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| 1 | /* | ||
| 2 | * Copyright (c) 1994, 2004, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | |||
| 28 | /** | ||
| 29 | * This class represents an observable object, or "data" | ||
| 30 | * in the model-view paradigm. It can be subclassed to represent an | ||
| 31 | * object that the application wants to have observed. | ||
| 32 | * <p> | ||
| 33 | * An observable object can have one or more observers. An observer | ||
| 34 | * may be any object that implements interface <tt>Observer</tt>. After an | ||
| 35 | * observable instance changes, an application calling the | ||
| 36 | * <code>Observable</code>'s <code>notifyObservers</code> method | ||
| 37 | * causes all of its observers to be notified of the change by a call | ||
| 38 | * to their <code>update</code> method. | ||
| 39 | * <p> | ||
| 40 | * The order in which notifications will be delivered is unspecified. | ||
| 41 | * The default implementation provided in the Observable class will | ||
| 42 | * notify Observers in the order in which they registered interest, but | ||
| 43 | * subclasses may change this order, use no guaranteed order, deliver | ||
| 44 | * notifications on separate threads, or may guarantee that their | ||
| 45 | * subclass follows this order, as they choose. | ||
| 46 | * <p> | ||
| 47 | * Note that this notification mechanism is has nothing to do with threads | ||
| 48 | * and is completely separate from the <tt>wait</tt> and <tt>notify</tt> | ||
| 49 | * mechanism of class <tt>Object</tt>. | ||
| 50 | * <p> | ||
| 51 | * When an observable object is newly created, its set of observers is | ||
| 52 | * empty. Two observers are considered the same if and only if the | ||
| 53 | * <tt>equals</tt> method returns true for them. | ||
| 54 | * | ||
| 55 | * @author Chris Warth | ||
| 56 | * @see java.util.Observable#notifyObservers() | ||
| 57 | * @see java.util.Observable#notifyObservers(java.lang.Object) | ||
| 58 | * @see java.util.Observer | ||
| 59 | * @see java.util.Observer#update(java.util.Observable, java.lang.Object) | ||
| 60 | * @since JDK1.0 | ||
| 61 | */ | ||
| 62 | public class Observable { | ||
| 63 | private boolean changed = false; | ||
| 64 | private Vector obs; | ||
| 65 | |||
| 66 | /** Construct an Observable with zero Observers. */ | ||
| 67 | |||
| 68 | public Observable() { | ||
| 69 | obs = new Vector(); | ||
| 70 | } | ||
| 71 | |||
| 72 | /** | ||
| 73 | * Adds an observer to the set of observers for this object, provided | ||
| 74 | * that it is not the same as some observer already in the set. | ||
| 75 | * The order in which notifications will be delivered to multiple | ||
| 76 | * observers is not specified. See the class comment. | ||
| 77 | * | ||
| 78 | * @param o an observer to be added. | ||
| 79 | * @throws NullPointerException if the parameter o is null. | ||
| 80 | */ | ||
| 81 | public synchronized void addObserver(Observer o) { | ||
| 82 | if (o == null) | ||
| 83 | throw new NullPointerException(); | ||
| 84 | if (!obs.contains(o)) { | ||
| 85 | obs.addElement(o); | ||
| 86 | } | ||
| 87 | } | ||
| 88 | |||
| 89 | /** | ||
| 90 | * Deletes an observer from the set of observers of this object. | ||
| 91 | * Passing <CODE>null</CODE> to this method will have no effect. | ||
| 92 | * @param o the observer to be deleted. | ||
| 93 | */ | ||
| 94 | public synchronized void deleteObserver(Observer o) { | ||
| 95 | obs.removeElement(o); | ||
| 96 | } | ||
| 97 | |||
| 98 | /** | ||
| 99 | * If this object has changed, as indicated by the | ||
| 100 | * <code>hasChanged</code> method, then notify all of its observers | ||
| 101 | * and then call the <code>clearChanged</code> method to | ||
| 102 | * indicate that this object has no longer changed. | ||
| 103 | * <p> | ||
| 104 | * Each observer has its <code>update</code> method called with two | ||
| 105 | * arguments: this observable object and <code>null</code>. In other | ||
| 106 | * words, this method is equivalent to: | ||
| 107 | * <blockquote><tt> | ||
| 108 | * notifyObservers(null)</tt></blockquote> | ||
| 109 | * | ||
| 110 | * @see java.util.Observable#clearChanged() | ||
| 111 | * @see java.util.Observable#hasChanged() | ||
