观察者模式-Observer Pattern

前言

Define a one-to-many dependency between objects so that when one object changes state,all its dependents are notified and updated automatically.

定义对象间一种一对多的依赖关系，使得每当一个对象改变状态，所有依赖于它的对象都会得到通知并被自动更新.

GitHub源码:

https://github.com/YEN-GitHub/PatternDemo/tree/master/src/BehavioralPattern2/ObserverPattern

题目

观察者有游戏观察者（GameObserver）和视频观察者（VideoObserver）。观察者中的更新函数（updata）只需输出具体Subject对象的状态和状态改变语句即可。目标对象(Subject）有哨兵（Sentry）和老师（teacher），一个目标对象可以对应多个和多种观察者对象，当客服端目标对象状态设置为（"高老师来了"），调用通知函数（notifyObserver）通知所有对应的观察者对象执行更新函数。其中老师（teacher）的状态还包括一个惩罚（panish）函数，惩罚（panish）函数输出如下“XXX  XXX（所有惩罚人的名字）把观察者模式的结构图抄写10遍”完成状态更新。

UML类图

代码

package BehavioralPattern2.ObserverPattern.demo1;/** * Created by yangenneng on 2017-06-14 10:37 * Abstract：抽象观察者角色 */public abstract class Observer {    protected String stuName;//学生姓名    protected Subject subject;//哨兵    /*构造函数*/    Observer(String stuName,Subject subject){        this.stuName=stuName;        this.subject=subject;    }    /*改变状态*/    public abstract void update();    public String getStuName() {        return stuName;    }    public void setStuName(String stuName) {        this.stuName = stuName;    }    public Subject getSubject() {        return subject;    }    public void setSubject(Subject subject) {        this.subject = subject;    }}

package BehavioralPattern2.ObserverPattern.demo1;import java.util.ArrayList;/** * Created by yangenneng on 2017-06-14 10:37 * Abstract：抽象主题角色-即哨兵 */public abstract class Subject {    protected String msg="";//通知信息    Subject(String msg){        this.msg=msg;    }    /*存放所有待通知的观察者*/    protected ArrayList<Observer> arrayList=new ArrayList<>();    /*增加被观察者*/    public void addObserver(Observer obj) {arrayList.add(obj);}    /*移除被观察者*/    public void removeObserver(Observer obj){arrayList.remove(obj);}    /*通知函数*/    public abstract void notifyObserver();    public String getMsg() {        return msg;    }    public void setMsg(String msg) {        this.msg = msg;    }}

package BehavioralPattern2.ObserverPattern.demo1;/** * Created by yangenneng on 2017-06-14 11:01 * Abstract：游戏观察者 */public class GameObserver extends Observer {    GameObserver(String name,Subject subject){super(name,subject);}    @Override    public void update() {        System.out.println(this.stuName+"切换状态，由游戏状态变为做实验状态");    }}

package BehavioralPattern2.ObserverPattern.demo1;/** * Created by yangenneng on 2017-06-14 11:02 * Abstract：视频观察者 */public class VideoObserver extends Observer {    VideoObserver(String name,Subject subject){super(name,subject);}    @Override    public void update() {        System.out.println(this.stuName+"切换状态，由视频状态变为做实验状态");    }}

package BehavioralPattern2.ObserverPattern.demo1;/** * Created by yangenneng on 2017-06-14 11:03 * Abstract：好人哨兵 */public class SentrySubject extends Subject{    SentrySubject(String msg) {        super(msg);    }    /*通知函数*/    public void notifyObserver(){        System.out.println(msg);        for (Observer observer:arrayList){            observer.update();        }    }}

package BehavioralPattern2.ObserverPattern.demo1;/** * Created by yangenneng on 2017-06-14 11:06 * Abstract：老师-哨兵 */public class TeacherSubject extends Subject{    TeacherSubject(String msg) {        super(msg);    }    /*通知函数*/    public void notifyObserver(){        System.out.println(msg);        for (Observer observer:arrayList){            observer.update();        }        panish();//惩罚    }    /*惩罚学生函数*/    public void panish(){        for (Observer observer:arrayList){            System.out.print(observer.getStuName()+ " ");        }        System.out.println("罚抄观察者模式10遍");    }}

package BehavioralPattern2.ObserverPattern.demo1;/** * Created by yangenneng on 2017-06-14 11:10 * Abstract：客户端测试 */public class Client {    public static void main(String[] args) {        Subject subject=new SentrySubject("");        Observer stu1=new GameObserver("张三",subject);        Observer stu2=new VideoObserver("李四",subject);        subject.addObserver(stu1);        subject.addObserver(stu2);        subject.notifyObserver();        System.out.println("-------------------------------------");        subject=new TeacherSubject("高老师来了");        subject.addObserver(stu1);        subject.addObserver(stu2);        subject.notifyObserver();    }}

运行结果

补充说明

模式可以用接口实现，这里用的是抽象类。用接口的话只要把一些属性放到具体的子类里去实现就行了.