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}