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 }