An integer hashmap : Customized Map « Collections Data Structure « Java






An integer hashmap

    
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * This is an integer hashmap that has the exact same features and interface as a normal Map except
 * that the key is directly an integer. So no hash is calculated or key object is stored.
 * 
 * @author jcompagner
 * 
 * @param <V>
 *            The value in the map
 */
public class IntHashMap<V> implements Cloneable, Serializable
{
  transient volatile Set<Integer> keySet = null;

  transient volatile Collection<V> values = null;

  /**
   * The default initial capacity - MUST be a power of two.
   */
  static final int DEFAULT_INITIAL_CAPACITY = 16;

  /**
   * The maximum capacity, used if a higher value is implicitly specified by either of the
   * constructors with arguments. MUST be a power of two <= 1<<30.
   */
  static final int MAXIMUM_CAPACITY = 1 << 30;

  /**
   * The load factor used when none specified in constructor.
   */
  static final float DEFAULT_LOAD_FACTOR = 0.75f;

  /**
   * The table, resized as necessary. Length MUST Always be a power of two.
   */
  transient Entry<V>[] table;

  /**
   * The number of key-value mappings contained in this identity hash map.
   */
  transient int size;

  /**
   * The next size value at which to resize (capacity * load factor).
   * 
   * @serial
   */
  int threshold;

  /**
   * The load factor for the hash table.
   * 
   * @serial
   */
  final float loadFactor;

  /**
   * The number of times this HashMap has been structurally modified Structural modifications are
   * those that change the number of mappings in the HashMap or otherwise modify its internal
   * structure (e.g., rehash). This field is used to make iterators on Collection-views of the
   * HashMap fail-fast. (See ConcurrentModificationException).
   */
  transient volatile int modCount;

  /**
   * Constructs an empty <tt>HashMap</tt> with the specified initial capacity and load factor.
   * 
   * @param initialCapacity
   *            The initial capacity.
   * @param loadFactor
   *            The load factor.
   * @throws IllegalArgumentException
   *             if the initial capacity is negative or the load factor is nonpositive.
   */
  @SuppressWarnings("unchecked")
  public IntHashMap(int initialCapacity, float loadFactor)
  {
    if (initialCapacity < 0)
    {
      throw new IllegalArgumentException("Illegal initial capacity: " + //$NON-NLS-1$
        initialCapacity);
    }
    if (initialCapacity > MAXIMUM_CAPACITY)
    {
      initialCapacity = MAXIMUM_CAPACITY;
    }
    if (loadFactor <= 0 || Float.isNaN(loadFactor))
    {
      throw new IllegalArgumentException("Illegal load factor: " + //$NON-NLS-1$
        loadFactor);
    }

    // Find a power of 2 >= initialCapacity
    int capacity = 1;
    while (capacity < initialCapacity)
    {
      capacity <<= 1;
    }

    this.loadFactor = loadFactor;
    threshold = (int)(capacity * loadFactor);
    table = new Entry[capacity];
    init();
  }

  /**
   * Constructs an empty <tt>HashMap</tt> with the specified initial capacity and the default
   * load factor (0.75).
   * 
   * @param initialCapacity
   *            the initial capacity.
   * @throws IllegalArgumentException
   *             if the initial capacity is negative.
   */
  public IntHashMap(int initialCapacity)
  {
    this(initialCapacity, DEFAULT_LOAD_FACTOR);
  }

  /**
   * Constructs an empty <tt>HashMap</tt> with the default initial capacity (16) and the default
   * load factor (0.75).
   */
  @SuppressWarnings("unchecked")
  public IntHashMap()
  {
    loadFactor = DEFAULT_LOAD_FACTOR;
    threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
    table = new Entry[DEFAULT_INITIAL_CAPACITY];
    init();
  }

  // internal utilities

  /**
   * Initialization hook for subclasses. This method is called in all constructors and
   * pseudo-constructors (clone, readObject) after HashMap has been initialized but before any
   * entries have been inserted. (In the absence of this method, readObject would require explicit
   * knowledge of subclasses.)
   */
  void init()
  {
  }

