# HG changeset patch
# User mduigou
# Date 1364341756 25200
# Node ID 4a022fae261dbc4d4cf9e371386de82b57d70e54
# Parent  38c1d0c2d6a6083eef8dfcd973f93c4e85b27184
7143928: Optimize empty HashMap and ArrayList
Reviewed-by: mduigou
Contributed-by: Sergey Linetskiy <sergey.linetskiy@oracle.com>, John Rose <john.rose@oracle.com>, Mike Duigou <mike.duigou@oracle.com>

diff --git a/src/share/classes/java/util/ArrayList.java b/src/share/classes/java/util/ArrayList.java
--- a/src/share/classes/java/util/ArrayList.java
+++ b/src/share/classes/java/util/ArrayList.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -104,6 +104,8 @@
 {
     private static final long serialVersionUID = 8683452581122892189L;
 
+    private static final Object EMPTY_ELEMENTDATA[] = new Object[0];
+
     /**
      * The array buffer into which the elements of the ArrayList are stored.
      * The capacity of the ArrayList is the length of this array buffer.
@@ -111,6 +113,11 @@
     private transient Object[] elementData;
 
     /**
+     * initial capacity.
+     */
+    private transient int initialCapacity;
+
+    /**
      * The size of the ArrayList (the number of elements it contains).
      *
      * @serial
@@ -129,7 +136,8 @@
         if (initialCapacity < 0)
             throw new IllegalArgumentException("Illegal Capacity: "+
                                                initialCapacity);
-        this.elementData = new Object[initialCapacity];
+        this.initialCapacity = initialCapacity;
+        elementData = EMPTY_ELEMENTDATA;
     }
 
     /**
@@ -162,8 +170,7 @@
      */
     public void trimToSize() {
         modCount++;
-        int oldCapacity = elementData.length;
-        if (size < oldCapacity) {
+        if (size < elementData.length) {
             elementData = Arrays.copyOf(elementData, size);
         }
     }
@@ -176,12 +183,21 @@
      * @param   minCapacity   the desired minimum capacity
      */
     public void ensureCapacity(int minCapacity) {
-        if (minCapacity > 0)
+        if(elementData != EMPTY_ELEMENTDATA) {
+            if (minCapacity > 0)
             ensureCapacityInternal(minCapacity);
+        } else {
+            // adjust eventual capacity if requested capacity is larger.
+            initialCapacity = Math.max(initialCapacity, minCapacity);
+        }
     }
 
     private void ensureCapacityInternal(int minCapacity) {
         modCount++;
+        if(elementData == EMPTY_ELEMENTDATA) {
+            minCapacity = Math.max(initialCapacity, minCapacity);
+        }
+
         // overflow-conscious code
         if (minCapacity - elementData.length > 0)
             grow(minCapacity);
@@ -702,7 +718,7 @@
         s.defaultWriteObject();
 
         // Write out array length
-        s.writeInt(elementData.length);
+        s.writeInt((elementData == EMPTY_ELEMENTDATA) ? initialCapacity : elementData.length);
 
         // Write out all elements in the proper order.
         for (int i=0; i<size; i++)
@@ -711,7 +727,6 @@
         if (modCount != expectedModCount) {
             throw new ConcurrentModificationException();
         }
-
     }
 
     /**
@@ -723,11 +738,15 @@
         // Read in size, and any hidden stuff
         s.defaultReadObject();
 
-        // Read in array length and allocate array
-        int arrayLength = s.readInt();
-        Object[] a = elementData = new Object[arrayLength];
+        // Read in array length
+        initialCapacity = s.readInt();
+        elementData = EMPTY_ELEMENTDATA;
 
-        // Read in all elements in the proper order.
+        // allocate array based upon size.
+        ensureCapacityInternal(size);
+
+        Object[] a = elementData;
+        // Read in all elements  the proper order.
         for (int i=0; i<size; i++)
             a[i] = s.readObject();
     }
diff --git a/src/share/classes/java/util/HashMap.java b/src/share/classes/java/util/HashMap.java
--- a/src/share/classes/java/util/HashMap.java
+++ b/src/share/classes/java/util/HashMap.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -144,9 +144,14 @@
     static final float DEFAULT_LOAD_FACTOR = 0.75f;
 
