source: trunk/src/gcc/libjava/java/util/AbstractMap.java@ 1213

/* AbstractMap.java -- Abstract implementation of most of Map
   Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
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exception statement from your version. */


package java.util;

/**
 * An abstract implementation of Map to make it easier to create your own
 * implementations. In order to create an unmodifiable Map, subclass
 * AbstractMap and implement the <code>entrySet</code> (usually via an
 * AbstractSet).  To make it modifiable, also implement <code>put</code>,
 * and have <code>entrySet().iterator()</code> support <code>remove</code>.
 * <p>
 *
 * It is recommended that classes which extend this support at least the
 * no-argument constructor, and a constructor which accepts another Map.
 * Further methods in this class may be overridden if you have a more
 * efficient implementation.
 *
 * @author Original author unknown
 * @author Bryce McKinlay
 * @author Eric Blake <[email protected]>
 * @see Map
 * @see Collection
 * @see HashMap
 * @see LinkedHashMap
 * @see TreeMap
 * @see WeakHashMap
 * @see IdentityHashMap
 * @since 1.2
 * @status updated to 1.4
 */
public abstract class AbstractMap implements Map
{
  /** An "enum" of iterator types. */
  // Package visible for use by subclasses.
  static final int KEYS = 0,
                   VALUES = 1,
                   ENTRIES = 2;

  /**
   * The cache for {@link #keySet()}.
   */
  // Package visible for use by subclasses.
  Set keys;

  /**
   * The cache for {@link #values()}.
   */
  // Package visible for use by subclasses.
  Collection values;

  /**
   * The main constructor, for use by subclasses.
   */
  protected AbstractMap()
  {
  }

  /**
   * Remove all entries from this Map (optional operation). This default
   * implementation calls entrySet().clear(). NOTE: If the entry set does
   * not permit clearing, then this will fail, too. Subclasses often
   * override this for efficiency.  Your implementation of entrySet() should
   * not call <code>AbstractMap.clear</code> unless you want an infinite loop.
   *
   * @throws UnsupportedOperationException if <code>entrySet().clear()</code>
   *         does not support clearing.
   * @see Set#clear()
   */
  public void clear()
  {
    entrySet().clear();
  }

  /**
   * Create a shallow copy of this Map, no keys or values are copied. The
   * default implementation simply calls <code>super.clone()</code>.
   *
   * @return the shallow clone
   * @throws CloneNotSupportedException if a subclass is not Cloneable
   * @see Cloneable
   * @see Object#clone()
   */
  protected Object clone() throws CloneNotSupportedException
  {
    AbstractMap copy = (AbstractMap) super.clone();
    // Clear out the caches; they are stale.
    copy.keys = null;
    copy.values = null;
    return copy;
  }

  /**
   * Returns true if this contains a mapping for the given key. This
   * implementation does a linear search, O(n), over the
   * <code>entrySet()</code>, returning <code>true</code> if a match
   * is found, <code>false</code> if the iteration ends. Many subclasses
   * can implement this more efficiently.
   *
   * @param key the key to search for
   * @return true if the map contains the key
   * @throws NullPointerException if key is <code>null</code> but the map
   *         does not permit null keys
   * @see #containsValue(Object)
   */
  public boolean containsKey(Object key)
  {
    Iterator entries = entrySet().iterator();
    int pos = size();
    while (--pos >= 0)
      if (equals(key, ((Map.Entry) entries.next()).getKey()))
        return true;
    return false;
  }

  /**
   * Returns true if this contains at least one mapping with the given value.
   * This implementation does a linear search, O(n), over the
   * <code>entrySet()</code>, returning <code>true</code> if a match
   * is found, <code>false</code> if the iteration ends. A match is
   * defined as <code>(value == null ? v == null : value.equals(v))</code>
   * Subclasses are unlikely to implement this more efficiently.
   *
   * @param value the value to search for
   * @return true if the map contains the value
   * @see #containsKey(Object)
   */
  public boolean containsValue(Object value)
  {
    Iterator entries = entrySet().iterator();
    int pos = size();
    while (--pos >= 0)