  /**
   * Returns index for hash code h.
   * 
   * @param h
   * @param length
   * @return The index for the hash integer for the given length
   */
  static int indexFor(int h, int length)
  {
    return h & (length - 1);
  }

  /**
   * Returns the number of key-value mappings in this map.
   * 
   * @return the number of key-value mappings in this map.
   */
  public int size()
  {
    return size;
  }

  /**
   * Returns <tt>true</tt> if this map contains no key-value mappings.
   * 
   * @return <tt>true</tt> if this map contains no key-value mappings.
   */
  public boolean isEmpty()
  {
    return size == 0;
  }

  /**
   * Returns the value to which the specified key is mapped in this identity hash map, or
   * <tt>null</tt> if the map contains no mapping for this key. A return value of <tt>null</tt>
   * does not <i>necessarily</i> indicate that the map contains no mapping for the key; it is
   * also possible that the map explicitly maps the key to <tt>null</tt>. The
   * <tt>containsKey</tt> method may be used to distinguish these two cases.
   * 
   * @param key
   *            the key whose associated value is to be returned.
   * @return the value to which this map maps the specified key, or <tt>null</tt> if the map
   *         contains no mapping for this key.
   * @see #put(int, Object)
   */
  public V get(int key)
  {
    int i = indexFor(key, table.length);
    Entry<V> e = table[i];
    while (true)
    {
      if (e == null)
      {
        return null;
      }
      if (key == e.key)
      {
        return e.value;
      }
      e = e.next;
    }
  }

  /**
   * Returns <tt>true</tt> if this map contains a mapping for the specified key.
   * 
   * @param key
   *            The key whose presence in this map is to be tested
   * @return <tt>true</tt> if this map contains a mapping for the specified key.
   */
  public boolean containsKey(int key)
  {
    int i = indexFor(key, table.length);
    Entry<V> e = table[i];
    while (e != null)
    {
      if (key == e.key)
      {
        return true;
      }
      e = e.next;
    }
    return false;
  }

  /**
   * Returns the entry associated with the specified key in the HashMap. Returns null if the
   * HashMap contains no mapping for this key.
   * 
   * @param key
   * @return The Entry object for the given hash key
   */
  Entry<V> getEntry(int key)
  {
    int i = indexFor(key, table.length);
    Entry<V> e = table[i];
    while (e != null && !(key == e.key))
    {
      e = e.next;
    }
    return e;
  }

  /**
   * Associates the specified value with the specified key in this map. If the map previously
   * contained a mapping for this key, the old value is replaced.
   * 
   * @param key
   *            key with which the specified value is to be associated.
   * @param value
   *            value to be associated with the specified key.
   * @return previous value associated with specified key, or <tt>null</tt> if there was no
   *         mapping for key. A <tt>null</tt> return can also indicate that the HashMap
   *         previously associated <tt>null</tt> with the specified key.
   */
  public V put(int key, V value)
  {
    int i = indexFor(key, table.length);

    for (Entry<V> e = table[i]; e != null; e = e.next)
    {
      if (key == e.key)
      {
        V oldValue = e.value;
        e.value = value;
        return oldValue;
      }
    }

    modCount++;
    addEntry(key, value, i);
    return null;
  }

  /**
   * This method is used instead of put by constructors and pseudoconstructors (clone,
   * readObject). It does not resize the table, check for comodification, etc. It calls
   * createEntry rather than addEntry.
   * 
   * @param key
   * @param value
   */
  private void putForCreate(int key, V value)
  {
    int i = indexFor(key, table.length);

    /**
     * Look for preexisting entry for key. This will never happen for clone or deserialize. It
     * will only happen for construction if the input Map is a sorted map whose ordering is
     * inconsistent w/ equals.
     */
    for (Entry<V> e = table[i]; e != null; e = e.next)
    {
      if (key == e.key)
      {
        e.value = value;
        return;
      }
    }

    createEntry(key, value, i);
  }

  void putAllForCreate(IntHashMap<V> m)
  {
    for (Iterator<Entry<V>> i = m.entrySet().iterator(); i.hasNext();)
    {
      Entry<V> e = i.next();
      putForCreate(e.getKey(), e.getValue());
    }
  }