     /**
+     * An empty table instance to share when the table is not inflated.
+     */
+    static final Entry<?,?>[] EMPTY_TABLE = {};
+
+    /**
      * The table, resized as necessary. Length MUST Always be a power of two.
      */
-    transient Entry<?,?>[] table;
+    transient Entry<?,?>[] table = EMPTY_TABLE;
 
     /**
      * The number of key-value mappings contained in this map.
@@ -187,13 +192,21 @@
          */
         static final long HASHSEED_OFFSET;
 
+        /**
+         * Offset of "final" initialCapacity field we must set in
+         * readObject() method.
+         */
+        static final long INITIAL_CAPACITY_OFFSET;
+
         static {
             try {
                 UNSAFE = sun.misc.Unsafe.getUnsafe();
                 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
                     HashMap.class.getDeclaredField("hashSeed"));
+                INITIAL_CAPACITY_OFFSET = UNSAFE.objectFieldOffset(
+                    HashMap.class.getDeclaredField("initialCapacity"));
             } catch (NoSuchFieldException | SecurityException e) {
-                throw new InternalError("Failed to record hashSeed offset", e);
+                throw new InternalError("Failed to record field offset", e);
             }
         }
     }
@@ -205,6 +218,11 @@
     transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
 
     /**
+     * The requested initial capacity increased to a power of two.
+     */
+    transient final int initialCapacity;
+
+    /**
      * Constructs an empty <tt>HashMap</tt> with the specified initial
      * capacity and load factor.
      *
@@ -224,13 +242,14 @@
                                                loadFactor);
 
         // Find a power of 2 >= initialCapacity
-        int capacity = 1;
-        while (capacity < initialCapacity)
-            capacity <<= 1;
+        int capacity = (capacity = Integer.highestOneBit(initialCapacity)) != 0
+                ? capacity
+                : 1;
+        capacity <<= (Integer.bitCount(initialCapacity) > 1) ? 1 : 0;
 
         this.loadFactor = loadFactor;
-        threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
-        table = new Entry<?,?>[capacity];
+        threshold = 0;
+        this.initialCapacity = capacity;
         init();
     }
 
@@ -265,9 +284,18 @@
     public HashMap(Map<? extends K, ? extends V> m) {
         this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
                       DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
+        inflateTable();
+
         putAllForCreate(m);
     }
 
+    /**
+     * Inflate the table
+     */
+    final void inflateTable() {
+      threshold = (int)Math.min(initialCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
+      table = new Entry[initialCapacity];
+    }
     // internal utilities
 
     /**
@@ -369,6 +397,10 @@
      */
     @SuppressWarnings("unchecked")
     final Entry<K,V> getEntry(Object key) {
+        if (isEmpty()) {
+            return null;
+        }
+
         int hash = (key == null) ? 0 : hash(key);
         for (Entry<?,?> e = table[indexFor(hash, table.length)];
              e != null;
@@ -381,7 +413,6 @@
         return null;
     }
 
-
     /**
      * Associates the specified value with the specified key in this map.
      * If the map previously contained a mapping for the key, the old
@@ -395,6 +426,9 @@
      *         previously associated <tt>null</tt> with <tt>key</tt>.)
      */
     public V put(K key, V value) {
+        if (table == EMPTY_TABLE) {
+            inflateTable();
+        }
         if (key == null)
             return putForNullKey(value);
         int hash = hash(key);
@@ -529,6 +563,10 @@
         if (numKeysToBeAdded == 0)
             return;
 
+        if (table == EMPTY_TABLE) {
+            inflateTable();
+        }
+
         /*
          * Expand the map if the map if the number of mappings to be added
          * is greater than or equal to threshold.  This is conservative; the
@@ -563,6 +601,9 @@
      *         previously associated <tt>null</tt> with <tt>key</tt>.)
      */
     public V remove(Object key) {
+        if(isEmpty()) {
+            return null;
+        }
         Entry<K,V> e = removeEntryForKey(key);
         return (e == null ? null : e.value);
     }
@@ -607,6 +648,9 @@
     final Entry<K,V> removeMapping(Object o) {
         if (!(o instanceof Map.Entry))
             return null;
+        if(isEmpty()) {
+            return null;
+        }
 
         Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
         Object key = entry.getKey();
@@ -641,9 +685,7 @@
      */
     public void clear() {
         modCount++;
-        Entry<?,?>[] tab = table;
-        for (int i = 0; i < tab.length; i++)
-            tab[i] = null;
+        Arrays.fill(table, null);
         size = 0;
     }
 
@@ -656,6 +698,10 @@
      *         specified value
      */
     public boolean containsValue(Object value) {
+        if(isEmpty()) {
+            return false;
+        }
+
         if (value == null)
             return containsNullValue();
 
@@ -693,7 +739,9 @@
         } catch (CloneNotSupportedException e) {
             // assert false;
         }
-        result.table = new Entry<?,?>[table.length];
+        result.table = (table == EMPTY_TABLE)
+            ? EMPTY_TABLE
+            : new Entry<?,?>[table.length];
         result.entrySet = null;
         result.modCount = 0;
         result.size = 0;
@@ -749,8 +797,7 @@
         }
 
         public final int hashCode() {
-            return (key==null   ? 0 : key.hashCode()) ^
-                   (value==null ? 0 : value.hashCode());
+            return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
         }
 
         public final String toString() {
@@ -1017,14 +1064,14 @@
     private void writeObject(java.io.ObjectOutputStream s)
         throws IOException
     {
-        Iterator<Map.Entry<K,V>> i =
-            (size > 0) ? entrySet0().iterator() : null;
-
         // Write out the threshold, loadfactor, and any hidden stuff
         s.defaultWriteObject();
 
         // Write out number of buckets
-        s.writeInt(table.length);
+        if (table==EMPTY_TABLE)
+            s.writeInt(initialCapacity); // power of 2.
+        else
+           s.writeInt(table.length);
 
         // Write out size (number of Mappings)
         s.writeInt(size);
@@ -1066,23 +1113,29 @@
             throw new InvalidObjectException("Illegal mappings count: " +
                                                mappings);
 
-        int initialCapacity = (int) Math.min(
+        int mappingsCapacity = Math.max((int) Math.min(
                 // capacity chosen by number of mappings
                 // and desired load (if >= 0.25)
                 mappings * Math.min(1 / loadFactor, 4.0f),
                 // we have limits...
-                HashMap.MAXIMUM_CAPACITY);
-        int capacity = 1;
-        // find smallest power of two which holds all mappings
-        while (capacity < initialCapacity) {
-            capacity <<= 1;
+                HashMap.MAXIMUM_CAPACITY), 0);
+        // Find a power of 2 >= mappingCapacity
+        int capacity = (capacity = Integer.highestOneBit(mappingsCapacity)) != 0
+                ? capacity
+                : 1;
+        capacity <<= (Integer.bitCount(mappingsCapacity) > 1) ? 1 : 0;
+        Holder.UNSAFE.putIntVolatile(this, Holder.INITIAL_CAPACITY_OFFSET,
+                capacity);
+
+        if(mappings > 0) {
+            inflateTable();
+        } else {
+            table = EMPTY_TABLE;
+            threshold = 0;
         }
 
-        table = new Entry<?,?>[capacity];
-        threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
         init();  // Give subclass a chance to do its thing.
 
-
         // Read the keys and values, and put the mappings in the HashMap
         for (int i=0; i<mappings; i++) {
             @SuppressWarnings("unchecked")
diff --git a/test/java/util/Map/Collisions.java b/test/java/util/Map/BasicSerialization.java
copy from test/java/util/Map/Collisions.java
copy to test/java/util/Map/BasicSerialization.java
--- a/test/java/util/Map/Collisions.java
+++ b/test/java/util/Map/BasicSerialization.java
@@ -23,403 +23,199 @@
 
 /*
  * @test
- * @bug 7126277
- * @run main Collisions -shortrun
- * @run main/othervm -Djdk.map.althashing.threshold=0 Collisions -shortrun
- * @summary Ensure Maps behave well with lots of hashCode() collisions.
+ * @bug 7143928
+ * @run testng BasicSerialization
+ * @summary Ensure Maps can be serialized and deserialized.
  * @author Mike Duigou
  */
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.ByteArrayInputStream;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentSkipListMap;
 
-public class Collisions {
+import org.testng.annotations.Test;
+import org.testng.annotations.DataProvider;
+import static org.testng.Assert.fail;
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertTrue;
+import static org.testng.Assert.assertFalse;
+import static org.testng.Assert.assertSame;
 
