Java tutorial
/* * Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javafx.beans; /** * An {@code Observable} is an entity that wraps content and allows to * observe the content for invalidations. * <p> * An implementation of {@code Observable} may support lazy evaluation, * which means that the content is not immediately recomputed after changes, but * lazily the next time it is requested. All bindings and properties in * this library support lazy evaluation. * <p> * Implementations of this class should strive to generate as few events as * possible to avoid wasting too much time in event handlers. Implementations in * this library mark themselves as invalid when the first invalidation event * occurs. They do not generate anymore invalidation events until their value is * recomputed and valid again. * * @see javafx.beans.value.ObservableValue * @see javafx.collections.ObservableList * @see javafx.collections.ObservableMap * * * @since JavaFX 2.0 */ public interface Observable { /** * Adds an {@link InvalidationListener} which will be notified whenever the * {@code Observable} becomes invalid. If the same * listener is added more than once, then it will be notified more than * once. That is, no check is made to ensure uniqueness. * <p> * Note that the same actual {@code InvalidationListener} instance may be * safely registered for different {@code Observables}. * <p> * The {@code Observable} stores a strong reference to the listener * which will prevent the listener from being garbage collected and may * result in a memory leak. It is recommended to either unregister a * listener by calling {@link #removeListener(InvalidationListener) * removeListener} after use or to use an instance of * {@link WeakInvalidationListener} avoid this situation. * * @see #removeListener(InvalidationListener) * * @param listener * The listener to register * @throws NullPointerException * if the listener is null */ void addListener(InvalidationListener listener); /** * Removes the given listener from the list of listeners, that are notified * whenever the value of the {@code Observable} becomes invalid. * <p> * If the given listener has not been previously registered (i.e. it was * never added) then this method call is a no-op. If it had been previously * added then it will be removed. If it had been added more than once, then * only the first occurrence will be removed. * * @see #addListener(InvalidationListener) * * @param listener * The listener to remove * @throws NullPointerException * if the listener is null */ void removeListener(InvalidationListener listener); }