  /**
   * Rehashes the contents of this map into a new array with a larger capacity. This method is
   * called automatically when the number of keys in this map reaches its threshold.
   * 
   * If current capacity is MAXIMUM_CAPACITY, this method does not resize the map, but but sets
   * threshold to Integer.MAX_VALUE. This has the effect of preventing future calls.
   * 
   * @param newCapacity
   *            the new capacity, MUST be a power of two; must be greater than current capacity
   *            unless current capacity is MAXIMUM_CAPACITY (in which case value is irrelevant).
   */
  @SuppressWarnings("unchecked")
  void resize(int newCapacity)
  {
    Entry<V>[] oldTable = table;
    int oldCapacity = oldTable.length;
    if (oldCapacity == MAXIMUM_CAPACITY)
    {
      threshold = Integer.MAX_VALUE;
      return;
    }

    Entry<V>[] newTable = new Entry[newCapacity];
    transfer(newTable);
    table = newTable;
    threshold = (int)(newCapacity * loadFactor);
  }

  /**
   * Transfer all entries from current table to newTable.
   * 
   * @param newTable
   */
  void transfer(Entry<V>[] newTable)
  {
    Entry<V>[] src = table;
    int newCapacity = newTable.length;
    for (int j = 0; j < src.length; j++)
    {
      Entry<V> e = src[j];
      if (e != null)
      {
        src[j] = null;
        do
        {
          Entry<V> next = e.next;
          int i = indexFor(e.key, newCapacity);
          e.next = newTable[i];
          newTable[i] = e;
          e = next;
        }
        while (e != null);
      }
    }
  }

  /**
   * Copies all of the mappings from the specified map to this map These mappings will replace any
   * mappings that this map had for any of the keys currently in the specified map.
   * 
   * @param m
   *            mappings to be stored in this map.
   * @throws NullPointerException
   *             if the specified map is null.
   */
  public void putAll(IntHashMap<V> m)
  {
    int numKeysToBeAdded = m.size();
    if (numKeysToBeAdded == 0)
    {
      return;
    }

    /*
     * 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 obvious condition is (m.size() + size) >=
     * threshold, but this condition could result in a map with twice the appropriate capacity,
     * if the keys to be added overlap with the keys already in this map. By using the
     * conservative calculation, we subject ourself to at most one extra resize.
     */
    if (numKeysToBeAdded > threshold)
    {
      int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
      if (targetCapacity > MAXIMUM_CAPACITY)
      {
        targetCapacity = MAXIMUM_CAPACITY;
      }
      int newCapacity = table.length;
      while (newCapacity < targetCapacity)
      {
        newCapacity <<= 1;
      }
      if (newCapacity > table.length)
      {
        resize(newCapacity);
      }
    }

    for (Iterator<Entry<V>> i = m.entrySet().iterator(); i.hasNext();)
    {
      Entry<V> e = i.next();
      put(e.getKey(), e.getValue());
    }
  }

  /**
   * Removes the mapping for this key from this map if present.
   * 
   * @param key
   *            key whose mapping is to be removed from the map.
   * @return previous value associated with specified key, or <tt>null</tt> if there was no
   *         mapping for key. A <tt>null</tt> return can also indicate that the map previously
   *         associated <tt>null</tt> with the specified key.
   */
  public V remove(int key)
  {
    Entry<V> e = removeEntryForKey(key);
    return (e == null ? null : e.value);
  }

  /**
   * Removes and returns the entry associated with the specified key in the HashMap. Returns null
   * if the HashMap contains no mapping for this key.
   * 
   * @param key
   * @return The Entry object that was removed
   */
  Entry<V> removeEntryForKey(int key)
  {
    int i = indexFor(key, table.length);
    Entry<V> prev = table[i];
    Entry<V> e = prev;

    while (e != null)
    {
      Entry<V> next = e.next;
      if (key == e.key)
      {
        modCount++;
        size--;
        if (prev == e)
        {
          table[i] = next;
        }
        else
        {
          prev.next = next;
        }
        return e;
      }
      prev = e;
      e = next;
    }

    return e;
  }

  /**
   * Special version of remove for EntrySet.
   * 
   * @param o
   * @return The entry that was removed
   */
  @SuppressWarnings("unchecked")
  Entry<V> removeMapping(Object o)
  {
    if (!(o instanceof Entry))
    {
      return null;
    }

