
       this.timestampColumn = timestampColumn;
     }
 
-    public RelDataType apply(RelDataTypeFactory typeFactory) {
+    @Override public RelDataType apply(RelDataTypeFactory typeFactory) {
       final RelDataTypeFactory.Builder builder = typeFactory.builder();
       for (Map.Entry<String, SqlTypeName> field : fields.entrySet()) {
         final String key = field.getKey();
diff --git a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTableFactory.java b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTableFactory.java
index 797a6c6a644..d1fe59aa051 100644
--- a/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTableFactory.java
+++ b/druid/src/main/java/org/apache/calcite/adapter/druid/DruidTableFactory.java
@@ -48,7 +48,7 @@ public class DruidTableFactory implements TableFactory {
   private DruidTableFactory() {}
 
   // name that is also the same name as a complex metric
-  public Table create(SchemaPlus schema, String name, Map operand,
+  @Override public Table create(SchemaPlus schema, String name, Map operand,
       RelDataType rowType) {
     final DruidSchema druidSchema = schema.unwrap(DruidSchema.class);
     // If "dataSource" operand is present it overrides the table name.
diff --git a/druid/src/main/java/org/apache/calcite/adapter/druid/Granularities.java b/druid/src/main/java/org/apache/calcite/adapter/druid/Granularities.java
index c5287c82d87..c0411236a71 100644
--- a/druid/src/main/java/org/apache/calcite/adapter/druid/Granularities.java
+++ b/druid/src/main/java/org/apache/calcite/adapter/druid/Granularities.java
@@ -75,7 +75,7 @@ private enum AllGranularity implements Granularity {
       generator.writeObject("all");
     }
 
-    @Nonnull public Type getType() {
+    @Override @Nonnull public Type getType() {
       return Type.ALL;
     }
   }
@@ -101,7 +101,7 @@ private PeriodGranularity(Type type, String period, String timeZone) {
       generator.writeEndObject();
     }
 
-    @Nonnull public Type getType() {
+    @Override @Nonnull public Type getType() {
       return type;
     }
   }
diff --git a/elasticsearch/src/main/java/org/apache/calcite/adapter/elasticsearch/ElasticsearchTable.java b/elasticsearch/src/main/java/org/apache/calcite/adapter/elasticsearch/ElasticsearchTable.java
index e14fd595113..e84d1238d50 100644
--- a/elasticsearch/src/main/java/org/apache/calcite/adapter/elasticsearch/ElasticsearchTable.java
+++ b/elasticsearch/src/main/java/org/apache/calcite/adapter/elasticsearch/ElasticsearchTable.java
@@ -345,7 +345,7 @@ public static class ElasticsearchQueryable<T> extends AbstractTableQueryable<T>
       super(queryProvider, schema, table, tableName);
     }
 
-    public Enumerator<T> enumerator() {
+    @Override public Enumerator<T> enumerator() {
       return null;
     }
 
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvFilterableTable.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvFilterableTable.java
index c9cae658c5b..6f0474d5189 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvFilterableTable.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvFilterableTable.java
@@ -48,18 +48,18 @@ public CsvFilterableTable(Source source, RelProtoDataType protoRowType) {
     super(source, protoRowType);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "CsvFilterableTable";
   }
 
-  public Enumerable<Object[]> scan(DataContext root, List<RexNode> filters) {
+  @Override public Enumerable<Object[]> scan(DataContext root, List<RexNode> filters) {
     final List<CsvFieldType> fieldTypes = getFieldTypes(root.getTypeFactory());
     final String[] filterValues = new String[fieldTypes.size()];
     filters.removeIf(filter -> addFilter(filter, filterValues));
     final List<Integer> fields = ImmutableIntList.identity(fieldTypes.size());
     final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         return new CsvEnumerator<>(source, cancelFlag, false, filterValues,
             CsvEnumerator.arrayConverter(fieldTypes, fields, false));
       }
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvScannableTable.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvScannableTable.java
index bdc2af02159..00827ebb29b 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvScannableTable.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvScannableTable.java
@@ -43,16 +43,16 @@ public class CsvScannableTable extends CsvTable
     super(source, protoRowType);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "CsvScannableTable";
   }
 
-  public Enumerable<Object[]> scan(DataContext root) {
+  @Override public Enumerable<Object[]> scan(DataContext root) {
     final List<CsvFieldType> fieldTypes = getFieldTypes(root.getTypeFactory());
     final List<Integer> fields = ImmutableIntList.identity(fieldTypes.size());
     final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         return new CsvEnumerator<>(source, cancelFlag, false, null,
             CsvEnumerator.arrayConverter(fieldTypes, fields, false));
       }
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvSchemaFactory.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvSchemaFactory.java
index cadeb598269..79b96af9cc9 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvSchemaFactory.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvSchemaFactory.java
@@ -39,7 +39,7 @@ public class CsvSchemaFactory implements SchemaFactory {
   private CsvSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     final String directory = (String) operand.get("directory");
     final File base =
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamScannableTable.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamScannableTable.java
index 828547362bf..2854be93965 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamScannableTable.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamScannableTable.java
@@ -49,16 +49,16 @@ public class CsvStreamScannableTable extends CsvScannableTable
     return true;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "CsvStreamScannableTable";
   }
 
-  public Enumerable<Object[]> scan(DataContext root) {
+  @Override public Enumerable<Object[]> scan(DataContext root) {
     final List<CsvFieldType> fieldTypes = getFieldTypes(root.getTypeFactory());
     final List<Integer> fields = ImmutableIntList.identity(fieldTypes.size());
     final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         return new CsvEnumerator<>(source, cancelFlag, true, null,
             CsvEnumerator.arrayConverter(fieldTypes, fields, true));
       }
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamTableFactory.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamTableFactory.java
index 965b2fbd81c..01c25904dd7 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamTableFactory.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvStreamTableFactory.java
@@ -40,7 +40,7 @@ public class CsvStreamTableFactory implements TableFactory<CsvTable> {
   public CsvStreamTableFactory() {
   }
 
-  public CsvTable create(SchemaPlus schema, String name,
+  @Override public CsvTable create(SchemaPlus schema, String name,
       Map<String, Object> operand, RelDataType rowType) {
     String fileName = (String) operand.get("file");
     File file = new File(fileName);
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTable.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTable.java
index 8f7cc78e075..1163cfe6ed0 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTable.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTable.java
@@ -43,7 +43,7 @@ public abstract class CsvTable extends AbstractTable {
     this.protoRowType = protoRowType;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     if (protoRowType != null) {
       return protoRowType.apply(typeFactory);
     }
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableFactory.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableFactory.java
index d3e74c1f96c..1e2c6370480 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableFactory.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableFactory.java
@@ -40,7 +40,7 @@ public class CsvTableFactory implements TableFactory<CsvTable> {
   public CsvTableFactory() {
   }
 
-  public CsvTable create(SchemaPlus schema, String name,
+  @Override public CsvTable create(SchemaPlus schema, String name,
       Map<String, Object> operand, RelDataType rowType) {
     String fileName = (String) operand.get("file");
     final File base =
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableScan.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableScan.java
index f591e292223..baf1fd082d7 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableScan.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTableScan.java
@@ -98,7 +98,7 @@ protected CsvTableScan(RelOptCluster cluster, RelOptTable table,
             / ((double) table.getRowType().getFieldCount() + 2D));
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     PhysType physType =
         PhysTypeImpl.of(
             implementor.getTypeFactory(),
diff --git a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTranslatableTable.java b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTranslatableTable.java
index e183200e226..703c00faee0 100644
--- a/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTranslatableTable.java
+++ b/example/csv/src/main/java/org/apache/calcite/adapter/csv/CsvTranslatableTable.java
@@ -47,7 +47,7 @@ public class CsvTranslatableTable extends CsvTable
     super(source, protoRowType);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "CsvTranslatableTable";
   }
 
@@ -57,7 +57,7 @@ public Enumerable<Object> project(final DataContext root,
       final int[] fields) {
     final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
     return new AbstractEnumerable<Object>() {
-      public Enumerator<Object> enumerator() {
+      @Override public Enumerator<Object> enumerator() {
         return new CsvEnumerator<>(
             source,
             cancelFlag,
@@ -67,21 +67,21 @@ public Enumerator<Object> enumerator() {
     };
   }
 
-  public Expression getExpression(SchemaPlus schema, String tableName,
+  @Override public Expression getExpression(SchemaPlus schema, String tableName,
       Class clazz) {
     return Schemas.tableExpression(schema, getElementType(), tableName, clazz);
   }
 
-  public Type getElementType() {
+  @Override public Type getElementType() {
     return Object[].class;
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     throw new UnsupportedOperationException();
   }
 
-  public RelNode toRel(
+  @Override public RelNode toRel(
       RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     // Request all fields.
diff --git a/example/function/src/main/java/org/apache/calcite/example/maze/Maze.java b/example/function/src/main/java/org/apache/calcite/example/maze/Maze.java
index 8f0f1bb048a..8be1e7e4606 100644
--- a/example/function/src/main/java/org/apache/calcite/example/maze/Maze.java
+++ b/example/function/src/main/java/org/apache/calcite/example/maze/Maze.java
@@ -114,11 +114,11 @@ public Enumerator<String> enumerator(final Set<Integer> solutionSet) {
       final StringBuilder b = new StringBuilder();
       final StringBuilder b2 = new StringBuilder();
 
-      public String current() {
+      @Override public String current() {
         return i % 2 == 0 ? b.toString() : b2.toString();
       }
 
-      public boolean moveNext() {
+      @Override public boolean moveNext() {
         if (i >= height * 2) {
           return false;
         }
@@ -131,11 +131,11 @@ public boolean moveNext() {
         return true;
       }
 
-      public void reset() {
+      @Override public void reset() {
         i = -1;
       }
 
-      public void close() {}
+      @Override public void close() {}
     };
   }
 
diff --git a/example/function/src/main/java/org/apache/calcite/example/maze/MazeTable.java b/example/function/src/main/java/org/apache/calcite/example/maze/MazeTable.java
index 8676b6939d9..64052dd1fab 100644
--- a/example/function/src/main/java/org/apache/calcite/example/maze/MazeTable.java
+++ b/example/function/src/main/java/org/apache/calcite/example/maze/MazeTable.java
@@ -79,13 +79,13 @@ public static ScannableTable solve(int width, int height, int seed) {
     return new MazeTable(width, height, seed, true);
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return typeFactory.builder()
         .add("S", SqlTypeName.VARCHAR, width * 3 + 1)
         .build();
   }
 
-  public Enumerable<Object[]> scan(DataContext root) {
+  @Override public Enumerable<Object[]> scan(DataContext root) {
     final Random random = seed >= 0 ? new Random(seed) : new Random();
     final Maze maze = new Maze(width, height);
     final PrintWriter pw = Util.printWriter(System.out);
@@ -94,7 +94,7 @@ public Enumerable<Object[]> scan(DataContext root) {
       maze.print(pw, true);
     }
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         final Set<Integer> solutionSet;
         if (solution) {
           solutionSet = maze.solve(0, 0);
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/CsvEnumerator.java b/file/src/main/java/org/apache/calcite/adapter/file/CsvEnumerator.java
index 091a4a18eeb..0cbcd90d7e6 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/CsvEnumerator.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/CsvEnumerator.java
@@ -169,11 +169,11 @@ static CSVReader openCsv(Source source) throws IOException {
     return new CSVReader(source.reader());
   }
 
-  public E current() {
+  @Override public E current() {
     return current;
   }
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     try {
     outer:
       for (;;) {
@@ -212,11 +212,11 @@ public boolean moveNext() {
     }
   }
 
-  public void reset() {
+  @Override public void reset() {
     throw new UnsupportedOperationException();
   }
 
-  public void close() {
+  @Override public void close() {
     try {
       reader.close();
     } catch (IOException e) {
@@ -331,7 +331,7 @@ static class ArrayRowConverter extends RowConverter<Object[]> {
       this.stream = stream;
     }
 
-    public Object[] convertRow(String[] strings) {
+    @Override public Object[] convertRow(String[] strings) {
       if (stream) {
         return convertStreamRow(strings);
       } else {
@@ -369,7 +369,7 @@ private SingleColumnRowConverter(CsvFieldType fieldType, int fieldIndex) {
       this.fieldIndex = fieldIndex;
     }
 
-    public Object convertRow(String[] strings) {
+    @Override public Object convertRow(String[] strings) {
       return convert(fieldType, strings[fieldIndex]);
     }
   }
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/CsvStreamReader.java b/file/src/main/java/org/apache/calcite/adapter/file/CsvStreamReader.java
index 633079a260d..fecdc3d6773 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/CsvStreamReader.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/CsvStreamReader.java
@@ -98,7 +98,7 @@ private CsvStreamReader(Source source, char separator, char quoteChar,
    *
    * @throws IOException if bad things happen during the read
    */
-  public String[] readNext() throws IOException {
+  @Override public String[] readNext() throws IOException {
     String[] result = null;
     do {
       String nextLine = getNextLine();
@@ -136,7 +136,7 @@ private String getNextLine() throws IOException {
    *
    * @throws IOException if the close fails
    */
-  public void close() throws IOException {
+  @Override public void close() throws IOException {
   }
 
   /** Watches for content being appended to a CSV file. */
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/CsvTable.java b/file/src/main/java/org/apache/calcite/adapter/file/CsvTable.java
index 20f0023f016..1ab4e705e17 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/CsvTable.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/CsvTable.java
@@ -44,7 +44,7 @@ public abstract class CsvTable extends AbstractTable {
     this.protoRowType = protoRowType;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     if (protoRowType != null) {
       return protoRowType.apply(typeFactory);
     }
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/CsvTableFactory.java b/file/src/main/java/org/apache/calcite/adapter/file/CsvTableFactory.java
index 75e992b7ef0..3809bad5d8a 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/CsvTableFactory.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/CsvTableFactory.java
@@ -40,7 +40,7 @@ public class CsvTableFactory implements TableFactory<CsvTable> {
   public CsvTableFactory() {
   }
 
-  public CsvTable create(SchemaPlus schema, String name,
+  @Override public CsvTable create(SchemaPlus schema, String name,
       Map<String, Object> operand, RelDataType rowType) {
     String fileName = (String) operand.get("file");
     final File base =
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/CsvTableScan.java b/file/src/main/java/org/apache/calcite/adapter/file/CsvTableScan.java
index 8d6eb87c9d5..9343e4089e8 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/CsvTableScan.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/CsvTableScan.java
@@ -97,7 +97,7 @@ protected CsvTableScan(RelOptCluster cluster, RelOptTable table,
             / ((double) table.getRowType().getFieldCount() + 2D));
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     PhysType physType =
         PhysTypeImpl.of(
             implementor.getTypeFactory(),
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/CsvTranslatableTable.java b/file/src/main/java/org/apache/calcite/adapter/file/CsvTranslatableTable.java
index 9f86c539432..2175f2d332e 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/CsvTranslatableTable.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/CsvTranslatableTable.java
@@ -49,7 +49,7 @@ public class CsvTranslatableTable extends CsvTable
     super(source, protoRowType);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "CsvTranslatableTable";
   }
 
@@ -59,28 +59,28 @@ public Enumerable<Object> project(final DataContext root,
       final int[] fields) {
     final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
     return new AbstractEnumerable<Object>() {
-      public Enumerator<Object> enumerator() {
+      @Override public Enumerator<Object> enumerator() {
         return new CsvEnumerator<>(source, cancelFlag,
             getFieldTypes(root.getTypeFactory()), ImmutableIntList.of(fields));
       }
     };
   }
 
-  public Expression getExpression(SchemaPlus schema, String tableName,
+  @Override public Expression getExpression(SchemaPlus schema, String tableName,
       Class clazz) {
     return Schemas.tableExpression(schema, getElementType(), tableName, clazz);
   }
 
-  public Type getElementType() {
+  @Override public Type getElementType() {
     return Object[].class;
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     throw new UnsupportedOperationException();
   }
 
-  public RelNode toRel(
+  @Override public RelNode toRel(
       RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     // Request all fields.
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/FileEnumerator.java b/file/src/main/java/org/apache/calcite/adapter/file/FileEnumerator.java
index 24614bb8d94..6b0ce467021 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/FileEnumerator.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/FileEnumerator.java
@@ -43,14 +43,14 @@ class FileEnumerator implements Enumerator<Object> {
     this.fields = fields;
   }
 
-  public Object current() {
+  @Override public Object current() {
     if (current == null) {
       this.moveNext();
     }
     return current;
   }
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     try {
       if (this.iterator.hasNext()) {
         final Elements row = this.iterator.next();
@@ -68,12 +68,12 @@ public boolean moveNext() {
   }
 
   // required by linq4j Enumerator interface
-  public void reset() {
+  @Override public void reset() {
     throw new UnsupportedOperationException();
   }
 
   // required by linq4j Enumerator interface
-  public void close() {
+  @Override public void close() {
   }
 
   /** Returns an array of integers {0, ..., n - 1}. */
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/FileReader.java b/file/src/main/java/org/apache/calcite/adapter/file/FileReader.java
index 736e065c3ef..db2636ca433 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/FileReader.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/FileReader.java
@@ -149,7 +149,7 @@ private String tableKey() {
     return "Table: {url: " + this.source + ", selector: " + this.selector + "}";
   }
 
-  public FileReaderIterator iterator() {
+  @Override public FileReaderIterator iterator() {
     if (this.tableElement == null) {
       try {
         getTable();
@@ -202,7 +202,7 @@ private static class FileReaderIterator implements Iterator<Elements> {
       this.rowIterator = rows.iterator();
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return this.rowIterator.hasNext();
     }
 
@@ -213,11 +213,11 @@ Elements next(String selector) {
     }
 
     // return th and td elements by default
-    public Elements next() {
+    @Override public Elements next() {
       return next("th,td");
     }
 
-    public void remove() {
+    @Override public void remove() {
       throw new UnsupportedOperationException("NFW - can't remove!");
     }
   }
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/FileSchemaFactory.java b/file/src/main/java/org/apache/calcite/adapter/file/FileSchemaFactory.java
index f0cc65451ac..43d952bbac5 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/FileSchemaFactory.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/FileSchemaFactory.java
@@ -43,7 +43,7 @@ public class FileSchemaFactory implements SchemaFactory {
   private FileSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     @SuppressWarnings("unchecked") List<Map<String, Object>> tables =
         (List) operand.get("tables");
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/FileTable.java b/file/src/main/java/org/apache/calcite/adapter/file/FileTable.java
index e6e76f94916..a71d2372241 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/FileTable.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/FileTable.java
@@ -71,26 +71,26 @@ static FileTable create(Source source, Map<String, Object> tableDef)
     return new FileTable(source, selector, index, null, fieldConfigs);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "FileTable";
   }
 
-  public Statistic getStatistic() {
+  @Override public Statistic getStatistic() {
     return Statistics.UNKNOWN;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     if (protoRowType != null) {
       return protoRowType.apply(typeFactory);
     }
     return this.converter.getRowType((JavaTypeFactory) typeFactory);
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new AbstractTableQueryable<T>(queryProvider, schema, this,
         tableName) {
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         try {
           FileEnumerator enumerator =
               new FileEnumerator(reader.iterator(), converter);
@@ -106,7 +106,7 @@ public Enumerator<T> enumerator() {
   /** Returns an enumerable over a given projection of the fields. */
   public Enumerable<Object> project(final int[] fields) {
     return new AbstractEnumerable<Object>() {
-      public Enumerator<Object> enumerator() {
+      @Override public Enumerator<Object> enumerator() {
         try {
           return new FileEnumerator(reader.iterator(), converter, fields);
         } catch (Exception e) {
@@ -116,7 +116,7 @@ public Enumerator<Object> enumerator() {
     };
   }
 
-  public RelNode toRel(RelOptTable.ToRelContext context,
+  @Override public RelNode toRel(RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     return new EnumerableTableScan(context.getCluster(),
         context.getCluster().traitSetOf(EnumerableConvention.INSTANCE),
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/FileTableScan.java b/file/src/main/java/org/apache/calcite/adapter/file/FileTableScan.java
index 7ec452962bb..4200ed569a5 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/FileTableScan.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/FileTableScan.java
@@ -78,7 +78,7 @@ protected FileTableScan(RelOptCluster cluster, RelOptTable table,
     return builder.build();
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     PhysType physType =
         PhysTypeImpl.of(
             implementor.getTypeFactory(),
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/JsonEnumerator.java b/file/src/main/java/org/apache/calcite/adapter/file/JsonEnumerator.java
index 7fd06405198..27fd5713e84 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/JsonEnumerator.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/JsonEnumerator.java
@@ -119,19 +119,19 @@ static JsonDataConverter deduceRowType(RelDataTypeFactory typeFactory, Source so
     return new JsonDataConverter(relDataType, list);
   }
 
-  public Object[] current() {
+  @Override public Object[] current() {
     return enumerator.current();
   }
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     return enumerator.moveNext();
   }
 
-  public void reset() {
+  @Override public void reset() {
     enumerator.reset();
   }
 
-  public void close() {
+  @Override public void close() {
     enumerator.close();
   }
 
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/JsonScannableTable.java b/file/src/main/java/org/apache/calcite/adapter/file/JsonScannableTable.java
index 2210b7e0a58..fe6010ad066 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/JsonScannableTable.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/JsonScannableTable.java
@@ -38,13 +38,13 @@ public JsonScannableTable(Source source) {
     super(source);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "JsonScannableTable";
   }
 
-  public Enumerable<Object[]> scan(DataContext root) {
+  @Override public Enumerable<Object[]> scan(DataContext root) {
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         return new JsonEnumerator(getDataList(root.getTypeFactory()));
       }
     };
diff --git a/file/src/main/java/org/apache/calcite/adapter/file/JsonTable.java b/file/src/main/java/org/apache/calcite/adapter/file/JsonTable.java
index 5fade31f160..17f2da8bdf7 100644
--- a/file/src/main/java/org/apache/calcite/adapter/file/JsonTable.java
+++ b/file/src/main/java/org/apache/calcite/adapter/file/JsonTable.java
@@ -38,7 +38,7 @@ public JsonTable(Source source) {
     this.source = source;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     if (rowType == null) {
       rowType = JsonEnumerator.deduceRowType(typeFactory, source).getRelDataType();
     }
@@ -55,7 +55,7 @@ public List<Object> getDataList(RelDataTypeFactory typeFactory) {
     return dataList;
   }
 
-  public Statistic getStatistic() {
+  @Override public Statistic getStatistic() {
     return Statistics.UNKNOWN;
   }
 }
diff --git a/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeSchemaFactory.java b/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeSchemaFactory.java
index 2a08b2946b6..1c3ad623d41 100644
--- a/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeSchemaFactory.java
+++ b/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeSchemaFactory.java
@@ -46,7 +46,7 @@ public GeodeSchemaFactory() {
     // Do Nothing
   }
 
-  public synchronized Schema create(SchemaPlus parentSchema, String name,
+  @Override public synchronized Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     Map map = (Map) operand;
     String locatorHost = (String) map.get(LOCATOR_HOST);
diff --git a/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeTable.java b/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeTable.java
index bbbd7f7da6b..1ff44c34653 100644
--- a/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeTable.java
+++ b/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeTable.java
@@ -70,7 +70,7 @@ public class GeodeTable extends AbstractQueryableTable implements TranslatableTa
     this.rowType = GeodeUtils.autodetectRelTypeFromRegion(region);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "GeodeTable {" + regionName + "}";
   }
 
@@ -195,7 +195,7 @@ public Enumerable<Object> query(final GemFireCache clientCache,
     LOGGER.info("OQL: " + oqlQuery);
 
     return new AbstractEnumerable<Object>() {
-      public Enumerator<Object> enumerator() {
+      @Override public Enumerator<Object> enumerator() {
         final QueryService queryService = clientCache.getQueryService();
         try {
           SelectResults results = (SelectResults) queryService.newQuery(oqlQuery).execute();
@@ -209,7 +209,7 @@ public Enumerator<Object> enumerator() {
     };
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new GeodeQueryable<>(queryProvider, schema, this, tableName);
   }
@@ -240,7 +240,7 @@ public GeodeQueryable(QueryProvider queryProvider, SchemaPlus schema,
     }
 
     // tzolov: this should never be called for queryable tables???
-    public Enumerator<T> enumerator() {
+    @Override public Enumerator<T> enumerator() {
       throw new UnsupportedOperationException("Enumerator on Queryable should never be called");
     }
 
diff --git a/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeToEnumerableConverter.java b/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeToEnumerableConverter.java
index c8649c610af..fc87daff749 100644
--- a/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeToEnumerableConverter.java
+++ b/geode/src/main/java/org/apache/calcite/adapter/geode/rel/GeodeToEnumerableConverter.java
@@ -98,11 +98,11 @@ protected GeodeToEnumerableConverter(RelOptCluster cluster,
         pref.prefer(JavaRowFormat.ARRAY));
 
     final List<Class> physFieldClasses = new AbstractList<Class>() {
-      public Class get(int index) {
+      @Override public Class get(int index) {
         return physType.fieldClass(index);
       }
 
-      public int size() {
+      @Override public int size() {
         return rowType.getFieldCount();
       }
     };
diff --git a/geode/src/main/java/org/apache/calcite/adapter/geode/simple/GeodeSimpleScannableTable.java b/geode/src/main/java/org/apache/calcite/adapter/geode/simple/GeodeSimpleScannableTable.java
index 6a94dbdf873..ddeeab2b25f 100644
--- a/geode/src/main/java/org/apache/calcite/adapter/geode/simple/GeodeSimpleScannableTable.java
+++ b/geode/src/main/java/org/apache/calcite/adapter/geode/simple/GeodeSimpleScannableTable.java
@@ -57,7 +57,7 @@ public GeodeSimpleScannableTable(String regionName, RelDataType relDataType,
 
   @Override public Enumerable<Object[]> scan(DataContext root) {
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         return new GeodeSimpleEnumerator<Object[]>(clientCache, regionName) {
           @Override public Object[] convert(Object obj) {
             Object values = convertToRowValues(relDataType.getFieldList(), obj);
diff --git a/kafka/src/main/java/org/apache/calcite/adapter/kafka/KafkaStreamTable.java b/kafka/src/main/java/org/apache/calcite/adapter/kafka/KafkaStreamTable.java
index 6e6dc2d5b65..334e7a6baae 100644
--- a/kafka/src/main/java/org/apache/calcite/adapter/kafka/KafkaStreamTable.java
+++ b/kafka/src/main/java/org/apache/calcite/adapter/kafka/KafkaStreamTable.java
@@ -59,7 +59,7 @@ public class KafkaStreamTable implements ScannableTable, StreamableTable {
   @Override public Enumerable<Object[]> scan(final DataContext root) {
     final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         if (tableOptions.getConsumer() != null) {
           return new KafkaMessageEnumerator(tableOptions.getConsumer(),
               tableOptions.getRowConverter(), cancelFlag);
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable.java
index 5c141e42385..d89614df364 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable.java
@@ -29,7 +29,7 @@
  * @param <T> Element type
  */
 public abstract class AbstractEnumerable<T> extends DefaultEnumerable<T> {
-  public Iterator<T> iterator() {
+  @Override public Iterator<T> iterator() {
     return Linq4j.enumeratorIterator(enumerator());
   }
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable2.java b/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable2.java
index 32585e2293f..774c9210eb5 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable2.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/AbstractEnumerable2.java
@@ -27,7 +27,7 @@
  * @param <T> Element type
  */
 public abstract class AbstractEnumerable2<T> extends DefaultEnumerable<T> {
-  public Enumerator<T> enumerator() {
+  @Override public Enumerator<T> enumerator() {
     return new Linq4j.IterableEnumerator<>(this);
   }
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/BaseQueryable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/BaseQueryable.java
index fe4a6350622..f0918b29034 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/BaseQueryable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/BaseQueryable.java
@@ -43,23 +43,23 @@ public BaseQueryable(QueryProvider provider, Type elementType,
     this.expression = expression;
   }
 
-  public QueryProvider getProvider() {
+  @Override public QueryProvider getProvider() {
     return provider;
   }
 
-  public Type getElementType() {
+  @Override public Type getElementType() {
     return elementType;
   }
 
-  public Expression getExpression() {
+  @Override public Expression getExpression() {
     return expression;
   }
 
-  public Iterator<TSource> iterator() {
+  @Override public Iterator<TSource> iterator() {
     return Linq4j.enumeratorIterator(enumerator());
   }
 
-  public Enumerator<TSource> enumerator() {
+  @Override public Enumerator<TSource> enumerator() {
     return provider.executeQuery(this);
   }
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/CartesianProductEnumerator.java b/linq4j/src/main/java/org/apache/calcite/linq4j/CartesianProductEnumerator.java
index 84bf1d35d80..0ac16b06512 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/CartesianProductEnumerator.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/CartesianProductEnumerator.java
@@ -35,7 +35,7 @@ protected CartesianProductEnumerator(List<Enumerator<T>> enumerators) {
     this.elements = (T[]) new Object[enumerators.size()];
   }
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     if (first) {
       int i = 0;
       for (Enumerator<T> enumerator : enumerators) {
@@ -65,14 +65,14 @@ public boolean moveNext() {
     return false;
   }
 
-  public void reset() {
+  @Override public void reset() {
     first = true;
     for (Enumerator<T> enumerator : enumerators) {
       enumerator.reset();
     }
   }
 
-  public void close() {
+  @Override public void close() {
     // If there is one or more exceptions, carry on and close all enumerators,
     // then throw the first.
     Throwable rte = null;
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultEnumerable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultEnumerable.java
index 3cc4c9ed0c8..17cafd2b496 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultEnumerable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultEnumerable.java
@@ -69,7 +69,7 @@ protected OrderedEnumerable<T> getThisOrdered() {
     return this;
   }
 
-  public <R> R foreach(Function1<T, R> func) {
+  @Override public <R> R foreach(Function1<T, R> func) {
     R result = null;
     try (Enumerator<T> enumerator = enumerator()) {
       while (enumerator.moveNext()) {
@@ -80,7 +80,7 @@ public <R> R foreach(Function1<T, R> func) {
     }
   }
 
-  public Queryable<T> asQueryable() {
+  @Override public Queryable<T> asQueryable() {
     return Extensions.asQueryable(this);
   }
 
@@ -89,189 +89,189 @@ protected OrderedQueryable<T> asOrderedQueryable() {
     return EnumerableDefaults.asOrderedQueryable(this);
   }
 
-  public T aggregate(Function2<T, T, T> func) {
+  @Override public T aggregate(Function2<T, T, T> func) {
     return EnumerableDefaults.aggregate(getThis(), func);
   }
 
-  public <TAccumulate> TAccumulate aggregate(TAccumulate seed,
+  @Override public <TAccumulate> TAccumulate aggregate(TAccumulate seed,
       Function2<TAccumulate, T, TAccumulate> func) {
     return EnumerableDefaults.aggregate(getThis(), seed, func);
   }
 
-  public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
+  @Override public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
       Function2<TAccumulate, T, TAccumulate> func,
       Function1<TAccumulate, TResult> selector) {
     return EnumerableDefaults.aggregate(getThis(), seed, func, selector);
   }
 
-  public boolean all(Predicate1<T> predicate) {
+  @Override public boolean all(Predicate1<T> predicate) {
     return EnumerableDefaults.all(getThis(), predicate);
   }
 
