Containers in Depth: Exercise 35

ContainersInDepth/MapPerformance.java

@@ -0,0 +1,67 @@
+import java.util.Iterator;
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Map;
+import java.util.HashMap;
+import java.util.TreeMap;
+import java.util.LinkedHashMap;
+import java.util.IdentityHashMap;
+import java.util.WeakHashMap;
+import java.util.Hashtable;
+
+public class MapPerformance {
+    static List<Test<Map<Integer, Integer>>> tests = new ArrayList<>();
+
+    static {
+        tests.add(new Test<Map<Integer, Integer>>("put") {
+            int test(Map<Integer, Integer> map, TestParam testParam) {
+                int loops = testParam.loops;
+                int size = testParam.size;
+                for (int i = 0; i < loops; ++i) {
+                    map.clear();
+                    for (int j = 0; j < size; ++j) {
+                        map.put(j, j);
+                    }
+                }
+                return loops * size;
+            }
+        });
+        tests.add(new Test<Map<Integer, Integer>>("get") {
+            int test(Map<Integer, Integer> map, TestParam testParam) {
+                int loops = testParam.loops;
+                int size = testParam.size * 2;
+                for (int i = 0; i < loops; ++i) {
+                    for (int j = 0; j < size; ++j) {
+                        map.get(j);
+                    }
+                }
+                return loops * size;
+            }
+        });
+        tests.add(new Test<Map<Integer, Integer>>("iterate") {
+            int test(Map<Integer, Integer> map, TestParam testParam) {
+                int loops = testParam.loops * 10;
+                for (int i = 0; i < loops; ++i) {
+                    Iterator iterator = map.entrySet().iterator();
+                    while (iterator.hasNext()) {
+                        iterator.next();
+                    }
+                }
+                return loops * map.size();
+            }
+        });
+    }
+
+    public static void main(String[] args) {
+        if (args.length > 0) {
+            Tester.defaultTestParams = TestParam.array(args);
+        }
+        Tester.run(new HashMap<Integer, Integer>(), tests);
+        Tester.run(new TreeMap<Integer, Integer>(), tests);
+        Tester.run(new LinkedHashMap<Integer, Integer>(), tests);
+        Tester.run(new IdentityHashMap<Integer, Integer>(), tests);
+        Tester.run(new WeakHashMap<Integer, Integer>(), tests);
+        Tester.run(new Hashtable<Integer, Integer>(), tests);
+        Tester.run(new SlowMap<Integer, Integer>(), tests);
+    }
+}

ContainersInDepth/README.md

@@ -241,3 +241,7 @@ because an `ArrayList` must create space and copy all its references forward dur
 2. `TreeSet` is used for sorted set.
 
 3. `LinkedHashSet` is for maintaining inserted order.
+
+## Chossing between Maps
+When you are using a `Map`, your first choice should be `HashMap`, 
+and only if you need a constantly sorted `Map` will you need `TreeMap`.