Spec-Zone .ru
спецификации, руководства, описания, API
|
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.value; 027 028import javafx.beans.InvalidationListener; 029import javafx.beans.Observable; 030 031/** 032 * An {@code ObservableValue} is an entity that wraps a value and allows to 033 * observe the value for changes. In general this interface should not be 034 * implemented directly but one of its sub-interfaces ( 035 * {@code ObservableBooleanValue} etc.). 036 * <p> 037 * The value of the {@code ObservableValue} can be requested with 038 * {@link #getValue()}. 039 * <p> 040 * An implementation of {@code ObservableValue} may support lazy evaluation, 041 * which means that the value is not immediately recomputed after changes, but 042 * lazily the next time the value is requested. All bindings and properties in 043 * this library support lazy evaluation. 044 * <p> 045 * An {@code ObservableValue} generates two types of events: change events and 046 * invalidation events. A change event indicates that the value has changed. An 047 * invalidation event is generated, if the current value is not valid anymore. 048 * This distinction becomes important, if the {@code ObservableValue} supports 049 * lazy evaluation, because for a lazily evaluated value one does not know if an 050 * invalid value really has changed until it is recomputed. For this reason, 051 * generating change events requires eager evaluation while invalidation events 052 * can be generated for eager and lazy implementations. 053 * <p> 054 * Implementations of this class should strive to generate as few events as 055 * possible to avoid wasting too much time in event handlers. Implementations in 056 * this library mark themselves as invalid when the first invalidation event 057 * occurs. They do not generate anymore invalidation events until their value is 058 * recomputed and valid again. 059 * <p> 060 * Two types of listeners can be attached to an {@code ObservableValue}: 061 * {@link InvalidationListener} to listen to invalidation events and 062 * {@link ChangeListener} to listen to change events. 063 * <p> 064 * Important note: attaching a {@code ChangeListener} enforces eager computation 065 * even if the implementation of the {@code ObservableValue} supports lazy 066 * evaluation. 067 * 068 * @param <T> 069 * The type of the wrapped value. 070 * 071 * @see ObservableBooleanValue 072 * @see ObservableDoubleValue 073 * @see ObservableFloatValue 074 * @see ObservableIntegerValue 075 * @see ObservableLongValue 076 * @see ObservableNumberValue 077 * @see ObservableObjectValue 078 * @see ObservableStringValue 079 * 080 * 081 */ 082public interface ObservableValue<T> extends Observable { 083 084 /** 085 * Adds a {@link ChangeListener} which will be notified whenever the value 086 * of the {@code ObservableValue} changes. If the same listener is added 087 * more than once, then it will be notified more than once. That is, no 088 * check is made to ensure uniqueness. 089 * <p> 090 * Note that the same actual {@code ChangeListener} instance may be safely 091 * registered for different {@code ObservableValues}. 092 * <p> 093 * The {@code ObservableValue} stores a strong reference to the listener 094 * which will prevent the listener from being garbage collected and may 095 * result in a memory leak. It is recommended to either unregister a 096 * listener by calling {@link #removeListener(ChangeListener) 097 * removeListener} after use or to use an instance of 098 * {@link WeakChangeListener} avoid this situation. 099 * 100 * @see #removeListener(ChangeListener) 101 * 102 * @param listener 103 * The listener to register 104 * @throws NullPointerException 105 * if the listener is null 106 */ 107 void addListener(ChangeListener<? super T> listener); 108 109 /** 110 * Removes the given listener from the list of listeners, that are notified 111 * whenever the value of the {@code ObservableValue} changes. 112 * <p> 113 * If the given listener has not been previously registered (i.e. it was 114 * never added) then this method call is a no-op. If it had been previously 115 * added then it will be removed. If it had been added more than once, then 116 * only the first occurrence will be removed. 117 * 118 * @see #addListener(ChangeListener) 119 * 120 * @param listener 121 * The listener to remove 122 * @throws NullPointerException 123 * if the listener is null 124 */ 125 void removeListener(ChangeListener<? super T> listener); 126 127 /** 128 * Returns the current value of this {@code ObservableValue} 129 * 130 * @return The current value 131 */ 132 T getValue(); 133}