-  public boolean any() {
+  @Override public boolean any() {
     return EnumerableDefaults.any(getThis());
   }
 
-  public boolean any(Predicate1<T> predicate) {
+  @Override public boolean any(Predicate1<T> predicate) {
     return EnumerableDefaults.any(getThis(), predicate);
   }
 
-  public Enumerable<T> asEnumerable() {
+  @Override public Enumerable<T> asEnumerable() {
     return EnumerableDefaults.asEnumerable(getThis());
   }
 
-  public BigDecimal average(BigDecimalFunction1<T> selector) {
+  @Override public BigDecimal average(BigDecimalFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public BigDecimal average(NullableBigDecimalFunction1<T> selector) {
+  @Override public BigDecimal average(NullableBigDecimalFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public double average(DoubleFunction1<T> selector) {
+  @Override public double average(DoubleFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public Double average(NullableDoubleFunction1<T> selector) {
+  @Override public Double average(NullableDoubleFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public int average(IntegerFunction1<T> selector) {
+  @Override public int average(IntegerFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public Integer average(NullableIntegerFunction1<T> selector) {
+  @Override public Integer average(NullableIntegerFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public long average(LongFunction1<T> selector) {
+  @Override public long average(LongFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public Long average(NullableLongFunction1<T> selector) {
+  @Override public Long average(NullableLongFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public float average(FloatFunction1<T> selector) {
+  @Override public float average(FloatFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public Float average(NullableFloatFunction1<T> selector) {
+  @Override public Float average(NullableFloatFunction1<T> selector) {
     return EnumerableDefaults.average(getThis(), selector);
   }
 
-  public <T2> Enumerable<T2> cast(Class<T2> clazz) {
+  @Override public <T2> Enumerable<T2> cast(Class<T2> clazz) {
     return EnumerableDefaults.cast(getThis(), clazz);
   }
 
-  public Enumerable<T> concat(Enumerable<T> enumerable1) {
+  @Override public Enumerable<T> concat(Enumerable<T> enumerable1) {
     return EnumerableDefaults.concat(getThis(), enumerable1);
   }
 
-  public boolean contains(T element) {
+  @Override public boolean contains(T element) {
     return EnumerableDefaults.contains(getThis(), element);
   }
 
-  public boolean contains(T element, EqualityComparer<T> comparer) {
+  @Override public boolean contains(T element, EqualityComparer<T> comparer) {
     return EnumerableDefaults.contains(getThis(), element, comparer);
   }
 
-  public int count() {
+  @Override public int count() {
     return EnumerableDefaults.count(getThis());
   }
 
-  public int count(Predicate1<T> predicate) {
+  @Override public int count(Predicate1<T> predicate) {
     return EnumerableDefaults.count(getThis(), predicate);
   }
 
-  public <TKey> OrderedEnumerable<T> createOrderedEnumerable(
+  @Override public <TKey> OrderedEnumerable<T> createOrderedEnumerable(
       Function1<T, TKey> keySelector, Comparator<TKey> comparator,
       boolean descending) {
     return EnumerableDefaults.createOrderedEnumerable(getThisOrdered(),
         keySelector, comparator, descending);
   }
 
-  public Enumerable<T> defaultIfEmpty() {
+  @Override public Enumerable<T> defaultIfEmpty() {
     return EnumerableDefaults.defaultIfEmpty(getThis());
   }
 
-  public Enumerable<T>  defaultIfEmpty(T value) {
+  @Override public Enumerable<T>  defaultIfEmpty(T value) {
     return EnumerableDefaults.defaultIfEmpty(getThis(), value);
   }
 
-  public Enumerable<T> distinct() {
+  @Override public Enumerable<T> distinct() {
     return EnumerableDefaults.distinct(getThis());
   }
 
-  public Enumerable<T> distinct(EqualityComparer<T> comparer) {
+  @Override public Enumerable<T> distinct(EqualityComparer<T> comparer) {
     return EnumerableDefaults.distinct(getThis(), comparer);
   }
 
-  public T elementAt(int index) {
+  @Override public T elementAt(int index) {
     return EnumerableDefaults.elementAt(getThis(), index);
   }
 
-  public T elementAtOrDefault(int index) {
+  @Override public T elementAtOrDefault(int index) {
     return EnumerableDefaults.elementAtOrDefault(getThis(), index);
   }
 
-  public Enumerable<T> except(Enumerable<T> enumerable1) {
+  @Override public Enumerable<T> except(Enumerable<T> enumerable1) {
     return except(enumerable1, false);
   }
 
-  public Enumerable<T> except(Enumerable<T> enumerable1, boolean all) {
+  @Override public Enumerable<T> except(Enumerable<T> enumerable1, boolean all) {
     return EnumerableDefaults.except(getThis(), enumerable1, all);
   }
 
-  public Enumerable<T> except(Enumerable<T> enumerable1,
+  @Override public Enumerable<T> except(Enumerable<T> enumerable1,
       EqualityComparer<T> comparer) {
     return except(enumerable1, comparer, false);
   }
 
-  public Enumerable<T> except(Enumerable<T> enumerable1,
+  @Override public Enumerable<T> except(Enumerable<T> enumerable1,
       EqualityComparer<T> comparer, boolean all) {
     return EnumerableDefaults.except(getThis(), enumerable1, comparer, all);
   }
 
-  public T first() {
+  @Override public T first() {
     return EnumerableDefaults.first(getThis());
   }
 
-  public T first(Predicate1<T> predicate) {
+  @Override public T first(Predicate1<T> predicate) {
     return EnumerableDefaults.first(getThis(), predicate);
   }
 
-  public T firstOrDefault() {
+  @Override public T firstOrDefault() {
     return EnumerableDefaults.firstOrDefault(getThis());
   }
 
-  public T firstOrDefault(Predicate1<T> predicate) {
+  @Override public T firstOrDefault(Predicate1<T> predicate) {
     return EnumerableDefaults.firstOrDefault(getThis(), predicate);
   }
 
-  public <TKey> Enumerable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Enumerable<Grouping<TKey, T>> groupBy(
       Function1<T, TKey> keySelector) {
     return EnumerableDefaults.groupBy(getThis(), keySelector);
   }
 
-  public <TKey> Enumerable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Enumerable<Grouping<TKey, T>> groupBy(
       Function1<T, TKey> keySelector, EqualityComparer<TKey> comparer) {
     return EnumerableDefaults.groupBy(getThis(), keySelector, comparer);
   }
 
-  public <TKey, TElement> Enumerable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Enumerable<Grouping<TKey, TElement>> groupBy(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector) {
     return EnumerableDefaults.groupBy(getThis(), keySelector, elementSelector);
   }
 
-  public <TKey, TElement> Enumerable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Enumerable<Grouping<TKey, TElement>> groupBy(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector,
       EqualityComparer<TKey> comparer) {
     return EnumerableDefaults.groupBy(getThis(), keySelector, elementSelector,
         comparer);
   }
 
-  public <TKey, TResult> Enumerable<TResult> groupBy(
+  @Override public <TKey, TResult> Enumerable<TResult> groupBy(
       Function1<T, TKey> keySelector,
       Function2<TKey, Enumerable<T>, TResult> elementSelector,
       EqualityComparer<TKey> comparer) {
@@ -279,20 +279,20 @@ public <TKey, TResult> Enumerable<TResult> groupBy(
         comparer);
   }
 
-  public <TKey, TResult> Enumerable<TResult> groupBy(
+  @Override public <TKey, TResult> Enumerable<TResult> groupBy(
       Function1<T, TKey> keySelector,
       Function2<TKey, Enumerable<T>, TResult> resultSelector) {
     return EnumerableDefaults.groupBy(getThis(), keySelector, resultSelector);
   }
 
-  public <TKey, TElement, TResult> Enumerable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Enumerable<TResult> groupBy(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector,
       Function2<TKey, Enumerable<TElement>, TResult> resultSelector) {
     return EnumerableDefaults.groupBy(getThis(), keySelector, elementSelector,
         resultSelector);
   }
 
-  public <TKey, TElement, TResult> Enumerable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Enumerable<TResult> groupBy(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector,
       Function2<TKey, Enumerable<TElement>, TResult> resultSelector,
       EqualityComparer<TKey> comparer) {
@@ -300,7 +300,7 @@ public <TKey, TElement, TResult> Enumerable<TResult> groupBy(
         resultSelector, comparer);
   }
 
-  public <TKey, TAccumulate, TResult> Enumerable<TResult> groupBy(
+  @Override public <TKey, TAccumulate, TResult> Enumerable<TResult> groupBy(
       Function1<T, TKey> keySelector,
       Function0<TAccumulate> accumulatorInitializer,
       Function2<TAccumulate, T, TAccumulate> accumulatorAdder,
@@ -309,7 +309,7 @@ public <TKey, TAccumulate, TResult> Enumerable<TResult> groupBy(
         accumulatorInitializer, accumulatorAdder, resultSelector);
   }
 
-  public <TKey, TAccumulate, TResult> Enumerable<TResult> groupBy(
+  @Override public <TKey, TAccumulate, TResult> Enumerable<TResult> groupBy(
       Function1<T, TKey> keySelector,
       Function0<TAccumulate> accumulatorInitializer,
       Function2<TAccumulate, T, TAccumulate> accumulatorAdder,
@@ -319,7 +319,7 @@ public <TKey, TAccumulate, TResult> Enumerable<TResult> groupBy(
         accumulatorInitializer, accumulatorAdder, resultSelector, comparer);
   }
 
-  public <TKey, TAccumulate, TResult> Enumerable<TResult> sortedGroupBy(
+  @Override public <TKey, TAccumulate, TResult> Enumerable<TResult> sortedGroupBy(
       Function1<T, TKey> keySelector,
       Function0<TAccumulate> accumulatorInitializer,
       Function2<TAccumulate, T, TAccumulate> accumulatorAdder,
@@ -330,7 +330,7 @@ public <TKey, TAccumulate, TResult> Enumerable<TResult> sortedGroupBy(
         accumulatorAdder, resultSelector, comparator);
   }
 
-  public <TInner, TKey, TResult> Enumerable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Enumerable<TResult> groupJoin(
       Enumerable<TInner> inner, Function1<T, TKey> outerKeySelector,
       Function1<TInner, TKey> innerKeySelector,
       Function2<T, Enumerable<TInner>, TResult> resultSelector) {
@@ -338,7 +338,7 @@ public <TInner, TKey, TResult> Enumerable<TResult> groupJoin(
         innerKeySelector, resultSelector);
   }
 
-  public <TInner, TKey, TResult> Enumerable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Enumerable<TResult> groupJoin(
       Enumerable<TInner> inner, Function1<T, TKey> outerKeySelector,
       Function1<TInner, TKey> innerKeySelector,
       Function2<T, Enumerable<TInner>, TResult> resultSelector,
@@ -347,33 +347,33 @@ public <TInner, TKey, TResult> Enumerable<TResult> groupJoin(
         innerKeySelector, resultSelector, comparer);
   }
 
-  public Enumerable<T> intersect(Enumerable<T> enumerable1) {
+  @Override public Enumerable<T> intersect(Enumerable<T> enumerable1) {
     return intersect(enumerable1, false);
   }
 
-  public Enumerable<T> intersect(Enumerable<T> enumerable1, boolean all) {
+  @Override public Enumerable<T> intersect(Enumerable<T> enumerable1, boolean all) {
     return EnumerableDefaults.intersect(getThis(), enumerable1, all);
   }
 
-  public Enumerable<T> intersect(Enumerable<T> enumerable1,
+  @Override public Enumerable<T> intersect(Enumerable<T> enumerable1,
       EqualityComparer<T> comparer) {
     return intersect(enumerable1, comparer, false);
   }
 
-  public Enumerable<T> intersect(Enumerable<T> enumerable1,
+  @Override public Enumerable<T> intersect(Enumerable<T> enumerable1,
       EqualityComparer<T> comparer, boolean all) {
     return EnumerableDefaults.intersect(getThis(), enumerable1, comparer, all);
   }
 
-  public <C extends Collection<? super T>> C into(C sink) {
+  @Override public <C extends Collection<? super T>> C into(C sink) {
     return EnumerableDefaults.into(getThis(), sink);
   }
 
-  public <C extends Collection<? super T>> C removeAll(C sink) {
+  @Override public <C extends Collection<? super T>> C removeAll(C sink) {
     return EnumerableDefaults.remove(getThis(), sink);
   }
 
-  public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
+  @Override public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
       Enumerable<TInner> inner, Function1<T, TKey> outerKeySelector,
       Function1<TInner, TKey> innerKeySelector,
       Function2<T, TInner, TResult> resultSelector) {
@@ -381,7 +381,7 @@ public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
         innerKeySelector, resultSelector);
   }
 
-  public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
+  @Override public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
       Enumerable<TInner> inner, Function1<T, TKey> outerKeySelector,
       Function1<TInner, TKey> innerKeySelector,
       Function2<T, TInner, TResult> resultSelector,
@@ -390,7 +390,7 @@ public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
         innerKeySelector, resultSelector, comparer);
   }
 
-  public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
+  @Override public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
       Enumerable<TInner> inner, Function1<T, TKey> outerKeySelector,
       Function1<TInner, TKey> innerKeySelector,
       Function2<T, TInner, TResult> resultSelector,
@@ -401,7 +401,7 @@ public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
         generateNullsOnRight);
   }
 
-  public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
+  @Override public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
       Enumerable<TInner> inner, Function1<T, TKey> outerKeySelector,
       Function1<TInner, TKey> innerKeySelector,
       Function2<T, TInner, TResult> resultSelector,
@@ -413,371 +413,371 @@ public <TInner, TKey, TResult> Enumerable<TResult> hashJoin(
         generateNullsOnRight, predicate);
   }
 
-  public <TInner, TResult> Enumerable<TResult> correlateJoin(
+  @Override public <TInner, TResult> Enumerable<TResult> correlateJoin(
       JoinType joinType, Function1<T, Enumerable<TInner>> inner,
       Function2<T, TInner, TResult> resultSelector) {
     return EnumerableDefaults.correlateJoin(joinType, getThis(), inner,
         resultSelector);
   }
 
-  public T last() {
+  @Override public T last() {
     return EnumerableDefaults.last(getThis());
   }
 
-  public T last(Predicate1<T> predicate) {
+  @Override public T last(Predicate1<T> predicate) {
     return EnumerableDefaults.last(getThis(), predicate);
   }
 
-  public T lastOrDefault() {
+  @Override public T lastOrDefault() {
     return EnumerableDefaults.lastOrDefault(getThis());
   }
 
-  public T lastOrDefault(Predicate1<T> predicate) {
+  @Override public T lastOrDefault(Predicate1<T> predicate) {
     return EnumerableDefaults.lastOrDefault(getThis(), predicate);
   }
 
-  public long longCount() {
+  @Override public long longCount() {
     return EnumerableDefaults.longCount(getThis());
   }
 
-  public long longCount(Predicate1<T> predicate) {
+  @Override public long longCount(Predicate1<T> predicate) {
     return EnumerableDefaults.longCount(getThis(), predicate);
   }
 
-  public T max() {
+  @Override public T max() {
     return (T) EnumerableDefaults.max((Enumerable) getThis());
   }
 
-  public BigDecimal max(BigDecimalFunction1<T> selector) {
+  @Override public BigDecimal max(BigDecimalFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public BigDecimal max(NullableBigDecimalFunction1<T> selector) {
+  @Override public BigDecimal max(NullableBigDecimalFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public double max(DoubleFunction1<T> selector) {
+  @Override public double max(DoubleFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public Double max(NullableDoubleFunction1<T> selector) {
+  @Override public Double max(NullableDoubleFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public int max(IntegerFunction1<T> selector) {
+  @Override public int max(IntegerFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public Integer max(NullableIntegerFunction1<T> selector) {
+  @Override public Integer max(NullableIntegerFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public long max(LongFunction1<T> selector) {
+  @Override public long max(LongFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public Long max(NullableLongFunction1<T> selector) {
+  @Override public Long max(NullableLongFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public float max(FloatFunction1<T> selector) {
+  @Override public float max(FloatFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public Float max(NullableFloatFunction1<T> selector) {
+  @Override public Float max(NullableFloatFunction1<T> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public <TResult extends Comparable<TResult>> TResult max(
+  @Override public <TResult extends Comparable<TResult>> TResult max(
       Function1<T, TResult> selector) {
     return EnumerableDefaults.max(getThis(), selector);
   }
 
-  public T min() {
+  @Override public T min() {
     return (T) EnumerableDefaults.min((Enumerable) getThis());
   }
 
-  public BigDecimal min(BigDecimalFunction1<T> selector) {
+  @Override public BigDecimal min(BigDecimalFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public BigDecimal min(NullableBigDecimalFunction1<T> selector) {
+  @Override public BigDecimal min(NullableBigDecimalFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public double min(DoubleFunction1<T> selector) {
+  @Override public double min(DoubleFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public Double min(NullableDoubleFunction1<T> selector) {
+  @Override public Double min(NullableDoubleFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public int min(IntegerFunction1<T> selector) {
+  @Override public int min(IntegerFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public Integer min(NullableIntegerFunction1<T> selector) {
+  @Override public Integer min(NullableIntegerFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public long min(LongFunction1<T> selector) {
+  @Override public long min(LongFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public Long min(NullableLongFunction1<T> selector) {
+  @Override public Long min(NullableLongFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public float min(FloatFunction1<T> selector) {
+  @Override public float min(FloatFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public Float min(NullableFloatFunction1<T> selector) {
+  @Override public Float min(NullableFloatFunction1<T> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public <TResult extends Comparable<TResult>> TResult min(
+  @Override public <TResult extends Comparable<TResult>> TResult min(
       Function1<T, TResult> selector) {
     return EnumerableDefaults.min(getThis(), selector);
   }
 
-  public <TResult> Enumerable<TResult> ofType(Class<TResult> clazz) {
+  @Override public <TResult> Enumerable<TResult> ofType(Class<TResult> clazz) {
     return EnumerableDefaults.ofType(getThis(), clazz);
   }
 
-  public <TKey extends Comparable> Enumerable<T> orderBy(
+  @Override public <TKey extends Comparable> Enumerable<T> orderBy(
       Function1<T, TKey> keySelector) {
     return EnumerableDefaults.orderBy(getThis(), keySelector);
   }
 
-  public <TKey> Enumerable<T> orderBy(Function1<T, TKey> keySelector,
+  @Override public <TKey> Enumerable<T> orderBy(Function1<T, TKey> keySelector,
       Comparator<TKey> comparator) {
     return EnumerableDefaults.orderBy(getThis(), keySelector, comparator);
   }
 
-  public <TKey extends Comparable> Enumerable<T> orderByDescending(
+  @Override public <TKey extends Comparable> Enumerable<T> orderByDescending(
       Function1<T, TKey> keySelector) {
     return EnumerableDefaults.orderByDescending(getThis(), keySelector);
   }
 
-  public <TKey> Enumerable<T> orderByDescending(Function1<T, TKey> keySelector,
+  @Override public <TKey> Enumerable<T> orderByDescending(Function1<T, TKey> keySelector,
       Comparator<TKey> comparator) {
     return EnumerableDefaults.orderByDescending(getThis(), keySelector,
         comparator);
   }
 
-  public Enumerable<T> reverse() {
+  @Override public Enumerable<T> reverse() {
     return EnumerableDefaults.reverse(getThis());
   }
 
-  public <TResult> Enumerable<TResult> select(Function1<T, TResult> selector) {
+  @Override public <TResult> Enumerable<TResult> select(Function1<T, TResult> selector) {
     return EnumerableDefaults.select(getThis(), selector);
   }
 
-  public <TResult> Enumerable<TResult> select(
+  @Override public <TResult> Enumerable<TResult> select(
       Function2<T, Integer, TResult> selector) {
     return EnumerableDefaults.select(getThis(), selector);
   }
 
-  public <TResult> Enumerable<TResult> selectMany(
+  @Override public <TResult> Enumerable<TResult> selectMany(
       Function1<T, Enumerable<TResult>> selector) {
     return EnumerableDefaults.selectMany(getThis(), selector);
   }
 
-  public <TResult> Enumerable<TResult> selectMany(
+  @Override public <TResult> Enumerable<TResult> selectMany(
       Function2<T, Integer, Enumerable<TResult>> selector) {
     return EnumerableDefaults.selectMany(getThis(), selector);
   }
 
-  public <TCollection, TResult> Enumerable<TResult> selectMany(
+  @Override public <TCollection, TResult> Enumerable<TResult> selectMany(
       Function2<T, Integer, Enumerable<TCollection>> collectionSelector,
       Function2<T, TCollection, TResult> resultSelector) {
     return EnumerableDefaults.selectMany(getThis(), collectionSelector,
         resultSelector);
   }
 
-  public <TCollection, TResult> Enumerable<TResult> selectMany(
+  @Override public <TCollection, TResult> Enumerable<TResult> selectMany(
       Function1<T, Enumerable<TCollection>> collectionSelector,
       Function2<T, TCollection, TResult> resultSelector) {
     return EnumerableDefaults.selectMany(getThis(), collectionSelector,
         resultSelector);
   }
 
-  public boolean sequenceEqual(Enumerable<T> enumerable1) {
+  @Override public boolean sequenceEqual(Enumerable<T> enumerable1) {
     return EnumerableDefaults.sequenceEqual(getThis(), enumerable1);
   }
 
-  public boolean sequenceEqual(Enumerable<T> enumerable1,
+  @Override public boolean sequenceEqual(Enumerable<T> enumerable1,
       EqualityComparer<T> comparer) {
     return EnumerableDefaults.sequenceEqual(getThis(), enumerable1, comparer);
   }
 
-  public T single() {
+  @Override public T single() {
     return EnumerableDefaults.single(getThis());
   }
 
-  public T single(Predicate1<T> predicate) {
+  @Override public T single(Predicate1<T> predicate) {
     return EnumerableDefaults.single(getThis(), predicate);
   }
 
-  public T singleOrDefault() {
+  @Override public T singleOrDefault() {
     return EnumerableDefaults.singleOrDefault(getThis());
   }
 
-  public T singleOrDefault(Predicate1<T> predicate) {
+  @Override public T singleOrDefault(Predicate1<T> predicate) {
     return EnumerableDefaults.singleOrDefault(getThis(), predicate);
   }
 
-  public Enumerable<T> skip(int count) {
+  @Override public Enumerable<T> skip(int count) {
     return EnumerableDefaults.skip(getThis(), count);
   }
 
-  public Enumerable<T> skipWhile(Predicate1<T> predicate) {
+  @Override public Enumerable<T> skipWhile(Predicate1<T> predicate) {
     return EnumerableDefaults.skipWhile(getThis(), predicate);
   }
 
-  public Enumerable<T> skipWhile(Predicate2<T, Integer> predicate) {
+  @Override public Enumerable<T> skipWhile(Predicate2<T, Integer> predicate) {
     return EnumerableDefaults.skipWhile(getThis(), predicate);
   }
 
-  public BigDecimal sum(BigDecimalFunction1<T> selector) {
+  @Override public BigDecimal sum(BigDecimalFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public BigDecimal sum(NullableBigDecimalFunction1<T> selector) {
+  @Override public BigDecimal sum(NullableBigDecimalFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public double sum(DoubleFunction1<T> selector) {
+  @Override public double sum(DoubleFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public Double sum(NullableDoubleFunction1<T> selector) {
+  @Override public Double sum(NullableDoubleFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public int sum(IntegerFunction1<T> selector) {
+  @Override public int sum(IntegerFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public Integer sum(NullableIntegerFunction1<T> selector) {
+  @Override public Integer sum(NullableIntegerFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public long sum(LongFunction1<T> selector) {
+  @Override public long sum(LongFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public Long sum(NullableLongFunction1<T> selector) {
+  @Override public Long sum(NullableLongFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public float sum(FloatFunction1<T> selector) {
+  @Override public float sum(FloatFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public Float sum(NullableFloatFunction1<T> selector) {
+  @Override public Float sum(NullableFloatFunction1<T> selector) {
     return EnumerableDefaults.sum(getThis(), selector);
   }
 
-  public Enumerable<T> take(int count) {
+  @Override public Enumerable<T> take(int count) {
     return EnumerableDefaults.take(getThis(), count);
   }
 
-  public Enumerable<T> takeWhile(Predicate1<T> predicate) {
+  @Override public Enumerable<T> takeWhile(Predicate1<T> predicate) {
     return EnumerableDefaults.takeWhile(getThis(), predicate);
   }
 
-  public Enumerable<T> takeWhile(Predicate2<T, Integer> predicate) {
+  @Override public Enumerable<T> takeWhile(Predicate2<T, Integer> predicate) {
     return EnumerableDefaults.takeWhile(getThis(), predicate);
   }
 
-  public <TKey extends Comparable<TKey>> OrderedEnumerable<T> thenBy(
+  @Override public <TKey extends Comparable<TKey>> OrderedEnumerable<T> thenBy(
       Function1<T, TKey> keySelector) {
     return EnumerableDefaults.thenBy(getThisOrdered(), keySelector);
   }
 
-  public <TKey> OrderedEnumerable<T> thenBy(Function1<T, TKey> keySelector,
+  @Override public <TKey> OrderedEnumerable<T> thenBy(Function1<T, TKey> keySelector,
       Comparator<TKey> comparator) {
     return EnumerableDefaults.thenByDescending(getThisOrdered(), keySelector,
         comparator);
   }
 
-  public <TKey extends Comparable<TKey>> OrderedEnumerable<T> thenByDescending(
+  @Override public <TKey extends Comparable<TKey>> OrderedEnumerable<T> thenByDescending(
       Function1<T, TKey> keySelector) {
     return EnumerableDefaults.thenByDescending(getThisOrdered(), keySelector);
   }
 
-  public <TKey> OrderedEnumerable<T> thenByDescending(
+  @Override public <TKey> OrderedEnumerable<T> thenByDescending(
       Function1<T, TKey> keySelector, Comparator<TKey> comparator) {
     return EnumerableDefaults.thenBy(getThisOrdered(), keySelector, comparator);
   }
 
-  public <TKey> Map<TKey, T> toMap(Function1<T, TKey> keySelector) {
+  @Override public <TKey> Map<TKey, T> toMap(Function1<T, TKey> keySelector) {
     return EnumerableDefaults.toMap(getThis(), keySelector);
   }
 
-  public <TKey> Map<TKey, T> toMap(Function1<T, TKey> keySelector,
+  @Override public <TKey> Map<TKey, T> toMap(Function1<T, TKey> keySelector,
       EqualityComparer<TKey> comparer) {
     return EnumerableDefaults.toMap(getThis(), keySelector, comparer);
   }
 
-  public <TKey, TElement> Map<TKey, TElement> toMap(
+  @Override public <TKey, TElement> Map<TKey, TElement> toMap(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector) {
     return EnumerableDefaults.toMap(getThis(), keySelector, elementSelector);
   }
 
-  public <TKey, TElement> Map<TKey, TElement> toMap(
+  @Override public <TKey, TElement> Map<TKey, TElement> toMap(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector,
       EqualityComparer<TKey> comparer) {
     return EnumerableDefaults.toMap(getThis(), keySelector, elementSelector,
         comparer);
   }
 
-  public List<T> toList() {
+  @Override public List<T> toList() {
     return EnumerableDefaults.toList(getThis());
   }
 
-  public <TKey> Lookup<TKey, T> toLookup(Function1<T, TKey> keySelector) {
+  @Override public <TKey> Lookup<TKey, T> toLookup(Function1<T, TKey> keySelector) {
     return EnumerableDefaults.toLookup(getThis(), keySelector);
   }
 
-  public <TKey> Lookup<TKey, T> toLookup(Function1<T, TKey> keySelector,
+  @Override public <TKey> Lookup<TKey, T> toLookup(Function1<T, TKey> keySelector,
       EqualityComparer<TKey> comparer) {
     return EnumerableDefaults.toLookup(getThis(), keySelector, comparer);
   }
 
-  public <TKey, TElement> Lookup<TKey, TElement> toLookup(
+  @Override public <TKey, TElement> Lookup<TKey, TElement> toLookup(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector) {
     return EnumerableDefaults.toLookup(getThis(), keySelector, elementSelector);
   }
 
-  public <TKey, TElement> Lookup<TKey, TElement> toLookup(
+  @Override public <TKey, TElement> Lookup<TKey, TElement> toLookup(
       Function1<T, TKey> keySelector, Function1<T, TElement> elementSelector,
       EqualityComparer<TKey> comparer) {
     return EnumerableDefaults.toLookup(getThis(), keySelector, elementSelector,
         comparer);
   }
 
-  public Enumerable<T> union(Enumerable<T> source1) {
+  @Override public Enumerable<T> union(Enumerable<T> source1) {
     return EnumerableDefaults.union(getThis(), source1);
   }
 
-  public Enumerable<T> union(Enumerable<T> source1,
+  @Override public Enumerable<T> union(Enumerable<T> source1,
       EqualityComparer<T> comparer) {
     return EnumerableDefaults.union(getThis(), source1, comparer);
   }
 
-  public Enumerable<T> where(Predicate1<T> predicate) {
+  @Override public Enumerable<T> where(Predicate1<T> predicate) {
     return EnumerableDefaults.where(getThis(), predicate);
   }
 
-  public Enumerable<T> where(Predicate2<T, Integer> predicate) {
+  @Override public Enumerable<T> where(Predicate2<T, Integer> predicate) {
     return EnumerableDefaults.where(getThis(), predicate);
   }
 
-  public <T1, TResult> Enumerable<TResult> zip(Enumerable<T1> source1,
+  @Override public <T1, TResult> Enumerable<TResult> zip(Enumerable<T1> source1,
       Function2<T, T1, TResult> resultSelector) {
     return EnumerableDefaults.zip(getThis(), source1, resultSelector);
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultQueryable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultQueryable.java
index 4d09d433ad4..4c1eddfa787 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultQueryable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/DefaultQueryable.java
@@ -72,7 +72,7 @@ protected OrderedQueryable<T> getThisOrderedQueryable() {
 
   @Override public Enumerable<T> asEnumerable() {
     return new AbstractEnumerable<T>() {
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         return DefaultQueryable.this.enumerator();
       }
     };
@@ -162,129 +162,129 @@ public Enumerator<T> enumerator() {
 
   // End disambiguate
 
-  public T aggregate(FunctionExpression<Function2<T, T, T>> selector) {
+  @Override public T aggregate(FunctionExpression<Function2<T, T, T>> selector) {
     return factory.aggregate(getThis(), selector);
   }
 
-  public <TAccumulate> TAccumulate aggregate(TAccumulate seed,
+  @Override public <TAccumulate> TAccumulate aggregate(TAccumulate seed,
       FunctionExpression<Function2<TAccumulate, T, TAccumulate>> selector) {
     return factory.aggregate(getThis(), seed, selector);
   }
 
-  public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
+  @Override public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
       FunctionExpression<Function2<TAccumulate, T, TAccumulate>> func,
       FunctionExpression<Function1<TAccumulate, TResult>> selector) {
     return factory.aggregate(getThis(), seed, func, selector);
   }
 
-  public boolean all(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public boolean all(FunctionExpression<Predicate1<T>> predicate) {
     return factory.all(getThis(), predicate);
   }
 
