Source code

001/*
002 * Copyright (c) 2012, 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.event;
027
028import java.lang.ref.WeakReference;
029
030/**
031 * Used in event handler registration in place of its associated event handler.
032 * Its sole purpose is to break the otherwise strong reference between an event
033 * handler container and its associated event handler. While the container still
034 * holds strong reference to the registered {@code WeakEventHandler} proxy, the
035 * proxy itself references the original handler only weakly and so doesn't
036 * prevent it from being garbage collected. Until this weak reference is broken,
037 * any event notification received by the proxy is forwarded to the original
038 * handler.
039 *
040 * @param <T> the event class this handler can handle
041 */
042public final class WeakEventHandler<T extends Event>
043        implements EventHandler<T> {
044    private final WeakReference<EventHandler<T>> weakRef;
045
046    /**
047     * Creates a new instance of {@code WeakEventHandler}.
048     *
049     * @param eventHandler the original event handler to which to forward event
050     *      notifications
051     */
052    public WeakEventHandler(final EventHandler<T> eventHandler) {
053        weakRef = new WeakReference<EventHandler<T>>(eventHandler);
054    }
055
056    /**
057     * Indicates whether the associated event handler has been garbage
058     * collected. Used by containers to detect when the storage of corresponding
059     * references to this {@code WeakEventHandler} is no longer necessary.
060     *
061     * @return {@code true} if the associated handler has been garbage
062     *      collected, {@code false} otherwise
063     */
064    public boolean wasGarbageCollected() {
065        return weakRef.get() == null;
066    }
067
068    /**
069     * Forwards event notification to the associated event handler.
070     *
071     * @param event the event which occurred
072     */
073    @Override
074    public void handle(final T event) {
075        final EventHandler<T> eventHandler = weakRef.get();
076        if (eventHandler != null) {
077            eventHandler.handle(event);
078        }
079    }
080
081    /* Used for testing. */
082    void clear() {
083        weakRef.clear();
084    }
085}