Java观察者模式例子

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 {@Overridepublic synchronized void addObserver(Observer o) {super.addObserver(o);}@Overridepublic synchronized void deleteObserver(Observer o) {super.deleteObserver(o);}@Overridepublic 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*/@Overridepublic void addObs(Observer o) {}@Overridepublic void deleteObs(Observer o) {}@Overridepublic 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;
}@Overridepublic 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1TemperatureShowImpl s = new TemperatureShowImpl();s.setTname("高温预报");t.addObserver(s);//创建观察者2TemperatureShowImpl 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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