-  public boolean any(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public boolean any(FunctionExpression<Predicate1<T>> predicate) {
     return factory.any(getThis(), predicate);
   }
 
-  public BigDecimal averageBigDecimal(
+  @Override public BigDecimal averageBigDecimal(
       FunctionExpression<BigDecimalFunction1<T>> selector) {
     return factory.averageBigDecimal(getThis(), selector);
   }
 
-  public BigDecimal averageNullableBigDecimal(
+  @Override public BigDecimal averageNullableBigDecimal(
       FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     return factory.averageNullableBigDecimal(getThis(), selector);
   }
 
-  public double averageDouble(FunctionExpression<DoubleFunction1<T>> selector) {
+  @Override public double averageDouble(FunctionExpression<DoubleFunction1<T>> selector) {
     return factory.averageDouble(getThis(), selector);
   }
 
-  public Double averageNullableDouble(
+  @Override public Double averageNullableDouble(
       FunctionExpression<NullableDoubleFunction1<T>> selector) {
     return factory.averageNullableDouble(getThis(), selector);
   }
 
-  public int averageInteger(FunctionExpression<IntegerFunction1<T>> selector) {
+  @Override public int averageInteger(FunctionExpression<IntegerFunction1<T>> selector) {
     return factory.averageInteger(getThis(), selector);
   }
 
-  public Integer averageNullableInteger(
+  @Override public Integer averageNullableInteger(
       FunctionExpression<NullableIntegerFunction1<T>> selector) {
     return factory.averageNullableInteger(getThis(), selector);
   }
 
-  public float averageFloat(FunctionExpression<FloatFunction1<T>> selector) {
+  @Override public float averageFloat(FunctionExpression<FloatFunction1<T>> selector) {
     return factory.averageFloat(getThis(), selector);
   }
 
-  public Float averageNullableFloat(
+  @Override public Float averageNullableFloat(
       FunctionExpression<NullableFloatFunction1<T>> selector) {
     return factory.averageNullableFloat(getThis(), selector);
   }
 
-  public long averageLong(FunctionExpression<LongFunction1<T>> selector) {
+  @Override public long averageLong(FunctionExpression<LongFunction1<T>> selector) {
     return factory.averageLong(getThis(), selector);
   }
 
-  public Long averageNullableLong(
+  @Override public Long averageNullableLong(
       FunctionExpression<NullableLongFunction1<T>> selector) {
     return factory.averageNullableLong(getThis(), selector);
   }
 
-  public Queryable<T> concat(Enumerable<T> source2) {
+  @Override public Queryable<T> concat(Enumerable<T> source2) {
     return factory.concat(getThis(), source2);
   }
 
-  public int count(FunctionExpression<Predicate1<T>> func) {
+  @Override public int count(FunctionExpression<Predicate1<T>> func) {
     return factory.count(getThis(), func);
   }
 
-  public T first(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T first(FunctionExpression<Predicate1<T>> predicate) {
     return factory.first(getThis(), predicate);
   }
 
-  public T firstOrDefault(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T firstOrDefault(FunctionExpression<Predicate1<T>> predicate) {
     return factory.firstOrDefault(getThis(), predicate);
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return factory.groupBy(getThis(), keySelector);
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       EqualityComparer<TKey> comparer) {
     return factory.groupBy(getThis(), keySelector, comparer);
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector) {
     return factory.groupBy(getThis(), keySelector, elementSelector);
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
       EqualityComparer<TKey> comparer) {
     return factory.groupBy(getThis(), keySelector, elementSelector, comparer);
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function2<TKey, Enumerable<T>, TResult>> resultSelector) {
     return factory.groupByK(getThis(), keySelector, resultSelector);
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function2<TKey, Enumerable<T>, TResult>> resultSelector,
       EqualityComparer<TKey> comparer) {
     return factory.groupByK(getThis(), keySelector, resultSelector, comparer);
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
       FunctionExpression<Function2<TKey, Enumerable<TElement>, TResult>> resultSelector) {
@@ -292,7 +292,7 @@ public <TKey, TElement, TResult> Queryable<TResult> groupBy(
         resultSelector);
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
       FunctionExpression<Function2<TKey, Enumerable<TElement>, TResult>> resultSelector,
@@ -301,7 +301,7 @@ public <TKey, TElement, TResult> Queryable<TResult> groupBy(
         resultSelector, comparer);
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -310,7 +310,7 @@ public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
         innerKeySelector, resultSelector);
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -320,7 +320,7 @@ public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
         innerKeySelector, resultSelector, comparer);
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -329,7 +329,7 @@ public <TInner, TKey, TResult> Queryable<TResult> join(
         resultSelector);
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -339,190 +339,190 @@ public <TInner, TKey, TResult> Queryable<TResult> join(
         resultSelector, comparer);
   }
 
-  public T last(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T last(FunctionExpression<Predicate1<T>> predicate) {
     return factory.last(getThis(), predicate);
   }
 
-  public T lastOrDefault(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T lastOrDefault(FunctionExpression<Predicate1<T>> predicate) {
     return factory.lastOrDefault(getThis(), predicate);
   }
 
-  public long longCount(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public long longCount(FunctionExpression<Predicate1<T>> predicate) {
     return factory.longCount(getThis(), predicate);
   }
 
-  public <TResult extends Comparable<TResult>> TResult max(
+  @Override public <TResult extends Comparable<TResult>> TResult max(
       FunctionExpression<Function1<T, TResult>> selector) {
     return factory.max(getThis(), selector);
   }
 
-  public <TResult extends Comparable<TResult>> TResult min(
+  @Override public <TResult extends Comparable<TResult>> TResult min(
       FunctionExpression<Function1<T, TResult>> selector) {
     return factory.min(getThis(), selector);
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderBy(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderBy(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return factory.orderBy(getThis(), keySelector);
   }
 
-  public <TKey> OrderedQueryable<T> orderBy(
+  @Override public <TKey> OrderedQueryable<T> orderBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return factory.orderBy(getThis(), keySelector, comparator);
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return factory.orderByDescending(getThis(), keySelector);
   }
 
-  public <TKey> OrderedQueryable<T> orderByDescending(
+  @Override public <TKey> OrderedQueryable<T> orderByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return factory.orderByDescending(getThis(), keySelector, comparator);
   }
 
-  public <TResult> Queryable<TResult> select(
+  @Override public <TResult> Queryable<TResult> select(
       FunctionExpression<Function1<T, TResult>> selector) {
     return factory.select(getThis(), selector);
   }
 
-  public <TResult> Queryable<TResult> selectN(
+  @Override public <TResult> Queryable<TResult> selectN(
       FunctionExpression<Function2<T, Integer, TResult>> selector) {
     return factory.selectN(getThis(), selector);
   }
 
-  public <TResult> Queryable<TResult> selectMany(
+  @Override public <TResult> Queryable<TResult> selectMany(
       FunctionExpression<Function1<T, Enumerable<TResult>>> selector) {
     return factory.selectMany(getThis(), selector);
   }
 
-  public <TResult> Queryable<TResult> selectManyN(
+  @Override public <TResult> Queryable<TResult> selectManyN(
       FunctionExpression<Function2<T, Integer, Enumerable<TResult>>> selector) {
     return factory.selectManyN(getThis(), selector);
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectMany(
+  @Override public <TCollection, TResult> Queryable<TResult> selectMany(
       FunctionExpression<Function2<T, Integer, Enumerable<TCollection>>>
         collectionSelector,
       FunctionExpression<Function2<T, TCollection, TResult>> resultSelector) {
     return factory.selectMany(getThis(), collectionSelector, resultSelector);
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectManyN(
+  @Override public <TCollection, TResult> Queryable<TResult> selectManyN(
       FunctionExpression<Function1<T, Enumerable<TCollection>>>
         collectionSelector,
       FunctionExpression<Function2<T, TCollection, TResult>> resultSelector) {
     return factory.selectManyN(getThis(), collectionSelector, resultSelector);
   }
 
-  public T single(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T single(FunctionExpression<Predicate1<T>> predicate) {
     return factory.single(getThis(), predicate);
   }
 
-  public T singleOrDefault(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T singleOrDefault(FunctionExpression<Predicate1<T>> predicate) {
     return factory.singleOrDefault(getThis(), predicate);
   }
 
-  public Queryable<T> skipWhile(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public Queryable<T> skipWhile(FunctionExpression<Predicate1<T>> predicate) {
     return factory.skipWhile(getThis(), predicate);
   }
 
-  public Queryable<T> skipWhileN(
+  @Override public Queryable<T> skipWhileN(
       FunctionExpression<Predicate2<T, Integer>> predicate) {
     return factory.skipWhileN(getThis(), predicate);
   }
 
-  public BigDecimal sumBigDecimal(
+  @Override public BigDecimal sumBigDecimal(
       FunctionExpression<BigDecimalFunction1<T>> selector) {
     return factory.sumBigDecimal(getThis(), selector);
   }
 
-  public BigDecimal sumNullableBigDecimal(
+  @Override public BigDecimal sumNullableBigDecimal(
       FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     return factory.sumNullableBigDecimal(getThis(), selector);
   }
 
-  public double sumDouble(FunctionExpression<DoubleFunction1<T>> selector) {
+  @Override public double sumDouble(FunctionExpression<DoubleFunction1<T>> selector) {
     return factory.sumDouble(getThis(), selector);
   }
 
-  public Double sumNullableDouble(
+  @Override public Double sumNullableDouble(
       FunctionExpression<NullableDoubleFunction1<T>> selector) {
     return factory.sumNullableDouble(getThis(), selector);
   }
 
-  public int sumInteger(FunctionExpression<IntegerFunction1<T>> selector) {
+  @Override public int sumInteger(FunctionExpression<IntegerFunction1<T>> selector) {
     return factory.sumInteger(getThis(), selector);
   }
 
-  public Integer sumNullableInteger(
+  @Override public Integer sumNullableInteger(
       FunctionExpression<NullableIntegerFunction1<T>> selector) {
     return factory.sumNullableInteger(getThis(), selector);
   }
 
-  public long sumLong(FunctionExpression<LongFunction1<T>> selector) {
+  @Override public long sumLong(FunctionExpression<LongFunction1<T>> selector) {
     return factory.sumLong(getThis(), selector);
   }
 
-  public Long sumNullableLong(
+  @Override public Long sumNullableLong(
       FunctionExpression<NullableLongFunction1<T>> selector) {
     return factory.sumNullableLong(getThis(), selector);
   }
 
-  public float sumFloat(FunctionExpression<FloatFunction1<T>> selector) {
+  @Override public float sumFloat(FunctionExpression<FloatFunction1<T>> selector) {
     return factory.sumFloat(getThis(), selector);
   }
 
-  public Float sumNullableFloat(
+  @Override public Float sumNullableFloat(
       FunctionExpression<NullableFloatFunction1<T>> selector) {
     return factory.sumNullableFloat(getThis(), selector);
   }
 
-  public Queryable<T> takeWhile(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public Queryable<T> takeWhile(FunctionExpression<Predicate1<T>> predicate) {
     return factory.takeWhile(getThis(), predicate);
   }
 
-  public Queryable<T> takeWhileN(
+  @Override public Queryable<T> takeWhileN(
       FunctionExpression<Predicate2<T, Integer>> predicate) {
     return factory.takeWhileN(getThis(), predicate);
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return factory.thenBy(getThisOrderedQueryable(), keySelector);
   }
 
-  public <TKey> OrderedQueryable<T> thenBy(
+  @Override public <TKey> OrderedQueryable<T> thenBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return factory.thenByDescending(getThisOrderedQueryable(), keySelector,
         comparator);
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return factory.thenByDescending(getThisOrderedQueryable(), keySelector);
   }
 
-  public <TKey> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey> OrderedQueryable<T> thenByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return factory.thenBy(getThisOrderedQueryable(), keySelector, comparator);
   }
 
-  public Queryable<T> where(
+  @Override public Queryable<T> where(
       FunctionExpression<? extends Predicate1<T>> predicate) {
     return factory.where(getThis(), predicate);
   }
 
-  public Queryable<T> whereN(
+  @Override public Queryable<T> whereN(
       FunctionExpression<? extends Predicate2<T, Integer>> predicate) {
     return factory.whereN(getThis(), predicate);
   }
 
-  public <T1, TResult> Queryable<TResult> zip(Enumerable<T1> source1,
+  @Override public <T1, TResult> Queryable<TResult> zip(Enumerable<T1> source1,
       FunctionExpression<Function2<T, T1, TResult>> resultSelector) {
     return factory.zip(getThis(), source1, resultSelector);
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerable.java
index 181d0358ee6..5d4300b8f00 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerable.java
@@ -33,6 +33,6 @@ public interface Enumerable<T>
    *
    * @see EnumerableDefaults#asQueryable(Enumerable)
    */
-  Queryable<T> asQueryable();
+  @Override Queryable<T> asQueryable();
 
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java b/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java
index e1b9de84d6f..5f4d484dbd6 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java
@@ -320,7 +320,7 @@ public static <TSource> Float average(Enumerable<TSource> source,
   public static <TSource, T2> Enumerable<T2> cast(
       final Enumerable<TSource> source, final Class<T2> clazz) {
     return new AbstractEnumerable<T2>() {
-      public Enumerator<T2> enumerator() {
+      @Override public Enumerator<T2> enumerator() {
         return new CastingEnumerator<>(source.enumerator(), clazz);
       }
     };
@@ -412,11 +412,11 @@ public static <TSource> Enumerable<TSource> defaultIfEmpty(
 
           private Iterator<TSource> rest;
 
-          public boolean hasNext() {
+          @Override public boolean hasNext() {
             return !nonFirst || rest.hasNext();
           }
 
-          public TSource next() {
+          @Override public TSource next() {
             if (nonFirst) {
               return rest.next();
             } else {
@@ -427,7 +427,7 @@ public TSource next() {
             }
           }
 
-          public void remove() {
+          @Override public void remove() {
             throw new UnsupportedOperationException("remove");
           }
         });
@@ -835,7 +835,7 @@ public static <TSource, TKey, TAccumulate, TResult> Enumerable<TResult> sortedGr
       final Function2<TKey, TAccumulate, TResult> resultSelector,
       final Comparator<TKey> comparator) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new SortedAggregateEnumerator(
           enumerable, keySelector, accumulatorInitializer,
           accumulatorAdder, resultSelector, comparator);
@@ -1037,24 +1037,24 @@ public static <TSource, TInner, TKey, TResult> Enumerable<TResult> groupJoin(
       final Enumerator<Map.Entry<TKey, TSource>> entries =
           Linq4j.enumerator(outerMap.entrySet());
 
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
-          public TResult current() {
+          @Override public TResult current() {
             final Map.Entry<TKey, TSource> entry = entries.current();
             final Enumerable<TInner> inners = innerLookup.get(entry.getKey());
             return resultSelector.apply(entry.getValue(),
                 inners == null ? Linq4j.emptyEnumerable() : inners);
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             return entries.moveNext();
           }
 
-          public void reset() {
+          @Override public void reset() {
             entries.reset();
           }
 
-          public void close() {
+          @Override public void close() {
           }
         };
       }
@@ -1078,24 +1078,24 @@ public static <TSource, TInner, TKey, TResult> Enumerable<TResult> groupJoin(
       final Enumerator<Map.Entry<TKey, TSource>> entries =
           Linq4j.enumerator(outerMap.entrySet());
 
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
-          public TResult current() {
+          @Override public TResult current() {
             final Map.Entry<TKey, TSource> entry = entries.current();
             final Enumerable<TInner> inners = innerLookup.get(entry.getKey());
             return resultSelector.apply(entry.getValue(),
                 inners == null ? Linq4j.emptyEnumerable() : inners);
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             return entries.moveNext();
           }
 
-          public void reset() {
+          @Override public void reset() {
             entries.reset();
           }
 
-          public void close() {
+          @Override public void close() {
           }
         };
       }
@@ -1284,7 +1284,7 @@ private static <TSource, TInner, TKey, TResult> Enumerable<TResult> hashEquiJoin
       final EqualityComparer<TKey> comparer, final boolean generateNullsOnLeft,
       final boolean generateNullsOnRight) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         final Lookup<TKey, TInner> innerLookup =
             comparer == null
                 ? inner.toLookup(innerKeySelector)
@@ -1298,11 +1298,11 @@ public Enumerator<TResult> enumerator() {
                   ? new HashSet<>(innerLookup.keySet())
                   : null;
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultSelector.apply(outers.current(), inners.current());
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             for (;;) {
               if (inners.moveNext()) {
                 return true;
@@ -1355,11 +1355,11 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             outers.reset();
           }
 
-          public void close() {
+          @Override public void close() {
             outers.close();
           }
         };
@@ -1378,7 +1378,7 @@ private static <TSource, TInner, TKey, TResult> Enumerable<TResult> hashJoinWith
       final boolean generateNullsOnRight, final Predicate2<TSource, TInner> predicate) {
 
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         /**
          * the innerToLookUp will refer the inner , if current join
          * is a right join, we should figure out the right list first, if
@@ -1402,11 +1402,11 @@ public Enumerator<TResult> enumerator() {
                   ? new ArrayList<>(innerToLookUp.toList())
                   : null;
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultSelector.apply(outers.current(), inners.current());
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             for (;;) {
               if (inners.moveNext()) {
                 return true;
@@ -1464,11 +1464,11 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             outers.reset();
           }
 
-          public void close() {
+          @Override public void close() {
             outers.close();
           }
         };
@@ -1489,7 +1489,7 @@ public static <TSource, TInner, TResult> Enumerable<TResult> correlateJoin(
     }
 
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           private Enumerator<TSource> outerEnumerator = outer.enumerator();
           private Enumerator<TInner> innerEnumerator;
@@ -1497,11 +1497,11 @@ public Enumerator<TResult> enumerator() {
           TInner innerValue;
           int state = 0; // 0 -- moving outer, 1 moving inner;
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultSelector.apply(outerValue, innerValue);
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             while (true) {
               switch (state) {
               case 0:
@@ -1554,13 +1554,13 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             state = 0;
             outerEnumerator.reset();
             closeInner();
           }
 
-          public void close() {
+          @Override public void close() {
             outerEnumerator.close();
             closeInner();
             outerValue = null;
@@ -1870,7 +1870,7 @@ private static <TSource, TInner, TKey> Enumerable<TSource> semiJoinWithPredicate
       final Predicate2<TSource, TInner> nonEquiPredicate) {
 
     return new AbstractEnumerable<TSource>() {
-      public Enumerator<TSource> enumerator() {
+      @Override public Enumerator<TSource> enumerator() {
         // CALCITE-2909 Delay the computation of the innerLookup until the
         // moment when we are sure
         // that it will be really needed, i.e. when the first outer
@@ -1914,7 +1914,7 @@ private static <TSource, TInner, TKey> Enumerable<TSource> semiEquiJoin_(
       final EqualityComparer<TKey> comparer,
       final boolean anti) {
     return new AbstractEnumerable<TSource>() {
-      public Enumerator<TSource> enumerator() {
+      @Override public Enumerator<TSource> enumerator() {
         // CALCITE-2909 Delay the computation of the innerLookup until the moment when we are sure
         // that it will be really needed, i.e. when the first outer enumerator item is processed
         final Supplier<Enumerable<TKey>> innerLookup = Suppliers.memoize(() ->
@@ -2014,7 +2014,7 @@ private static <TSource, TInner, TResult> Enumerable<TResult> nestedLoopJoinOpti
     }
 
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           private Enumerator<TSource> outerEnumerator = outer.enumerator();
           private Enumerator<TInner> innerEnumerator = null;
@@ -2183,7 +2183,7 @@ public static boolean isMergeJoinSupported(JoinType joinType) {
       throw new UnsupportedOperationException("MergeJoin unsupported for join type " + joinType);
     }
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new MergeJoinEnumerator<>(outer, inner, outerKeySelector, innerKeySelector,
             extraPredicate, resultSelector, joinType, comparator);
       }
@@ -2748,11 +2748,11 @@ public static <TSource> Enumerable<TSource> reverse(
     final int n = list.size();
     return Linq4j.asEnumerable(
         new AbstractList<TSource>() {
-          public TSource get(int index) {
+          @Override public TSource get(int index) {
             return list.get(n - 1 - index);
           }
 
-          public int size() {
+          @Override public int size() {
             return n;
           }
         });
@@ -2769,23 +2769,23 @@ public static <TSource, TResult> Enumerable<TResult> select(
       return (Enumerable<TResult>) source;
     }
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           final Enumerator<TSource> enumerator = source.enumerator();
 
-          public TResult current() {
+          @Override public TResult current() {
             return selector.apply(enumerator.current());
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             return enumerator.moveNext();
           }
 
-          public void reset() {
+          @Override public void reset() {
             enumerator.reset();
           }
 
-          public void close() {
+          @Override public void close() {
             enumerator.close();
           }
         };
@@ -2801,16 +2801,16 @@ public static <TSource, TResult> Enumerable<TResult> select(
       final Enumerable<TSource> source,
       final Function2<TSource, Integer, TResult> selector) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           final Enumerator<TSource> enumerator = source.enumerator();
           int n = -1;
 
-          public TResult current() {
+          @Override public TResult current() {
             return selector.apply(enumerator.current(), n);
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             if (enumerator.moveNext()) {
               ++n;
               return true;
@@ -2819,11 +2819,11 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             enumerator.reset();
           }
 
-          public void close() {
+          @Override public void close() {
             enumerator.close();
           }
         };
@@ -2840,16 +2840,16 @@ public static <TSource, TResult> Enumerable<TResult> selectMany(
       final Enumerable<TSource> source,
       final Function1<TSource, Enumerable<TResult>> selector) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           Enumerator<TSource> sourceEnumerator = source.enumerator();
           Enumerator<TResult> resultEnumerator = Linq4j.emptyEnumerator();
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultEnumerator.current();
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             for (;;) {
               if (resultEnumerator.moveNext()) {
                 return true;
@@ -2862,12 +2862,12 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             sourceEnumerator.reset();
             resultEnumerator = Linq4j.emptyEnumerator();
           }
 
-          public void close() {
+          @Override public void close() {
             sourceEnumerator.close();
             resultEnumerator.close();
           }
@@ -2886,17 +2886,17 @@ public static <TSource, TResult> Enumerable<TResult> selectMany(
       final Enumerable<TSource> source,
       final Function2<TSource, Integer, Enumerable<TResult>> selector) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           int index = -1;
           Enumerator<TSource> sourceEnumerator = source.enumerator();
           Enumerator<TResult> resultEnumerator = Linq4j.emptyEnumerator();
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultEnumerator.current();
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             for (;;) {
               if (resultEnumerator.moveNext()) {
                 return true;
@@ -2910,12 +2910,12 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             sourceEnumerator.reset();
             resultEnumerator = Linq4j.emptyEnumerator();
           }
 
-          public void close() {
+          @Override public void close() {
             sourceEnumerator.close();
             resultEnumerator.close();
           }
@@ -2936,18 +2936,18 @@ public static <TSource, TCollection, TResult> Enumerable<TResult> selectMany(
       final Function2<TSource, Integer, Enumerable<TCollection>> collectionSelector,
       final Function2<TSource, TCollection, TResult> resultSelector) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           int index = -1;
           Enumerator<TSource> sourceEnumerator = source.enumerator();
           Enumerator<TCollection> collectionEnumerator = Linq4j.emptyEnumerator();
           Enumerator<TResult> resultEnumerator = Linq4j.emptyEnumerator();
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultEnumerator.current();
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             for (;;) {
               if (resultEnumerator.moveNext()) {
                 return true;
@@ -2961,19 +2961,19 @@ public boolean moveNext() {
                   .enumerator();
               resultEnumerator =
                   new TransformedEnumerator<TCollection, TResult>(collectionEnumerator) {
-                    protected TResult transform(TCollection collectionElement) {
+                    @Override protected TResult transform(TCollection collectionElement) {
                       return resultSelector.apply(sourceElement, collectionElement);
                     }
                   };
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             sourceEnumerator.reset();
             resultEnumerator = Linq4j.emptyEnumerator();
           }
 
-          public void close() {
+          @Override public void close() {
             sourceEnumerator.close();
             resultEnumerator.close();
           }
@@ -2993,17 +2993,17 @@ public static <TSource, TCollection, TResult> Enumerable<TResult> selectMany(
       final Function1<TSource, Enumerable<TCollection>> collectionSelector,
       final Function2<TSource, TCollection, TResult> resultSelector) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           Enumerator<TSource> sourceEnumerator = source.enumerator();
           Enumerator<TCollection> collectionEnumerator = Linq4j.emptyEnumerator();
           Enumerator<TResult> resultEnumerator = Linq4j.emptyEnumerator();
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultEnumerator.current();
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             boolean incremented = false;
             for (;;) {
               if (resultEnumerator.moveNext()) {
@@ -3017,19 +3017,19 @@ public boolean moveNext() {
                   .enumerator();
               resultEnumerator =
                   new TransformedEnumerator<TCollection, TResult>(collectionEnumerator) {
-                    protected TResult transform(TCollection collectionElement) {
+                    @Override protected TResult transform(TCollection collectionElement) {
                       return resultSelector.apply(sourceElement, collectionElement);
                     }
                   };
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             sourceEnumerator.reset();
             resultEnumerator = Linq4j.emptyEnumerator();
           }
 
-          public void close() {
+          @Override public void close() {
             sourceEnumerator.close();
             resultEnumerator.close();
           }
@@ -3059,10 +3059,10 @@ public static <TSource> boolean sequenceEqual(Enumerable<TSource> first,
     Objects.requireNonNull(second);
     if (comparer == null) {
       comparer = new EqualityComparer<TSource>() {
-        public boolean equal(TSource v1, TSource v2) {
+        @Override public boolean equal(TSource v1, TSource v2) {
           return Objects.equals(v1, v2);
         }
-        public int hashCode(TSource tSource) {
+        @Override public int hashCode(TSource tSource) {
           return Objects.hashCode(tSource);
         }
       };
@@ -3215,7 +3215,7 @@ public static <TSource> Enumerable<TSource> skipWhile(
       final Enumerable<TSource> source,
       final Predicate2<TSource, Integer> predicate) {
     return new AbstractEnumerable<TSource>() {
-      public Enumerator<TSource> enumerator() {
+      @Override public Enumerator<TSource> enumerator() {
         return new SkipWhileEnumerator<>(source.enumerator(), predicate);
       }
     };
@@ -3368,7 +3368,7 @@ public static <TSource> Enumerable<TSource> takeWhile(
       final Enumerable<TSource> source,
       final Predicate2<TSource, Integer> predicate) {
     return new AbstractEnumerable<TSource>() {
-      public Enumerator<TSource> enumerator() {
+      @Override public Enumerator<TSource> enumerator() {
         return new TakeWhileEnumerator<>(source.enumerator(), predicate);
       }
     };
@@ -3383,7 +3383,7 @@ public static <TSource> Enumerable<TSource> takeWhileLong(
       final Enumerable<TSource> source,
       final Predicate2<TSource, Long> predicate) {
     return new AbstractEnumerable<TSource>() {
-      public Enumerator<TSource> enumerator() {
+      @Override public Enumerator<TSource> enumerator() {
         return new TakeWhileLongEnumerator<>(source.enumerator(), predicate);
       }
     };
@@ -3647,7 +3647,7 @@ public static <TSource> Enumerable<TSource> where(
       final Enumerable<TSource> source, final Predicate1<TSource> predicate) {
     assert predicate != null;
     return new AbstractEnumerable<TSource>() {
-      public Enumerator<TSource> enumerator() {
+      @Override public Enumerator<TSource> enumerator() {
         final Enumerator<TSource> enumerator = source.enumerator();
         return EnumerableDefaults.where(enumerator, predicate);
       }
@@ -3658,11 +3658,11 @@ private static <TSource> Enumerator<TSource> where(
       final Enumerator<TSource> enumerator,
       final Predicate1<TSource> predicate) {
     return new Enumerator<TSource>() {
-      public TSource current() {
+      @Override public TSource current() {
         return enumerator.current();
       }
 
-      public boolean moveNext() {
+      @Override public boolean moveNext() {
         while (enumerator.moveNext()) {
           if (predicate.apply(enumerator.current())) {
             return true;
@@ -3671,11 +3671,11 @@ public boolean moveNext() {
         return false;
       }
 
-      public void reset() {
+      @Override public void reset() {
         enumerator.reset();
       }
 
-      public void close() {
+      @Override public void close() {
         enumerator.close();
       }
     };
@@ -3690,16 +3690,16 @@ public static <TSource> Enumerable<TSource> where(
       final Enumerable<TSource> source,
       final Predicate2<TSource, Integer> predicate) {
     return new AbstractEnumerable<TSource>() {
-      public Enumerator<TSource> enumerator() {
+      @Override public Enumerator<TSource> enumerator() {
         return new Enumerator<TSource>() {
           final Enumerator<TSource> enumerator = source.enumerator();
           int n = -1;
 
-          public TSource current() {
+          @Override public TSource current() {
             return enumerator.current();
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             while (enumerator.moveNext()) {
               ++n;
               if (predicate.apply(enumerator.current(), n)) {
@@ -3709,12 +3709,12 @@ public boolean moveNext() {
             return false;
           }
 
-          public void reset() {
+          @Override public void reset() {
             enumerator.reset();
             n = -1;
           }
 
-          public void close() {
+          @Override public void close() {
             enumerator.close();
           }
         };
@@ -3731,22 +3731,22 @@ public static <T0, T1, TResult> Enumerable<TResult> zip(
       final Enumerable<T0> first, final Enumerable<T1> second,
       final Function2<T0, T1, TResult> resultSelector) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         return new Enumerator<TResult>() {
           final Enumerator<T0> e1 = first.enumerator();
           final Enumerator<T1> e2 = second.enumerator();
 
-          public TResult current() {
+          @Override public TResult current() {
             return resultSelector.apply(e1.current(), e2.current());
           }
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             return e1.moveNext() && e2.moveNext();
           }
-          public void reset() {
+          @Override public void reset() {
             e1.reset();
             e2.reset();
           }
-          public void close() {
+          @Override public void close() {
             e1.close();
             e2.close();
           }
@@ -3801,11 +3801,11 @@ static class TakeWhileEnumerator<TSource> implements Enumerator<TSource> {
       this.predicate = predicate;
     }
 
-    public TSource current() {
+    @Override public TSource current() {
       return enumerator.current();
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       if (!done) {
         if (enumerator.moveNext()
             && predicate.apply(enumerator.current(), ++n)) {
@@ -3817,13 +3817,13 @@ public boolean moveNext() {
       return false;
     }
 
-    public void reset() {
+    @Override public void reset() {
       enumerator.reset();
       done = false;
       n = -1;
     }
 
-    public void close() {
+    @Override public void close() {
       enumerator.close();
     }
   }
@@ -3844,11 +3844,11 @@ static class TakeWhileLongEnumerator<TSource> implements Enumerator<TSource> {
       this.predicate = predicate;
     }
 
-    public TSource current() {
+    @Override public TSource current() {
       return enumerator.current();
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       if (!done) {
         if (enumerator.moveNext()
             && predicate.apply(enumerator.current(), ++n)) {
@@ -3860,13 +3860,13 @@ public boolean moveNext() {
       return false;
     }
 
