IntMap provides a simple hashmap from keys to integers : Customized Map « Collections Data Structure « Java

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2. Collections Data Structure
3. Customized Map

IntMap provides a simple hashmap from keys to integers

   
/*
 * Copyright (c) 2001-2008 Caucho Technology, Inc.  All rights reserved.
 *
 * The Apache Software License, Version 1.1
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Caucho Technology (http://www.caucho.com/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "Burlap", "Resin", and "Caucho" must not be used to
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 * 5. Products derived from this software may not be called "Resin"
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 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL CAUCHO TECHNOLOGY OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
 * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * @author Scott Ferguson
 */


/**
 * The IntMap provides a simple hashmap from keys to integers.  The API is
 * an abbreviation of the HashMap collection API.
 *
 * <p>The convenience of IntMap is avoiding all the silly wrapping of
 * integers.
 */
public class IdentityIntMap {
  /**
   * Encoding of a null entry.  Since NULL is equal to Integer.MIN_VALUE, 
   * it's impossible to distinguish between the two.
   */
  public final static int NULL = 0xdeadbeef; // Integer.MIN_VALUE + 1;

  private static final Object DELETED = new Object();

  private Object []_keys;
  private int []_values;

  private int _size;
  private int _mask;

  /**
   * Create a new IntMap.  Default size is 16.
   */
  public IdentityIntMap()
  {
    _keys = new Object[256];
    _values = new int[256];

    _mask = _keys.length - 1;
    _size = 0;
  }

  /**
   * Clear the hashmap.
   */
  public void clear()
  {
    Object []keys = _keys;
    int []values = _values;

    for (int i = keys.length - 1; i >= 0; i--) {
      keys[i] = null;
      values[i] = 0;
    }

    _size = 0;
  }
  /**
   * Returns the current number of entries in the map.
   */
  public int size()
  {
    return _size;
  }

  /**
   * Puts a new value in the property table with the appropriate flags
   */
  public int get(Object key)
  {
    int mask = _mask;
    int hash = System.identityHashCode(key) % mask & mask;

    Object []keys = _keys;

    while (true) {
      Object mapKey = keys[hash];

      if (mapKey == null)
        return NULL;
      else if (mapKey == key)
        return _values[hash];

      hash = (hash + 1) % mask;
    }
  }

  /**
   * Expands the property table
   */
  private void resize(int newSize)
  {
    Object []newKeys = new Object[newSize];
    int []newValues = new int[newSize];

    int mask = _mask = newKeys.length - 1;

    Object []keys = _keys;
    int values[] = _values;

    for (int i = keys.length - 1; i >= 0; i--) {
      Object key = keys[i];

      if (key == null || key == DELETED)
        continue;

      int hash = System.identityHashCode(key) % mask & mask;

      while (true) {
        if (newKeys[hash] == null) {
          newKeys[hash] = key;
          newValues[hash] = values[i];
          break;
        }

        hash = (hash + 1) % mask;
      }
    }

    _keys = newKeys;
    _values = newValues;
  }

  /**
   * Puts a new value in the property table with the appropriate flags
   */
  public int put(Object key, int value)
  {
    int mask = _mask;
    int hash = System.identityHashCode(key) % mask & mask;

    Object []keys = _keys;

    while (true) {
      Object testKey = keys[hash];

      if (testKey == null || testKey == DELETED) {
        keys[hash] = key;
        _values[hash] = value;

        _size++;

        if (keys.length <= 4 * _size)
          resize(4 * keys.length);

        return NULL;
      }
      else if (key != testKey) {
        hash = (hash + 1) % mask;

        continue;
      }
      else {
        int old = _values[hash];

        _values[hash] = value;

        return old;
      }
    }
  }

  /**
   * Deletes the entry.  Returns true if successful.
   */
  public int remove(Object key)
  {
    int mask = _mask;
    int hash = System.identityHashCode(key) % mask & mask;

    while (true) {
      Object mapKey = _keys[hash];

      if (mapKey == null)
        return NULL;
      else if (mapKey == key) {
        _keys[hash] = DELETED;

        _size--;

        return _values[hash];
      }

      hash = (hash + 1) % mask;
    }
  }

  public String toString()
  {
    StringBuffer sbuf = new StringBuffer();

    sbuf.append("IntMap[");
    boolean isFirst = true;

    for (int i = 0; i <= _mask; i++) {
      if (_keys[i] != null && _keys[i] != DELETED) {
        if (! isFirst)
          sbuf.append(", ");

        isFirst = false;
        sbuf.append(_keys[i]);
        sbuf.append(":");
        sbuf.append(_values[i]);
      }
    }
    sbuf.append("]");

    return sbuf.toString();
  }
}

   
    
    
  

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