Int HashMap : Customized Map « Collections Data Structure « Java






Int HashMap

   
/*
 * $Id: ArrayListStack.java 4448 2006-02-14 20:54:57Z jonathanlocke $ $Revision:
 * 4448 $ $Date: 2006-02-14 21:54:57 +0100 (di, 14 feb 2006) $
 * 
 * 
 * Licensed 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 a int 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
 */
public class IntHashMap implements Cloneable, Serializable
{
  transient volatile Set keySet = null;

  transient volatile Collection 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[] 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.
   */
  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).
   */
  public IntHashMap()
  {
    this.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 Object get(int key)
  {
    int i = indexFor(key, table.length);
    Entry e = table[i];
    while (true)
    {
      if (e == null)
      {
        return e;
      }
      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 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 getEntry(int key)
  {
    int i = indexFor(key, table.length);
    Entry 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 Object put(int key, Object value)
  {
    int i = indexFor(key, table.length);

    for (Entry e = table[i]; e != null; e = e.next)
    {
      if (key == e.key)
      {
        Object 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, Object 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 e = table[i]; e != null; e = e.next)
    {
      if (key == e.key)
      {
        e.value = value;
        return;
      }
    }

    createEntry(key, value, i);
  }

  void putAllForCreate(IntHashMap m)
  {
    for (Iterator i = m.entrySet().iterator(); i.hasNext();)
    {
      Entry e = (Entry)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).
   */
  void resize(int newCapacity)
  {
    Entry[] oldTable = table;
    int oldCapacity = oldTable.length;
    if (oldCapacity == MAXIMUM_CAPACITY)
    {
      threshold = Integer.MAX_VALUE;
      return;
    }

    Entry[] 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[] newTable)
  {
    Entry[] src = table;
    int newCapacity = newTable.length;
    for (int j = 0; j < src.length; j++)
    {
      Entry e = src[j];
      if (e != null)
      {
        src[j] = null;
        do
        {
          Entry 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 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 i = m.entrySet().iterator(); i.hasNext();)
    {
      Entry e = (Entry)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 Object remove(int key)
  {
    Entry e = removeEntryForKey(key);
    return (e == null ? e : 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 removeEntryForKey(int key)
  {
    int i = indexFor(key, table.length);
    Entry prev = table[i];
    Entry e = prev;

    while (e != null)
    {
      Entry 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
   */
  Entry removeMapping(Object o)
  {
    if (!(o instanceof Entry))
    {
      return null;
    }

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

    while (e != null)
    {
      Entry 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 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 tab[] = table;
    for (int i = 0; i < tab.length; i++)
    {
      for (Entry 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 tab[] = table;
    for (int i = 0; i < tab.length; i++)
    {
      for (Entry 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.
   */
  public Object clone() throws CloneNotSupportedException
  {
    IntHashMap result = null;
    try
    {
      result = (IntHashMap)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
   */
  public static class Entry
  {
    final int key;
    Object value;
    Entry next;

    /**
     * Create new entry.
     * 
     * @param k
     * @param v
     * @param n
     */
    Entry(int k, Object v, Entry 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 Object getValue()
    {
      return value;
    }

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

    /**
     * @see java.lang.Object#equals(java.lang.Object)
     */
    public boolean equals(Object o)
    {
      if (!(o instanceof Entry))
      {
        return false;
      }
      Entry e = (Entry)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()
     */
    public int hashCode()
    {
      return key ^ (value == null ? 0 : value.hashCode());
    }

    /**
     * @see java.lang.Object#toString()
     */
    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, Object value, int bucketIndex)
  {
    table[bucketIndex] = new Entry(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, Object value, int bucketIndex)
  {
    table[bucketIndex] = new Entry(key, value, table[bucketIndex]);
    size++;
  }

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

    HashIterator()
    {
      expectedModCount = modCount;
      Entry[] t = table;
      int i = t.length;
      Entry 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 nextEntry()
    {
      if (modCount != expectedModCount)
      {
        throw new ConcurrentModificationException();
      }
      Entry e = next;
      if (e == null)
      {
        throw new NoSuchElementException();
      }

      Entry n = e.next;
      Entry[] 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;
      IntHashMap.this.removeEntryForKey(k);
      expectedModCount = modCount;
    }

  }

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

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

  private class EntryIterator extends HashIterator
  {
    /**
     * @see java.util.Iterator#next()
     */
    public Object next()
    {
      return nextEntry();
    }
  }

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

  Iterator newValueIterator()
  {
    return new ValueIterator();
  }

  Iterator newEntryIterator()
  {
    return new EntryIterator();
  }

  // Views

  private transient Set 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 keySet()
  {
    Set ks = keySet;
    return (ks != null ? ks : (keySet = new KeySet()));
  }

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

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

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

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

    /**
     * @see java.util.AbstractCollection#clear()
     */
    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 values()
  {
    Collection vs = values;
    return (vs != null ? vs : (values = new Values()));
  }

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

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

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

    /**
     * @see java.util.AbstractCollection#clear()
     */
    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 entrySet()
  {
    Set es = entrySet;
    return (es != null ? es : (entrySet = new EntrySet()));
  }

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

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

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

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

    /**
     * @see java.util.AbstractCollection#clear()
     */
    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 i = entrySet().iterator(); i.hasNext();)
    {
      Entry e = (Entry)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
   */
  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();
      Object value = s.readObject();
      putForCreate(key, value);
    }
  }

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

  float loadFactor()
  {
    return loadFactor;
  }
}

   
    
    
  








Related examples in the same category

1.Ordered Map
2.Case Insensitive Map
3.A Map collection with real-time behavior
4.Cache Map
5.Map implementation Optimized for Strings keys
6.An integer hashmap
7.An IdentityMap that uses reference-equality instead of object-equality
8.Int Object HashMap
9.Concurrent Skip List Map
10.A hash map that uses primitive ints for the key rather than objects.
11.Integer Map
12.Copy On Write Map
13.Expiring Map
14.Array Map
15.Int Object HashMap (from CERN)
16.Int HashMap from jodd.org
17.String Map
18.List Map
19.Map using Locale objects as keys
20.Map with keys iterated in insertion order
21.Most Recently Used Map
22.Multi Map
23.MultiMap is a Java version of the C++ STL class std::multimap
24.Object Int Map
25.Sequenced HashMap
26.Int Int Map
27.Int Object Map
28.Identity HashMap
29.A java.util.Map interface which can only hold a single object
30.A multi valued Map
31.A simple hashmap from keys to integers
32.A memory-efficient hash map.
33.An implementation of the java.util.Map interface which can only hold a single object.
34.Utility methods for operating on memory-efficient maps.
35.CaseBlindHashMap - a HashMap extension, using Strings as key values.
36.A fixed size map implementation.
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.