-    public void reset() {
+    @Override public void reset() {
       enumerator.reset();
       done = false;
       n = -1;
     }
 
-    public void close() {
+    @Override public void close() {
       enumerator.close();
     }
   }
@@ -3887,11 +3887,11 @@ static class SkipWhileEnumerator<TSource> implements Enumerator<TSource> {
       this.predicate = predicate;
     }
 
-    public TSource current() {
+    @Override public TSource current() {
       return enumerator.current();
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       for (;;) {
         if (!enumerator.moveNext()) {
           return false;
@@ -3906,13 +3906,13 @@ public boolean moveNext() {
       }
     }
 
-    public void reset() {
+    @Override public void reset() {
       enumerator.reset();
       started = false;
       n = -1;
     }
 
-    public void close() {
+    @Override public void close() {
       enumerator.close();
     }
   }
@@ -3929,19 +3929,19 @@ static class CastingEnumerator<T> implements Enumerator<T> {
       this.clazz = clazz;
     }
 
-    public T current() {
+    @Override public T current() {
       return clazz.cast(enumerator.current());
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       return enumerator.moveNext();
     }
 
-    public void reset() {
+    @Override public void reset() {
       enumerator.reset();
     }
 
-    public void close() {
+    @Override public void close() {
       enumerator.close();
     }
   }
@@ -3997,16 +3997,16 @@ protected WrapMap(Function0<Map<Wrapped<K>, V>> mapProvider, EqualityComparer<K>
               map.entrySet().iterator();
 
           return new Iterator<Entry<K, V>>() {
-            public boolean hasNext() {
+            @Override public boolean hasNext() {
               return iterator.hasNext();
             }
 
-            public Entry<K, V> next() {
+            @Override public Entry<K, V> next() {
               Entry<Wrapped<K>, V> next = iterator.next();
               return new SimpleEntry<>(next.getKey().element, next.getValue());
             }
 
-            public void remove() {
+            @Override public void remove() {
               iterator.remove();
             }
           };
@@ -4063,20 +4063,20 @@ private static class LookupResultEnumerable<TResult, TKey, TAccumulate>
       this.resultSelector = resultSelector;
     }
 
-    public Iterator<TResult> iterator() {
+    @Override public Iterator<TResult> iterator() {
       final Iterator<Map.Entry<TKey, TAccumulate>> iterator =
           map.entrySet().iterator();
       return new Iterator<TResult>() {
-        public boolean hasNext() {
+        @Override public boolean hasNext() {
           return iterator.hasNext();
         }
 
-        public TResult next() {
+        @Override public TResult next() {
           final Map.Entry<TKey, TAccumulate> entry = iterator.next();
           return resultSelector.apply(entry.getKey(), entry.getValue());
         }
 
-        public void remove() {
+        @Override public void remove() {
           throw new UnsupportedOperationException();
         }
       };
@@ -4370,14 +4370,14 @@ private boolean advanceRight(TInner right, TKey rightKey) {
       return false;
     }
 
-    public TResult current() {
+    @Override public TResult current() {
       if (current == DUMMY) {
         throw new NoSuchElementException();
       }
       return current;
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       for (;;) {
         if (results != null) {
           if (results.moveNext()) {
@@ -4404,7 +4404,7 @@ public boolean moveNext() {
       }
     }
 
-    public void reset() {
+    @Override public void reset() {
       done = false;
       results = null;
       current = (TResult) DUMMY;
@@ -4416,7 +4416,7 @@ public void reset() {
       start();
     }
 
-    public void close() {
+    @Override public void close() {
       leftEnumerator.close();
       if (rightEnumerator != null) {
         rightEnumerator.close();
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableOrderedQueryable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableOrderedQueryable.java
index 0fe30bfeba8..a53e006f674 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableOrderedQueryable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableOrderedQueryable.java
@@ -35,25 +35,25 @@ class EnumerableOrderedQueryable<T> extends EnumerableQueryable<T>
     super(provider, rowType, expression, enumerable);
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return QueryableDefaults.thenBy(asOrderedQueryable(), keySelector);
   }
 
-  public <TKey> OrderedQueryable<T> thenBy(
+  @Override public <TKey> OrderedQueryable<T> thenBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return QueryableDefaults.thenBy(asOrderedQueryable(), keySelector,
         comparator);
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return QueryableDefaults.thenByDescending(asOrderedQueryable(),
         keySelector);
   }
 
-  public <TKey> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey> OrderedQueryable<T> thenByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return QueryableDefaults.thenByDescending(asOrderedQueryable(), keySelector,
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableQueryable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableQueryable.java
index 77f1ba12540..a6724b7825e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableQueryable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableQueryable.java
@@ -72,21 +72,21 @@ protected Queryable<T> queryable() {
     return this;
   }
 
-  public Iterator<T> iterator() {
+  @Override public Iterator<T> iterator() {
     return enumerable.iterator();
   }
 
-  public Enumerator<T> enumerator() {
+  @Override public Enumerator<T> enumerator() {
     return enumerable.enumerator();
   }
 
   // Disambiguate
 
-  public Queryable<T> union(Enumerable<T> source1) {
+  @Override public Queryable<T> union(Enumerable<T> source1) {
     return EnumerableDefaults.union(getThis(), source1).asQueryable();
   }
 
-  public Queryable<T> union(Enumerable<T> source1,
+  @Override public Queryable<T> union(Enumerable<T> source1,
       EqualityComparer<T> comparer) {
     return EnumerableDefaults.union(getThis(), source1, comparer).asQueryable();
   }
@@ -129,15 +129,15 @@ public Queryable<T> union(Enumerable<T> source1,
     return EnumerableDefaults.except(getThis(), enumerable1, all).asQueryable();
   }
 
-  public Queryable<T> take(int count) {
+  @Override public Queryable<T> take(int count) {
     return EnumerableDefaults.take(getThis(), count).asQueryable();
   }
 
-  public Queryable<T> skip(int count) {
+  @Override public Queryable<T> skip(int count) {
     return EnumerableDefaults.skip(getThis(), count).asQueryable();
   }
 
-  public Queryable<T> reverse() {
+  @Override public Queryable<T> reverse() {
     return EnumerableDefaults.reverse(getThis()).asQueryable();
   }
 
@@ -157,135 +157,135 @@ public Queryable<T> reverse() {
     return EnumerableDefaults.defaultIfEmpty(getThis()).asQueryable();
   }
 
-  public <T2> Queryable<T2> cast(Class<T2> clazz) {
+  @Override public <T2> Queryable<T2> cast(Class<T2> clazz) {
     return EnumerableDefaults.cast(getThis(), clazz).asQueryable();
   }
 
   // Queryable methods
 
-  public Type getElementType() {
+  @Override public Type getElementType() {
     return elementType;
   }
 
-  public Expression getExpression() {
+  @Override public Expression getExpression() {
     return expression;
   }
 
-  public QueryProvider getProvider() {
+  @Override public QueryProvider getProvider() {
     return provider;
   }
 
   // .............
 
-  public T aggregate(FunctionExpression<Function2<T, T, T>> selector) {
+  @Override public T aggregate(FunctionExpression<Function2<T, T, T>> selector) {
     return EnumerableDefaults.aggregate(getThis(), selector.getFunction());
   }
 
-  public <TAccumulate> TAccumulate aggregate(TAccumulate seed,
+  @Override public <TAccumulate> TAccumulate aggregate(TAccumulate seed,
       FunctionExpression<Function2<TAccumulate, T, TAccumulate>> selector) {
     return EnumerableDefaults.aggregate(getThis(), seed,
         selector.getFunction());
   }
 
-  public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
+  @Override public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
       FunctionExpression<Function2<TAccumulate, T, TAccumulate>> func,
       FunctionExpression<Function1<TAccumulate, TResult>> selector) {
     return EnumerableDefaults.aggregate(getThis(), seed, func.getFunction(),
         selector.getFunction());
   }
 
-  public boolean all(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public boolean all(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.all(getThis(), predicate.getFunction());
   }
 
-  public boolean any(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public boolean any(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.any(getThis(), predicate.getFunction());
   }
 
-  public BigDecimal averageBigDecimal(
+  @Override public BigDecimal averageBigDecimal(
       FunctionExpression<BigDecimalFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public BigDecimal averageNullableBigDecimal(
+  @Override public BigDecimal averageNullableBigDecimal(
       FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public double averageDouble(FunctionExpression<DoubleFunction1<T>> selector) {
+  @Override public double averageDouble(FunctionExpression<DoubleFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public Double averageNullableDouble(
+  @Override public Double averageNullableDouble(
       FunctionExpression<NullableDoubleFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public int averageInteger(FunctionExpression<IntegerFunction1<T>> selector) {
+  @Override public int averageInteger(FunctionExpression<IntegerFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public Integer averageNullableInteger(
+  @Override public Integer averageNullableInteger(
       FunctionExpression<NullableIntegerFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public float averageFloat(FunctionExpression<FloatFunction1<T>> selector) {
+  @Override public float averageFloat(FunctionExpression<FloatFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public Float averageNullableFloat(
+  @Override public Float averageNullableFloat(
       FunctionExpression<NullableFloatFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public long averageLong(FunctionExpression<LongFunction1<T>> selector) {
+  @Override public long averageLong(FunctionExpression<LongFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public Long averageNullableLong(
+  @Override public Long averageNullableLong(
       FunctionExpression<NullableLongFunction1<T>> selector) {
     return EnumerableDefaults.average(getThis(), selector.getFunction());
   }
 
-  public Queryable<T> concat(Enumerable<T> source2) {
+  @Override public Queryable<T> concat(Enumerable<T> source2) {
     return EnumerableDefaults.concat(getThis(), source2).asQueryable();
   }
 
-  public int count(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public int count(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.count(getThis(), predicate.getFunction());
   }
 
-  public T first(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T first(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.first(getThis(), predicate.getFunction());
   }
 
-  public T firstOrDefault(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T firstOrDefault(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.firstOrDefault(getThis(),
         predicate.getFunction());
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return EnumerableDefaults.groupBy(getThis(), keySelector.getFunction())
         .asQueryable();
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       EqualityComparer<TKey> comparer) {
     return EnumerableDefaults.groupBy(getThis(), keySelector.getFunction(),
         comparer).asQueryable();
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector) {
     return EnumerableDefaults.groupBy(getThis(), keySelector.getFunction(),
         elementSelector.getFunction()).asQueryable();
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
       EqualityComparer<TKey> comparer) {
@@ -293,14 +293,14 @@ public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
         elementSelector.getFunction(), comparer).asQueryable();
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function2<TKey, Enumerable<T>, TResult>> resultSelector) {
     return EnumerableDefaults.groupBy(getThis(), keySelector.getFunction(),
         resultSelector.getFunction()).asQueryable();
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function2<TKey, Enumerable<T>, TResult>> resultSelector,
       EqualityComparer<TKey> comparer) {
@@ -308,7 +308,7 @@ public <TKey, TResult> Queryable<TResult> groupByK(
         resultSelector.getFunction(), comparer).asQueryable();
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
       FunctionExpression<Function2<TKey, Enumerable<TElement>, TResult>> resultSelector) {
@@ -317,7 +317,7 @@ public <TKey, TElement, TResult> Queryable<TResult> groupBy(
         .asQueryable();
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       FunctionExpression<Function1<T, TElement>> elementSelector,
       FunctionExpression<Function2<TKey, Enumerable<TElement>, TResult>> resultSelector,
@@ -327,7 +327,7 @@ public <TKey, TElement, TResult> Queryable<TResult> groupBy(
         .asQueryable();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -337,7 +337,7 @@ public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
         resultSelector.getFunction()).asQueryable();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -348,7 +348,7 @@ public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
         resultSelector.getFunction(), comparer).asQueryable();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -358,7 +358,7 @@ public <TInner, TKey, TResult> Queryable<TResult> join(
         resultSelector.getFunction()).asQueryable();
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       Enumerable<TInner> inner,
       FunctionExpression<Function1<T, TKey>> outerKeySelector,
       FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
@@ -369,35 +369,35 @@ public <TInner, TKey, TResult> Queryable<TResult> join(
         resultSelector.getFunction(), comparer).asQueryable();
   }
 
-  public T last(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T last(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.last(getThis(), predicate.getFunction());
   }
 
-  public T lastOrDefault(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T lastOrDefault(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.lastOrDefault(getThis(), predicate.getFunction());
   }
 
-  public long longCount(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public long longCount(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.longCount(getThis(), predicate.getFunction());
   }
 
-  public <TResult extends Comparable<TResult>> TResult max(
+  @Override public <TResult extends Comparable<TResult>> TResult max(
       FunctionExpression<Function1<T, TResult>> selector) {
     return EnumerableDefaults.max(getThis(), selector.getFunction());
   }
 
-  public <TResult extends Comparable<TResult>> TResult min(
+  @Override public <TResult extends Comparable<TResult>> TResult min(
       FunctionExpression<Function1<T, TResult>> selector) {
     return EnumerableDefaults.min(getThis(), selector.getFunction());
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderBy(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderBy(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return EnumerableDefaults.asOrderedQueryable(
         EnumerableDefaults.orderBy(getThis(), keySelector.getFunction()));
   }
 
-  public <TKey> OrderedQueryable<T> orderBy(
+  @Override public <TKey> OrderedQueryable<T> orderBy(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return EnumerableDefaults.asOrderedQueryable(
@@ -405,14 +405,14 @@ public <TKey> OrderedQueryable<T> orderBy(
             comparator));
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector) {
     return EnumerableDefaults.asOrderedQueryable(
         EnumerableDefaults.orderByDescending(getThis(),
             keySelector.getFunction()));
   }
 
-  public <TKey> OrderedQueryable<T> orderByDescending(
+  @Override public <TKey> OrderedQueryable<T> orderByDescending(
       FunctionExpression<Function1<T, TKey>> keySelector,
       Comparator<TKey> comparator) {
     return EnumerableDefaults.asOrderedQueryable(
@@ -420,31 +420,31 @@ public <TKey> OrderedQueryable<T> orderByDescending(
             keySelector.getFunction(), comparator));
   }
 
-  public <TResult> Queryable<TResult> select(
+  @Override public <TResult> Queryable<TResult> select(
       FunctionExpression<Function1<T, TResult>> selector) {
     return EnumerableDefaults.select(getThis(), selector.getFunction())
         .asQueryable();
   }
 
-  public <TResult> Queryable<TResult> selectN(
+  @Override public <TResult> Queryable<TResult> selectN(
       FunctionExpression<Function2<T, Integer, TResult>> selector) {
     return EnumerableDefaults.select(getThis(), selector.getFunction())
         .asQueryable();
   }
 
-  public <TResult> Queryable<TResult> selectMany(
+  @Override public <TResult> Queryable<TResult> selectMany(
       FunctionExpression<Function1<T, Enumerable<TResult>>> selector) {
     return EnumerableDefaults.selectMany(getThis(), selector.getFunction())
         .asQueryable();
   }
 
-  public <TResult> Queryable<TResult> selectManyN(
+  @Override public <TResult> Queryable<TResult> selectManyN(
       FunctionExpression<Function2<T, Integer, Enumerable<TResult>>> selector) {
     return EnumerableDefaults.selectMany(getThis(), selector.getFunction())
         .asQueryable();
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectMany(
+  @Override public <TCollection, TResult> Queryable<TResult> selectMany(
       FunctionExpression<Function2<T, Integer, Enumerable<TCollection>>>
         collectionSelector,
       FunctionExpression<Function2<T, TCollection, TResult>> resultSelector) {
@@ -453,7 +453,7 @@ public <TCollection, TResult> Queryable<TResult> selectMany(
         .asQueryable();
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectManyN(
+  @Override public <TCollection, TResult> Queryable<TResult> selectManyN(
       FunctionExpression<Function1<T, Enumerable<TCollection>>>
         collectionSelector,
       FunctionExpression<Function2<T, TCollection, TResult>> resultSelector) {
@@ -462,107 +462,107 @@ public <TCollection, TResult> Queryable<TResult> selectManyN(
         .asQueryable();
   }
 
-  public T single(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T single(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.single(getThis(), predicate.getFunction());
   }
 
-  public T singleOrDefault(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public T singleOrDefault(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.singleOrDefault(getThis(),
         predicate.getFunction());
   }
 
-  public Queryable<T> skipWhile(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public Queryable<T> skipWhile(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.skipWhile(getThis(), predicate.getFunction())
         .asQueryable();
   }
 
-  public Queryable<T> skipWhileN(
+  @Override public Queryable<T> skipWhileN(
       FunctionExpression<Predicate2<T, Integer>> predicate) {
     return EnumerableDefaults.skipWhile(getThis(), predicate.getFunction())
         .asQueryable();
   }
 
-  public BigDecimal sumBigDecimal(
+  @Override public BigDecimal sumBigDecimal(
       FunctionExpression<BigDecimalFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public BigDecimal sumNullableBigDecimal(
+  @Override public BigDecimal sumNullableBigDecimal(
       FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public double sumDouble(FunctionExpression<DoubleFunction1<T>> selector) {
+  @Override public double sumDouble(FunctionExpression<DoubleFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public Double sumNullableDouble(
+  @Override public Double sumNullableDouble(
       FunctionExpression<NullableDoubleFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public int sumInteger(FunctionExpression<IntegerFunction1<T>> selector) {
+  @Override public int sumInteger(FunctionExpression<IntegerFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public Integer sumNullableInteger(
+  @Override public Integer sumNullableInteger(
       FunctionExpression<NullableIntegerFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public long sumLong(FunctionExpression<LongFunction1<T>> selector) {
+  @Override public long sumLong(FunctionExpression<LongFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public Long sumNullableLong(
+  @Override public Long sumNullableLong(
       FunctionExpression<NullableLongFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public float sumFloat(FunctionExpression<FloatFunction1<T>> selector) {
+  @Override public float sumFloat(FunctionExpression<FloatFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public Float sumNullableFloat(
+  @Override public Float sumNullableFloat(
       FunctionExpression<NullableFloatFunction1<T>> selector) {
     return EnumerableDefaults.sum(getThis(), selector.getFunction());
   }
 
-  public Queryable<T> takeWhile(FunctionExpression<Predicate1<T>> predicate) {
+  @Override public Queryable<T> takeWhile(FunctionExpression<Predicate1<T>> predicate) {
     return EnumerableDefaults.takeWhile(getThis(), predicate.getFunction())
         .asQueryable();
   }
 
-  public Queryable<T> takeWhileN(
+  @Override public Queryable<T> takeWhileN(
       FunctionExpression<Predicate2<T, Integer>> predicate) {
     return EnumerableDefaults.takeWhile(getThis(), predicate.getFunction())
         .asQueryable();
   }
 
-  public Queryable<T> where(
+  @Override public Queryable<T> where(
       FunctionExpression<? extends Predicate1<T>> predicate) {
     return EnumerableDefaults.where(getThis(), predicate.getFunction())
         .asQueryable();
   }
 
-  public Queryable<T> whereN(
+  @Override public Queryable<T> whereN(
       FunctionExpression<? extends Predicate2<T, Integer>> predicate) {
     return EnumerableDefaults.where(getThis(), predicate.getFunction())
         .asQueryable();
   }
 
-  public <T1, TResult> Queryable<TResult> zip(Enumerable<T1> source1,
+  @Override public <T1, TResult> Queryable<TResult> zip(Enumerable<T1> source1,
       FunctionExpression<Function2<T, T1, TResult>> resultSelector) {
     return EnumerableDefaults.zip(getThis(), source1,
         resultSelector.getFunction()).asQueryable();
   }
 
-  public T aggregate(Function2<T, T, T> func) {
+  @Override public T aggregate(Function2<T, T, T> func) {
     return EnumerableDefaults.aggregate(getThis(), func);
   }
 
 
-  public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
+  @Override public <TAccumulate, TResult> TResult aggregate(TAccumulate seed,
       Function2<TAccumulate, T, TAccumulate> func,
       Function1<TAccumulate, TResult> selector) {
     return EnumerableDefaults.aggregate(getThis(), seed, func, selector);
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerator.java b/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerator.java
index 90bc29ce039..bd9e28be31f 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerator.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/Enumerator.java
@@ -123,5 +123,5 @@ public interface Enumerator<T> extends AutoCloseable {
    * <p>This method is idempotent. Calling it multiple times has the same effect
    * as calling it once.
    */
-  void close();
+  @Override void close();
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/ExtendedQueryable.java b/linq4j/src/main/java/org/apache/calcite/linq4j/ExtendedQueryable.java
index 573dcb90849..1f5db136958 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/ExtendedQueryable.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/ExtendedQueryable.java
@@ -159,7 +159,7 @@ Long averageNullableLong(
   /**
    * Concatenates two sequences.
    */
-  Queryable<TSource> concat(Enumerable<TSource> source2);
+  @Override Queryable<TSource> concat(Enumerable<TSource> source2);
 
   /**
    * Returns the number of elements in the specified
@@ -172,26 +172,26 @@ Long averageNullableLong(
    * the type parameter's default value in a singleton collection if
    * the sequence is empty.
    */
-  Queryable<TSource> defaultIfEmpty();
+  @Override Queryable<TSource> defaultIfEmpty();
 
   /**
    * Returns distinct elements from a sequence by using
    * the default equality comparer to compare values.
    */
-  Queryable<TSource> distinct();
+  @Override Queryable<TSource> distinct();
 
   /**
    * Returns distinct elements from a sequence by using
    * a specified EqualityComparer&lt;TSource&gt; to compare values.
    */
-  Queryable<TSource> distinct(EqualityComparer<TSource> comparer);
+  @Override Queryable<TSource> distinct(EqualityComparer<TSource> comparer);
 
   /**
    * Produces the set difference of two sequences by
    * using the default equality comparer to compare values,
    * eliminate duplicates. (Defined by Enumerable.)
    */
-  Queryable<TSource> except(Enumerable<TSource> enumerable);
+  @Override Queryable<TSource> except(Enumerable<TSource> enumerable);
 
   /**
    * Produces the set difference of two sequences by
@@ -199,14 +199,14 @@ Long averageNullableLong(
    * using {@code all} to indicate whether to eliminate duplicates.
    * (Defined by Enumerable.)
    */
-  Queryable<TSource> except(Enumerable<TSource> enumerable, boolean all);
+  @Override Queryable<TSource> except(Enumerable<TSource> enumerable, boolean all);
 
   /**
    * Produces the set difference of two sequences by
    * using the specified {@code EqualityComparer<TSource>} to compare
    * values, eliminate duplicates.
    */
-  Queryable<TSource> except(Enumerable<TSource> enumerable,
+  @Override Queryable<TSource> except(Enumerable<TSource> enumerable,
       EqualityComparer<TSource> comparer);
 
   /**
@@ -214,7 +214,7 @@ Queryable<TSource> except(Enumerable<TSource> enumerable,
    * using the specified {@code EqualityComparer<TSource>} to compare
    * values, using {@code all} to indicate whether to eliminate duplicates.
    */
-  Queryable<TSource> except(Enumerable<TSource> enumerable,
+  @Override Queryable<TSource> except(Enumerable<TSource> enumerable,
       EqualityComparer<TSource> comparer, boolean all);
   /**
    * Returns the first element of a sequence that
@@ -342,7 +342,7 @@ <TInner, TKey, TResult> Queryable<TResult> groupJoin(Enumerable<TInner> inner,
    * using the default equality comparer to compare values,
    * eliminate duplicates.(Defined by Queryable.)
    */
-  Queryable<TSource> intersect(Enumerable<TSource> enumerable);
+  @Override Queryable<TSource> intersect(Enumerable<TSource> enumerable);
 
   /**
    * Produces the set intersection of two sequences by
@@ -350,14 +350,14 @@ <TInner, TKey, TResult> Queryable<TResult> groupJoin(Enumerable<TInner> inner,
    * using {@code all} to indicate whether to eliminate duplicates.
    * (Defined by Queryable.)
    */
-  Queryable<TSource> intersect(Enumerable<TSource> enumerable, boolean all);
+  @Override Queryable<TSource> intersect(Enumerable<TSource> enumerable, boolean all);
 
   /**
    * Produces the set intersection of two sequences by
    * using the specified {@code EqualityComparer<TSource>} to compare
    * values, eliminate duplicates.
    */
-  Queryable<TSource> intersect(Enumerable<TSource> enumerable,
+  @Override Queryable<TSource> intersect(Enumerable<TSource> enumerable,
       EqualityComparer<TSource> comparer);
 
   /**
@@ -365,7 +365,7 @@ Queryable<TSource> intersect(Enumerable<TSource> enumerable,
    * using the specified {@code EqualityComparer<TSource>} to compare
    * values, using {@code all} to indicate whether to eliminate duplicates.
    */
-  Queryable<TSource> intersect(Enumerable<TSource> enumerable,
+  @Override Queryable<TSource> intersect(Enumerable<TSource> enumerable,
       EqualityComparer<TSource> comparer, boolean all);
 
   /**
@@ -443,9 +443,9 @@ <TResult extends Comparable<TResult>> TResult min(
    * <p>NOTE: clazz parameter not present in C# LINQ; necessary because of
    * Java type erasure.</p>
    */
-  <TResult> Queryable<TResult> ofType(Class<TResult> clazz);
+  @Override <TResult> Queryable<TResult> ofType(Class<TResult> clazz);
 
-  <T2> Queryable<T2> cast(Class<T2> clazz);
+  @Override <T2> Queryable<T2> cast(Class<T2> clazz);
 
   /**
    * Sorts the elements of a sequence in ascending
@@ -480,7 +480,7 @@ <TKey> OrderedQueryable<TSource> orderByDescending(
   /**
    * Inverts the order of the elements in a sequence.
    */
-  Queryable<TSource> reverse();
+  @Override Queryable<TSource> reverse();
 
 
   /**
@@ -564,7 +564,7 @@ <TCollection, TResult> Queryable<TResult> selectManyN(
    * exception if there is more than one element in the
    * sequence.
    */
-  TSource singleOrDefault();
+  @Override TSource singleOrDefault();
 
   /**
    * Returns the only element of a sequence that
@@ -578,7 +578,7 @@ <TCollection, TResult> Queryable<TResult> selectManyN(
    * Bypasses a specified number of elements in a
    * sequence and then returns the remaining elements.
    */
-  Queryable<TSource> skip(int count);
+  @Override Queryable<TSource> skip(int count);
 
   /**
    * Bypasses elements in a sequence as long as a
@@ -677,7 +677,7 @@ Float sumNullableFloat(
    * Returns a specified number of contiguous elements
    * from the start of a sequence.
    */
-  Queryable<TSource> take(int count);
+  @Override Queryable<TSource> take(int count);
 
   /**
    * Returns elements from a sequence as long as a
@@ -698,13 +698,13 @@ Queryable<TSource> takeWhileN(
    * Produces the set union of two sequences by using
    * the default equality comparer.
    */
-  Queryable<TSource> union(Enumerable<TSource> source1);
+  @Override Queryable<TSource> union(Enumerable<TSource> source1);
 
   /**
    * Produces the set union of two sequences by using a
    * specified {@code EqualityComparer<TSource>}.
    */
-  Queryable<TSource> union(Enumerable<TSource> source1,
+  @Override Queryable<TSource> union(Enumerable<TSource> source1,
       EqualityComparer<TSource> comparer);
 
   /**
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/GroupingImpl.java b/linq4j/src/main/java/org/apache/calcite/linq4j/GroupingImpl.java
index 9444dc540cf..dcc83601eb9 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/GroupingImpl.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/GroupingImpl.java
@@ -55,23 +55,23 @@ class GroupingImpl<K, V> extends AbstractEnumerable<V>
   }
 
   // implement Map.Entry
-  public Enumerable<V> getValue() {
+  @Override public Enumerable<V> getValue() {
     return Linq4j.asEnumerable(values);
   }
 
   // implement Map.Entry
-  public Enumerable<V> setValue(Enumerable<V> value) {
+  @Override public Enumerable<V> setValue(Enumerable<V> value) {
     // immutable
     throw new UnsupportedOperationException();
   }
 
   // implement Map.Entry
   // implement Grouping
-  public K getKey() {
+  @Override public K getKey() {
     return key;
   }
 
-  public Enumerator<V> enumerator() {
+  @Override public Enumerator<V> enumerator() {
     return Linq4j.enumerator(values);
   }
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/Linq4j.java b/linq4j/src/main/java/org/apache/calcite/linq4j/Linq4j.java
index b1251e898b0..dab1d5edfc6 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/Linq4j.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/Linq4j.java
@@ -50,31 +50,31 @@ public static Method getMethod(String className, String methodName,
    * enumerator method; does not attempt optimization.
    */
   public static final QueryProvider DEFAULT_PROVIDER = new QueryProviderImpl() {
-    public <T> Enumerator<T> executeQuery(Queryable<T> queryable) {
+    @Override public <T> Enumerator<T> executeQuery(Queryable<T> queryable) {
       return queryable.enumerator();
     }
   };
 
   private static final Enumerator<Object> EMPTY_ENUMERATOR =
       new Enumerator<Object>() {
-        public Object current() {
+        @Override public Object current() {
           throw new NoSuchElementException();
         }
 
-        public boolean moveNext() {
+        @Override public boolean moveNext() {
           return false;
         }
 
-        public void reset() {
+        @Override public void reset() {
         }
 
-        public void close() {
+        @Override public void close() {
         }
       };
 
   public static final Enumerable<?> EMPTY_ENUMERABLE =
       new AbstractEnumerable<Object>() {
-        public Enumerator<Object> enumerator() {
+        @Override public Enumerator<Object> enumerator() {
           return EMPTY_ENUMERATOR;
         }
       };
@@ -206,7 +206,7 @@ private static <V> Enumerator<V> listEnumerator(List<? extends V> list) {
   public static <F, E> Enumerator<E> transform(Enumerator<F> enumerator,
       final Function1<F, E> func) {
     return new TransformedEnumerator<F, E>(enumerator) {
-      protected E transform(F from) {
+      @Override protected E transform(F from) {
         return func.apply(from);
       }
     };
@@ -292,7 +292,7 @@ public static <TSource, TResult> Enumerable<TResult> ofType(
    */
   public static <T> Enumerable<T> singletonEnumerable(final T element) {
     return new AbstractEnumerable<T>() {
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         return singletonEnumerator(element);
       }
     };
@@ -450,14 +450,14 @@ static class IterableEnumerator<T> implements Enumerator<T> {
       current = (T) DUMMY;
     }
 
-    public T current() {
+    @Override public T current() {
       if (current == DUMMY) {
         throw new NoSuchElementException();
       }
       return current;
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       if (iterator.hasNext()) {
         current = iterator.next();
         return true;
@@ -466,12 +466,12 @@ public boolean moveNext() {
       return false;
     }
 
-    public void reset() {
+    @Override public void reset() {
       iterator = iterable.iterator();
       current = (T) DUMMY;
     }
 
-    public void close() {
+    @Override public void close() {
       final Iterator<? extends T> iterator1 = this.iterator;
       this.iterator = null;
       closeIterator(iterator1);
@@ -488,17 +488,17 @@ static class CompositeEnumerable<E> extends AbstractEnumerable<E> {
       this.enumerableList = enumerableList;
     }
 
