观察者模式

来源：互联网发布：无锡亚信数据有限公司编辑：程序博客网时间：2024/06/05 17:36

GoF设计模式里面的观察者模式的UML图
这里写图片描述

PS：发布和订阅（事件监听，mq，多路IO复用）
例如：XX楼盘5-1开盘，你肯定不知道，如果你想知道，肯定要去楼盘登记，留下电话号5-1号销售就会打电话通知你。

Subject 就是抽象主题：它负责管理所有观察者的引用，同时定义主要的事件操作。
ConcreteSubject 具体主题：它实现了抽象主题的所有定义的接口，当自己发生变化时，会通知所有观察者。
Observer 观察者：监听主题发生变化相应的操作接口。

代码案例

public class EventObject implements Serializable {    private String type;    private Object data;    public EventObject(String type, Object data) {        this.type = type;        this.data = data;    }    public String getType() {        return type;    }    public Object getData() {        return data;    }}//subjectpublic interface Lifecycle {    public void addLifecycleListener(LifecycleListener listener);    public void removeLifecycleListener(LifecycleListener listener);    public void fireLifecycleEvent(String type,Object data);}//ConcreteSubject public class LifecycleSubject implements Lifecycle {    private CopyOnWriteArrayList<LifecycleListener> cwal = new CopyOnWriteArrayList();    @Override    public void addLifecycleListener(LifecycleListener listener) {        cwal.add(listener);    }    @Override    public void removeLifecycleListener(LifecycleListener listener) {        cwal.remove(listener);    }    @Override    public void fireLifecycleEvent(String type, Object data) {        EventObject event = new EventObject(type, data);        for (int i = 0; i < cwal.size(); i++) {            cwal.get(i).lifecycleEvent(event);        }    }}//观察者行为public interface LifecycleListener {    public void lifecycleEvent(EventObject event);}//具体的观察者public class ObserverSubject implements LifecycleListener {    @Override    public void lifecycleEvent(EventObject event) {        System.out.println(event.getType() + "=" + event.getData());    }}public class Client {    public static void main(String[] args) {        LifecycleSubject lifecycleSubject = new LifecycleSubject();        lifecycleSubject.addLifecycleListener(new ObserverSubject());        lifecycleSubject.fireLifecycleEvent("start", "how are you");    }}

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