Source for java.lang.ref.WeakReference

   1: /* java.lang.ref.WeakReference
   2:    Copyright (C) 1999, 2004 Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10:  
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: 
  39: package java.lang.ref;
  40: 
  41: /**
  42:  * A weak reference will be cleared, if the object is only weakly
  43:  * reachable.  It is useful for lookup tables, where you aren't
  44:  * interested in an entry, if the key isn't reachable anymore.
  45:  * <code>WeakHashtable</code> is a complete implementation of such a
  46:  * table. <br>
  47:  *
  48:  * It is also useful to make objects unique: You create a set of weak
  49:  * references to those objects, and when you create a new object you
  50:  * look in this set, if the object already exists and return it.  If
  51:  * an object is not referenced anymore, the reference will
  52:  * automatically cleared, and you may remove it from the set. <br>
  53:  *
  54:  * @author Jochen Hoenicke 
  55:  * @see java.util.WeakHashMap 
  56:  */
  57: public class WeakReference<T>
  58:   extends Reference<T>
  59: {
  60:   /**
  61:    * Create a new weak reference, that is not registered to any queue.
  62:    * @param referent the object we refer to.
  63:    */
  64:   public WeakReference(T referent)
  65:   {
  66:     super(referent);
  67:   }
  68: 
  69:   /**
  70:    * Create a new weak reference.
  71:    * @param referent the object we refer to.
  72:    * @param q the reference queue to register on.
  73:    * @exception NullPointerException if q is null.
  74:    */
  75:   public WeakReference(T referent, ReferenceQueue<? super T> q)
  76:   {
  77:     super(referent, q);
  78:   }
  79: }