    Entry<V> entry = (Entry<V>)o;
    int key = entry.getKey();
    int i = indexFor(key, table.length);
    Entry<V> prev = table[i];
    Entry<V> e = prev;

    while (e != null)
    {
      Entry<V> next = e.next;
      if (e.key == key && e.equals(entry))
      {
        modCount++;
        size--;
        if (prev == e)
        {
          table[i] = next;
        }
        else
        {
          prev.next = next;
        }
        return e;
      }
      prev = e;
      e = next;
    }

    return e;
  }

  /**
   * Removes all mappings from this map.
   */
  public void clear()
  {
    modCount++;
    Entry<V> tab[] = table;
    for (int i = 0; i < tab.length; i++)
    {
      tab[i] = null;
    }
    size = 0;
  }

  /**
   * Returns <tt>true</tt> if this map maps one or more keys to the specified value.
   * 
   * @param value
   *            value whose presence in this map is to be tested.
   * @return <tt>true</tt> if this map maps one or more keys to the specified value.
   */
  public boolean containsValue(Object value)
  {
    if (value == null)
    {
      return containsNullValue();
    }

    Entry<V> tab[] = table;
    for (int i = 0; i < tab.length; i++)
    {
      for (Entry<V> e = tab[i]; e != null; e = e.next)
      {
        if (value.equals(e.value))
        {
          return true;
        }
      }
    }
    return false;
  }

  /**
   * Special-case code for containsValue with null argument
   * 
   * @return boolean true if there is a null value in this map
   */
  private boolean containsNullValue()
  {
    Entry<V> tab[] = table;
    for (int i = 0; i < tab.length; i++)
    {
      for (Entry<V> e = tab[i]; e != null; e = e.next)
      {
        if (e.value == null)
        {
          return true;
        }
      }
    }
    return false;
  }

  /**
   * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and values themselves
   * are not cloned.
   * 
   * @return a shallow copy of this map.
   */
  @SuppressWarnings("unchecked")
  @Override
  public Object clone() throws CloneNotSupportedException
  {
    IntHashMap<V> result = null;
    try
    {
      result = (IntHashMap<V>)super.clone();
      result.table = new Entry[table.length];
      result.entrySet = null;
      result.modCount = 0;
      result.size = 0;
      result.init();
      result.putAllForCreate(this);
    }
    catch (CloneNotSupportedException e)
    {
      // assert false;
    }
    return result;
  }

  /**
   * @author jcompagner
   * @param <V>
   *            type of value object
   */
  public static class Entry<V>
  {
    final int key;
    V value;
    Entry<V> next;

    /**
     * Create new entry.
     * 
     * @param k
     * @param v
     * @param n
     */
    Entry(int k, V v, Entry<V> n)
    {
      value = v;
      next = n;
      key = k;
    }

    /**
     * @return The int key of this entry
     */
    public int getKey()
    {
      return key;
    }

    /**
     * @return Gets the value object of this entry
     */
    public V getValue()
    {
      return value;
    }

    /**
     * @param newValue
     * @return The previous value
     */
    public V setValue(V newValue)
    {
      V oldValue = value;
      value = newValue;
      return oldValue;
    }

    /**
     * @see java.lang.Object#equals(java.lang.Object)
     */
    @SuppressWarnings("unchecked")
    @Override
    public boolean equals(Object o)
    {
      if (!(o instanceof Entry))
      {
        return false;
      }
      Entry<V> e = (Entry<V>)o;
      int k1 = getKey();
      int k2 = e.getKey();
      if (k1 == k2)
      {
        Object v1 = getValue();
        Object v2 = e.getValue();
        if (v1 == v2 || (v1 != null && v1.equals(v2)))
        {
          return true;
        }
      }
      return false;
    }