-    public Enumerator<E> enumerator() {
+    @Override public Enumerator<E> enumerator() {
       return new Enumerator<E>() {
         // Never null.
         Enumerator<E> current = emptyEnumerator();
         final Enumerator<Enumerable<E>> enumerableEnumerator = iterableEnumerator(enumerableList);
 
-        public E current() {
+        @Override public E current() {
           return current.current();
         }
 
-        public boolean moveNext() {
+        @Override public boolean moveNext() {
           for (;;) {
             if (current.moveNext()) {
               return true;
@@ -512,12 +512,12 @@ public boolean moveNext() {
           }
         }
 
-        public void reset() {
+        @Override public void reset() {
           enumerableEnumerator.reset();
           current = emptyEnumerator();
         }
 
-        public void close() {
+        @Override public void close() {
           current.close();
           current = emptyEnumerator();
         }
@@ -535,7 +535,7 @@ static class IterableEnumerable<T> extends AbstractEnumerable2<T> {
       this.iterable = iterable;
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return iterable.iterator();
     }
 
@@ -625,19 +625,19 @@ private static class SingletonEnumerator<E> implements Enumerator<E> {
       this.e = e;
     }
 
-    public E current() {
+    @Override public E current() {
       return e;
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       return i++ == 0;
     }
 
-    public void reset() {
+    @Override public void reset() {
       i = 0;
     }
 
-    public void close() {
+    @Override public void close() {
     }
   }
 
@@ -647,19 +647,19 @@ public void close() {
   private static class SingletonNullEnumerator<E> implements Enumerator<E> {
     int i = 0;
 
-    public E current() {
+    @Override public E current() {
       return null;
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       return i++ == 0;
     }
 
-    public void reset() {
+    @Override public void reset() {
       i = 0;
     }
 
-    public void close() {
+    @Override public void close() {
     }
   }
 
@@ -676,21 +676,21 @@ private static class EnumeratorIterator<T>
       hasNext = enumerator.moveNext();
     }
 
-    public boolean hasNext() {
+    @Override public boolean hasNext() {
       return hasNext;
     }
 
-    public T next() {
+    @Override public T next() {
       T t = enumerator.current();
       hasNext = enumerator.moveNext();
       return t;
     }
 
-    public void remove() {
+    @Override public void remove() {
       throw new UnsupportedOperationException();
     }
 
-    public void close() {
+    @Override public void close() {
       enumerator.close();
     }
   }
@@ -706,19 +706,19 @@ private static class ListEnumerator<V> implements Enumerator<V> {
       this.list = list;
     }
 
-    public V current() {
+    @Override public V current() {
       return list.get(i);
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       return ++i < list.size();
     }
 
-    public void reset() {
+    @Override public void reset() {
       i = -1;
     }
 
-    public void close() {
+    @Override public void close() {
     }
   }
 
@@ -732,7 +732,7 @@ private static class CartesianProductListEnumerator<E>
       super(enumerators);
     }
 
-    public List<E> current() {
+    @Override public List<E> current() {
       return Arrays.asList(elements.clone());
     }
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/LookupImpl.java b/linq4j/src/main/java/org/apache/calcite/linq4j/LookupImpl.java
index def63c4fad2..7a5c4d4f41f 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/LookupImpl.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/LookupImpl.java
@@ -46,26 +46,26 @@ class LookupImpl<K, V> extends AbstractEnumerable<Grouping<K, V>>
     this.map = map;
   }
 
-  public Enumerator<Grouping<K, V>> enumerator() {
+  @Override public Enumerator<Grouping<K, V>> enumerator() {
     return new Enumerator<Grouping<K, V>>() {
       Enumerator<Entry<K, List<V>>> enumerator = Linq4j.enumerator(
           map.entrySet());
 
-      public Grouping<K, V> current() {
+      @Override public Grouping<K, V> current() {
         final Entry<K, List<V>> keyAndList = enumerator.current();
         return new GroupingImpl<>(keyAndList.getKey(),
             keyAndList.getValue());
       }
 
-      public boolean moveNext() {
+      @Override public boolean moveNext() {
         return enumerator.moveNext();
       }
 
-      public void reset() {
+      @Override public void reset() {
         enumerator.reset();
       }
 
-      public void close() {
+      @Override public void close() {
         enumerator.close();
       }
     };
@@ -73,129 +73,129 @@ public void close() {
 
   // Map methods
 
-  public int size() {
+  @Override public int size() {
     return map.size();
   }
 
-  public boolean isEmpty() {
+  @Override public boolean isEmpty() {
     return map.isEmpty();
   }
 
-  public boolean containsKey(Object key) {
+  @Override public boolean containsKey(Object key) {
     return map.containsKey(key);
   }
 
-  public boolean containsValue(Object value) {
+  @Override public boolean containsValue(Object value) {
     @SuppressWarnings("unchecked")
     List<V> list = (List<V>) value;
     return map.containsValue(list);
   }
 
-  public Enumerable<V> get(Object key) {
+  @Override public Enumerable<V> get(Object key) {
     final List<V> list = map.get(key);
     return list == null ? null : Linq4j.asEnumerable(list);
   }
 
-  public Enumerable<V> put(K key, Enumerable<V> value) {
+  @Override public Enumerable<V> put(K key, Enumerable<V> value) {
     final List<V> list = map.put(key, value.toList());
     return list == null ? null : Linq4j.asEnumerable(list);
   }
 
-  public Enumerable<V> remove(Object key) {
+  @Override public Enumerable<V> remove(Object key) {
     final List<V> list = map.remove(key);
     return list == null ? null : Linq4j.asEnumerable(list);
   }
 
-  public void putAll(Map<? extends K, ? extends Enumerable<V>> m) {
+  @Override public void putAll(Map<? extends K, ? extends Enumerable<V>> m) {
     for (Entry<? extends K, ? extends Enumerable<V>> entry : m.entrySet()) {
       map.put(entry.getKey(), entry.getValue().toList());
     }
   }
 
-  public void clear() {
+  @Override public void clear() {
     map.clear();
   }
 
-  public Set<K> keySet() {
+  @Override public Set<K> keySet() {
     return map.keySet();
   }
 
-  public Collection<Enumerable<V>> values() {
+  @Override public Collection<Enumerable<V>> values() {
     final Collection<List<V>> lists = map.values();
     return new AbstractCollection<Enumerable<V>>() {
-      public Iterator<Enumerable<V>> iterator() {
+      @Override public Iterator<Enumerable<V>> iterator() {
         return new Iterator<Enumerable<V>>() {
           final Iterator<List<V>> iterator = lists.iterator();
 
-          public boolean hasNext() {
+          @Override public boolean hasNext() {
             return iterator.hasNext();
           }
 
-          public Enumerable<V> next() {
+          @Override public Enumerable<V> next() {
             return Linq4j.asEnumerable(iterator.next());
           }
 
-          public void remove() {
+          @Override public void remove() {
             iterator.remove();
           }
         };
       }
 
-      public int size() {
+      @Override public int size() {
         return lists.size();
       }
     };
   }
 
-  public Set<Entry<K, Enumerable<V>>> entrySet() {
+  @Override public Set<Entry<K, Enumerable<V>>> entrySet() {
     final Set<Entry<K, List<V>>> entries = map.entrySet();
     return new AbstractSet<Entry<K, Enumerable<V>>>() {
-      public Iterator<Entry<K, Enumerable<V>>> iterator() {
+      @Override public Iterator<Entry<K, Enumerable<V>>> iterator() {
         final Iterator<Entry<K, List<V>>> iterator = entries.iterator();
         return new Iterator<Entry<K, Enumerable<V>>>() {
-          public boolean hasNext() {
+          @Override public boolean hasNext() {
             return iterator.hasNext();
           }
 
-          public Entry<K, Enumerable<V>> next() {
+          @Override public Entry<K, Enumerable<V>> next() {
             final Entry<K, List<V>> entry = iterator.next();
             return new AbstractMap.SimpleEntry<>(entry.getKey(),
                 Linq4j.asEnumerable(entry.getValue()));
           }
 
-          public void remove() {
+          @Override public void remove() {
             iterator.remove();
           }
         };
       }
 
-      public int size() {
+      @Override public int size() {
         return entries.size();
       }
     };
   }
 
-  public <TResult> Enumerable<TResult> applyResultSelector(
+  @Override public <TResult> Enumerable<TResult> applyResultSelector(
       final Function2<K, Enumerable<V>, TResult> resultSelector) {
     return new AbstractEnumerable<TResult>() {
-      public Enumerator<TResult> enumerator() {
+      @Override public Enumerator<TResult> enumerator() {
         final Enumerator<Grouping<K, V>> groupingEnumerator =
             LookupImpl.this.enumerator();
         return new Enumerator<TResult>() {
-          public TResult current() {
+          @Override public TResult current() {
             final Grouping<K, V> grouping = groupingEnumerator.current();
             return resultSelector.apply(grouping.getKey(), grouping);
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             return groupingEnumerator.moveNext();
           }
 
-          public void reset() {
+          @Override public void reset() {
             groupingEnumerator.reset();
           }
 
-          public void close() {
+          @Override public void close() {
             groupingEnumerator.close();
           }
         };
@@ -209,17 +209,17 @@ public void close() {
    */
   public Enumerable<V> valuesEnumerable() {
     return new AbstractEnumerable<V>() {
-      public Enumerator<V> enumerator() {
+      @Override public Enumerator<V> enumerator() {
         final Enumerator<Enumerable<V>> listEnumerator =
             Linq4j.iterableEnumerator(values());
         return new Enumerator<V>() {
           Enumerator<V> enumerator = Linq4j.emptyEnumerator();
 
-          public V current() {
+          @Override public V current() {
             return enumerator.current();
           }
 
-          public boolean moveNext() {
+          @Override public boolean moveNext() {
             for (;;) {
               if (enumerator.moveNext()) {
                 return true;
@@ -233,12 +233,12 @@ public boolean moveNext() {
             }
           }
 
-          public void reset() {
+          @Override public void reset() {
             listEnumerator.reset();
             enumerator = Linq4j.emptyEnumerator();
           }
 
-          public void close() {
+          @Override public void close() {
             enumerator.close();
           }
         };
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/Ord.java b/linq4j/src/main/java/org/apache/calcite/linq4j/Ord.java
index 500952980ba..7e92686a1f4 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/Ord.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/Ord.java
@@ -63,15 +63,15 @@ public static <E> Iterator<Ord<E>> zip(final Iterator<? extends E> iterator) {
     return new Iterator<Ord<E>>() {
       int n = 0;
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return iterator.hasNext();
       }
 
-      public Ord<E> next() {
+      @Override public Ord<E> next() {
         return Ord.of(n++, iterator.next());
       }
 
-      public void remove() {
+      @Override public void remove() {
         iterator.remove();
       }
     };
@@ -114,29 +114,29 @@ public static <E> Iterable<Ord<E>> reverse(Iterable<? extends E> elements) {
     return () -> new Iterator<Ord<E>>() {
       int i = elementList.size() - 1;
 
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return i >= 0;
       }
 
-      public Ord<E> next() {
+      @Override public Ord<E> next() {
         return Ord.of(i, elementList.get(i--));
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException("remove");
       }
     };
   }
 
-  public Integer getKey() {
+  @Override public Integer getKey() {
     return i;
   }
 
-  public E getValue() {
+  @Override public E getValue() {
     return e;
   }
 
-  public E setValue(E value) {
+  @Override public E setValue(E value) {
     throw new UnsupportedOperationException();
   }
 
@@ -185,11 +185,11 @@ private static class OrdList<E> extends AbstractList<Ord<E>> {
       this.elements = elements;
     }
 
-    public Ord<E> get(int index) {
+    @Override public Ord<E> get(int index) {
       return Ord.of(index, elements.get(index));
     }
 
-    public int size() {
+    @Override public int size() {
       return elements.size();
     }
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/QueryProviderImpl.java b/linq4j/src/main/java/org/apache/calcite/linq4j/QueryProviderImpl.java
index 3484c977f8b..a9fafcbe352 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/QueryProviderImpl.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/QueryProviderImpl.java
@@ -33,19 +33,19 @@ public QueryProviderImpl() {
     super();
   }
 
-  public <T> Queryable<T> createQuery(Expression expression, Class<T> rowType) {
+  @Override public <T> Queryable<T> createQuery(Expression expression, Class<T> rowType) {
     return new QueryableImpl<>(this, rowType, expression);
   }
 
-  public <T> Queryable<T> createQuery(Expression expression, Type rowType) {
+  @Override public <T> Queryable<T> createQuery(Expression expression, Type rowType) {
     return new QueryableImpl<>(this, rowType, expression);
   }
 
-  public <T> T execute(Expression expression, Class<T> type) {
+  @Override public <T> T execute(Expression expression, Class<T> type) {
     throw new UnsupportedOperationException();
   }
 
-  public <T> T execute(Expression expression, Type type) {
+  @Override public <T> T execute(Expression expression, Type type) {
     throw new UnsupportedOperationException();
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableDefaults.java b/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableDefaults.java
index 8200c17470d..b4f5a069429 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableDefaults.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableDefaults.java
@@ -225,7 +225,7 @@ public static <T, T2> Queryable<T2> cast(final Queryable<T> source,
       final Class<T2> clazz) {
     return new BaseQueryable<T2>(source.getProvider(), clazz,
         source.getExpression()) {
-      public Enumerator<T2> enumerator() {
+      @Override public Enumerator<T2> enumerator() {
         return new EnumerableDefaults.CastingEnumerator<>(source.enumerator(),
             clazz);
       }
@@ -910,7 +910,7 @@ public static <T> Queryable<T> skipWhileN(final Queryable<T> source,
       final FunctionExpression<Predicate2<T, Integer>> predicate) {
     return new BaseQueryable<T>(source.getProvider(), source.getElementType(),
         source.getExpression()) {
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         return new EnumerableDefaults.SkipWhileEnumerator<>(
             source.enumerator(), predicate.getFunction());
       }
@@ -1045,7 +1045,7 @@ public static <T> Queryable<T> takeWhileN(final Queryable<T> source,
       final FunctionExpression<Predicate2<T, Integer>> predicate) {
     return new BaseQueryable<T>(source.getProvider(), source.getElementType(),
         source.getExpression()) {
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         return new EnumerableDefaults.TakeWhileEnumerator<>(
             source.enumerator(), predicate.getFunction());
       }
@@ -1118,7 +1118,7 @@ public static <T> Queryable<T> union(Queryable<T> source0,
   public static <T> Queryable<T> where(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.where(source, predicate);
       }
     };
@@ -1156,14 +1156,14 @@ public interface Replayable<T> extends Queryable<T> {
    * @param <T> element type */
   public abstract static class ReplayableQueryable<T>
       extends DefaultQueryable<T> implements Replayable<T> {
-    public void replay(QueryableFactory<T> factory) {
+    @Override public void replay(QueryableFactory<T> factory) {
     }
 
-    public Iterator<T> iterator() {
+    @Override public Iterator<T> iterator() {
       return Linq4j.enumeratorIterator(enumerator());
     }
 
-    public Enumerator<T> enumerator() {
+    @Override public Enumerator<T> enumerator() {
       return getProvider().executeQuery(this);
     }
 
@@ -1198,15 +1198,15 @@ protected NonLeafReplayableQueryable(Queryable<T> original) {
       this.original = original;
     }
 
-    public Type getElementType() {
+    @Override public Type getElementType() {
       return original.getElementType();
     }
 
-    public Expression getExpression() {
+    @Override public Expression getExpression() {
       return original.getExpression();
     }
 
-    public QueryProvider getProvider() {
+    @Override public QueryProvider getProvider() {
       return original.getProvider();
     }
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableRecorder.java b/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableRecorder.java
index 17d399d58f7..c7c47b92d9e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableRecorder.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/QueryableRecorder.java
@@ -55,635 +55,635 @@ public static <T> QueryableRecorder<T> instance() {
     return INSTANCE;
   }
 
-  public T aggregate(final Queryable<T> source,
+  @Override public T aggregate(final Queryable<T> source,
       final FunctionExpression<Function2<T, T, T>> func) {
     return new QueryableDefaults.NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.aggregate(source, func);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TAccumulate> TAccumulate aggregate(final Queryable<T> source,
+  @Override public <TAccumulate> TAccumulate aggregate(final Queryable<T> source,
       final TAccumulate seed,
       final FunctionExpression<Function2<TAccumulate, T, TAccumulate>> func) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.aggregate(source, seed, func);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TAccumulate, TResult> TResult aggregate(final Queryable<T> source,
+  @Override public <TAccumulate, TResult> TResult aggregate(final Queryable<T> source,
       final TAccumulate seed,
       final FunctionExpression<Function2<TAccumulate, T, TAccumulate>> func,
       final FunctionExpression<Function1<TAccumulate, TResult>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.aggregate(source, seed, func, selector);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public boolean all(final Queryable<T> source,
+  @Override public boolean all(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.all(source, predicate);
       }
     }.<Boolean>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public boolean any(final Queryable<T> source) {
+  @Override public boolean any(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.any(source);
       }
     }.<Boolean>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public boolean any(final Queryable<T> source,
+  @Override public boolean any(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.any(source, predicate);
       }
     }.<Boolean>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public BigDecimal averageBigDecimal(final Queryable<T> source,
+  @Override public BigDecimal averageBigDecimal(final Queryable<T> source,
       final FunctionExpression<BigDecimalFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageBigDecimal(source, selector);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public BigDecimal averageNullableBigDecimal(final Queryable<T> source,
+  @Override public BigDecimal averageNullableBigDecimal(final Queryable<T> source,
       final FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageNullableBigDecimal(source, selector);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public double averageDouble(final Queryable<T> source,
+  @Override public double averageDouble(final Queryable<T> source,
       final FunctionExpression<DoubleFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageDouble(source, selector);
       }
     }.<Double>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Double averageNullableDouble(final Queryable<T> source,
+  @Override public Double averageNullableDouble(final Queryable<T> source,
       final FunctionExpression<NullableDoubleFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageNullableDouble(source, selector);
       }
     }.<Double>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public int averageInteger(final Queryable<T> source,
+  @Override public int averageInteger(final Queryable<T> source,
       final FunctionExpression<IntegerFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageInteger(source, selector);
       }
     }.<Integer>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Integer averageNullableInteger(final Queryable<T> source,
+  @Override public Integer averageNullableInteger(final Queryable<T> source,
       final FunctionExpression<NullableIntegerFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageNullableInteger(source, selector);
       }
     }.<Integer>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public float averageFloat(final Queryable<T> source,
+  @Override public float averageFloat(final Queryable<T> source,
       final FunctionExpression<FloatFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageFloat(source, selector);
       }
     }.<Float>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Float averageNullableFloat(final Queryable<T> source,
+  @Override public Float averageNullableFloat(final Queryable<T> source,
       final FunctionExpression<NullableFloatFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageNullableFloat(source, selector);
       }
     }.<Float>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public long averageLong(final Queryable<T> source,
+  @Override public long averageLong(final Queryable<T> source,
       final FunctionExpression<LongFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageLong(source, selector);
       }
     }.<Long>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Long averageNullableLong(final Queryable<T> source,
+  @Override public Long averageNullableLong(final Queryable<T> source,
       final FunctionExpression<NullableLongFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.averageNullableLong(source, selector);
       }
     }.<Long>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <T2> Queryable<T2> cast(final Queryable<T> source,
+  @Override public <T2> Queryable<T2> cast(final Queryable<T> source,
       final Class<T2> clazz) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.cast(source, clazz);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Queryable<T> concat(final Queryable<T> source,
+  @Override public Queryable<T> concat(final Queryable<T> source,
       final Enumerable<T> source2) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.concat(source, source2);
       }
     };
   }
 
-  public boolean contains(final Queryable<T> source, final T element) {
+  @Override public boolean contains(final Queryable<T> source, final T element) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.contains(source, element);
       }
     }.<Boolean>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public boolean contains(final Queryable<T> source, final T element,
+  @Override public boolean contains(final Queryable<T> source, final T element,
       final EqualityComparer<T> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.contains(source, element, comparer);
       }
     }.<Boolean>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public int count(final Queryable<T> source) {
+  @Override public int count(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.count(source);
       }
     }.<Integer>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public int count(final Queryable<T> source,
+  @Override public int count(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> func) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.count(source, func);
       }
     }.<Integer>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Queryable<T> defaultIfEmpty(final Queryable<T> source) {
+  @Override public Queryable<T> defaultIfEmpty(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.defaultIfEmpty(source);
       }
     };
   }
 
-  public Queryable<T> defaultIfEmpty(final Queryable<T> source, final T value) {
+  @Override public Queryable<T> defaultIfEmpty(final Queryable<T> source, final T value) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.defaultIfEmpty(source, value);
       }
     };
   }
 
-  public Queryable<T> distinct(final Queryable<T> source) {
+  @Override public Queryable<T> distinct(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.distinct(source);
       }
     };
   }
 
-  public Queryable<T> distinct(final Queryable<T> source,
+  @Override public Queryable<T> distinct(final Queryable<T> source,
       final EqualityComparer<T> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.distinct(source, comparer);
       }
     };
   }
 
-  public T elementAt(final Queryable<T> source, final int index) {
+  @Override public T elementAt(final Queryable<T> source, final int index) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.elementAt(source, index);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T elementAtOrDefault(final Queryable<T> source, final int index) {
+  @Override public T elementAtOrDefault(final Queryable<T> source, final int index) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.elementAtOrDefault(source, index);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Queryable<T> except(final Queryable<T> source,
+  @Override public Queryable<T> except(final Queryable<T> source,
       final Enumerable<T> enumerable) {
     return except(source, enumerable, false);
   }
 
-  public Queryable<T> except(final Queryable<T> source,
+  @Override public Queryable<T> except(final Queryable<T> source,
       final Enumerable<T> enumerable, boolean all) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.except(source, enumerable, all);
       }
     };
   }
 
-  public Queryable<T> except(final Queryable<T> source,
+  @Override public Queryable<T> except(final Queryable<T> source,
       final Enumerable<T> enumerable, final EqualityComparer<T> comparer) {
     return except(source, enumerable, comparer, false);
   }
 
-  public Queryable<T> except(final Queryable<T> source,
+  @Override public Queryable<T> except(final Queryable<T> source,
       final Enumerable<T> enumerable, final EqualityComparer<T> comparer, boolean all) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.except(source, enumerable, comparer, all);
       }
     };
   }
 
-  public T first(final Queryable<T> source) {
+  @Override public T first(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.first(source);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T first(final Queryable<T> source,
+  @Override public T first(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.first(source, predicate);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T firstOrDefault(final Queryable<T> source) {
+  @Override public T firstOrDefault(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.firstOrDefault(source);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T firstOrDefault(final Queryable<T> source,
+  @Override public T firstOrDefault(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.firstOrDefault(source, predicate);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(final Queryable<T> source,
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupBy(source, keySelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey> Queryable<Grouping<TKey, T>> groupBy(final Queryable<T> source,
+  @Override public <TKey> Queryable<Grouping<TKey, T>> groupBy(final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final EqualityComparer<TKey> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupBy(source, keySelector, comparer);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final FunctionExpression<Function1<T, TElement>> elementSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupBy(source, keySelector, elementSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
+  @Override public <TKey, TElement> Queryable<Grouping<TKey, TElement>> groupBy(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final FunctionExpression<Function1<T, TElement>> elementSelector,
       final EqualityComparer<TKey> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupBy(source, keySelector, elementSelector, comparer);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final FunctionExpression<Function2<TKey, Enumerable<T>, TResult>> resultSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupByK(source, keySelector, resultSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey, TResult> Queryable<TResult> groupByK(final Queryable<T> source,
+  @Override public <TKey, TResult> Queryable<TResult> groupByK(final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final FunctionExpression<Function2<TKey, Enumerable<T>, TResult>> resultSelector,
       final EqualityComparer<TKey> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupByK(source, keySelector, resultSelector, comparer);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final FunctionExpression<Function1<T, TElement>> elementSelector,
       final FunctionExpression<Function2<TKey, Enumerable<TElement>, TResult>> resultSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupBy(source, keySelector, elementSelector, resultSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey, TElement, TResult> Queryable<TResult> groupBy(
+  @Override public <TKey, TElement, TResult> Queryable<TResult> groupBy(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final FunctionExpression<Function1<T, TElement>> elementSelector,
       final FunctionExpression<Function2<TKey, Enumerable<TElement>, TResult>> resultSelector,
       final EqualityComparer<TKey> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupBy(source, keySelector, elementSelector, resultSelector,
             comparer);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       final Queryable<T> source, final Enumerable<TInner> inner,
       final FunctionExpression<Function1<T, TKey>> outerKeySelector,
       final FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
       final FunctionExpression<Function2<T, Enumerable<TInner>, TResult>> resultSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupJoin(source, inner, outerKeySelector, innerKeySelector,
             resultSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> groupJoin(
       final Queryable<T> source, final Enumerable<TInner> inner,
       final FunctionExpression<Function1<T, TKey>> outerKeySelector,
       final FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
       final FunctionExpression<Function2<T, Enumerable<TInner>, TResult>> resultSelector,
       final EqualityComparer<TKey> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.groupJoin(source, inner, outerKeySelector, innerKeySelector,
             resultSelector, comparer);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Queryable<T> intersect(final Queryable<T> source,
+  @Override public Queryable<T> intersect(final Queryable<T> source,
       final Enumerable<T> enumerable) {
     return intersect(source, enumerable, false);
   }
 
-  public Queryable<T> intersect(final Queryable<T> source,
+  @Override public Queryable<T> intersect(final Queryable<T> source,
       final Enumerable<T> enumerable, boolean all) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.intersect(source, enumerable, all);
       }
     };
   }
 
-  public Queryable<T> intersect(final Queryable<T> source,
+  @Override public Queryable<T> intersect(final Queryable<T> source,
       final Enumerable<T> enumerable, final EqualityComparer<T> comparer) {
     return intersect(source, enumerable, comparer, false);
   }
 
-  public Queryable<T> intersect(final Queryable<T> source,
+  @Override public Queryable<T> intersect(final Queryable<T> source,
       final Enumerable<T> enumerable, final EqualityComparer<T> comparer, boolean all) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.intersect(source, enumerable, comparer, all);
       }
     };
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       final Queryable<T> source, final Enumerable<TInner> inner,
       final FunctionExpression<Function1<T, TKey>> outerKeySelector,
       final FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
       final FunctionExpression<Function2<T, TInner, TResult>> resultSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.join(source, inner, outerKeySelector, innerKeySelector,
             resultSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TInner, TKey, TResult> Queryable<TResult> join(
+  @Override public <TInner, TKey, TResult> Queryable<TResult> join(
       final Queryable<T> source, final Enumerable<TInner> inner,
       final FunctionExpression<Function1<T, TKey>> outerKeySelector,
       final FunctionExpression<Function1<TInner, TKey>> innerKeySelector,
       final FunctionExpression<Function2<T, TInner, TResult>> resultSelector,
       final EqualityComparer<TKey> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.join(source, inner, outerKeySelector, innerKeySelector,
             resultSelector, comparer);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T last(final Queryable<T> source) {
+  @Override public T last(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.last(source);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T last(final Queryable<T> source,
+  @Override public T last(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.last(source, predicate);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T lastOrDefault(final Queryable<T> source) {
+  @Override public T lastOrDefault(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.lastOrDefault(source);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T lastOrDefault(final Queryable<T> source,
+  @Override public T lastOrDefault(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.lastOrDefault(source, predicate);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public long longCount(final Queryable<T> source) {
+  @Override public long longCount(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.longCount(source);
       }
     }.<Long>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public long longCount(final Queryable<T> source,
+  @Override public long longCount(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.longCount(source, predicate);
       }
     }.longCount(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T max(final Queryable<T> source) {
+  @Override public T max(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.max(source);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TResult extends Comparable<TResult>> TResult max(
+  @Override public <TResult extends Comparable<TResult>> TResult max(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TResult>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.max(source, selector);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T min(final Queryable<T> source) {
+  @Override public T min(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.min(source);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TResult extends Comparable<TResult>> TResult min(
+  @Override public <TResult extends Comparable<TResult>> TResult min(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TResult>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.min(source, selector);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TResult> Queryable<TResult> ofType(final Queryable<T> source,
+  @Override public <TResult> Queryable<TResult> ofType(final Queryable<T> source,
       final Class<TResult> clazz) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.ofType(source, clazz);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderBy(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderBy(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.orderBy(source, keySelector);
       }
     };
   }
 
-  public <TKey> OrderedQueryable<T> orderBy(final Queryable<T> source,
+  @Override public <TKey> OrderedQueryable<T> orderBy(final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final Comparator<TKey> comparator) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.orderBy(source, keySelector, comparator);
       }
     };
   }
 
-  public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
+  @Override public <TKey extends Comparable> OrderedQueryable<T> orderByDescending(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.orderByDescending(source, keySelector);
       }
     };
   }
 
-  public <TKey> OrderedQueryable<T> orderByDescending(final Queryable<T> source,
+  @Override public <TKey> OrderedQueryable<T> orderByDescending(final Queryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final Comparator<TKey> comparator) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.orderByDescending(source, keySelector, comparator);
       }
     };
   }
 
-  public Queryable<T> reverse(final Queryable<T> source) {
+  @Override public Queryable<T> reverse(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.reverse(source);
       }
     };
   }
 
-  public <TResult> Queryable<TResult> select(final Queryable<T> source,
+  @Override public <TResult> Queryable<TResult> select(final Queryable<T> source,
       final FunctionExpression<Function1<T, TResult>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.select(source, selector);
       }
 
@@ -693,336 +693,336 @@ public void replay(QueryableFactory<T> factory) {
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TResult> Queryable<TResult> selectN(final Queryable<T> source,
+  @Override public <TResult> Queryable<TResult> selectN(final Queryable<T> source,
       final FunctionExpression<Function2<T, Integer, TResult>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.selectN(source, selector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TResult> Queryable<TResult> selectMany(final Queryable<T> source,
+  @Override public <TResult> Queryable<TResult> selectMany(final Queryable<T> source,
       final FunctionExpression<Function1<T, Enumerable<TResult>>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.selectMany(source, selector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TResult> Queryable<TResult> selectManyN(final Queryable<T> source,
+  @Override public <TResult> Queryable<TResult> selectManyN(final Queryable<T> source,
       final FunctionExpression<Function2<T, Integer, Enumerable<TResult>>>
         selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.selectManyN(source, selector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectMany(
+  @Override public <TCollection, TResult> Queryable<TResult> selectMany(
       final Queryable<T> source,
       final FunctionExpression<Function2<T, Integer, Enumerable<TCollection>>>
         collectionSelector,
       final FunctionExpression<Function2<T, TCollection, TResult>>
         resultSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.selectMany(source, collectionSelector, resultSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public <TCollection, TResult> Queryable<TResult> selectManyN(
+  @Override public <TCollection, TResult> Queryable<TResult> selectManyN(
       final Queryable<T> source,
       final FunctionExpression<Function1<T, Enumerable<TCollection>>>
         collectionSelector,
       final FunctionExpression<Function2<T, TCollection, TResult>>
         resultSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.selectManyN(source, collectionSelector, resultSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
   }
 