+public class BasicSerialization {
+
+    enum IntegerEnum {
+
+        e0, e1, e2, e3, e4, e5, e6, e7, e8, e9,
+        e10, e11, e12, e13, e14, e15, e16, e17, e18, e19,
+        e20, e21, e22, e23, e24, e25, e26, e27, e28, e29,
+        e30, e31, e32, e33, e34, e35, e36, e37, e38, e39,
+        e40, e41, e42, e43, e44, e45, e46, e47, e48, e49,
+        e50, e51, e52, e53, e54, e55, e56, e57, e58, e59,
+        e60, e61, e62, e63, e64, e65, e66, e67, e68, e69,
+        e70, e71, e72, e73, e74, e75, e76, e77, e78, e79,
+        e80, e81, e82, e83, e84, e85, e86, e87, e88, e89,
+        e90, e91, e92, e93, e94, e95, e96, e97, e98, e99,
+        EXTRA_KEY;
+        public static final int SIZE = values().length;
+    };
+    private static final int TEST_SIZE = IntegerEnum.SIZE - 1;
     /**
-     * Number of elements per map.
+     * Realized keys ensure that there is always a hard ref to all test objects.
      */
-    private static final int TEST_SIZE = 5000;
+    private static final IntegerEnum[] KEYS = new IntegerEnum[TEST_SIZE];
+    /**
+     * Realized values ensure that there is always a hard ref to all test
+     * objects.
+     */
+    private static final String[] VALUES = new String[TEST_SIZE];
 
-    final static class HashableInteger implements Comparable<HashableInteger> {
+    static {
+        IntegerEnum[] keys = IntegerEnum.values();
+        for (int each = 0; each < TEST_SIZE; each++) {
+            KEYS[each] = keys[each];
+            VALUES[each] = keys[each].name();
+        }
+    }
+    private static final IntegerEnum EXTRA_KEY = IntegerEnum.EXTRA_KEY;
+    private static final String EXTRA_VALUE = IntegerEnum.EXTRA_KEY.name();
 
-        final int value;
-        final int hashmask; //yes duplication
+    public static <K, V> Map<K, V> mapClone(Map<K, V> map) {
+        Method cloneMethod;
 
-        HashableInteger(int value, int hashmask) {
-            this.value = value;
-            this.hashmask = hashmask;
+        try {
+            cloneMethod = map.getClass().getMethod("clone", new Class[]{});
+        } catch (NoSuchMethodException | SecurityException all) {
+            cloneMethod = null;
         }
 
-        @Override
-        public boolean equals(Object obj) {
-            if (obj instanceof HashableInteger) {
-                HashableInteger other = (HashableInteger) obj;
+        if (null != cloneMethod) {
+            try {
+                Map<K, V> result = (Map<K, V>)cloneMethod.invoke(map, new Object[]{});
+                return result;
+            } catch (Exception all) {
+                fail("clone() failed " + map.getClass().getSimpleName(), all);
+                return null;
+            }
+        } else {
+            Constructor<? extends Map> copyConstructor;
+            try {
+                copyConstructor = (Constructor<? extends Map>)map.getClass().getConstructor(new Class[]{Map.class});
 
-                return other.value == value;
-            }
+                Map<K, V> result = (Map<K, V>)copyConstructor.newInstance(new Object[]{map});
 
