Spec-Zone .ru
спецификации, руководства, описания, API
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001/* 002 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved. 003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 004 * 005 * This code is free software; you can redistribute it and/or modify it 006 * under the terms of the GNU General Public License version 2 only, as 007 * published by the Free Software Foundation. Oracle designates this 008 * particular file as subject to the "Classpath" exception as provided 009 * by Oracle in the LICENSE file that accompanied this code. 010 * 011 * This code is distributed in the hope that it will be useful, but WITHOUT 012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 014 * version 2 for more details (a copy is included in the LICENSE file that 015 * accompanied this code). 016 * 017 * You should have received a copy of the GNU General Public License version 018 * 2 along with this work; if not, write to the Free Software Foundation, 019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 020 * 021 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 022 * or visit www.oracle.com if you need additional information or have any 023 * questions. 024 */ 025 026package javafx.beans; 027 028import java.lang.ref.WeakReference; 029 030/** 031 * A {@code WeakInvalidationListener} can be used, if an {@link Observable} 032 * should only maintain a weak reference to the listener. This helps to avoid 033 * memory leaks, that can occur if observers are not unregistered from observed 034 * objects after use. 035 * <p> 036 * {@code WeakInvalidationListener} are created by passing in the original 037 * {@link InvalidationListener}. The {@code WeakInvalidationListener} should 038 * then be registered to listen for changes of the observed object. 039 * <p> 040 * Note: You have to keep a reference to the {@code InvalidationListener}, that 041 * was passed in as long as it is in use, otherwise it will be garbage collected 042 * to soon. 043 * 044 * @see InvalidationListener 045 * @see Observable 046 * 047 * 048 */ 049public final class WeakInvalidationListener implements InvalidationListener, WeakListener { 050 051 private final WeakReference<InvalidationListener> ref; 052 053 /** 054 * The constructor of {@code WeakInvalidationListener}. 055 * 056 * @param listener 057 * The original listener that should be notified 058 */ 059 public WeakInvalidationListener(InvalidationListener listener) { 060 if (listener == null) { 061 throw new NullPointerException("Listener must be specified."); 062 } 063 this.ref = new WeakReference<InvalidationListener>(listener); 064 } 065 066 /** 067 * {@inheritDoc} 068 */ 069 @Override 070 public boolean wasGarbageCollected() { 071 return (ref.get() == null); 072 } 073 074 /** 075 * {@inheritDoc} 076 */ 077 @Override 078 public void invalidated(Observable observable) { 079 InvalidationListener listener = ref.get(); 080 if (listener != null) { 081 listener.invalidated(observable); 082 } else { 083 // The weakly reference listener has been garbage collected, 084 // so this WeakListener will now unhook itself from the 085 // source bean 086 observable.removeListener(this); 087 } 088 } 089}