-  public boolean sequenceEqual(final Queryable<T> source,
+  @Override public boolean sequenceEqual(final Queryable<T> source,
       final Enumerable<T> enumerable) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sequenceEqual(source, enumerable);
       }
     }.<Boolean>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public boolean sequenceEqual(final Queryable<T> source,
+  @Override public boolean sequenceEqual(final Queryable<T> source,
       final Enumerable<T> enumerable, final EqualityComparer<T> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sequenceEqual(source, enumerable, comparer);
       }
     }.<Boolean>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T single(final Queryable<T> source) {
+  @Override public T single(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.single(source);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T single(final Queryable<T> source,
+  @Override public T single(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.single(source, predicate);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T singleOrDefault(final Queryable<T> source) {
+  @Override public T singleOrDefault(final Queryable<T> source) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.singleOrDefault(source);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public T singleOrDefault(final Queryable<T> source,
+  @Override public T singleOrDefault(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.singleOrDefault(source, predicate);
       }
     }.single(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Queryable<T> skip(final Queryable<T> source, final int count) {
+  @Override public Queryable<T> skip(final Queryable<T> source, final int count) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.skip(source, count);
       }
     };
   }
 
-  public Queryable<T> skipWhile(final Queryable<T> source,
+  @Override public Queryable<T> skipWhile(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.skipWhile(source, predicate);
       }
     };
   }
 
-  public Queryable<T> skipWhileN(final Queryable<T> source,
+  @Override public Queryable<T> skipWhileN(final Queryable<T> source,
       final FunctionExpression<Predicate2<T, Integer>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.skipWhileN(source, predicate);
       }
     };
   }
 
-  public BigDecimal sumBigDecimal(final Queryable<T> source,
+  @Override public BigDecimal sumBigDecimal(final Queryable<T> source,
       final FunctionExpression<BigDecimalFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumBigDecimal(source, selector);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public BigDecimal sumNullableBigDecimal(final Queryable<T> source,
+  @Override public BigDecimal sumNullableBigDecimal(final Queryable<T> source,
       final FunctionExpression<NullableBigDecimalFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumNullableBigDecimal(source, selector);
       }
     }.castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public double sumDouble(final Queryable<T> source,
+  @Override public double sumDouble(final Queryable<T> source,
       final FunctionExpression<DoubleFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumDouble(source, selector);
       }
     }.<Double>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Double sumNullableDouble(final Queryable<T> source,
+  @Override public Double sumNullableDouble(final Queryable<T> source,
       final FunctionExpression<NullableDoubleFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumNullableDouble(source, selector);
       }
     }.<Double>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public int sumInteger(final Queryable<T> source,
+  @Override public int sumInteger(final Queryable<T> source,
       final FunctionExpression<IntegerFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumInteger(source, selector);
       }
     }.<Integer>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Integer sumNullableInteger(final Queryable<T> source,
+  @Override public Integer sumNullableInteger(final Queryable<T> source,
       final FunctionExpression<NullableIntegerFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumNullableInteger(source, selector);
       }
     }.<Integer>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public long sumLong(final Queryable<T> source,
+  @Override public long sumLong(final Queryable<T> source,
       final FunctionExpression<LongFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumLong(source, selector);
       }
     }.<Long>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Long sumNullableLong(final Queryable<T> source,
+  @Override public Long sumNullableLong(final Queryable<T> source,
       final FunctionExpression<NullableLongFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumNullableLong(source, selector);
       }
     }.<Long>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public float sumFloat(final Queryable<T> source,
+  @Override public float sumFloat(final Queryable<T> source,
       final FunctionExpression<FloatFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumFloat(source, selector);
       }
     }.<Float>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Float sumNullableFloat(final Queryable<T> source,
+  @Override public Float sumNullableFloat(final Queryable<T> source,
       final FunctionExpression<NullableFloatFunction1<T>> selector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.sumNullableFloat(source, selector);
       }
     }.<Float>castSingle(); // CHECKSTYLE: IGNORE 0
   }
 
-  public Queryable<T> take(final Queryable<T> source, final int count) {
+  @Override public Queryable<T> take(final Queryable<T> source, final int count) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.take(source, count);
       }
     };
   }
 
-  public Queryable<T> takeWhile(final Queryable<T> source,
+  @Override public Queryable<T> takeWhile(final Queryable<T> source,
       final FunctionExpression<Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.takeWhile(source, predicate);
       }
     };
   }
 
-  public Queryable<T> takeWhileN(final Queryable<T> source,
+  @Override public Queryable<T> takeWhileN(final Queryable<T> source,
       final FunctionExpression<Predicate2<T, Integer>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.takeWhileN(source, predicate);
       }
     };
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenBy(
       final OrderedQueryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.thenBy(source, keySelector);
       }
     };
   }
 
-  public <TKey> OrderedQueryable<T> thenBy(final OrderedQueryable<T> source,
+  @Override public <TKey> OrderedQueryable<T> thenBy(final OrderedQueryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final Comparator<TKey> comparator) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.thenBy(source, keySelector, comparator);
       }
     };
   }
 
-  public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey extends Comparable<TKey>> OrderedQueryable<T> thenByDescending(
       final OrderedQueryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.thenByDescending(source, keySelector);
       }
     };
   }
 
-  public <TKey> OrderedQueryable<T> thenByDescending(
+  @Override public <TKey> OrderedQueryable<T> thenByDescending(
       final OrderedQueryable<T> source,
       final FunctionExpression<Function1<T, TKey>> keySelector,
       final Comparator<TKey> comparator) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.thenByDescending(source, keySelector, comparator);
       }
     };
   }
 
-  public Queryable<T> union(final Queryable<T> source,
+  @Override public Queryable<T> union(final Queryable<T> source,
       final Enumerable<T> source1) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.union(source, source1);
       }
     };
   }
 
-  public Queryable<T> union(final Queryable<T> source,
+  @Override public Queryable<T> union(final Queryable<T> source,
       final Enumerable<T> source1, final EqualityComparer<T> comparer) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.union(source, source1, comparer);
       }
     };
   }
 
-  public Queryable<T> where(final Queryable<T> source,
+  @Override public Queryable<T> where(final Queryable<T> source,
       final FunctionExpression<? extends Predicate1<T>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.where(source, predicate);
       }
     };
   }
 
-  public Queryable<T> whereN(final Queryable<T> source,
+  @Override public Queryable<T> whereN(final Queryable<T> source,
       final FunctionExpression<? extends Predicate2<T, Integer>> predicate) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.whereN(source, predicate);
       }
     };
   }
 
-  public <T1, TResult> Queryable<TResult> zip(final Queryable<T> source,
+  @Override public <T1, TResult> Queryable<TResult> zip(final Queryable<T> source,
       final Enumerable<T1> source1,
       final FunctionExpression<Function2<T, T1, TResult>> resultSelector) {
     return new NonLeafReplayableQueryable<T>(source) {
-      public void replay(QueryableFactory<T> factory) {
+      @Override public void replay(QueryableFactory<T> factory) {
         factory.zip(source, source1, resultSelector);
       }
     }.castQueryable(); // CHECKSTYLE: IGNORE 0
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/TransformedEnumerator.java b/linq4j/src/main/java/org/apache/calcite/linq4j/TransformedEnumerator.java
index 60a056fe0e3..cea0bcf3b87 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/TransformedEnumerator.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/TransformedEnumerator.java
@@ -31,19 +31,19 @@ public TransformedEnumerator(Enumerator<F> enumerator) {
 
   protected abstract E transform(F from);
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     return enumerator.moveNext();
   }
 
-  public E current() {
+  @Override public E current() {
     return transform(enumerator.current());
   }
 
-  public void reset() {
+  @Override public void reset() {
     enumerator.reset();
   }
 
-  public void close() {
+  @Override public void close() {
     enumerator.close();
   }
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/function/Functions.java b/linq4j/src/main/java/org/apache/calcite/linq4j/function/Functions.java
index 539ea5016d3..58deaaefbbc 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/function/Functions.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/function/Functions.java
@@ -268,11 +268,11 @@ public static <T1> Function1<T1, Float> adapt(final FloatFunction1<T1> f) {
   public static <T1, R> List<R> adapt(final List<T1> list,
       final Function1<T1, R> f) {
     return new AbstractList<R>() {
-      public R get(int index) {
+      @Override public R get(int index) {
         return f.apply(list.get(index));
       }
 
-      public int size() {
+      @Override public int size() {
         return list.size();
       }
     };
@@ -288,11 +288,11 @@ public int size() {
   public static <T, R> List<R> adapt(final T[] ts,
       final Function1<T, R> f) {
     return new AbstractList<R>() {
-      public R get(int index) {
+      @Override public R get(int index) {
         return f.apply(ts[index]);
       }
 
-      public int size() {
+      @Override public int size() {
         return ts.length;
       }
     };
@@ -491,11 +491,11 @@ public static <T, T2> EqualityComparer<T> selectorComparer(
   /** Array equality comparer. */
   private static class ArrayEqualityComparer
       implements EqualityComparer<Object[]> {
-    public boolean equal(Object[] v1, Object[] v2) {
+    @Override public boolean equal(Object[] v1, Object[] v2) {
       return Arrays.deepEquals(v1, v2);
     }
 
-    public int hashCode(Object[] t) {
+    @Override public int hashCode(Object[] t) {
       return Arrays.deepHashCode(t);
     }
   }
@@ -503,11 +503,11 @@ public int hashCode(Object[] t) {
   /** Identity equality comparer. */
   private static class IdentityEqualityComparer
       implements EqualityComparer<Object> {
-    public boolean equal(Object v1, Object v2) {
+    @Override public boolean equal(Object v1, Object v2) {
       return Objects.equals(v1, v2);
     }
 
-    public int hashCode(Object t) {
+    @Override public int hashCode(Object t) {
       return t == null ? 0x789d : t.hashCode();
     }
   }
@@ -524,14 +524,14 @@ private static final class SelectorEqualityComparer<T, T2>
       this.selector = selector;
     }
 
-    public boolean equal(T v1, T v2) {
+    @Override public boolean equal(T v1, T v2) {
       return v1 == v2
           || v1 != null
           && v2 != null
           && Objects.equals(selector.apply(v1), selector.apply(v2));
     }
 
-    public int hashCode(T t) {
+    @Override public int hashCode(T t) {
       return t == null ? 0x789d : selector.apply(t).hashCode();
     }
   }
@@ -539,7 +539,7 @@ public int hashCode(T t) {
   /** Nulls first comparator. */
   private static class NullsFirstComparator
       implements Comparator<Comparable>, Serializable {
-    public int compare(Comparable o1, Comparable o2) {
+    @Override public int compare(Comparable o1, Comparable o2) {
       if (o1 == o2) {
         return 0;
       }
@@ -557,7 +557,7 @@ public int compare(Comparable o1, Comparable o2) {
   /** Nulls last comparator. */
   private static class NullsLastComparator
       implements Comparator<Comparable>, Serializable {
-    public int compare(Comparable o1, Comparable o2) {
+    @Override public int compare(Comparable o1, Comparable o2) {
       if (o1 == o2) {
         return 0;
       }
@@ -575,7 +575,7 @@ public int compare(Comparable o1, Comparable o2) {
   /** Nulls first reverse comparator. */
   private static class NullsFirstReverseComparator
       implements Comparator<Comparable>, Serializable  {
-    public int compare(Comparable o1, Comparable o2) {
+    @Override public int compare(Comparable o1, Comparable o2) {
       if (o1 == o2) {
         return 0;
       }
@@ -593,7 +593,7 @@ public int compare(Comparable o1, Comparable o2) {
   /** Nulls last reverse comparator. */
   private static class NullsLastReverseComparator
       implements Comparator<Comparable>, Serializable  {
-    public int compare(Comparable o1, Comparable o2) {
+    @Override public int compare(Comparable o1, Comparable o2) {
       if (o1 == o2) {
         return 0;
       }
@@ -615,15 +615,15 @@ public int compare(Comparable o1, Comparable o2) {
    * @param <T1> second argument type */
   private static final class Ignore<R, T0, T1>
       implements Function0<R>, Function1<T0, R>, Function2<T0, T1, R> {
-    public R apply() {
+    @Override public R apply() {
       return null;
     }
 
-    public R apply(T0 p0) {
+    @Override public R apply(T0 p0) {
       return null;
     }
 
-    public R apply(T0 p0, T1 p1) {
+    @Override public R apply(T0 p0, T1 p1) {
       return null;
     }
 
@@ -643,11 +643,11 @@ private static class GeneratingList<E> extends AbstractList<E>
       this.fn = fn;
     }
 
-    public int size() {
+    @Override public int size() {
       return size;
     }
 
-    public E get(int index) {
+    @Override public E get(int index) {
       return fn.apply(index);
     }
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/AbstractNode.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/AbstractNode.java
index 014db9045cc..dbbb0286077 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/AbstractNode.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/AbstractNode.java
@@ -52,7 +52,7 @@ public Type getType() {
     return writer.toString();
   }
 
-  public void accept(ExpressionWriter writer) {
+  @Override public void accept(ExpressionWriter writer) {
     accept(writer, 0, 0);
   }
 
@@ -65,7 +65,7 @@ void accept(ExpressionWriter writer, int lprec, int rprec) {
         "un-parse not supported: " + getClass() + ":" + nodeType);
   }
 
-  public Node accept(Shuttle shuttle) {
+  @Override public Node accept(Shuttle shuttle) {
     throw new RuntimeException(
         "visit not supported: " + getClass() + ":" + nodeType);
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ArrayLengthRecordField.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ArrayLengthRecordField.java
index d6a6e2061e8..cabb59bb11e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ArrayLengthRecordField.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ArrayLengthRecordField.java
@@ -34,27 +34,27 @@ public ArrayLengthRecordField(String fieldName, Class clazz) {
     this.clazz = clazz;
   }
 
-  public boolean nullable() {
+  @Override public boolean nullable() {
     return false;
   }
 
-  public String getName() {
+  @Override public String getName() {
     return fieldName;
   }
 
-  public Type getType() {
+  @Override public Type getType() {
     return int.class;
   }
 
-  public int getModifiers() {
+  @Override public int getModifiers() {
     return 0;
   }
 
-  public Object get(Object o) throws IllegalAccessException {
+  @Override public Object get(Object o) throws IllegalAccessException {
     return Array.getLength(o);
   }
 
-  public Type getDeclaringClass() {
+  @Override public Type getDeclaringClass() {
     return clazz;
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BinaryExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BinaryExpression.java
index a18025c2c9f..bd41b048d13 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BinaryExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BinaryExpression.java
@@ -44,11 +44,11 @@ public class BinaryExpression extends Expression {
     return visitor.visit(this, expression0, expression1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public Object evaluate(Evaluator evaluator) {
+  @Override public Object evaluate(Evaluator evaluator) {
     switch (nodeType) {
     case AndAlso:
       return (Boolean) expression0.evaluate(evaluator)
@@ -203,7 +203,7 @@ public Object evaluate(Evaluator evaluator) {
     }
   }
 
-  void accept(ExpressionWriter writer, int lprec, int rprec) {
+  @Override void accept(ExpressionWriter writer, int lprec, int rprec) {
     if (writer.requireParentheses(this, lprec, rprec)) {
       return;
     }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BlockStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BlockStatement.java
index 2aaa40bbf9d..8d8945c5358 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BlockStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/BlockStatement.java
@@ -59,7 +59,7 @@ private boolean distinctVariables(boolean fail) {
     return shuttle.visit(this, newStatements);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ClassDeclaration.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ClassDeclaration.java
index f4e0c9a266c..6920caad9dc 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ClassDeclaration.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ClassDeclaration.java
@@ -42,7 +42,7 @@ public ClassDeclaration(int modifier, String name, Type extended,
     this.implemented = implemented;
   }
 
-  public void accept(ExpressionWriter writer) {
+  @Override public void accept(ExpressionWriter writer) {
     String modifiers = Modifier.toString(modifier);
     writer.append(modifiers);
     if (!modifiers.isEmpty()) {
@@ -59,14 +59,14 @@ public void accept(ExpressionWriter writer) {
     writer.newlineAndIndent();
   }
 
-  public ClassDeclaration accept(Shuttle shuttle) {
+  @Override public ClassDeclaration accept(Shuttle shuttle) {
     shuttle = shuttle.preVisit(this);
     final List<MemberDeclaration> members1 =
         Expressions.acceptMemberDeclarations(memberDeclarations, shuttle);
     return shuttle.visit(this, members1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalExpression.java
index 55c00cefba4..64400e60015 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalExpression.java
@@ -41,7 +41,7 @@ public ConditionalExpression(List<Node> expressionList, Type type) {
     this.expressionList = expressionList;
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalStatement.java
index 9d15a458bed..952e435197e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalStatement.java
@@ -46,7 +46,7 @@ public ConditionalStatement(List<Node> expressionList) {
     return shuttle.visit(this, list);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstantExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstantExpression.java
index 38b75879bc5..78cf208f33c 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstantExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstantExpression.java
@@ -54,7 +54,7 @@ public ConstantExpression(Type type, Object value) {
     }
   }
 
-  public Object evaluate(Evaluator evaluator) {
+  @Override public Object evaluate(Evaluator evaluator) {
     return value;
   }
 
@@ -62,7 +62,7 @@ public Object evaluate(Evaluator evaluator) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstructorDeclaration.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstructorDeclaration.java
index 5cac1b91cae..aff9d788d07 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstructorDeclaration.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstructorDeclaration.java
@@ -52,11 +52,11 @@ public ConstructorDeclaration(int modifier, Type declaredAgainst,
     return shuttle.visit(this, body);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public void accept(ExpressionWriter writer) {
+  @Override public void accept(ExpressionWriter writer) {
     String modifiers = Modifier.toString(modifier);
     writer.append(modifiers);
     if (!modifiers.isEmpty()) {
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeclarationStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeclarationStatement.java
index 31a529dcecc..84e2eba433d 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeclarationStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeclarationStatement.java
@@ -45,7 +45,7 @@ public DeclarationStatement(int modifiers, ParameterExpression parameter,
     return shuttle.visit(this, initializer);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DefaultExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DefaultExpression.java
index 57381686917..93fca6aad6d 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DefaultExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DefaultExpression.java
@@ -28,7 +28,7 @@ public DefaultExpression(Class type) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeterministicCodeOptimizer.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeterministicCodeOptimizer.java
index e9168071c70..430bcf5193b 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeterministicCodeOptimizer.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DeterministicCodeOptimizer.java
@@ -224,7 +224,7 @@ && isMethodDeterministic(methodCallExpression.method)) {
    * @param expression input expression
    * @return parameter of the already existing declaration, or null
    */
-  protected ParameterExpression findDeclaredExpression(Expression expression) {
+  @Override protected ParameterExpression findDeclaredExpression(Expression expression) {
     if (!dedup.isEmpty()) {
       ParameterExpression pe = dedup.get(expression);
       if (pe != null) {
@@ -369,7 +369,7 @@ protected boolean allMethodsDeterministic(Class klass) {
    *
    * @return new Visitor that is used to optimize class declarations
    */
-  protected DeterministicCodeOptimizer goDeeper() {
+  @Override protected DeterministicCodeOptimizer goDeeper() {
     return new DeterministicCodeOptimizer(this);
   }
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DynamicExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DynamicExpression.java
index e56f1b89918..1bba6b3a397 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DynamicExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/DynamicExpression.java
@@ -28,7 +28,7 @@ public DynamicExpression(Class type) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expression.java
index ed8a0391f61..9ec2984874e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expression.java
@@ -34,7 +34,7 @@ public abstract class Expression extends AbstractNode {
    * @param nodeType Node type
    * @param type Type of the expression
    */
-  public Expression(ExpressionType nodeType, Type type) {
+  protected Expression(ExpressionType nodeType, Type type) {
     super(nodeType, type);
     assert nodeType != null;
     assert type != null;
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expressions.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expressions.java
index 8260055542d..f62c8a8f5c2 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expressions.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Expressions.java
@@ -3265,31 +3265,31 @@ private static class FluentArrayList<T> extends ArrayList<T>
       super(c);
     }
 
-    public FluentList<T> append(T t) {
+    @Override public FluentList<T> append(T t) {
       add(t);
       return this;
     }
 
-    public FluentList<T> appendIf(boolean condition, T t) {
+    @Override public FluentList<T> appendIf(boolean condition, T t) {
       if (condition) {
         add(t);
       }
       return this;
     }
 
-    public FluentList<T> appendIfNotNull(T t) {
+    @Override public FluentList<T> appendIfNotNull(T t) {
       if (t != null) {
         add(t);
       }
       return this;
     }
 
-    public FluentList<T> appendAll(Iterable<T> ts) {
+    @Override public FluentList<T> appendAll(Iterable<T> ts) {
       addAll(toCollection(ts));
       return this;
     }
 
-    public FluentList<T> appendAll(T... ts) {
+    @Override public FluentList<T> appendAll(T... ts) {
       addAll(Arrays.asList(ts));
       return this;
     }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FieldDeclaration.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FieldDeclaration.java
index 7780f8c4dfb..ca235274ac3 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FieldDeclaration.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FieldDeclaration.java
@@ -43,11 +43,11 @@ public FieldDeclaration(int modifier, ParameterExpression parameter,
     return shuttle.visit(this, initializer);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public void accept(ExpressionWriter writer) {
+  @Override public void accept(ExpressionWriter writer) {
     String modifiers = Modifier.toString(modifier);
     writer.append(modifiers);
     if (!modifiers.isEmpty()) {
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForEachStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForEachStatement.java
index d2cc3eff9dd..a76ee68901b 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForEachStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForEachStatement.java
@@ -44,7 +44,7 @@ public ForEachStatement(ParameterExpression parameter, Expression iterable,
     return shuttle.visit(this, parameter, iterable1, body1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForStatement.java
index feb2b616451..3b7c9a5d1a1 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ForStatement.java
@@ -54,7 +54,7 @@ public ForStatement(List<DeclarationStatement> declarations,
     return shuttle.visit(this, decls1, condition1, post1, body1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FunctionExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FunctionExpression.java
index 6ebf8b60a7c..8e1afaeab07 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FunctionExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/FunctionExpression.java
@@ -72,7 +72,7 @@ public FunctionExpression(Class<F> type, BlockStatement body,
     return shuttle.visit(this, body);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/GotoStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/GotoStatement.java
index 4c00e62f70c..8d0332f1b85 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/GotoStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/GotoStatement.java
@@ -61,7 +61,7 @@ public class GotoStatement extends Statement {
     return shuttle.visit(this, expression1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/IndexExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/IndexExpression.java
index 0f1c909f722..50bb8633d46 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/IndexExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/IndexExpression.java
@@ -43,7 +43,7 @@ public IndexExpression(Expression array, List<Expression> indexExpressions) {
     return shuttle.visit(this, array, indexExpressions);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/InvocationExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/InvocationExpression.java
index aa83443aa02..dc91a62072d 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/InvocationExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/InvocationExpression.java
@@ -29,7 +29,7 @@ public InvocationExpression(ExpressionType nodeType, Class type) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LabelStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LabelStatement.java
index 38a5d279892..a65e78616b9 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LabelStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LabelStatement.java
@@ -37,7 +37,7 @@ public LabelStatement(Expression defaultValue, ExpressionType nodeType) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LambdaExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LambdaExpression.java
index ee4386d40d4..dddafee40f4 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LambdaExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/LambdaExpression.java
@@ -29,7 +29,7 @@ public LambdaExpression(ExpressionType nodeType, Class type) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ListInitExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ListInitExpression.java
index 59e2e4cc6b0..cf69b932d8e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ListInitExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ListInitExpression.java
@@ -28,7 +28,7 @@ public ListInitExpression(ExpressionType nodeType, Class type) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberDeclaration.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberDeclaration.java
index c2463313838..a3a5e2d3e80 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberDeclaration.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberDeclaration.java
@@ -20,5 +20,5 @@
  * Declaration of a member of a class.
  */
 public abstract class MemberDeclaration implements Node {
-  public abstract MemberDeclaration accept(Shuttle shuttle);
+  @Override public abstract MemberDeclaration accept(Shuttle shuttle);
 }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberExpression.java
index d746ea19e58..945f49a335e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberExpression.java
@@ -48,11 +48,11 @@ public MemberExpression(Expression expression, PseudoField field) {
     return shuttle.visit(this, expression1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public Object evaluate(Evaluator evaluator) {
+  @Override public Object evaluate(Evaluator evaluator) {
     final Object o = expression == null
         ? null
         : expression.evaluate(evaluator);
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberInitExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberInitExpression.java
index 1757660ad63..749a75ee124 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberInitExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MemberInitExpression.java
@@ -29,7 +29,7 @@ public MemberInitExpression() {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodCallExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodCallExpression.java
index f98cfe0be02..5317367685b 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodCallExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodCallExpression.java
@@ -60,7 +60,7 @@ public class MethodCallExpression extends Expression {
     return shuttle.visit(this, targetExpression, expressions);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodDeclaration.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodDeclaration.java
index f40c15fb04a..a864f61c98f 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodDeclaration.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/MethodDeclaration.java
@@ -53,11 +53,11 @@ public MethodDeclaration(int modifier, String name, Type resultType,
     return shuttle.visit(this, body);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public void accept(ExpressionWriter writer) {
+  @Override public void accept(ExpressionWriter writer) {
     String modifiers = Modifier.toString(modifier);
     writer.append(modifiers);
     if (!modifiers.isEmpty()) {
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewArrayExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewArrayExpression.java
index 54cba746fde..59850c7ea2c 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewArrayExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewArrayExpression.java
@@ -49,7 +49,7 @@ public NewArrayExpression(Type type, int dimension, Expression bound,
     return shuttle.visit(this, dimension, bound, expressions);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewExpression.java
index d42d67f5cf2..36e0916817e 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/NewExpression.java
@@ -50,7 +50,7 @@ public NewExpression(Type type, List<Expression> arguments,
     return shuttle.visit(this, arguments, memberDeclarations);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ParameterExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ParameterExpression.java
index fb7eaf2d22d..c51283731c0 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ParameterExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ParameterExpression.java
@@ -47,11 +47,11 @@ public ParameterExpression(int modifier, Type type, String name) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  public Object evaluate(Evaluator evaluator) {
+  @Override public Object evaluate(Evaluator evaluator) {
     return evaluator.peek(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Primitive.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Primitive.java
index f95105d9391..05074468f83 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Primitive.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Primitive.java
@@ -253,11 +253,11 @@ public static Class unbox(Class type) {
   public static List<?> asList(final Object array) {
     // REVIEW: A per-type list might be more efficient. (Or might not.)
     return new AbstractList() {
-      public Object get(int index) {
+      @Override public Object get(int index) {
         return Array.get(array, index);
       }
 
-      public int size() {
+      @Override public int size() {
         return Array.getLength(array);
       }
     };
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ReflectedPseudoField.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ReflectedPseudoField.java
index 4dc11a7b53d..4a5ace11f62 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ReflectedPseudoField.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ReflectedPseudoField.java
@@ -31,23 +31,23 @@ public ReflectedPseudoField(Field field) {
     this.field = field;
   }
 
-  public String getName() {
+  @Override public String getName() {
     return field.getName();
   }
 
-  public Type getType() {
+  @Override public Type getType() {
     return field.getType();
   }
 
-  public int getModifiers() {
+  @Override public int getModifiers() {
     return field.getModifiers();
   }
 
-  public Object get(Object o) throws IllegalAccessException {
+  @Override public Object get(Object o) throws IllegalAccessException {
     return field.get(o);
   }
 
-  public Class<?> getDeclaringClass() {
+  @Override public Class<?> getDeclaringClass() {
     return field.getDeclaringClass();
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/SwitchStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/SwitchStatement.java
index 2ebcdc1bd8d..62265ebb262 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/SwitchStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/SwitchStatement.java
@@ -29,7 +29,7 @@ public SwitchStatement(ExpressionType nodeType) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TernaryExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TernaryExpression.java
index 00ef60c370f..f42011dbaeb 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TernaryExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TernaryExpression.java
@@ -46,11 +46,11 @@ public class TernaryExpression extends Expression {
     return shuttle.visit(this, expression0, expression1, expression2);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  void accept(ExpressionWriter writer, int lprec, int rprec) {
+  @Override void accept(ExpressionWriter writer, int lprec, int rprec) {
     if (writer.requireParentheses(this, lprec, rprec)) {
       return;
     }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ThrowStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ThrowStatement.java
index 0cd427d70d0..8b3504bff28 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ThrowStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/ThrowStatement.java
@@ -35,7 +35,7 @@ public ThrowStatement(Expression expression) {
     return shuttle.visit(this, expression);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TryStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TryStatement.java
index 0ee3d7a96b1..cf3d4dd2891 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TryStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TryStatement.java
@@ -50,7 +50,7 @@ public TryStatement(Statement body, List<CatchBlock> catchBlocks,
     return shuttle.visit(this, body1, catchBlocks1, fynally1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TypeBinaryExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TypeBinaryExpression.java
index 967c228849c..869a960e2f8 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TypeBinaryExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/TypeBinaryExpression.java
@@ -40,11 +40,11 @@ public TypeBinaryExpression(ExpressionType nodeType, Expression expression,
     return shuttle.visit(this, expression);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  void accept(ExpressionWriter writer, int lprec, int rprec) {
+  @Override void accept(ExpressionWriter writer, int lprec, int rprec) {
     if (writer.requireParentheses(this, lprec, rprec)) {
       return;
     }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Types.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Types.java
index a449a46a925..1eae6210449 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Types.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/Types.java
@@ -555,15 +555,15 @@ static class ParameterizedTypeImpl implements ParameterizedType {
       return buf.toString();
     }
 
-    public Type[] getActualTypeArguments() {
+    @Override public Type[] getActualTypeArguments() {
       return typeArguments.toArray(new Type[0]);
     }
 
-    public Type getRawType() {
+    @Override public Type getRawType() {
       return rawType;
     }
 
-    public Type getOwnerType() {
+    @Override public Type getOwnerType() {
       return ownerType;
     }
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/UnaryExpression.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/UnaryExpression.java
index d07e545aa81..f3eeda61e9f 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/UnaryExpression.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/UnaryExpression.java
@@ -37,11 +37,11 @@ public class UnaryExpression extends Expression {
     return shuttle.visit(this, expression);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  void accept(ExpressionWriter writer, int lprec, int rprec) {
+  @Override void accept(ExpressionWriter writer, int lprec, int rprec) {
     switch (nodeType) {
     case Convert:
       if (!writer.requireParentheses(this, lprec, rprec)) {
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/VisitorImpl.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/VisitorImpl.java
index 8d8431f2775..ffc84e83d78 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/VisitorImpl.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/VisitorImpl.java
@@ -29,38 +29,38 @@ public VisitorImpl() {
     super();
   }
 
-  public R visit(BinaryExpression binaryExpression) {
+  @Override public R visit(BinaryExpression binaryExpression) {
     R r0 = binaryExpression.expression0.accept(this);
     R r1 = binaryExpression.expression1.accept(this);
     return r1;
   }
 
-  public R visit(BlockStatement blockStatement) {
+  @Override public R visit(BlockStatement blockStatement) {
     return Expressions.acceptNodes(blockStatement.statements, this);
   }
 
-  public R visit(ClassDeclaration classDeclaration) {
+  @Override public R visit(ClassDeclaration classDeclaration) {
     return Expressions.acceptNodes(classDeclaration.memberDeclarations, this);
   }
 