-            return false;
-        }
-
-        @Override
-        public int hashCode() {
-            return value % hashmask;
-        }
-
-        @Override
-        public int compareTo(HashableInteger o) {
-            return value - o.value;
-        }
-
-        @Override
-        public String toString() {
-            return Integer.toString(value);
-        }
-    }
-
-    private static Object[][] makeTestData(int size) {
-        HashableInteger UNIQUE_OBJECTS[] = new HashableInteger[size];
-        HashableInteger COLLIDING_OBJECTS[] = new HashableInteger[size];
-        String UNIQUE_STRINGS[] = new String[size];
-        String COLLIDING_STRINGS[] = new String[size];
-
-        for (int i = 0; i < size; i++) {
-            UNIQUE_OBJECTS[i] = new HashableInteger(i, Integer.MAX_VALUE);
-            COLLIDING_OBJECTS[i] = new HashableInteger(i, 10);
-            UNIQUE_STRINGS[i] = unhash(i);
-            COLLIDING_STRINGS[i] = (0 == i % 2)
-                    ? UNIQUE_STRINGS[i / 2]
-                    : "\u0000\u0000\u0000\u0000\u0000" + COLLIDING_STRINGS[i - 1];
-        }
-
-     return new Object[][] {
-            new Object[]{"Unique Objects", UNIQUE_OBJECTS},
-            new Object[]{"Colliding Objects", COLLIDING_OBJECTS},
-            new Object[]{"Unique Strings", UNIQUE_STRINGS},
-            new Object[]{"Colliding Strings", COLLIDING_STRINGS}
-        };
-    }
-
-    /**
-     * Returns a string with a hash equal to the argument.
-     *
-     * @return string with a hash equal to the argument.
-     */
-    public static String unhash(int target) {
-        StringBuilder answer = new StringBuilder();
-        if (target < 0) {
-            // String with hash of Integer.MIN_VALUE, 0x80000000
-            answer.append("\\u0915\\u0009\\u001e\\u000c\\u0002");
-
-            if (target == Integer.MIN_VALUE) {
-                return answer.toString();
-            }
-            // Find target without sign bit set
-            target = target & Integer.MAX_VALUE;
-        }
-
-        unhash0(answer, target);
-        return answer.toString();
-    }
-
-    private static void unhash0(StringBuilder partial, int target) {
-        int div = target / 31;
-        int rem = target % 31;
-
-        if (div <= Character.MAX_VALUE) {
-            if (div != 0) {
-                partial.append((char) div);
-            }
-            partial.append((char) rem);
-        } else {
-            unhash0(partial, div);
-            partial.append((char) rem);
-        }
-    }
-
-    private static void realMain(String[] args) throws Throwable {
-        boolean shortRun = args.length > 0 && args[0].equals("-shortrun");
-
-        Object[][] mapKeys = makeTestData(shortRun ? (TEST_SIZE / 2) : TEST_SIZE);
-
-        // loop through data sets
-        for (Object[] keys_desc : mapKeys) {
-            Map<Object, Object>[] maps = (Map<Object, Object>[]) new Map[]{
-                        new HashMap<>(),
-                        new Hashtable<>(),
-                        new IdentityHashMap<>(),
-                        new LinkedHashMap<>(),
-                        new TreeMap<>(),
-                        new WeakHashMap<>(),
-                        new ConcurrentHashMap<>(),
-                        new ConcurrentSkipListMap<>()
-                    };
-
-            // for each map type.
-            for (Map<Object, Object> map : maps) {
-                String desc = (String) keys_desc[0];
-                Object[] keys = (Object[]) keys_desc[1];
-                try {
-                    testMap(map, desc, keys);
-                } catch(Exception all) {
-                    unexpected("Failed for " + map.getClass().getName() + " with " + desc, all);
-                }
+                return result;
+            } catch (Exception all) {
+                return serialClone(map);
             }
         }
     }
 
-    private static <T> void testMap(Map<T, T> map, String keys_desc, T[] keys) {
-        System.out.println(map.getClass() + " : " + keys_desc);
-        System.out.flush();
-        testInsertion(map, keys_desc, keys);
+    @Test(dataProvider = "Map<IntegerEnum,String>")
+    public void testSerialization(String description, Map<IntegerEnum, String> map) {
+        Object foo = new Object();
 
-        if (keys[0] instanceof HashableInteger) {
-            testIntegerIteration((Map<HashableInteger, HashableInteger>) map, (HashableInteger[]) keys);
-        } else {
-            testStringIteration((Map<String, String>) map, (String[]) keys);
-        }
+        Map<IntegerEnum, String> clone = mapClone(map);
+        Map<IntegerEnum, String> serialClone = serialClone(map);
 
-        testContainsKey(map, keys_desc, keys);
+        assertEquals(map, map, description + ":should equal self");
+        assertEquals(clone, map, description + ":should equal clone");
+        assertEquals(map, clone, description + ": should equal orginal map");
+        assertEquals(serialClone, map, description + ": should equal deserialized clone");
+        assertEquals(map, serialClone, description + ": should equal original map");
+        assertEquals(serialClone, clone, description + ": deserialized clone should equal clone");
+        assertEquals(clone, serialClone, description + ": clone should equal deserialized clone");
 
