001/* java.lang.ref.WeakReference
002   Copyright (C) 1999, 2004 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.lang.ref;
040
041/**
042 * A weak reference will be cleared, if the object is only weakly
043 * reachable.  It is useful for lookup tables, where you aren't
044 * interested in an entry, if the key isn't reachable anymore.
045 * <code>WeakHashtable</code> is a complete implementation of such a
046 * table. <br>
047 *
048 * It is also useful to make objects unique: You create a set of weak
049 * references to those objects, and when you create a new object you
050 * look in this set, if the object already exists and return it.  If
051 * an object is not referenced anymore, the reference will
052 * automatically cleared, and you may remove it from the set. <br>
053 *
054 * @author Jochen Hoenicke
055 * @see java.util.WeakHashMap
056 */
057public class WeakReference<T>
058  extends Reference<T>
059{
060  /**
061   * Create a new weak reference, that is not registered to any queue.
062   * @param referent the object we refer to.
063   */
064  public WeakReference(T referent)
065  {
066    super(referent);
067  }
068
069  /**
070   * Create a new weak reference.
071   * @param referent the object we refer to.
072   * @param q the reference queue to register on.
073   * @exception NullPointerException if q is null.
074   */
075  public WeakReference(T referent, ReferenceQueue<? super T> q)
076  {
077    super(referent, q);
078  }
079}