-  public R visit(ConditionalExpression conditionalExpression) {
+  @Override public R visit(ConditionalExpression conditionalExpression) {
     return Expressions.acceptNodes(conditionalExpression.expressionList, this);
   }
 
-  public R visit(ConditionalStatement conditionalStatement) {
+  @Override public R visit(ConditionalStatement conditionalStatement) {
     return Expressions.acceptNodes(conditionalStatement.expressionList, this);
   }
 
-  public R visit(ConstantExpression constantExpression) {
+  @Override public R visit(ConstantExpression constantExpression) {
     return null;
   }
 
-  public R visit(ConstructorDeclaration constructorDeclaration) {
+  @Override public R visit(ConstructorDeclaration constructorDeclaration) {
     R r0 = Expressions.acceptNodes(constructorDeclaration.parameters, this);
     return constructorDeclaration.body.accept(this);
   }
 
-  public R visit(DeclarationStatement declarationStatement) {
+  @Override public R visit(DeclarationStatement declarationStatement) {
     R r = declarationStatement.parameter.accept(this);
     if (declarationStatement.initializer != null) {
       r = declarationStatement.initializer.accept(this);
@@ -68,67 +68,67 @@ public R visit(DeclarationStatement declarationStatement) {
     return r;
   }
 
-  public R visit(DefaultExpression defaultExpression) {
+  @Override public R visit(DefaultExpression defaultExpression) {
     return null;
   }
 
-  public R visit(DynamicExpression dynamicExpression) {
+  @Override public R visit(DynamicExpression dynamicExpression) {
     return null;
   }
 
-  public R visit(FieldDeclaration fieldDeclaration) {
+  @Override public R visit(FieldDeclaration fieldDeclaration) {
     R r0 = fieldDeclaration.parameter.accept(this);
     return fieldDeclaration.initializer == null ? null
         : fieldDeclaration.initializer.accept(this);
   }
 
-  public R visit(ForStatement forStatement) {
+  @Override public R visit(ForStatement forStatement) {
     R r0 = Expressions.acceptNodes(forStatement.declarations, this);
     R r1 = forStatement.condition.accept(this);
     R r2 = forStatement.post.accept(this);
     return forStatement.body.accept(this);
   }
 
-  public R visit(ForEachStatement forEachStatement) {
+  @Override public R visit(ForEachStatement forEachStatement) {
     R r0 = forEachStatement.parameter.accept(this);
     R r1 = forEachStatement.iterable.accept(this);
     return forEachStatement.body.accept(this);
   }
 
-  public R visit(FunctionExpression functionExpression) {
+  @Override public R visit(FunctionExpression functionExpression) {
     @SuppressWarnings("unchecked") final List<Node> parameterList =
         functionExpression.parameterList;
     R r0 = Expressions.acceptNodes(parameterList, this);
     return functionExpression.body.accept(this);
   }
 
-  public R visit(GotoStatement gotoStatement) {
+  @Override public R visit(GotoStatement gotoStatement) {
     return gotoStatement.expression == null ? null
         : gotoStatement.expression.accept(this);
   }
 
-  public R visit(IndexExpression indexExpression) {
+  @Override public R visit(IndexExpression indexExpression) {
     R r0 = indexExpression.array.accept(this);
     return Expressions.acceptNodes(indexExpression.indexExpressions, this);
   }
 
-  public R visit(InvocationExpression invocationExpression) {
+  @Override public R visit(InvocationExpression invocationExpression) {
     return null;
   }
 
-  public R visit(LabelStatement labelStatement) {
+  @Override public R visit(LabelStatement labelStatement) {
     return labelStatement.defaultValue.accept(this);
   }
 
-  public R visit(LambdaExpression lambdaExpression) {
+  @Override public R visit(LambdaExpression lambdaExpression) {
     return null;
   }
 
-  public R visit(ListInitExpression listInitExpression) {
+  @Override public R visit(ListInitExpression listInitExpression) {
     return null;
   }
 
-  public R visit(MemberExpression memberExpression) {
+  @Override public R visit(MemberExpression memberExpression) {
     R r = null;
     if (memberExpression.expression != null) {
       r = memberExpression.expression.accept(this);
@@ -136,11 +136,11 @@ public R visit(MemberExpression memberExpression) {
     return r;
   }
 
-  public R visit(MemberInitExpression memberInitExpression) {
+  @Override public R visit(MemberInitExpression memberInitExpression) {
     return null;
   }
 
-  public R visit(MethodCallExpression methodCallExpression) {
+  @Override public R visit(MethodCallExpression methodCallExpression) {
     R r = null;
     if (methodCallExpression.targetExpression != null) {
       r = methodCallExpression.targetExpression.accept(this);
@@ -148,12 +148,12 @@ public R visit(MethodCallExpression methodCallExpression) {
     return Expressions.acceptNodes(methodCallExpression.expressions, this);
   }
 
-  public R visit(MethodDeclaration methodDeclaration) {
+  @Override public R visit(MethodDeclaration methodDeclaration) {
     R r0 = Expressions.acceptNodes(methodDeclaration.parameters, this);
     return methodDeclaration.body.accept(this);
   }
 
-  public R visit(NewArrayExpression newArrayExpression) {
+  @Override public R visit(NewArrayExpression newArrayExpression) {
     R r = null;
     if (newArrayExpression.bound != null) {
       r = newArrayExpression.bound.accept(this);
@@ -161,30 +161,30 @@ public R visit(NewArrayExpression newArrayExpression) {
     return Expressions.acceptNodes(newArrayExpression.expressions, this);
   }
 
-  public R visit(NewExpression newExpression) {
+  @Override public R visit(NewExpression newExpression) {
     R r0 = Expressions.acceptNodes(newExpression.arguments, this);
     return Expressions.acceptNodes(newExpression.memberDeclarations, this);
   }
 
-  public R visit(ParameterExpression parameterExpression) {
+  @Override public R visit(ParameterExpression parameterExpression) {
     return null;
   }
 
-  public R visit(SwitchStatement switchStatement) {
+  @Override public R visit(SwitchStatement switchStatement) {
     return null;
   }
 
-  public R visit(TernaryExpression ternaryExpression) {
+  @Override public R visit(TernaryExpression ternaryExpression) {
     R r0 = ternaryExpression.expression0.accept(this);
     R r1 = ternaryExpression.expression1.accept(this);
     return ternaryExpression.expression2.accept(this);
   }
 
-  public R visit(ThrowStatement throwStatement) {
+  @Override public R visit(ThrowStatement throwStatement) {
     return throwStatement.expression.accept(this);
   }
 
-  public R visit(TryStatement tryStatement) {
+  @Override public R visit(TryStatement tryStatement) {
     R r = tryStatement.body.accept(this);
     for (CatchBlock catchBlock : tryStatement.catchBlocks) {
       r = catchBlock.parameter.accept(this);
@@ -196,15 +196,15 @@ public R visit(TryStatement tryStatement) {
     return r;
   }
 
-  public R visit(TypeBinaryExpression typeBinaryExpression) {
+  @Override public R visit(TypeBinaryExpression typeBinaryExpression) {
     return typeBinaryExpression.expression.accept(this);
   }
 
-  public R visit(UnaryExpression unaryExpression) {
+  @Override public R visit(UnaryExpression unaryExpression) {
     return unaryExpression.expression.accept(this);
   }
 
-  public R visit(WhileStatement whileStatement) {
+  @Override public R visit(WhileStatement whileStatement) {
     R r0 = whileStatement.condition.accept(this);
     return whileStatement.body.accept(this);
   }
diff --git a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/WhileStatement.java b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/WhileStatement.java
index 76ab8b0f286..aa77d634bd8 100644
--- a/linq4j/src/main/java/org/apache/calcite/linq4j/tree/WhileStatement.java
+++ b/linq4j/src/main/java/org/apache/calcite/linq4j/tree/WhileStatement.java
@@ -40,7 +40,7 @@ public WhileStatement(Expression condition, Statement body) {
     return shuttle.visit(this, condition1, body1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  @Override public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoAggregate.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoAggregate.java
index 9d7fd8fcc24..d95b2638825 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoAggregate.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoAggregate.java
@@ -92,7 +92,7 @@ public MongoAggregate(RelOptCluster cluster, RelTraitSet traitSet,
     }
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
     List<String> list = new ArrayList<>();
     final List<String> inNames =
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoEnumerator.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoEnumerator.java
index b4a3bb27c56..a4d4074630a 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoEnumerator.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoEnumerator.java
@@ -47,11 +47,11 @@ class MongoEnumerator implements Enumerator<Object> {
     this.getter = getter;
   }
 
-  public Object current() {
+  @Override public Object current() {
     return current;
   }
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     try {
       if (cursor.hasNext()) {
         Document map = cursor.next();
@@ -66,11 +66,11 @@ public boolean moveNext() {
     }
   }
 
-  public void reset() {
+  @Override public void reset() {
     throw new UnsupportedOperationException();
   }
 
-  public void close() {
+  @Override public void close() {
     if (cursor instanceof MongoCursor) {
       ((MongoCursor) cursor).close();
     }
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoFilter.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoFilter.java
index 61a35c06f6c..158b44bac84 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoFilter.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoFilter.java
@@ -62,12 +62,12 @@ public MongoFilter(
     return super.computeSelfCost(planner, mq).multiplyBy(0.1);
   }
 
-  public MongoFilter copy(RelTraitSet traitSet, RelNode input,
+  @Override public MongoFilter copy(RelTraitSet traitSet, RelNode input,
       RexNode condition) {
     return new MongoFilter(getCluster(), traitSet, input, condition);
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
     Translator translator =
         new Translator(implementor.rexBuilder,
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoProject.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoProject.java
index b465fd5e7b3..9b0328cf9d3 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoProject.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoProject.java
@@ -64,7 +64,7 @@ public MongoProject(RelOptCluster cluster, RelTraitSet traitSet,
     return super.computeSelfCost(planner, mq).multiplyBy(0.1);
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
 
     final MongoRules.RexToMongoTranslator translator =
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSchemaFactory.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSchemaFactory.java
index c9775363d4e..f5863023493 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSchemaFactory.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSchemaFactory.java
@@ -36,7 +36,7 @@ public class MongoSchemaFactory implements SchemaFactory {
   public MongoSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     final String host = (String) operand.get("host");
     final String database = (String) operand.get("database");
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSort.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSort.java
index 8bd8cce9d57..d48bd93dd3c 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSort.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoSort.java
@@ -56,7 +56,7 @@ public MongoSort(RelOptCluster cluster, RelTraitSet traitSet,
         fetch);
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.visitChild(0, getInput());
     if (!collation.getFieldCollations().isEmpty()) {
       final List<String> keys = new ArrayList<>();
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTable.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTable.java
index c78d537c0ae..e3d46e5c8b4 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTable.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTable.java
@@ -60,11 +60,11 @@ public class MongoTable extends AbstractQueryableTable
     this.collectionName = collectionName;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "MongoTable {" + collectionName + "}";
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     final RelDataType mapType =
         typeFactory.createMapType(
             typeFactory.createSqlType(SqlTypeName.VARCHAR),
@@ -73,12 +73,12 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return typeFactory.builder().add("_MAP", mapType).build();
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new MongoQueryable<>(queryProvider, schema, this, tableName);
   }
 
-  public RelNode toRel(
+  @Override public RelNode toRel(
       RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     final RelOptCluster cluster = context.getCluster();
@@ -107,7 +107,7 @@ private Enumerable<Object> find(MongoDatabase mongoDb, String filterJson,
         projectJson == null ? null : BsonDocument.parse(projectJson);
     final Function1<Document, Object> getter = MongoEnumerator.getter(fields);
     return new AbstractEnumerable<Object>() {
-      public Enumerator<Object> enumerator() {
+      @Override public Enumerator<Object> enumerator() {
         @SuppressWarnings("unchecked") final FindIterable<Document> cursor =
             collection.find(filter).projection(project);
         return new MongoEnumerator(cursor.iterator(), getter);
@@ -138,7 +138,7 @@ private Enumerable<Object> aggregate(final MongoDatabase mongoDb,
     final Function1<Document, Object> getter =
         MongoEnumerator.getter(fields);
     return new AbstractEnumerable<Object>() {
-      public Enumerator<Object> enumerator() {
+      @Override public Enumerator<Object> enumerator() {
         final Iterator<Document> resultIterator;
         try {
           resultIterator = mongoDb.getCollection(collectionName)
@@ -162,7 +162,7 @@ public static class MongoQueryable<T> extends AbstractTableQueryable<T> {
       super(queryProvider, schema, table, tableName);
     }
 
-    public Enumerator<T> enumerator() {
+    @Override public Enumerator<T> enumerator() {
       //noinspection unchecked
       final Enumerable<T> enumerable =
           (Enumerable<T>) getTable().find(getMongoDb(), null, null, null);
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTableScan.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTableScan.java
index 4a6657b82af..3c32629b059 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTableScan.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoTableScan.java
@@ -84,7 +84,7 @@ protected MongoTableScan(RelOptCluster cluster, RelTraitSet traitSet,
     }
   }
 
-  public void implement(Implementor implementor) {
+  @Override public void implement(Implementor implementor) {
     implementor.mongoTable = mongoTable;
     implementor.table = table;
   }
diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoToEnumerableConverter.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoToEnumerableConverter.java
index 5d95e2c9a7b..91db089cdf6 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoToEnumerableConverter.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoToEnumerableConverter.java
@@ -66,7 +66,7 @@ protected MongoToEnumerableConverter(
     return super.computeSelfCost(planner, mq).multiplyBy(.1);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     // Generates a call to "find" or "aggregate", depending upon whether
     // an aggregate is present.
     //
diff --git a/pig/src/main/java/org/apache/calcite/adapter/pig/PigSchemaFactory.java b/pig/src/main/java/org/apache/calcite/adapter/pig/PigSchemaFactory.java
index bf4cea9488a..ad7e0db8d2e 100644
--- a/pig/src/main/java/org/apache/calcite/adapter/pig/PigSchemaFactory.java
+++ b/pig/src/main/java/org/apache/calcite/adapter/pig/PigSchemaFactory.java
@@ -36,7 +36,7 @@ public class PigSchemaFactory implements SchemaFactory {
   private PigSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     return new PigSchema();
   }
diff --git a/pig/src/main/java/org/apache/calcite/adapter/pig/PigTableFactory.java b/pig/src/main/java/org/apache/calcite/adapter/pig/PigTableFactory.java
index c6436d654bc..7604f3a7e9f 100644
--- a/pig/src/main/java/org/apache/calcite/adapter/pig/PigTableFactory.java
+++ b/pig/src/main/java/org/apache/calcite/adapter/pig/PigTableFactory.java
@@ -36,7 +36,7 @@ public PigTableFactory() {
   }
 
   @SuppressWarnings("unchecked")
-  public PigTable create(SchemaPlus schema, String name,
+  @Override public PigTable create(SchemaPlus schema, String name,
       Map<String, Object> operand, RelDataType rowType) {
     String fileName = (String) operand.get("file");
     File file = new File(fileName);
diff --git a/pig/src/main/java/org/apache/calcite/adapter/pig/PigToEnumerableConverter.java b/pig/src/main/java/org/apache/calcite/adapter/pig/PigToEnumerableConverter.java
index 94d325d4be7..4a6fe1b74f0 100644
--- a/pig/src/main/java/org/apache/calcite/adapter/pig/PigToEnumerableConverter.java
+++ b/pig/src/main/java/org/apache/calcite/adapter/pig/PigToEnumerableConverter.java
@@ -65,7 +65,7 @@ protected PigToEnumerableConverter(
    * store results in a predefined file so they can be read here and returned as
    * a {@code Result} object.
    */
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     final BlockBuilder list = new BlockBuilder();
     final PhysType physType =
         PhysTypeImpl.of(implementor.getTypeFactory(), rowType,
diff --git a/piglet/src/main/java/org/apache/calcite/piglet/PigRelSqlUdfs.java b/piglet/src/main/java/org/apache/calcite/piglet/PigRelSqlUdfs.java
index 9ff48cbe80f..c34425c39ca 100644
--- a/piglet/src/main/java/org/apache/calcite/piglet/PigRelSqlUdfs.java
+++ b/piglet/src/main/java/org/apache/calcite/piglet/PigRelSqlUdfs.java
@@ -181,7 +181,7 @@ private static SqlOperandMetadata multisetProjectionCheck() {
     final int paramCount = 2;
 
     return new SqlOperandMetadata() {
-      public boolean checkOperandTypes(
+      @Override public boolean checkOperandTypes(
           SqlCallBinding callBinding, boolean throwOnFailure) {
         // Need at least two arguments
         if (callBinding.getOperandCount() < 2) {
@@ -212,19 +212,19 @@ public boolean checkOperandTypes(
         return true;
       }
 
-      public SqlOperandCountRange getOperandCountRange() {
+      @Override public SqlOperandCountRange getOperandCountRange() {
         return SqlOperandCountRanges.from(2);
       }
 
-      public String getAllowedSignatures(SqlOperator op, String opName) {
+      @Override public String getAllowedSignatures(SqlOperator op, String opName) {
         return opName + "(...)";
       }
 
-      public boolean isOptional(int i) {
+      @Override public boolean isOptional(int i) {
         return false;
       }
 
-      public Consistency getConsistency() {
+      @Override public Consistency getConsistency() {
         return Consistency.NONE;
       }
 
diff --git a/piglet/src/main/java/org/apache/calcite/piglet/PigRelToSqlConverter.java b/piglet/src/main/java/org/apache/calcite/piglet/PigRelToSqlConverter.java
index 65674cc7178..674a54e7ce7 100644
--- a/piglet/src/main/java/org/apache/calcite/piglet/PigRelToSqlConverter.java
+++ b/piglet/src/main/java/org/apache/calcite/piglet/PigRelToSqlConverter.java
@@ -88,7 +88,7 @@ public class PigRelToSqlConverter extends RelToSqlConverter {
 
   // CHECKSTYLE: IGNORE 1
   /** @see #dispatch */
-  public Result visit(Window e) {
+  @Override public Result visit(Window e) {
     final Result x = visitInput(e, 0, Clause.SELECT);
     final Builder builder = x.builder(e);
     final List<SqlNode> selectList =
diff --git a/piglet/src/main/java/org/apache/calcite/piglet/PigTypes.java b/piglet/src/main/java/org/apache/calcite/piglet/PigTypes.java
index 373925f771d..15418cf65ee 100644
--- a/piglet/src/main/java/org/apache/calcite/piglet/PigTypes.java
+++ b/piglet/src/main/java/org/apache/calcite/piglet/PigTypes.java
@@ -72,7 +72,7 @@ public RelDataType createMapType(RelDataType keyType,
       return createTypeWithNullability(super.createMapType(keyType, valueType), nullable);
     }
 
-    public RelDataType toSql(RelDataType type) {
+    @Override public RelDataType toSql(RelDataType type) {
       if (type instanceof JavaType
           && ((JavaType) type).getJavaClass() == DataBag.class) {
         // We don't know the structure of each tuple inside the bag until the runtime.
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/DuTableFunction.java b/plus/src/main/java/org/apache/calcite/adapter/os/DuTableFunction.java
index 98d388f85e3..3a0a72369b4 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/DuTableFunction.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/DuTableFunction.java
@@ -41,7 +41,7 @@ private DuTableFunction() {}
 
   public static ScannableTable eval(boolean b) {
     return new ScannableTable() {
-      public Enumerable<Object[]> scan(DataContext root) {
+      @Override public Enumerable<Object[]> scan(DataContext root) {
         return Processes.processLines("du", "-ak")
             .select(a0 -> {
               final String[] fields = a0.split("\t");
@@ -49,26 +49,26 @@ public Enumerable<Object[]> scan(DataContext root) {
             });
       }
 
-      public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+      @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         return typeFactory.builder()
             .add("size_k", SqlTypeName.BIGINT)
             .add("path", SqlTypeName.VARCHAR)
             .build();
       }
 
-      public Statistic getStatistic() {
+      @Override public Statistic getStatistic() {
         return Statistics.of(1000d, ImmutableList.of(ImmutableBitSet.of(1)));
       }
 
-      public Schema.TableType getJdbcTableType() {
+      @Override public Schema.TableType getJdbcTableType() {
         return Schema.TableType.TABLE;
       }
 
-      public boolean isRolledUp(String column) {
+      @Override public boolean isRolledUp(String column) {
         return false;
       }
 
-      public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+      @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
           SqlNode parent, CalciteConnectionConfig config) {
         return true;
       }
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/FilesTableFunction.java b/plus/src/main/java/org/apache/calcite/adapter/os/FilesTableFunction.java
index 603fabb8d6a..769e20f0984 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/FilesTableFunction.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/FilesTableFunction.java
@@ -56,7 +56,7 @@ private FilesTableFunction() {}
    */
   public static ScannableTable eval(final String path) {
     return new ScannableTable() {
-      public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+      @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         return typeFactory.builder()
             .add("access_time", SqlTypeName.TIMESTAMP) // %A@ sec since epoch
             .add("block_count", SqlTypeName.INTEGER) // %b in 512B blocks
@@ -144,7 +144,7 @@ private Enumerable<String> sourceMacOs() {
         return Processes.processLines('\n', args);
       }
 
-      public Enumerable<Object[]> scan(DataContext root) {
+      @Override public Enumerable<Object[]> scan(DataContext root) {
         final RelDataType rowType = getRowType(root.getTypeFactory());
         final List<String> fieldNames =
             ImmutableList.copyOf(rowType.getFieldNames());
@@ -160,16 +160,16 @@ public Enumerable<Object[]> scan(DataContext root) {
           enumerable = sourceLinux();
         }
         return new AbstractEnumerable<Object[]>() {
-          public Enumerator<Object[]> enumerator() {
+          @Override public Enumerator<Object[]> enumerator() {
             final Enumerator<String> e = enumerable.enumerator();
             return new Enumerator<Object[]>() {
               Object[] current;
 
-              public Object[] current() {
+              @Override public Object[] current() {
                 return current;
               }
 
-              public boolean moveNext() {
+              @Override public boolean moveNext() {
                 current = new Object[fieldNames.size()];
                 for (int i = 0; i < current.length; i++) {
                   if (!e.moveNext()) {
@@ -226,11 +226,11 @@ private int count(String s, char c) {
                 return n;
               }
 
-              public void reset() {
+              @Override public void reset() {
                 throw new UnsupportedOperationException();
               }
 
-              public void close() {
+              @Override public void close() {
                 e.close();
               }
 
@@ -259,19 +259,19 @@ private Object field(String field, String value) {
         };
       }
 
-      public Statistic getStatistic() {
+      @Override public Statistic getStatistic() {
         return Statistics.of(1000d, ImmutableList.of(ImmutableBitSet.of(1)));
       }
 
-      public Schema.TableType getJdbcTableType() {
+      @Override public Schema.TableType getJdbcTableType() {
         return Schema.TableType.TABLE;
       }
 
-      public boolean isRolledUp(String column) {
+      @Override public boolean isRolledUp(String column) {
         return false;
       }
 
-      public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+      @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
           SqlNode parent, CalciteConnectionConfig config) {
         return true;
       }
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/GitCommitsTableFunction.java b/plus/src/main/java/org/apache/calcite/adapter/os/GitCommitsTableFunction.java
index 435df784cb3..e92751f3f2f 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/GitCommitsTableFunction.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/GitCommitsTableFunction.java
@@ -53,24 +53,24 @@ private GitCommitsTableFunction() {}
 
   public static ScannableTable eval(boolean b) {
     return new ScannableTable() {
-      public Enumerable<Object[]> scan(DataContext root) {
+      @Override public Enumerable<Object[]> scan(DataContext root) {
         final Enumerable<String> enumerable =
             Processes.processLines("git", "log", "--pretty=raw");
         return new AbstractEnumerable<Object[]>() {
-          public Enumerator<Object[]> enumerator() {
+          @Override public Enumerator<Object[]> enumerator() {
             final Enumerator<String> e = enumerable.enumerator();
             return new Enumerator<Object[]>() {
               private Object[] objects;
               private final StringBuilder b = new StringBuilder();
 
-              public Object[] current() {
+              @Override public Object[] current() {
                 if (objects == null) {
                   throw new NoSuchElementException();
                 }
                 return objects;
               }
 
-              public boolean moveNext() {
+              @Override public boolean moveNext() {
                 if (!e.moveNext()) {
                   objects = null;
                   return false;
@@ -127,11 +127,11 @@ public boolean moveNext() {
                 }
               }
 
-              public void reset() {
+              @Override public void reset() {
                 throw new UnsupportedOperationException();
               }
 
-              public void close() {
+              @Override public void close() {
                 e.close();
               }
             };
@@ -139,7 +139,7 @@ public void close() {
         };
       }
 
-      public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+      @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         return typeFactory.builder()
             .add("commit", SqlTypeName.CHAR, 40)
             .add("tree", SqlTypeName.CHAR, 40)
@@ -153,19 +153,19 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
             .build();
       }
 
-      public Statistic getStatistic() {
+      @Override public Statistic getStatistic() {
         return Statistics.of(1000d, ImmutableList.of(ImmutableBitSet.of(0)));
       }
 
-      public Schema.TableType getJdbcTableType() {
+      @Override public Schema.TableType getJdbcTableType() {
         return Schema.TableType.TABLE;
       }
 
-      public boolean isRolledUp(String column) {
+      @Override public boolean isRolledUp(String column) {
         return false;
       }
 
-      public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+      @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
           SqlNode parent, CalciteConnectionConfig config) {
         return true;
       }
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/JpsTableFunction.java b/plus/src/main/java/org/apache/calcite/adapter/os/JpsTableFunction.java
index 9bc9cce4e0a..fda75aa7378 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/JpsTableFunction.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/JpsTableFunction.java
@@ -42,7 +42,7 @@ private JpsTableFunction() {
 
   public static ScannableTable eval(boolean b) {
     return new ScannableTable() {
-      public Enumerable<Object[]> scan(DataContext root) {
+      @Override public Enumerable<Object[]> scan(DataContext root) {
         return Processes.processLines("jps", "-mlvV")
             .select(a0 -> {
               final String[] fields = a0.split(" ");
@@ -50,26 +50,26 @@ public Enumerable<Object[]> scan(DataContext root) {
             });
       }
 
-      public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+      @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         return typeFactory.builder()
             .add("pid", SqlTypeName.BIGINT)
             .add("info", SqlTypeName.VARCHAR)
             .build();
       }
 
-      public Statistic getStatistic() {
+      @Override public Statistic getStatistic() {
         return Statistics.of(1000d, ImmutableList.of(ImmutableBitSet.of(1)));
       }
 
-      public Schema.TableType getJdbcTableType() {
+      @Override public Schema.TableType getJdbcTableType() {
         return Schema.TableType.TABLE;
       }
 
-      public boolean isRolledUp(String column) {
+      @Override public boolean isRolledUp(String column) {
         return false;
       }
 
-      public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+      @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
           SqlNode parent, CalciteConnectionConfig config) {
         return true;
       }
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/Processes.java b/plus/src/main/java/org/apache/calcite/adapter/os/Processes.java
index d397166096a..06e4e6447bc 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/Processes.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/Processes.java
@@ -77,7 +77,7 @@ private static class ProcessLinesEnumerator
       this.processSupplier = processSupplier;
     }
 
-    public Enumerator<String> enumerator() {
+    @Override public Enumerator<String> enumerator() {
       final Process process = processSupplier.get();
       final InputStream is = process.getInputStream();
       final BufferedInputStream bis =
@@ -88,11 +88,11 @@ public Enumerator<String> enumerator() {
       return new Enumerator<String>() {
         private String line;
 
-        public String current() {
+        @Override public String current() {
           return line;
         }
 
-        public boolean moveNext() {
+        @Override public boolean moveNext() {
           try {
             line = br.readLine();
             return line != null;
@@ -101,11 +101,11 @@ public boolean moveNext() {
           }
         }
 
-        public void reset() {
+        @Override public void reset() {
           throw new UnsupportedOperationException();
         }
 
-        public void close() {
+        @Override public void close() {
           try {
             br.close();
           } catch (IOException e) {
@@ -128,7 +128,7 @@ private static class SeparatedLinesEnumerable
       this.sep = sep;
     }
 
-    public Enumerator<String> enumerator() {
+    @Override public Enumerator<String> enumerator() {
       final Process process = processSupplier.get();
       final InputStream is = process.getInputStream();
       final BufferedInputStream bis =
@@ -140,11 +140,11 @@ public Enumerator<String> enumerator() {
         private final StringBuilder b = new StringBuilder();
         private String line;
 
-        public String current() {
+        @Override public String current() {
           return line;
         }
 
-        public boolean moveNext() {
+        @Override public boolean moveNext() {
           try {
             for (;;) {
               int c = br.read();
@@ -163,11 +163,11 @@ public boolean moveNext() {
           }
         }
 
-        public void reset() {
+        @Override public void reset() {
           throw new UnsupportedOperationException();
         }
 
-        public void close() {
+        @Override public void close() {
           try {
             br.close();
           } catch (IOException e) {
@@ -187,7 +187,7 @@ private static class ProcessFactory implements Supplier<Process> {
       this.args = args;
     }
 
-    public Process get() {
+    @Override public Process get() {
       try {
         return new ProcessBuilder().command(args).start();
       } catch (IOException e) {
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/PsTableFunction.java b/plus/src/main/java/org/apache/calcite/adapter/os/PsTableFunction.java
index 1085ec1b35c..5962c6b6c94 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/PsTableFunction.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/PsTableFunction.java
@@ -53,7 +53,7 @@ private PsTableFunction() {}
 
   public static ScannableTable eval(boolean b) {
     return new ScannableTable() {
-      public Enumerable<Object[]> scan(DataContext root) {
+      @Override public Enumerable<Object[]> scan(DataContext root) {
         final RelDataType rowType = getRowType(root.getTypeFactory());
         final List<String> fieldNames =
             ImmutableList.copyOf(rowType.getFieldNames());
@@ -77,7 +77,7 @@ public Enumerable<Object[]> scan(DataContext root) {
         return Processes.processLines(args)
             .select(
                 new Function1<String, Object[]>() {
-                  public Object[] apply(String line) {
+                  @Override public Object[] apply(String line) {
                     final String[] fields = line.trim().split(" +");
                     final Object[] values = new Object[fieldNames.size()];
                     for (int i = 0; i < values.length; i++) {
@@ -136,7 +136,7 @@ private Object field(String field, String value) {
                 });
       }
 
-      public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+      @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         return typeFactory.builder()
             .add("pid", SqlTypeName.INTEGER)
             .add("ppid", SqlTypeName.INTEGER)
@@ -158,19 +158,19 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
             .build();
       }
 
-      public Statistic getStatistic() {
+      @Override public Statistic getStatistic() {
         return Statistics.of(1000d, ImmutableList.of(ImmutableBitSet.of(1)));
       }
 
-      public Schema.TableType getJdbcTableType() {
+      @Override public Schema.TableType getJdbcTableType() {
         return Schema.TableType.TABLE;
       }
 
-      public boolean isRolledUp(String column) {
+      @Override public boolean isRolledUp(String column) {
         return false;
       }
 
