观察者模式

定义了一种一对多的依赖关系,让多个观察者对象同时监听某一主题对象,在它的状态发生变化时,会通知所有的观察者.

import java.util.ArrayList;import java.util.List;/** * 内容提供者 * @author fan * */public class Subject {    private List<Observe> observers = new ArrayList<>();    private int State;    public int getState() {        return State;    }    public void setState(int state) {        State = state;        notificationAll();    }    public void attach(Observe observer) {        observers.add(observer);    }    private void notificationAll() {        // TODO Auto-generated method stub        for (Observe observe : observers) {            observe.update();        }    }}/** * 观察者抽象类 * @author fan * */public abstract class Observe {    protected Subject subject;    public abstract void update();}/** * 观察实体类 * @author fan * */public class Observer extends Observe {    Observer(Subject subject) {        this.subject = subject;        this.subject.attach(this);    }    @Override    public void update() {        // TODO Auto-generated method stub        System.out.println(this.subject.getState());    }}//测试public class Test {    public static void main(String[] args) {        Subject subject= new Subject();        new Observer(subject);        subject.setState(1);        subject.setState(2);        subject.setState(3);    }}//res123