    /**
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode()
    {
      return key ^ (value == null ? 0 : value.hashCode());
    }

    /**
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString()
    {
      return getKey() + "=" + getValue(); //$NON-NLS-1$
    }
  }

  /**
   * Add a new entry with the specified key, value and hash code to the specified bucket. It is
   * the responsibility of this method to resize the table if appropriate.
   * 
   * Subclass overrides this to alter the behavior of put method.
   * 
   * @param key
   * @param value
   * @param bucketIndex
   */
  void addEntry(int key, V value, int bucketIndex)
  {
    table[bucketIndex] = new Entry<V>(key, value, table[bucketIndex]);
    if (size++ >= threshold)
    {
      resize(2 * table.length);
    }
  }

  /**
   * Like addEntry except that this version is used when creating entries as part of Map
   * construction or "pseudo-construction" (cloning, deserialization). This version needn't worry
   * about resizing the table.
   * 
   * Subclass overrides this to alter the behavior of HashMap(Map), clone, and readObject.
   * 
   * @param key
   * @param value
   * @param bucketIndex
   */
  void createEntry(int key, V value, int bucketIndex)
  {
    table[bucketIndex] = new Entry<V>(key, value, table[bucketIndex]);
    size++;
  }

  private abstract class HashIterator<H> implements Iterator<H>
  {
    Entry<V> next; // next entry to return
    int expectedModCount; // For fast-fail
    int index; // current slot
    Entry<V> current; // current entry

    HashIterator()
    {
      expectedModCount = modCount;
      Entry<V>[] t = table;
      int i = t.length;
      Entry<V> n = null;
      if (size != 0)
      { // advance to first entry
        while (i > 0 && (n = t[--i]) == null)
        {
          /* NoOp */;
        }
      }
      next = n;
      index = i;
    }

    /**
     * @see java.util.Iterator#hasNext()
     */
    public boolean hasNext()
    {
      return next != null;
    }

    Entry<V> nextEntry()
    {
      if (modCount != expectedModCount)
      {
        throw new ConcurrentModificationException();
      }
      Entry<V> e = next;
      if (e == null)
      {
        throw new NoSuchElementException();
      }

      Entry<V> n = e.next;
      Entry<V>[] t = table;
      int i = index;
      while (n == null && i > 0)
      {
        n = t[--i];
      }
      index = i;
      next = n;
      return current = e;
    }

    /**
     * @see java.util.Iterator#remove()
     */
    public void remove()
    {
      if (current == null)
      {
        throw new IllegalStateException();
      }
      if (modCount != expectedModCount)
      {
        throw new ConcurrentModificationException();
      }
      int k = current.key;
      current = null;
      removeEntryForKey(k);
      expectedModCount = modCount;
    }

  }

  private class ValueIterator extends HashIterator<V>
  {
    /**
     * @see java.util.Iterator#next()
     */
    public V next()
    {
      return nextEntry().value;
    }
  }

  private class KeyIterator extends HashIterator<Integer>
  {
    /**
     * @see java.util.Iterator#next()
     */
    public Integer next()
    {
      return new Integer(nextEntry().getKey());
    }
  }

  private class EntryIterator extends HashIterator<Entry<V>>
  {
    /**
     * @see java.util.Iterator#next()
     */
    public Entry<V> next()
    {
      Entry<V> nextEntry = nextEntry();
      return nextEntry;
    }
  }

  // Subclass overrides these to alter behavior of views' iterator() method
  Iterator<Integer> newKeyIterator()
  {
    return new KeyIterator();
  }

  Iterator<V> newValueIterator()
  {
    return new ValueIterator();
  }

  Iterator<Entry<V>> newEntryIterator()
  {
    return new EntryIterator();
  }

  // Views

  private transient Set<Entry<V>> entrySet = null;

