1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196
/* * @(#)Observable.java 1.39 05/11/17 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util; /** * This class represents an observable object, or "data" * in the model-view paradigm. It can be subclassed to represent an * object that the application wants to have observed. * <p> * An observable object can have one or more observers. An observer * may be any object that implements interface <tt>Observer</tt>. After an * observable instance changes, an application calling the * <code>Observable</code>'s <code>notifyObservers</code> method * causes all of its observers to be notified of the change by a call * to their <code>update</code> method. * <p> * The order in which notifications will be delivered is unspecified. * The default implementation provided in the Observable class will * notify Observers in the order in which they registered interest, but * subclasses may change this order, use no guaranteed order, deliver * notifications on separate threads, or may guarantee that their * subclass follows this order, as they choose. * <p> * Note that this notification mechanism is has nothing to do with threads * and is completely separate from the <tt>wait</tt> and <tt>notify</tt> * mechanism of class <tt>Object</tt>. * <p> * When an observable object is newly created, its set of observers is * empty. Two observers are considered the same if and only if the * <tt>equals</tt> method returns true for them. * * @author Chris Warth * @version 1.39, 11/17/05 * @see java.util.Observable#notifyObservers() * @see java.util.Observable#notifyObservers(java.lang.Object) * @see java.util.Observer * @see java.util.Observer#update(java.util.Observable, java.lang.Object) * @since JDK1.0 */ public class Observable { private boolean changed = false; private Vector obs; /** Construct an Observable with zero Observers. */ public Observable() { obs = new Vector(); } /** * Adds an observer to the set of observers for this object, provided * that it is not the same as some observer already in the set. * The order in which notifications will be delivered to multiple * observers is not specified. See the class comment. * * @param o an observer to be added. * @throws NullPointerException if the parameter o is null. */ public synchronized void addObserver(Observer o) { if (o == null) throw new NullPointerException(); if (!obs.contains(o)) { obs.addElement(o); } } /** * Deletes an observer from the set of observers of this object. * Passing <CODE>null</CODE> to this method will have no effect. * @param o the observer to be deleted. */ public synchronized void deleteObserver(Observer o) { obs.removeElement(o); } /** * If this object has changed, as indicated by the * <code>hasChanged</code> method, then notify all of its observers * and then call the <code>clearChanged</code> method to * indicate that this object has no longer changed. * <p> * Each observer has its <code>update</code> method called with two * arguments: this observable object and <code>null</code>. In other * words, this method is equivalent to: * <blockquote><tt> * notifyObservers(null)</tt></blockquote> * * @see java.util.Observable#clearChanged() * @see java.util.Observable#hasChanged() * @see java.util.Observer#update(java.util.Observable, java.lang.Object) */ public void notifyObservers() { notifyObservers(null); } /** * If this object has changed, as indicated by the * <code>hasChanged</code> method, then notify all of its observers * and then call the <code>clearChanged</code> method to indicate * that this object has no longer changed. * <p> * Each observer has its <code>update</code> method called with two * arguments: this observable object and the <code>arg</code> argument. * * @param arg any object. * @see java.util.Observable#clearChanged() * @see java.util.Observable#hasChanged() * @see java.util.Observer#update(java.util.Observable, java.lang.Object) */ public void notifyObservers(Object arg) { /* * a temporary array buffer, used as a snapshot of the state of * current Observers. */ Object[] arrLocal; synchronized (this) { /* We don't want the Observer doing callbacks into * arbitrary code while holding its own Monitor. * The code where we extract each Observable from * the Vector and store the state of the Observer * needs synchronization, but notifying observers * does not (should not). The worst result of any * potential race-condition here is that: * 1) a newly-added Observer will miss a * notification in progress * 2) a recently unregistered Observer will be * wrongly notified when it doesn't care */ if (!changed) return; arrLocal = obs.toArray(); clearChanged(); } for (int i = arrLocal.length-1; i>=0; i--) ((Observer)arrLocal[i]).update(this, arg); } /** * Clears the observer list so that this object no longer has any observers. */ public synchronized void deleteObservers() { obs.removeAllElements(); } /** * Marks this <tt>Observable</tt> object as having been changed; the * <tt>hasChanged</tt> method will now return <tt>true</tt>. */ protected synchronized void setChanged() { changed = true; } /** * Indicates that this object has no longer changed, or that it has * already notified all of its observers of its most recent change, * so that the <tt>hasChanged</tt> method will now return <tt>false</tt>. * This method is called automatically by the * <code>notifyObservers</code> methods. * * @see java.util.Observable#notifyObservers() * @see java.util.Observable#notifyObservers(java.lang.Object) */ protected synchronized void clearChanged() { changed = false; } /** * Tests if this object has changed. * * @return <code>true</code> if and only if the <code>setChanged</code> * method has been called more recently than the * <code>clearChanged</code> method on this object; * <code>false</code> otherwise. * @see java.util.Observable#clearChanged() * @see java.util.Observable#setChanged() */ public synchronized boolean hasChanged() { return changed; } /** * Returns the number of observers of this <tt>Observable</tt> object. * * @return the number of observers of this object. */ public synchronized int countObservers() { return obs.size(); } }