-        testRemove(map, keys_desc, keys);
+        assertFalse(map.containsKey(EXTRA_KEY), description + ":unexpected key");
+        assertFalse(clone.containsKey(EXTRA_KEY), description + ":unexpected key");
+        assertFalse(serialClone.containsKey(EXTRA_KEY), description + ":unexpected key");
+        map.put(EXTRA_KEY, EXTRA_VALUE);
+        clone.put(EXTRA_KEY, EXTRA_VALUE);
+        serialClone.put(EXTRA_KEY, EXTRA_VALUE);
+        assertTrue(map.containsKey(EXTRA_KEY), description + ":missing key");
+        assertTrue(clone.containsKey(EXTRA_KEY), description + ":missing key");
+        assertTrue(serialClone.containsKey(EXTRA_KEY), description + ":missing key");
+        assertSame(map.get(EXTRA_KEY), EXTRA_VALUE, description + ":wrong value");
+        assertSame(clone.get(EXTRA_KEY), EXTRA_VALUE, description + ":wrong value");
+        assertSame(serialClone.get(EXTRA_KEY), EXTRA_VALUE, description + ":wrong value");
 
-        map.clear();
-        testInsertion(map, keys_desc, keys);
-        testKeysIteratorRemove(map, keys_desc, keys);
-
-        map.clear();
-        testInsertion(map, keys_desc, keys);
-        testValuesIteratorRemove(map, keys_desc, keys);
-
-        map.clear();
-        testInsertion(map, keys_desc, keys);
-        testEntriesIteratorRemove(map, keys_desc, keys);
-
-        check(map.isEmpty());
+        assertEquals(map, map, description + ":should equal self");
+        assertEquals(clone, map, description + ":should equal clone");
+        assertEquals(map, clone, description + ": should equal orginal map");
+        assertEquals(serialClone, map, description + ": should equal deserialized clone");
+        assertEquals(map, serialClone, description + ": should equal original map");
+        assertEquals(serialClone, clone, description + ": deserialized clone should equal clone");
+        assertEquals(clone, serialClone, description + ": clone should equal deserialized clone");
     }
 
-    private static <T> void testInsertion(Map<T, T> map, String keys_desc, T[] keys) {
-        check("map empty", (map.size() == 0) && map.isEmpty());
-
-        for (int i = 0; i < keys.length; i++) {
-            check(String.format("insertion: map expected size m%d != i%d", map.size(), i),
-                    map.size() == i);
-            check(String.format("insertion: put(%s[%d])", keys_desc, i), null == map.put(keys[i], keys[i]));
-            check(String.format("insertion: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
-            check(String.format("insertion: containsValue(%s[%d])", keys_desc, i), map.containsValue(keys[i]));
-        }
-
-        check(String.format("map expected size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-    }
-
-    private static void testIntegerIteration(Map<HashableInteger, HashableInteger> map, HashableInteger[] keys) {
-        check(String.format("map expected size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-
-        BitSet all = new BitSet(keys.length);
-        for (Map.Entry<HashableInteger, HashableInteger> each : map.entrySet()) {
-            check("Iteration: key already seen", !all.get(each.getKey().value));
-            all.set(each.getKey().value);
-        }
-
-        all.flip(0, keys.length);
-        check("Iteration: some keys not visited", all.isEmpty());
-
-        for (HashableInteger each : map.keySet()) {
-            check("Iteration: key already seen", !all.get(each.value));
-            all.set(each.value);
-        }
-
-        all.flip(0, keys.length);
-        check("Iteration: some keys not visited", all.isEmpty());
-
-        int count = 0;
-        for (HashableInteger each : map.values()) {
-            count++;
-        }
-
-        check(String.format("Iteration: value count matches size m%d != c%d", map.size(), count),
-                map.size() == count);
-    }
-
-    private static void testStringIteration(Map<String, String> map, String[] keys) {
-        check(String.format("map expected size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-
-        BitSet all = new BitSet(keys.length);
-        for (Map.Entry<String, String> each : map.entrySet()) {
-            String key = each.getKey();
-            boolean longKey = key.length() > 5;
-            int index = key.hashCode() + (longKey ? keys.length / 2 : 0);
-            check("key already seen", !all.get(index));
-            all.set(index);
-        }
-
-        all.flip(0, keys.length);
-        check("some keys not visited", all.isEmpty());
-
-        for (String each : map.keySet()) {
-            boolean longKey = each.length() > 5;
-            int index = each.hashCode() + (longKey ? keys.length / 2 : 0);
-            check("key already seen", !all.get(index));
-            all.set(index);
-        }
-
-        all.flip(0, keys.length);
-        check("some keys not visited", all.isEmpty());
-
-        int count = 0;
-        for (String each : map.values()) {
-            count++;
-        }
-
-        check(String.format("value count matches size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-    }
-
-    private static <T> void testContainsKey(Map<T, T> map, String keys_desc, T[] keys) {
-        for (int i = 0; i < keys.length; i++) {
-            T each = keys[i];
-            check("containsKey: " + keys_desc + "[" + i + "]" + each, map.containsKey(each));
+    static byte[] serializedForm(Object obj) {
+        try {
+            ByteArrayOutputStream baos = new ByteArrayOutputStream();
+            new ObjectOutputStream(baos).writeObject(obj);
+            return baos.toByteArray();
+        } catch (IOException e) {
+            fail("Unexpected Exception", e);
+            return null;
         }
     }
 
