<p>Observer.java</p> <div id="scid:9D7513F9-C04C-4721-824A-2B34F0212519:613cf5c0-e32f-4bc0-9128-4562a774f1f0" class="wlWriterEditableSmartContent" style="float: none; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; display: inline; padding-right: 0px"><pre class="brush: java; gutter: true; first-line: 1; tab-size: 4; toolbar: true; width: 400px; height: 116px;" style=" width: 400px; height: 116px;overflow: auto;">package cn.foxeye.design.observer;

public interface Observer {

void update(String state);

} </pre><!-- Code inserted with Steve Dunn's Windows Live Writer Code Formatter Plugin. http://dunnhq.com --></div>

<p>Subject.java</p>

<div id="scid:9D7513F9-C04C-4721-824A-2B34F0212519:85481259-b3a5-4731-9e08-0edbd5847752" class="wlWriterEditableSmartContent" style="float: none; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; display: inline; padding-right: 0px"><pre class="brush: java; gutter: true; first-line: 1; tab-size: 4; toolbar: true; width: 602px; height: 418px;" style=" width: 602px; height: 418px;overflow: auto;">package cn.foxeye.design.observer;

import java.util.ArrayList; import java.util.List;

public abstract class Subject {

private List<Observer> observers = new ArrayList<Observer>();public void attach(Observer observer) {this.observers.add(observer);System.out.println("Attached an Observer. ");
}public void dettach(Observer observer) {this.observers.remove(observer);System.out.println("Remove an Observer.");
}public void notifyObservers(String state) {for (Observer observer : observers) {observer.update(state);}
}

} </pre><!-- Code inserted with Steve Dunn's Windows Live Writer Code Formatter Plugin. http://dunnhq.com --></div>

<p>ConcreteObserver.java</p>

<div id="scid:9D7513F9-C04C-4721-824A-2B34F0212519:20b56b5f-32bd-4aa2-a61c-cc433a457380" class="wlWriterEditableSmartContent" style="float: none; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; display: inline; padding-right: 0px"><pre class="brush: java; gutter: true; first-line: 1; tab-size: 4; toolbar: true; width: 605px; height: 540px;" style=" width: 605px; height: 540px;overflow: auto;">package cn.foxeye.design.observer;

public class ConcreteObserver implements Observer {

private String name;
private String state;public ConcreteObserver(String name) {this.name = name;
}public void update(String state) {setState(state);System.out.println(name + "状态修改为：" + state);
}public String getState() {return state;
}public void setState(String state) {this.state = state;
}public String getName() {return name;
}public void setName(String name) {this.name = name;
}

} </pre><!-- Code inserted with Steve Dunn's Windows Live Writer Code Formatter Plugin. http://dunnhq.com --></div>

<p>ConcreteSubject.java</p>

<div id="scid:9D7513F9-C04C-4721-824A-2B34F0212519:d7aa01ec-f20a-4b25-ae4b-0563db4042ea" class="wlWriterEditableSmartContent" style="float: none; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; display: inline; padding-right: 0px"><pre class="brush: java; gutter: true; first-line: 1; tab-size: 4; toolbar: true; width: 605px; height: 264px;" style=" width: 605px; height: 264px;overflow: auto;">package cn.foxeye.design.observer;

public class ConcreteSubject extends Subject {

private String state;public String getState() {return state;
}public void changeState(String state) {this.state = state;System.out.println("主题状态变为：" + state);this.notifyObservers(state);
}

} </pre><!-- Code inserted with Steve Dunn's Windows Live Writer Code Formatter Plugin. http://dunnhq.com --></div>

<p>ObserverDesignDemo.java</p>

<div id="scid:9D7513F9-C04C-4721-824A-2B34F0212519:c2553ba7-f9fb-4b0f-bc8a-6bc25875ff04" class="wlWriterEditableSmartContent" style="float: none; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; display: inline; padding-right: 0px"><pre class="brush: java; gutter: true; first-line: 1; tab-size: 4; toolbar: true; width: 628px; height: 309px;" style=" width: 628px; height: 309px;overflow: auto;">package cn.foxeye.design.observer;

public class ObserverDesignDemo {

public static void main(String[] args) {ConcreteSubject subject = new ConcreteSubject();for (int i = 0; i < 10; i++) {Observer observer = new ConcreteObserver("张三" + i);subject.attach(observer);}subject.changeState("已读");}

} </pre><!-- Code inserted with Steve Dunn's Windows Live Writer Code Formatter Plugin. http://dunnhq.com --></div>