Simplify collection type adapters slightly. (#2791)

* Simplify collection type adapters slightly.

By moving some computations to the factory, we can pass fewer parameters
to the constructor.

* Fix formatting.

Author: eamonnmcmanus

gson/src/main/java/com/google/gson/internal/bind/CollectionTypeAdapterFactory.java

@@ -49,10 +49,12 @@ public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
 
     Type elementType = $Gson$Types.getCollectionElementType(type, rawType);
     TypeAdapter<?> elementTypeAdapter = gson.getAdapter(TypeToken.get(elementType));
+    TypeAdapter<?> wrappedTypeAdapter =
+        new TypeAdapterRuntimeTypeWrapper<>(gson, elementTypeAdapter, elementType);
     ObjectConstructor<T> constructor = constructorConstructor.get(typeToken);
 
     @SuppressWarnings({"unchecked", "rawtypes"}) // create() doesn't define a type parameter
-    TypeAdapter<T> result = new Adapter(gson, elementType, elementTypeAdapter, constructor);
+    TypeAdapter<T> result = new Adapter(wrappedTypeAdapter, constructor);
     return result;
   }
 
@@ -61,12 +63,8 @@ private static final class Adapter<E> extends TypeAdapter<Collection<E>> {
     private final ObjectConstructor<? extends Collection<E>> constructor;
 
     public Adapter(
-        Gson context,
-        Type elementType,
-        TypeAdapter<E> elementTypeAdapter,
-        ObjectConstructor<? extends Collection<E>> constructor) {
-      this.elementTypeAdapter =
-          new TypeAdapterRuntimeTypeWrapper<>(context, elementTypeAdapter, elementType);
+        TypeAdapter<E> elementTypeAdapter, ObjectConstructor<? extends Collection<E>> constructor) {
+      this.elementTypeAdapter = elementTypeAdapter;
       this.constructor = constructor;
     }
 

gson/src/main/java/com/google/gson/internal/bind/MapTypeAdapterFactory.java

@@ -132,15 +132,19 @@ public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
     }
 
     Type[] keyAndValueTypes = $Gson$Types.getMapKeyAndValueTypes(type, rawType);
-    TypeAdapter<?> keyAdapter = getKeyAdapter(gson, keyAndValueTypes[0]);
-    TypeAdapter<?> valueAdapter = gson.getAdapter(TypeToken.get(keyAndValueTypes[1]));
+    Type keyType = keyAndValueTypes[0];
+    Type valueType = keyAndValueTypes[1];
+    TypeAdapter<?> keyAdapter = getKeyAdapter(gson, keyType);
+    TypeAdapter<?> wrappedKeyAdapter =
+        new TypeAdapterRuntimeTypeWrapper<>(gson, keyAdapter, keyType);
+    TypeAdapter<?> valueAdapter = gson.getAdapter(TypeToken.get(valueType));
+    TypeAdapter<?> wrappedValueAdapter =
+        new TypeAdapterRuntimeTypeWrapper<>(gson, valueAdapter, valueType);
     ObjectConstructor<T> constructor = constructorConstructor.get(typeToken);
 
     @SuppressWarnings({"unchecked", "rawtypes"})
     // we don't define a type parameter for the key or value types
-    TypeAdapter<T> result =
-        new Adapter(
-            gson, keyAndValueTypes[0], keyAdapter, keyAndValueTypes[1], valueAdapter, constructor);
+    TypeAdapter<T> result = new Adapter(wrappedKeyAdapter, wrappedValueAdapter, constructor);
     return result;
   }
 
@@ -157,15 +161,11 @@ private final class Adapter<K, V> extends TypeAdapter<Map<K, V>> {
     private final ObjectConstructor<? extends Map<K, V>> constructor;
 
     public Adapter(
-        Gson context,
-        Type keyType,
         TypeAdapter<K> keyTypeAdapter,
-        Type valueType,
         TypeAdapter<V> valueTypeAdapter,
         ObjectConstructor<? extends Map<K, V>> constructor) {
-      this.keyTypeAdapter = new TypeAdapterRuntimeTypeWrapper<>(context, keyTypeAdapter, keyType);
-      this.valueTypeAdapter =
-          new TypeAdapterRuntimeTypeWrapper<>(context, valueTypeAdapter, valueType);
+      this.keyTypeAdapter = keyTypeAdapter;
+      this.valueTypeAdapter = valueTypeAdapter;
       this.constructor = constructor;
     }