-    private static <T> void testRemove(Map<T, T> map, String keys_desc, T[] keys) {
-        check(String.format("remove: map expected size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-
-        for (int i = 0; i < keys.length; i++) {
-            T each = keys[i];
-            check("remove: " + keys_desc + "[" + i + "]" + each, null != map.remove(each));
-        }
-
-        check(String.format("remove: map empty. size=%d", map.size()),
-                (map.size() == 0) && map.isEmpty());
+    static Object readObject(byte[] bytes) throws IOException, ClassNotFoundException {
+        InputStream is = new ByteArrayInputStream(bytes);
+        return new ObjectInputStream(is).readObject();
     }
 
-    private static <T> void testKeysIteratorRemove(Map<T, T> map, String keys_desc, T[] keys) {
-        check(String.format("remove: map expected size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-
-        Iterator<T> each = map.keySet().iterator();
-        while (each.hasNext()) {
-            T t = each.next();
-            each.remove();
-            check("not removed: " + each, !map.containsKey(t) );
-        }
-
-        check(String.format("remove: map empty. size=%d", map.size()),
-                (map.size() == 0) && map.isEmpty());
-    }
-
-    private static <T> void testValuesIteratorRemove(Map<T, T> map, String keys_desc, T[] keys) {
-        check(String.format("remove: map expected size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-
-        Iterator<T> each = map.values().iterator();
-        while (each.hasNext()) {
-            T t = each.next();
-            each.remove();
-            check("not removed: " + each, !map.containsValue(t) );
-        }
-
-        check(String.format("remove: map empty. size=%d", map.size()),
-                (map.size() == 0) && map.isEmpty());
-    }
-
-    private static <T> void testEntriesIteratorRemove(Map<T, T> map, String keys_desc, T[] keys) {
-        check(String.format("remove: map expected size m%d != k%d", map.size(), keys.length),
-                map.size() == keys.length);
-
-        Iterator<Map.Entry<T,T>> each = map.entrySet().iterator();
-        while (each.hasNext()) {
-            Map.Entry<T,T> t = each.next();
-            T key = t.getKey();
-            T value = t.getValue();
-            each.remove();
-            check("not removed: " + each, (map instanceof IdentityHashMap) || !map.entrySet().contains(t) );
-            check("not removed: " + each, !map.containsKey(key) );
-            check("not removed: " + each, !map.containsValue(value));
-        }
-
-        check(String.format("remove: map empty. size=%d", map.size()),
-                (map.size() == 0) && map.isEmpty());
-    }
-
-    //--------------------- Infrastructure ---------------------------
-    static volatile int passed = 0, failed = 0;
-
-    static void pass() {
-        passed++;
-    }
-
-    static void fail() {
-        failed++;
-        (new Error("Failure")).printStackTrace(System.err);
-    }
-
-    static void fail(String msg) {
-        failed++;
-        (new Error("Failure: " + msg)).printStackTrace(System.err);
-    }
-
-    static void abort() {
-        fail();
-        System.exit(1);
-    }
-
-    static void abort(String msg) {
-        fail(msg);
-        System.exit(1);
-    }
-
-    static void unexpected(String msg, Throwable t) {
-        System.err.println("Unexpected: " + msg);
-        unexpected(t);
-    }
-
-    static void unexpected(Throwable t) {
-        failed++;
-        t.printStackTrace(System.err);
-    }
-
-    static void check(boolean cond) {
-        if (cond) {
-            pass();
-        } else {
-            fail();
+    @SuppressWarnings("unchecked")
+    static <T> T serialClone(T obj) {
+        try {
+            return (T)readObject(serializedForm(obj));
+        } catch (IOException | ClassNotFoundException e) {
+            fail("Unexpected Exception", e);
+            return null;
         }
     }
 
