001 /* java.lang.ref.PhantomReference 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 phantom reference is useful, to get notified, when an object got 043 * finalized. You can't access that object though, since it is 044 * finalized. This is the reason, why <code>get()</code> always 045 * returns null. 046 * 047 * @author Jochen Hoenicke 048 */ 049 public class PhantomReference<T> 050 extends Reference<T> 051 { 052 /** 053 * Creates a new phantom reference. 054 * @param referent the object that should be watched. 055 * @param q the queue that should be notified, if the referent was 056 * finalized. This mustn't be <code>null</code>. 057 * @exception NullPointerException if q is null. 058 */ 059 public PhantomReference(T referent, ReferenceQueue<? super T> q) 060 { 061 super(referent, q); 062 } 063 064 /** 065 * Returns the object, this reference refers to. 066 * @return <code>null</code>, since the refered object may be 067 * finalized and thus not accessible. 068 */ 069 public T get() 070 { 071 return null; 072 } 073 }