-      public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+      @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
           SqlNode parent, CalciteConnectionConfig config) {
         return true;
       }
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/SqlShell.java b/plus/src/main/java/org/apache/calcite/adapter/os/SqlShell.java
index 6370c675ce2..1d477bc4435 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/SqlShell.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/SqlShell.java
@@ -192,7 +192,7 @@ private static void addFunction(StringBuilder b, String name, Class c) {
   /** Output format. */
   enum Format {
     SPACED {
-      protected void output(PrintWriter out, ResultSet r) throws SQLException {
+      @Override protected void output(PrintWriter out, ResultSet r) throws SQLException {
         final int n = r.getMetaData().getColumnCount();
         final StringBuilder b = new StringBuilder();
         while (r.next()) {
@@ -208,7 +208,7 @@ protected void output(PrintWriter out, ResultSet r) throws SQLException {
       }
     },
     HEADERS {
-      protected void output(PrintWriter out, ResultSet r) throws SQLException {
+      @Override protected void output(PrintWriter out, ResultSet r) throws SQLException {
         final ResultSetMetaData m = r.getMetaData();
         final int n = m.getColumnCount();
         final StringBuilder b = new StringBuilder();
@@ -224,7 +224,7 @@ protected void output(PrintWriter out, ResultSet r) throws SQLException {
       }
     },
     CSV {
-      protected void output(PrintWriter out, ResultSet r) throws SQLException {
+      @Override protected void output(PrintWriter out, ResultSet r) throws SQLException {
         // We aim to comply with https://tools.ietf.org/html/rfc4180.
         // It's a bug if we don't.
         final ResultSetMetaData m = r.getMetaData();
@@ -268,7 +268,7 @@ private void value(StringBuilder b, String s) {
       }
     },
     JSON {
-      protected void output(PrintWriter out, final ResultSet r)
+      @Override protected void output(PrintWriter out, final ResultSet r)
           throws SQLException {
         final ResultSetMetaData m = r.getMetaData();
         final int n = m.getColumnCount();
@@ -323,7 +323,7 @@ protected void output(PrintWriter out, final ResultSet r)
       }
     },
     MYSQL {
-      protected void output(PrintWriter out, final ResultSet r)
+      @Override protected void output(PrintWriter out, final ResultSet r)
           throws SQLException {
         // E.g.
         // +-------+--------+
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/StdinTableFunction.java b/plus/src/main/java/org/apache/calcite/adapter/os/StdinTableFunction.java
index 7e226e065ea..26e36cd3ca9 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/StdinTableFunction.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/StdinTableFunction.java
@@ -50,25 +50,25 @@ private StdinTableFunction() {}
 
   public static ScannableTable eval(boolean b) {
     return new ScannableTable() {
-      public Enumerable<Object[]> scan(DataContext root) {
+      @Override public Enumerable<Object[]> scan(DataContext root) {
         final InputStream is = DataContext.Variable.STDIN.get(root);
         return new AbstractEnumerable<Object[]>() {
           final InputStreamReader in =
               new InputStreamReader(is, StandardCharsets.UTF_8);
           final BufferedReader br = new BufferedReader(in);
-          public Enumerator<Object[]> enumerator() {
+          @Override public Enumerator<Object[]> enumerator() {
             return new Enumerator<Object[]>() {
               String line;
               int i;
 
-              public Object[] current() {
+              @Override public Object[] current() {
                 if (line == null) {
                   throw new NoSuchElementException();
                 }
                 return new Object[] {i, line};
               }
 
-              public boolean moveNext() {
+              @Override public boolean moveNext() {
                 try {
                   line = br.readLine();
                   ++i;
@@ -78,11 +78,11 @@ public boolean moveNext() {
                 }
               }
 
-              public void reset() {
+              @Override public void reset() {
                 throw new UnsupportedOperationException();
               }
 
-              public void close() {
+              @Override public void close() {
                 try {
                   br.close();
                 } catch (IOException e) {
@@ -94,26 +94,26 @@ public void close() {
         };
       }
 
-      public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+      @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         return typeFactory.builder()
             .add("ordinal", SqlTypeName.INTEGER)
             .add("line", SqlTypeName.VARCHAR)
             .build();
       }
 
-      public Statistic getStatistic() {
+      @Override public Statistic getStatistic() {
         return Statistics.of(1000d, ImmutableList.of(ImmutableBitSet.of(1)));
       }
 
-      public Schema.TableType getJdbcTableType() {
+      @Override public Schema.TableType getJdbcTableType() {
         return Schema.TableType.TABLE;
       }
 
-      public boolean isRolledUp(String column) {
+      @Override public boolean isRolledUp(String column) {
         return false;
       }
 
-      public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+      @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
           SqlNode parent, CalciteConnectionConfig config) {
         return true;
       }
diff --git a/plus/src/main/java/org/apache/calcite/adapter/os/VmstatTableFunction.java b/plus/src/main/java/org/apache/calcite/adapter/os/VmstatTableFunction.java
index e5b64295564..263c6d5474d 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/os/VmstatTableFunction.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/os/VmstatTableFunction.java
@@ -46,7 +46,7 @@ private VmstatTableFunction() {}
 
   public static ScannableTable eval(boolean b) {
     return new ScannableTable() {
-      public Enumerable<Object[]> scan(DataContext root) {
+      @Override public Enumerable<Object[]> scan(DataContext root) {
         final RelDataType rowType = getRowType(root.getTypeFactory());
         final List<String> fieldNames =
             ImmutableList.copyOf(rowType.getFieldNames());
@@ -69,7 +69,7 @@ public Enumerable<Object[]> scan(DataContext root) {
         return Processes.processLines(args)
             .select(
                 new Function1<String, Object[]>() {
-                  public Object[] apply(String line) {
+                  @Override public Object[] apply(String line) {
                     final String[] fields = line.trim().split("\\s+");
                     final Object[] values = new Object[fieldNames.size()];
                     for (int i = 0; i < values.length; i++) {
@@ -97,7 +97,7 @@ private Object field(String field, String value) {
                 });
       }
 
-      public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+      @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         final String osName = System.getProperty("os.name");
         final RelDataTypeFactory.Builder builder = typeFactory.builder();
         switch (osName) {
@@ -149,19 +149,19 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         }
       }
 
-      public Statistic getStatistic() {
+      @Override public Statistic getStatistic() {
         return Statistics.of(1000d, ImmutableList.of(ImmutableBitSet.of(1)));
       }
 
-      public Schema.TableType getJdbcTableType() {
+      @Override public Schema.TableType getJdbcTableType() {
         return Schema.TableType.TABLE;
       }
 
-      public boolean isRolledUp(String column) {
+      @Override public boolean isRolledUp(String column) {
         return false;
       }
 
-      public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
+      @Override public boolean rolledUpColumnValidInsideAgg(String column, SqlCall call,
           SqlNode parent, CalciteConnectionConfig config) {
         return true;
       }
diff --git a/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchema.java b/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchema.java
index 903bd2ae51f..68840bad5ca 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchema.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchema.java
@@ -151,12 +151,12 @@ private class TpcdsQueryableTable<E extends com.teradata.tpcds.Table>
       return Statistics.of(rowCount, ImmutableList.of());
     }
 
-    public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
+    @Override public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
         final SchemaPlus schema, final String tableName) {
       //noinspection unchecked
       return (Queryable) new AbstractTableQueryable<Object[]>(queryProvider,
           schema, this, tableName) {
-        public Enumerator<Object[]> enumerator() {
+        @Override public Enumerator<Object[]> enumerator() {
           final Session session =
               Session.getDefaultSession()
                   .withTable(tpcdsTable)
@@ -167,7 +167,7 @@ public Enumerator<Object[]> enumerator() {
                   new Function1<List<List<String>>, Enumerable<Object[]>>() {
                     final Column[] columns = tpcdsTable.getColumns();
 
-                    public Enumerable<Object[]> apply(
+                    @Override public Enumerable<Object[]> apply(
                         List<List<String>> inRows) {
                       final List<Object[]> rows = new ArrayList<>();
                       for (List<String> strings : inRows) {
@@ -186,7 +186,7 @@ public Enumerable<Object[]> apply(
       };
     }
 
-    public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+    @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
       final RelDataTypeFactory.Builder builder = typeFactory.builder();
       for (Column column : tpcdsTable.getColumns()) {
         builder.add(column.getName().toUpperCase(Locale.ROOT),
diff --git a/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchemaFactory.java b/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchemaFactory.java
index c29f9fe8721..07e8aab1106 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchemaFactory.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/tpcds/TpcdsSchemaFactory.java
@@ -34,7 +34,7 @@ public class TpcdsSchemaFactory implements SchemaFactory {
   public TpcdsSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     @SuppressWarnings("RawTypeCanBeGeneric") final Map map = operand;
     double scale = Util.first((Double) map.get("scale"), 1D);
diff --git a/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchema.java b/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchema.java
index 9b01a917f66..5812225b86f 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchema.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchema.java
@@ -91,17 +91,17 @@ private class TpchQueryableTable<E extends TpchEntity>
       this.tpchTable = tpchTable;
     }
 
-    public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
+    @Override public <T> Queryable<T> asQueryable(final QueryProvider queryProvider,
         final SchemaPlus schema, final String tableName) {
       //noinspection unchecked
       return (Queryable) new AbstractTableQueryable<Object[]>(queryProvider,
           schema, this, tableName) {
-        public Enumerator<Object[]> enumerator() {
+        @Override public Enumerator<Object[]> enumerator() {
           final Enumerator<E> iterator =
               Linq4j.iterableEnumerator(
                   tpchTable.createGenerator(scaleFactor, part, partCount));
           return new Enumerator<Object[]>() {
-            public Object[] current() {
+            @Override public Object[] current() {
               final List<TpchColumn<E>> columns = tpchTable.getColumns();
               final Object[] objects = new Object[columns.size()];
               int i = 0;
@@ -128,22 +128,22 @@ private Object value(TpchColumn<E> tpchColumn, E current) {
               }
             }
 
-            public boolean moveNext() {
+            @Override public boolean moveNext() {
               return iterator.moveNext();
             }
 
-            public void reset() {
+            @Override public void reset() {
               iterator.reset();
             }
 
-            public void close() {
+            @Override public void close() {
             }
           };
         }
       };
     }
 
-    public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+    @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
       final RelDataTypeFactory.Builder builder = typeFactory.builder();
       String prefix = "";
       if (columnPrefix) {
diff --git a/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchemaFactory.java b/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchemaFactory.java
index 710f0f09dc4..ab73c85d7bf 100644
--- a/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchemaFactory.java
+++ b/plus/src/main/java/org/apache/calcite/adapter/tpch/TpchSchemaFactory.java
@@ -34,7 +34,7 @@ public class TpchSchemaFactory implements SchemaFactory {
   public TpchSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus parentSchema, String name,
+  @Override public Schema create(SchemaPlus parentSchema, String name,
       Map<String, Object> operand) {
     Map map = (Map) operand;
     double scale = Util.first((Double) map.get("scale"), 1D);
diff --git a/plus/src/main/java/org/apache/calcite/chinook/ConnectionFactory.java b/plus/src/main/java/org/apache/calcite/chinook/ConnectionFactory.java
index 582a5a15dad..18b0df5f0a1 100644
--- a/plus/src/main/java/org/apache/calcite/chinook/ConnectionFactory.java
+++ b/plus/src/main/java/org/apache/calcite/chinook/ConnectionFactory.java
@@ -29,7 +29,7 @@ public class ConnectionFactory implements Quidem.ConnectionFactory {
 
   private static final CalciteConnectionProvider CALCITE = new CalciteConnectionProvider();
 
-  public Connection connect(String db, boolean bln) throws Exception {
+  @Override public Connection connect(String db, boolean bln) throws Exception {
     return DatabaseWrapper.valueOf(db).connection();
   }
 
diff --git a/redis/src/main/java/org/apache/calcite/adapter/redis/RedisEnumerator.java b/redis/src/main/java/org/apache/calcite/adapter/redis/RedisEnumerator.java
index a964677ddf6..5edb5d063e2 100644
--- a/redis/src/main/java/org/apache/calcite/adapter/redis/RedisEnumerator.java
+++ b/redis/src/main/java/org/apache/calcite/adapter/redis/RedisEnumerator.java
@@ -64,19 +64,19 @@ static Map<String, Object> deduceRowType(RedisTableFieldInfo tableFieldInfo) {
     return fieldBuilder;
   }
 
-  public Object[] current() {
+  @Override public Object[] current() {
     return enumerator.current();
   }
 
-  public boolean moveNext() {
+  @Override public boolean moveNext() {
     return enumerator.moveNext();
   }
 
-  public void reset() {
+  @Override public void reset() {
     enumerator.reset();
   }
 
-  public void close() {
+  @Override public void close() {
     enumerator.close();
   }
 }
diff --git a/redis/src/main/java/org/apache/calcite/adapter/redis/RedisSchemaFactory.java b/redis/src/main/java/org/apache/calcite/adapter/redis/RedisSchemaFactory.java
index 6ad14b26c4a..bfc36ec2bb5 100644
--- a/redis/src/main/java/org/apache/calcite/adapter/redis/RedisSchemaFactory.java
+++ b/redis/src/main/java/org/apache/calcite/adapter/redis/RedisSchemaFactory.java
@@ -37,7 +37,7 @@ public class RedisSchemaFactory implements SchemaFactory {
   public RedisSchemaFactory() {
   }
 
-  public Schema create(SchemaPlus schema, String name,
+  @Override public Schema create(SchemaPlus schema, String name,
       Map<String, Object> operand) {
     Preconditions.checkArgument(operand.get("tables") != null,
         "tables must be specified");
diff --git a/redis/src/main/java/org/apache/calcite/adapter/redis/RedisTable.java b/redis/src/main/java/org/apache/calcite/adapter/redis/RedisTable.java
index 2a56c424f11..f6ddbdf9f40 100644
--- a/redis/src/main/java/org/apache/calcite/adapter/redis/RedisTable.java
+++ b/redis/src/main/java/org/apache/calcite/adapter/redis/RedisTable.java
@@ -64,7 +64,7 @@ public RedisTable(
     this.redisConfig = redisConfig;
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     if (protoRowType != null) {
       return protoRowType.apply(typeFactory);
     }
@@ -102,7 +102,7 @@ static Table create(
 
   @Override public Enumerable<Object[]> scan(DataContext root) {
     return new AbstractEnumerable<Object[]>() {
-      public Enumerator<Object[]> enumerator() {
+      @Override public Enumerator<Object[]> enumerator() {
         return new RedisEnumerator(redisConfig, schema, tableName);
       }
     };
diff --git a/server/src/main/java/org/apache/calcite/server/MutableArrayTable.java b/server/src/main/java/org/apache/calcite/server/MutableArrayTable.java
index f450edc2bbd..9f7d52522fd 100644
--- a/server/src/main/java/org/apache/calcite/server/MutableArrayTable.java
+++ b/server/src/main/java/org/apache/calcite/server/MutableArrayTable.java
@@ -62,32 +62,32 @@ class MutableArrayTable extends AbstractModifiableTable
         Objects.requireNonNull(initializerExpressionFactory);
   }
 
-  public Collection getModifiableCollection() {
+  @Override public Collection getModifiableCollection() {
     return rows;
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new AbstractTableQueryable<T>(queryProvider, schema, this,
         tableName) {
-      public Enumerator<T> enumerator() {
+      @Override public Enumerator<T> enumerator() {
         //noinspection unchecked
         return (Enumerator<T>) Linq4j.enumerator(rows);
       }
     };
   }
 
-  public Type getElementType() {
+  @Override public Type getElementType() {
     return Object[].class;
   }
 
-  public Expression getExpression(SchemaPlus schema, String tableName,
+  @Override public Expression getExpression(SchemaPlus schema, String tableName,
       Class clazz) {
     return Schemas.tableExpression(schema, getElementType(),
         tableName, clazz);
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     return protoRowType.apply(typeFactory);
   }
 
diff --git a/spark/src/main/java/org/apache/calcite/adapter/spark/EnumerableToSparkConverter.java b/spark/src/main/java/org/apache/calcite/adapter/spark/EnumerableToSparkConverter.java
index f3c0c3021b7..076585b3a8d 100644
--- a/spark/src/main/java/org/apache/calcite/adapter/spark/EnumerableToSparkConverter.java
+++ b/spark/src/main/java/org/apache/calcite/adapter/spark/EnumerableToSparkConverter.java
@@ -61,7 +61,7 @@ protected EnumerableToSparkConverter(RelOptCluster cluster,
     return super.computeSelfCost(planner, mq).multiplyBy(.01);
   }
 
-  public Result implementSpark(Implementor implementor) {
+  @Override public Result implementSpark(Implementor implementor) {
     // Generate:
     //   Enumerable source = ...;
     //   return SparkRuntime.createRdd(sparkContext, source);
diff --git a/spark/src/main/java/org/apache/calcite/adapter/spark/HttpServer.java b/spark/src/main/java/org/apache/calcite/adapter/spark/HttpServer.java
index b646005e351..a7ceb422faf 100644
--- a/spark/src/main/java/org/apache/calcite/adapter/spark/HttpServer.java
+++ b/spark/src/main/java/org/apache/calcite/adapter/spark/HttpServer.java
@@ -165,15 +165,15 @@ private static String findLocalIpAddress() throws IOException {
 
   private static <E> Iterable<E> iterable(final Enumeration<E> enumeration) {
     return () -> new Iterator<E>() {
-      public boolean hasNext() {
+      @Override public boolean hasNext() {
         return enumeration.hasMoreElements();
       }
 
-      public E next() {
+      @Override public E next() {
         return enumeration.nextElement();
       }
 
-      public void remove() {
+      @Override public void remove() {
         throw new UnsupportedOperationException();
       }
     };
diff --git a/spark/src/main/java/org/apache/calcite/adapter/spark/JdbcToSparkConverter.java b/spark/src/main/java/org/apache/calcite/adapter/spark/JdbcToSparkConverter.java
index 5090f68ad3c..73d0e2b89fb 100644
--- a/spark/src/main/java/org/apache/calcite/adapter/spark/JdbcToSparkConverter.java
+++ b/spark/src/main/java/org/apache/calcite/adapter/spark/JdbcToSparkConverter.java
@@ -65,7 +65,7 @@ protected JdbcToSparkConverter(RelOptCluster cluster, RelTraitSet traits,
     return super.computeSelfCost(planner, mq).multiplyBy(.1);
   }
 
-  public SparkRel.Result implementSpark(SparkRel.Implementor implementor) {
+  @Override public SparkRel.Result implementSpark(SparkRel.Implementor implementor) {
     // Generate:
     //   ResultSetEnumerable.of(schema.getDataSource(), "select ...")
     final BlockBuilder list = new BlockBuilder();
diff --git a/spark/src/main/java/org/apache/calcite/adapter/spark/SparkHandlerImpl.java b/spark/src/main/java/org/apache/calcite/adapter/spark/SparkHandlerImpl.java
index 2a6992410fb..975bf775348 100644
--- a/spark/src/main/java/org/apache/calcite/adapter/spark/SparkHandlerImpl.java
+++ b/spark/src/main/java/org/apache/calcite/adapter/spark/SparkHandlerImpl.java
@@ -83,7 +83,7 @@ public static CalcitePrepare.SparkHandler instance() {
     return Holder.INSTANCE;
   }
 
-  public RelNode flattenTypes(RelOptPlanner planner, RelNode rootRel,
+  @Override public RelNode flattenTypes(RelOptPlanner planner, RelNode rootRel,
       boolean restructure) {
     RelNode root2 =
         planner.changeTraits(rootRel,
@@ -91,22 +91,22 @@ public RelNode flattenTypes(RelOptPlanner planner, RelNode rootRel,
     return planner.changeTraits(root2, rootRel.getTraitSet().simplify());
   }
 
-  public void registerRules(RuleSetBuilder builder) {
+  @Override public void registerRules(RuleSetBuilder builder) {
     for (RelOptRule rule : SparkRules.rules()) {
       builder.addRule(rule);
     }
     builder.removeRule(EnumerableRules.ENUMERABLE_VALUES_RULE);
   }
 
-  public Object sparkContext() {
+  @Override public Object sparkContext() {
     return sparkContext;
   }
 
-  public boolean enabled() {
+  @Override public boolean enabled() {
     return true;
   }
 
-  public ArrayBindable compile(ClassDeclaration expr, String s) {
+  @Override public ArrayBindable compile(ClassDeclaration expr, String s) {
     final String className = "CalciteProgram" + classId.getAndIncrement();
     final String classFileName = className + ".java";
     String source = "public class " + className + "\n"
diff --git a/spark/src/main/java/org/apache/calcite/adapter/spark/SparkRules.java b/spark/src/main/java/org/apache/calcite/adapter/spark/SparkRules.java
index fc5274e6bba..6cac1c0c0a2 100644
--- a/spark/src/main/java/org/apache/calcite/adapter/spark/SparkRules.java
+++ b/spark/src/main/java/org/apache/calcite/adapter/spark/SparkRules.java
@@ -195,7 +195,7 @@ public static class SparkValues extends Values implements SparkRel {
           getCluster(), rowType, tuples, traitSet);
     }
 
-    public Result implementSpark(Implementor implementor) {
+    @Override public Result implementSpark(Implementor implementor) {
 /*
             return Linq4j.asSpark(
                 new Object[][] {
@@ -315,7 +315,7 @@ public SparkCalc(RelOptCluster cluster, RelTraitSet traitSet, RelNode input,
       return planner.getCostFactory().makeCost(dRows, dCpu, dIo);
     }
 
-    public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
+    @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
       return new SparkCalc(
           getCluster(),
           traitSet,
@@ -328,7 +328,7 @@ public int getFlags() {
       return 1;
     }
 
-    public Result implementSpark(Implementor implementor) {
+    @Override public Result implementSpark(Implementor implementor) {
       final JavaTypeFactory typeFactory = implementor.getTypeFactory();
       final BlockBuilder builder = new BlockBuilder();
       final SparkRel child = (SparkRel) getInput();
diff --git a/spark/src/main/java/org/apache/calcite/adapter/spark/SparkToEnumerableConverter.java b/spark/src/main/java/org/apache/calcite/adapter/spark/SparkToEnumerableConverter.java
index 4883bcaf539..57345f9affa 100644
--- a/spark/src/main/java/org/apache/calcite/adapter/spark/SparkToEnumerableConverter.java
+++ b/spark/src/main/java/org/apache/calcite/adapter/spark/SparkToEnumerableConverter.java
@@ -66,7 +66,7 @@ protected SparkToEnumerableConverter(RelOptCluster cluster,
     return super.computeSelfCost(planner, mq).multiplyBy(.01);
   }
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     // Generate:
     //   RDD rdd = ...;
     //   return SparkRuntime.asEnumerable(rdd);
@@ -101,23 +101,23 @@ private static class SparkImplementorImpl extends SparkRel.Implementor {
       this.implementor = implementor;
     }
 
-    public SparkRel.Result result(PhysType physType,
+    @Override public SparkRel.Result result(PhysType physType,
         BlockStatement blockStatement) {
       return new SparkRel.Result(physType, blockStatement);
     }
 
-    SparkRel.Result visitInput(SparkRel parent, int ordinal, SparkRel input) {
+    @Override SparkRel.Result visitInput(SparkRel parent, int ordinal, SparkRel input) {
       if (parent != null) {
         assert input == parent.getInputs().get(ordinal);
       }
       return input.implementSpark(this);
     }
 
-    public JavaTypeFactory getTypeFactory() {
+    @Override public JavaTypeFactory getTypeFactory() {
       return implementor.getTypeFactory();
     }
 
-    public SqlConformance getConformance() {
+    @Override public SqlConformance getConformance() {
       return implementor.getConformance();
     }
   }
diff --git a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkDriver.java b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkDriver.java
index 874713c3ec0..77f76d27ad6 100644
--- a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkDriver.java
+++ b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkDriver.java
@@ -45,11 +45,11 @@ protected SplunkDriver() {
     new SplunkDriver().register();
   }
 
-  protected String getConnectStringPrefix() {
+  @Override protected String getConnectStringPrefix() {
     return "jdbc:splunk:";
   }
 
-  protected DriverVersion createDriverVersion() {
+  @Override protected DriverVersion createDriverVersion() {
     return new SplunkDriverVersion();
   }
 
@@ -91,12 +91,12 @@ protected DriverVersion createDriverVersion() {
 
   /** Connection that looks up responses from a static map. */
   private static class MockSplunkConnection implements SplunkConnection {
-    public Enumerator<Object> getSearchResultEnumerator(String search,
+    @Override public Enumerator<Object> getSearchResultEnumerator(String search,
         Map<String, String> otherArgs, List<String> fieldList) {
       throw null;
     }
 
-    public void getSearchResults(String search, Map<String, String> otherArgs,
+    @Override public void getSearchResults(String search, Map<String, String> otherArgs,
         List<String> fieldList, SearchResultListener srl) {
       throw new UnsupportedOperationException();
     }
@@ -110,14 +110,14 @@ private static class WrappingSplunkConnection implements SplunkConnection {
       this.connection = connection;
     }
 
-    public void getSearchResults(String search, Map<String, String> otherArgs,
+    @Override public void getSearchResults(String search, Map<String, String> otherArgs,
         List<String> fieldList, SearchResultListener srl) {
       System.out.println("search='" + search
           + "', otherArgs=" + otherArgs
           + ", fieldList='" + fieldList);
     }
 
-    public Enumerator<Object> getSearchResultEnumerator(String search,
+    @Override public Enumerator<Object> getSearchResultEnumerator(String search,
         Map<String, String> otherArgs, List<String> fieldList) {
       throw new UnsupportedOperationException();
     }
diff --git a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkQuery.java b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkQuery.java
index 445aece6b5f..4603f5b9002 100644
--- a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkQuery.java
+++ b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkQuery.java
@@ -53,11 +53,11 @@ public SplunkQuery(
     assert search != null;
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "SplunkQuery {" + search + "}";
   }
 
-  public Enumerator<T> enumerator() {
+  @Override public Enumerator<T> enumerator() {
     //noinspection unchecked
     return (Enumerator<T>) splunkConnection.getSearchResultEnumerator(
         search, getArgs(), fieldList);
diff --git a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTable.java b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTable.java
index 79e277d6de9..a3a82612d04 100644
--- a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTable.java
+++ b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTable.java
@@ -41,11 +41,11 @@ private SplunkTable() {
     super(Object[].class);
   }
 
-  public String toString() {
+  @Override public String toString() {
     return "SplunkTable";
   }
 
-  public RelDataType getRowType(RelDataTypeFactory typeFactory) {
+  @Override public RelDataType getRowType(RelDataTypeFactory typeFactory) {
     RelDataType stringType =
         ((JavaTypeFactory) typeFactory).createType(String.class);
     return typeFactory.builder()
@@ -55,12 +55,12 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
         .build();
   }
 
-  public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
+  @Override public <T> Queryable<T> asQueryable(QueryProvider queryProvider,
       SchemaPlus schema, String tableName) {
     return new SplunkTableQueryable<>(queryProvider, schema, this, tableName);
   }
 
-  public RelNode toRel(
+  @Override public RelNode toRel(
       RelOptTable.ToRelContext context,
       RelOptTable relOptTable) {
     return new SplunkTableScan(
@@ -85,7 +85,7 @@ public static class SplunkTableQueryable<T>
       super(queryProvider, schema, table, tableName);
     }
 
-    public Enumerator<T> enumerator() {
+    @Override public Enumerator<T> enumerator() {
       final SplunkQuery<T> query = createQuery("search", null, null, null);
       return query.enumerator();
     }
diff --git a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTableScan.java b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTableScan.java
index 031c1ad43c5..8a4012a07f5 100644
--- a/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTableScan.java
+++ b/splunk/src/main/java/org/apache/calcite/adapter/splunk/SplunkTableScan.java
@@ -120,7 +120,7 @@ protected SplunkTableScan(
           String.class,
           List.class);
 
-  public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
     Map map = ImmutableMap.builder()
         .put("search", search)
         .put("earliest", Util.first(earliest, ""))
diff --git a/splunk/src/main/java/org/apache/calcite/adapter/splunk/search/SplunkConnectionImpl.java b/splunk/src/main/java/org/apache/calcite/adapter/splunk/search/SplunkConnectionImpl.java
index 916eb70fe10..af6a951b265 100644
--- a/splunk/src/main/java/org/apache/calcite/adapter/splunk/search/SplunkConnectionImpl.java
+++ b/splunk/src/main/java/org/apache/calcite/adapter/splunk/search/SplunkConnectionImpl.java
@@ -122,14 +122,14 @@ private void connect() {
     }
   }
 
-  public void getSearchResults(String search, Map<String, String> otherArgs,
+  @Override public void getSearchResults(String search, Map<String, String> otherArgs,
       List<String> fieldList, SearchResultListener srl) {
     assert srl != null;
     Enumerator<Object> x = getSearchResults_(search, otherArgs, fieldList, srl);
     assert x == null;
   }
 
-  public Enumerator<Object> getSearchResultEnumerator(String search,
+  @Override public Enumerator<Object> getSearchResultEnumerator(String search,
       Map<String, String> otherArgs, List<String> fieldList) {
     return getSearchResults_(search, otherArgs, fieldList, null);
   }
@@ -302,11 +302,11 @@ public CountingSearchResultListener(boolean print) {
       this.print = print;
     }
 
-    public void setFieldNames(String[] fieldNames) {
+    @Override public void setFieldNames(String[] fieldNames) {
       this.fieldNames = fieldNames;
     }
 
-    public boolean processSearchResult(String[] values) {
+    @Override public boolean processSearchResult(String[] values) {
       resultCount++;
       if (print) {
         for (int i = 0; i < this.fieldNames.length; ++i) {
@@ -383,11 +383,11 @@ public SplunkResultEnumerator(InputStream in, List<String> wantedFields) {
       }
     }
 
-    public Object current() {
+    @Override public Object current() {
       return current;
     }
 
-    public boolean moveNext() {
+    @Override public boolean moveNext() {
       try {
         String[] line;
         while ((line = csvReader.readNext()) != null) {
@@ -425,11 +425,11 @@ public boolean moveNext() {
       return false;
     }
 
-    public void reset() {
+    @Override public void reset() {
       throw new UnsupportedOperationException();
     }
 
-    public void close() {
+    @Override public void close() {
       try {
         csvReader.close();
       } catch (IOException e) {
diff --git a/ubenchmark/src/jmh/java/org/apache/calcite/benchmarks/StatementTest.java b/ubenchmark/src/jmh/java/org/apache/calcite/benchmarks/StatementTest.java
index ad794cbc514..0c9bbc50361 100644
--- a/ubenchmark/src/jmh/java/org/apache/calcite/benchmarks/StatementTest.java
+++ b/ubenchmark/src/jmh/java/org/apache/calcite/benchmarks/StatementTest.java
@@ -241,7 +241,7 @@ public Employee(int empid, int deptno, String name, float salary,
       this.commission = commission;
     }
 
-    public String toString() {
+    @Override public String toString() {
       return "Employee [empid: " + empid + ", deptno: " + deptno
           + ", name: " + name + "]";
     }
@@ -261,7 +261,7 @@ public Department(
     }
 
 
-    public String toString() {
+    @Override public String toString() {
       return "Department [deptno: " + deptno + ", name: " + name
           + ", employees: " + employees + "]";
     }