001    /* java.lang.ref.WeakReference
002       Copyright (C) 1999, 2004 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package 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     */
057    public 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    }