设计模式之观察者（Observer）模式 代码详解

import java.util.ArrayList;

import java.util.List;



/**

 * User: HYY

 * Date: 13-10-28

 * Time: 下午1:34

 * To change this template use File | Settings | File Templates.

 */



/**

 * 这里使用接口是因为各个观察者可能有各自的独特的方法和属性，因此将其抽象成方法

 */

interface Observer {

    void update();

}



interface Subject {

    void addObserver(Observer observer);



    void deleteObserver(Observer observer);



    void notifyObservers();

}



class ConcreteObserver implements Observer {

    private String ObserverName;

    private Subject subject;//一个指向主题的引用，



    public ConcreteObserver(String ObserverName, Subject subject) {

        this.ObserverName = ObserverName;

        this.subject = subject;

        if (this.subject != null) {

            this.subject.addObserver(this);

        }

    }



    @Override

    public void update() {

        //在这个方法中可以通过它，来判断自己关注的数据是否发生变化，并作出相应的行动

        System.out.println(ObserverName + " 已经被更新！");

    }

}



class ConcreteSubject implements Subject {

    List<Observer> observerList;



    public ConcreteSubject() {

        this.observerList = new ArrayList<Observer>();

    }



    @Override

    public void addObserver(Observer observer) {

        if (observer != null) {

            if (observerList.contains(observer)) {

                System.out.println("已有该观察者，无需添加！");

            } else {

                observerList.add(observer);

            }

        }

    }



    @Override

    public void deleteObserver(Observer observer) {

        observerList.remove(observer);

    }



    @Override

    public void notifyObservers() {

        for (Observer observer : observerList) {

            observer.update();

        }

    }

}



public class MyObserverTest {

    public static void main(String[] args) {

        //初始化4个观察者和一个被观察对象，构造函数自动将观察的对象附上关系

        ConcreteSubject subject = new ConcreteSubject();



        ConcreteObserver observer1 = new ConcreteObserver("观察者（1）", subject);

        ConcreteObserver observer2 = new ConcreteObserver("观察者（2）", subject);

        ConcreteObserver observer3 = new ConcreteObserver("观察者（3）", subject);

        ConcreteObserver observer4 = new ConcreteObserver("观察者（4）", subject);



        subject.notifyObservers();

    }

}