| 112 | * @see java.util.Observer#update(java.util.Observable, java.lang.Object) | ||
| 113 | */ | ||
| 114 | public void notifyObservers() { | ||
| 115 | notifyObservers(null); | ||
| 116 | } | ||
| 117 | |||
| 118 | /** | ||
| 119 | * If this object has changed, as indicated by the | ||
| 120 | * <code>hasChanged</code> method, then notify all of its observers | ||
| 121 | * and then call the <code>clearChanged</code> method to indicate | ||
| 122 | * that this object has no longer changed. | ||
| 123 | * <p> | ||
| 124 | * Each observer has its <code>update</code> method called with two | ||
| 125 | * arguments: this observable object and the <code>arg</code> argument. | ||
| 126 | * | ||
| 127 | * @param arg any object. | ||
| 128 | * @see java.util.Observable#clearChanged() | ||
| 129 | * @see java.util.Observable#hasChanged() | ||
| 130 | * @see java.util.Observer#update(java.util.Observable, java.lang.Object) | ||
| 131 | */ | ||
| 132 | public void notifyObservers(Object arg) { | ||
| 133 | /* | ||
| 134 | * a temporary array buffer, used as a snapshot of the state of | ||
| 135 | * current Observers. | ||
| 136 | */ | ||
| 137 | Object[] arrLocal; | ||
| 138 | |||
| 139 | synchronized (this) { | ||
| 140 | /* We don't want the Observer doing callbacks into | ||
| 141 | * arbitrary code while holding its own Monitor. | ||
| 142 | * The code where we extract each Observable from | ||
| 143 | * the Vector and store the state of the Observer | ||
| 144 | * needs synchronization, but notifying observers | ||
| 145 | * does not (should not). The worst result of any | ||
| 146 | * potential race-condition here is that: | ||
| 147 | * 1) a newly-added Observer will miss a | ||
| 148 | * notification in progress | ||
| 149 | * 2) a recently unregistered Observer will be | ||
| 150 | * wrongly notified when it doesn't care | ||
| 151 | */ | ||
| 152 | if (!changed) | ||
| 153 | return; | ||
| 154 | arrLocal = obs.toArray(); | ||
| 155 | clearChanged(); | ||
| 156 | } | ||
| 157 | |||
| 158 | for (int i = arrLocal.length-1; i>=0; i--) | ||
| 159 | ((Observer)arrLocal[i]).update(this, arg); | ||
| 160 | } | ||
| 161 | |||
| 162 | /** | ||
| 163 | * Clears the observer list so that this object no longer has any observers. | ||
| 164 | */ | ||
| 165 | public synchronized void deleteObservers() { | ||
| 166 | obs.removeAllElements(); | ||
| 167 | } | ||
| 168 | |||
| 169 | /** | ||
| 170 | * Marks this <tt>Observable</tt> object as having been changed; the | ||
| 171 | * <tt>hasChanged</tt> method will now return <tt>true</tt>. | ||
| 172 | */ | ||
| 173 | protected synchronized void setChanged() { | ||
| 174 | changed = true; | ||
| 175 | } | ||
| 176 | |||
| 177 | /** | ||
| 178 | * Indicates that this object has no longer changed, or that it has | ||
| 179 | * already notified all of its observers of its most recent change, | ||
| 180 | * so that the <tt>hasChanged</tt> method will now return <tt>false</tt>. | ||
| 181 | * This method is called automatically by the | ||
| 182 | * <code>notifyObservers</code> methods. | ||
| 183 | * | ||
| 184 | * @see java.util.Observable#notifyObservers() | ||
| 185 | * @see java.util.Observable#notifyObservers(java.lang.Object) | ||
| 186 | */ | ||
| 187 | protected synchronized void clearChanged() { | ||
| 188 | changed = false; | ||
| 189 | } | ||
| 190 | |||
| 191 | /** | ||
| 192 | * Tests if this object has changed. | ||
| 193 | * | ||
| 194 | * @return <code>true</code> if and only if the <code>setChanged</code> | ||
| 195 | * method has been called more recently than the | ||
| 196 | * <code>clearChanged</code> method on this object; | ||
| 197 | * <code>false</code> otherwise. | ||
| 198 | * @see java.util.Observable#clearChanged() | ||
| 199 | * @see java.util.Observable#setChanged() | ||
| 200 | */ | ||
| 201 | public synchronized boolean hasChanged() { | ||
| 202 | return changed; | ||
| 203 | } | ||
| 204 | |||
| 205 | /** | ||
| 206 | * Returns the number of observers of this <tt>Observable</tt> object. | ||
| 207 | * | ||
| 208 | * @return the number of observers of this object. | ||
| 209 | */ | ||
| 210 | public synchronized int countObservers() { | ||
| 211 | return obs.size(); | ||
| 212 | } | ||
| 213 | } | ||