被观察者的接口类
import java.util.Observer; /** * 气温预报(观察者模式) * @author Administrator *被观察者接口即subject目标接口气温 */ public interface Temperature{ //增加观察者 public void addObs(Observer o); //删除观察者 public void deleteObs(Observer o); //通知观察者 public void notifyObs(int t); }
被观察者实现类
/** * 具体主题被观察者 * @author Administrator * */ public class TemperatureImpl extends Observable implements Temperature { @Override public synchronized void addObserver(Observer o) { super.addObserver(o); } @Override public synchronized void deleteObserver(Observer o) { super.deleteObserver(o); } @Override public void notifyObservers(Object arg) { super.setChanged(); super.notifyObservers(arg); } /** * 当具体被观察者类集成Observable时这些其实时不需要的,因为在Observable类中其实已经有定义, * 上面的重写这些方法已经足够(也可不重写直接调用父类的方法) * 如果采用下面的方法就相当于自己实现观察者模式,不用api中提供的类 * 必须加上相应的Vector obs观察者数组用于存放观察者列表 */ @Override public void addObs(Observer o) { } @Override public void deleteObs(Observer o) { } @Override public void notifyObs(int t) { } }
观察者接口类
import java.util.Observer; /** * 气温显示(根据气温的实时变化来实时显示) * @author Administrator * */ public interface TemperatureShow extends Observer { }
观察者实现类
import java.util.Observable; public class TemperatureShowImpl implements TemperatureShow { public String tname; public String getTname() { return tname; } public void setTname(String tname) { this.tname = tname; } @Override public void update(Observable o, Object arg) { System.out.println(tname+":"+arg); } }
测试类
public class TestMain{ public static double i=0; public static void main(String[] args) { //创建被观察者 TemperatureImpl t = new TemperatureImpl(); //创建观察者1 TemperatureShowImpl s = new TemperatureShowImpl(); s.setTname("高温预报"); t.addObserver(s); //创建观察者2 TemperatureShowImpl s1 = new TemperatureShowImpl(); s1.setTname("低温预报"); t.addObserver(s1); t.notifyObservers(Math.random()); } }
这里附上Observable类
/* * @(#)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(); } }
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