Java（观察者模式 observer）

来源：互联网发布：少儿编程编辑：程序博客网时间：2024/04/29 09:07

/** * 被观察者接口（抽象的被观察者接口） *  * */public interface AbstractWatched {/** * 增加一个观察者 * @param abstractWatcher */public void addWatcher(AbstractWatcher watcher);/** * 删除一个观察者 * @param abstractWatcher */public void removeWatcher(AbstractWatcher watcher);/** * 删除所有观察者 */public void removeAllWatchers();/** * 改变被观察者的状态 */public void changeStatus();}

/** * 抽象的观察者角色 *  * */public interface AbstractWatcher {    /**     * 观察者的更新操作     */    public void update();}

/** * 具体的被观察者实现 *  * */public class ConcreteWatched implements AbstractWatched {private List<AbstractWatcher> watchers = new ArrayList<AbstractWatcher>();@Overridepublic void addWatcher(AbstractWatcher watcher) {watchers.add(watcher);}@Overridepublic void changeStatus() {System.out.println("status changed");for (AbstractWatcher watcher : watchers) {watcher.update();//通知所有的观察者自动更新}}@Overridepublic void removeAllWatchers() {watchers.clear();}@Overridepublic void removeWatcher(AbstractWatcher watcher) {watchers.remove(watcher);}}

/** * 具体的观察者角色 *  * */public class ConcreteWatcher implements AbstractWatcher {@Overridepublic void update() {System.out.println("watcher updated");}}

public class Client {public static void main(String[] args) {AbstractWatched watched = new ConcreteWatched();AbstractWatcher watcher1 = new ConcreteWatcher();watched.addWatcher(watcher1);AbstractWatcher watcher2 = new ConcreteWatcher();watched.addWatcher(watcher2);AbstractWatcher watcher3 = new ConcreteWatcher();watched.addWatcher(watcher3);watched.changeStatus();System.out.println("-------------------------");watched.removeWatcher(watcher1);watched.changeStatus();}}

观察者模式在Java中占据举足轻重的位置，在AWT1.1和使用SAX解析xml文件中，都使用到观察者模式。所以Java内置也对观察者模式提供了API

import java.util.Observable;/** * 被观察者，需要继承Observable类 * @author yinhao * */public class Watched extends Observable {//测试方法public void count(int number){for (;number >= 0; number--) {setChanged();//标识下，被观察者已经改变了，必须调用该方法，才会通知其他的观察者notifyObservers();//通知观察者状态已改变try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}}}}

import java.util.Observable;import java.util.Observer;/** * 观察者，需要实现Observer接口 * @author yinhao * */public class Watcher implements Observer {@Overridepublic void update(Observable o, Object arg) {System.out.println("updated");}}

public class Client {public static void main(String[] args) {Watched watched = new Watched();Watcher watcher = new Watcher();watched.addObserver(watcher);watched.count(10);}}

0 0