-    static void check(String desc, boolean cond) {
-        if (cond) {
-            pass();
-        } else {
-            fail(desc);
-        }
+    @DataProvider(name = "Map<IntegerEnum,String>", parallel = true)
+    private static Iterator<Object[]> makeMaps() {
+        return Arrays.asList(
+            // empty
+            new Object[]{"HashMap", new HashMap()},
+            new Object[]{"LinkedHashMap", new LinkedHashMap()},
+            new Object[]{"Collections.checkedMap(HashMap)", Collections.checkedMap(new HashMap(), IntegerEnum.class, String.class)},
+            new Object[]{"Collections.synchronizedMap(HashMap)", Collections.synchronizedMap(new HashMap())},
+            // null hostile
+            new Object[]{"EnumMap", new EnumMap(IntegerEnum.class)},
+            new Object[]{"Hashtable", new Hashtable()},
+            new Object[]{"TreeMap", new TreeMap()},
+            new Object[]{"ConcurrentHashMap", new ConcurrentHashMap()},
+            new Object[]{"ConcurrentSkipListMap", new ConcurrentSkipListMap()},
+            new Object[]{"Collections.checkedMap(ConcurrentHashMap)", Collections.checkedMap(new ConcurrentHashMap(), IntegerEnum.class, String.class)},
+            new Object[]{"Collections.synchronizedMap(EnumMap)", Collections.synchronizedMap(new EnumMap(IntegerEnum.class))},
+            // filled
+            new Object[]{"HashMap", fillMap(new HashMap())},
+            new Object[]{"LinkedHashMap", fillMap(new LinkedHashMap())},
+            new Object[]{"Collections.checkedMap(HashMap)", Collections.checkedMap(fillMap(new HashMap()), IntegerEnum.class, String.class)},
+            new Object[]{"Collections.synchronizedMap(HashMap)", Collections.synchronizedMap(fillMap(new HashMap()))},
+            // null hostile
+            new Object[]{"EnumMap", fillMap(new EnumMap(IntegerEnum.class))},
+            new Object[]{"Hashtable", fillMap(new Hashtable())},
+            new Object[]{"TreeMap", fillMap(new TreeMap())},
+            new Object[]{"ConcurrentHashMap", fillMap(new ConcurrentHashMap())},
+            new Object[]{"ConcurrentSkipListMap", fillMap(new ConcurrentSkipListMap())},
+            new Object[]{"Collections.checkedMap(ConcurrentHashMap)", Collections.checkedMap(fillMap(new ConcurrentHashMap()), IntegerEnum.class, String.class)},
+            new Object[]{"Collections.synchronizedMap(EnumMap)", Collections.synchronizedMap(fillMap(new EnumMap(IntegerEnum.class)))}).iterator();
     }
 
-    static void equal(Object x, Object y) {
-        if (Objects.equals(x, y)) {
-            pass();
-        } else {
-            fail(x + " not equal to " + y);
-        }
-    }
-
-    public static void main(String[] args) throws Throwable {
-        Thread.currentThread().setName(Collisions.class.getName());
-//        Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
-        try {
-            realMain(args);
-        } catch (Throwable t) {
-            unexpected(t);
+    private static Map<IntegerEnum, String> fillMap(Map<IntegerEnum, String> result) {
+        for (int each = 0; each < TEST_SIZE; each++) {
+            result.put(KEYS[each], VALUES[each]);
         }
 
-        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
-        if (failed > 0) {
-            throw new Error("Some tests failed");
-        }
+        return result;
     }
 }