  /**
   * Returns a set view of the keys contained in this map. The set is backed by the map, so
   * changes to the map are reflected in the set, and vice-versa. The set supports element
   * removal, which removes the corresponding mapping from this map, via the
   * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
   * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support the <tt>add</tt>
   * or <tt>addAll</tt> operations.
   * 
   * @return a set view of the keys contained in this map.
   */
  public Set<Integer> keySet()
  {
    Set<Integer> ks = keySet;
    return (ks != null ? ks : (keySet = new KeySet()));
  }

  private class KeySet extends AbstractSet<Integer>
  {
    /**
     * @see java.util.AbstractCollection#iterator()
     */
    @Override
    public Iterator<Integer> iterator()
    {
      return newKeyIterator();
    }

    /**
     * @see java.util.AbstractCollection#size()
     */
    @Override
    public int size()
    {
      return size;
    }

    /**
     * @see java.util.AbstractCollection#contains(java.lang.Object)
     */
    @Override
    public boolean contains(Object o)
    {
      if (o instanceof Number)
      {
        return containsKey(((Number)o).intValue());
      }
      return false;
    }

    /**
     * @see java.util.AbstractCollection#remove(java.lang.Object)
     */
    @Override
    public boolean remove(Object o)
    {
      if (o instanceof Number)
      {
        return removeEntryForKey(((Number)o).intValue()) != null;
      }
      return false;
    }

    /**
     * @see java.util.AbstractCollection#clear()
     */
    @Override
    public void clear()
    {
      IntHashMap.this.clear();
    }
  }

  /**
   * Returns a collection view of the values contained in this map. The collection is backed by
   * the map, so changes to the map are reflected in the collection, and vice-versa. The
   * collection supports element removal, which removes the corresponding mapping from this map,
   * via the <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, <tt>removeAll</tt>,
   * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support the <tt>add</tt>
   * or <tt>addAll</tt> operations.
   * 
   * @return a collection view of the values contained in this map.
   */
  public Collection<V> values()
  {
    Collection<V> vs = values;
    return (vs != null ? vs : (values = new Values()));
  }

  private class Values extends AbstractCollection<V>
  {
    /**
     * @see java.util.AbstractCollection#iterator()
     */
    @Override
    public Iterator<V> iterator()
    {
      return newValueIterator();
    }

    /**
     * @see java.util.AbstractCollection#size()
     */
    @Override
    public int size()
    {
      return size;
    }

    /**
     * @see java.util.AbstractCollection#contains(java.lang.Object)
     */
    @Override
    public boolean contains(Object o)
    {
      return containsValue(o);
    }

    /**
     * @see java.util.AbstractCollection#clear()
     */
    @Override
    public void clear()
    {
      IntHashMap.this.clear();
    }
  }

  /**
   * Returns a collection view of the mappings contained in this map. Each element in the returned
   * collection is a <tt>Map.Entry</tt>. The collection is backed by the map, so changes to the
   * map are reflected in the collection, and vice-versa. The collection supports element removal,
   * which removes the corresponding mapping from the map, via the <tt>Iterator.remove</tt>,
   * <tt>Collection.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
   * <tt>clear</tt> operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
   * operations.
   * 
   * @return a collection view of the mappings contained in this map.
   * @see Map.Entry
   */
  public Set<Entry<V>> entrySet()
  {
    Set<Entry<V>> es = entrySet;
    return (es != null ? es : (entrySet = new EntrySet()));
  }

  private class EntrySet extends AbstractSet<Entry<V>>
  {
    /**
     * @see java.util.AbstractCollection#iterator()
     */
    @Override
    public Iterator<Entry<V>> iterator()
    {
      return newEntryIterator();
    }

    /**
     * @see java.util.AbstractCollection#contains(java.lang.Object)
     */
    @SuppressWarnings("unchecked")
    @Override
    public boolean contains(Object o)
    {
      if (!(o instanceof Entry))
      {
        return false;
      }
      Entry<V> e = (Entry<V>)o;
      Entry<V> candidate = getEntry(e.getKey());
      return candidate != null && candidate.equals(e);
    }

    /**
     * @see java.util.AbstractCollection#remove(java.lang.Object)
     */
    @Override
    public boolean remove(Object o)
    {
      return removeMapping(o) != null;
    }

    /**
     * @see java.util.AbstractCollection#size()
     */
    @Override
    public int size()
    {
      return size;
    }

    /**
     * @see java.util.AbstractCollection#clear()
     */
    @Override
    public void clear()
    {
      IntHashMap.this.clear();
    }
  }

  /**
   * Save the state of the <tt>HashMap</tt> instance to a stream (i.e., serialize it).
   * 
   * @param s
   *            The ObjectOutputStream
   * @throws IOException
   * 
   * @serialData The <i>capacity</i> of the HashMap (the length of the bucket array) is emitted
   *             (int), followed by the <i>size</i> of the HashMap (the number of key-value
   *             mappings), followed by the key (Object) and value (Object) for each key-value
   *             mapping represented by the HashMap The key-value mappings are emitted in the
   *             order that they are returned by <tt>entrySet().iterator()</tt>.
   * 
   */
  private void writeObject(java.io.ObjectOutputStream s) throws IOException
  {
    // Write out the threshold, loadfactor, and any hidden stuff
    s.defaultWriteObject();

    // Write out number of buckets
    s.writeInt(table.length);

    // Write out size (number of Mappings)
    s.writeInt(size);

    // Write out keys and values (alternating)
    for (Iterator<Entry<V>> i = entrySet().iterator(); i.hasNext();)
    {
      Entry<V> e = i.next();
      s.writeInt(e.getKey());
      s.writeObject(e.getValue());
    }
  }

  private static final long serialVersionUID = 362498820763181265L;

  /**
   * Reconstitute the <tt>HashMap</tt> instance from a stream (i.e., deserialize it).
   * 
   * @param s
   * @throws IOException
   * @throws ClassNotFoundException
   */
  @SuppressWarnings("unchecked")
  private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException
  {
    // Read in the threshold, loadfactor, and any hidden stuff
    s.defaultReadObject();

    // Read in number of buckets and allocate the bucket array;
    int numBuckets = s.readInt();
    table = new Entry[numBuckets];

    init(); // Give subclass a chance to do its thing.

    // Read in size (number of Mappings)
    int size = s.readInt();

    // Read the keys and values, and put the mappings in the HashMap
    for (int i = 0; i < size; i++)
    {
      int key = s.readInt();
      V value = (V)s.readObject();
      putForCreate(key, value);
    }
  }

  // These methods are used when serializing HashSets
  int capacity()
  {
    return table.length;
  }

  float loadFactor()
  {
    return loadFactor;
  }
}

   
    
    
    
  








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2.Case Insensitive Map
3.A Map collection with real-time behavior
4.Cache Map
5.Map implementation Optimized for Strings keys
6.An IdentityMap that uses reference-equality instead of object-equality
7.Int Object HashMap
8.Concurrent Skip List Map
9.A hash map that uses primitive ints for the key rather than objects.
10.Integer Map
11.Copy On Write Map
12.Expiring Map
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15.Int HashMap from jodd.org
16.String Map
17.List Map
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21.Multi Map
22.MultiMap is a Java version of the C++ STL class std::multimap
23.Object Int Map
24.Sequenced HashMap
25.Int Int Map
26.Int Object Map
27.Identity HashMap
28.A java.util.Map interface which can only hold a single object
29.A multi valued Map
30.A simple hashmap from keys to integers
31.A memory-efficient hash map.
32.An implementation of the java.util.Map interface which can only hold a single object.
33.Utility methods for operating on memory-efficient maps.
34.CaseBlindHashMap - a HashMap extension, using Strings as key values.
35.A fixed size map implementation.
36.Int HashMap
37.IntMap provides a simple hashmap from keys to integers
38.Complex Key HashMap
39.A Map with multiple values for a key
40.A Map that accepts int or Integer keys only
41.A Map where keys are compared by object identity, rather than equals()
42.Type-safe Map, from char array to String value
43.A hashtable-based Map implementation with soft keys
44.List ordered map
45.Hash map using String values as keys mapped to primitive int values.
46.Lookup table that stores a list of strings
47.HashNMap stores multiple values by a single key value. Values can be retrieved using a direct query or by creating an enumeration over the stored elements.
48.Combines multiple values to form a single composite key. MultiKey can often be used as an alternative to nested maps.