设计模式——观察者模式

1.什么是观察者模式

观察者模式，简单理解是目标对象和观察者之间的联动模式，当目标对象发生表示时，会通知到观察者（一个或者多个）。

 

2.观察者模式的应用场景

2.1 当一个对象改变时，同时需要改变其他对象，但不清楚有多少个对象待改变时。

2.2   当一个抽象模型有两个方面, 其中一个方面依赖于另一方面。将这二者封装在独立的对象中以使它们可以各自独立地改变和复用。

 

3.java jdk中提供的Observable类和Observer接口

WeatherConet.java

package com.asiainfo.test.observerjdk;

/**
 * 天气状态
 * @author hasee
 *
 */
public class WeatherConet {
    static String SUNNY = "阳光灿烂";
    static String RAINY = "下雨了";
    static String SONW = "下雪了";
}

ConcreteWeatherSubject.java，继承jdk提供的Observable 类

package com.asiainfo.test.observerjdk;

import java.util.Observable;

/**
 * 目标对象，保存了所有的注册的观察者对象，并且提供观察者对象的注册和删除的方法
 * @author luke
 *
 */
public class ConcreteWeatherSubject extends Observable {
    private String weatherContent;
    
    public String getWeatherContent() {
        return weatherContent;
    }
    
    
    //当目标对象状态发生变化时，通知对应的对象
    public void setWeatherContent(String weatherContent) {
        this.weatherContent = weatherContent;
        this.setChanged();
        this.notifyObservers(weatherContent);
    }
    
     
}

 

ConcreteWeatherObserver.java，实现jdk提供的Observer 接口

package com.asiainfo.test.observerjdk;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Observable;
import java.util.Observer;

/**
 * 观察者实现类，提供update方法，供目标对象发生变化时调用，通知观察者
 * @author hasee
 *
 */
public class ConcreteWeatherObserver implements Observer {
    static Map<String,String> observerMap;
    static {
        observerMap = new LinkedHashMap<String,String>();
        observerMap.put("Mum", "妈妈");
        observerMap.put("GrilFriend", "女朋友");
    }
    //观察者的名称
    private String observerName;
    //观察者获取的天气内容
    private String weatherContent;
    //提醒内容
    private String remindThing;
    
    
    @Override
    public void update(Observable o, Object arg) {
        ConcreteWeatherSubject subject = (ConcreteWeatherSubject)o;
        String weatherContent = subject.getWeatherContent();
        System.out.println(observerName + "收到了" + weatherContent + "," + remindThing);
    }


    public String getObserverName() {
        return observerName;
    }


    public void setObserverName(String observerName) {
        this.observerName = observerName;
    }


    public String getWeatherContent() {
        return weatherContent;
    }


    public void setWeatherContent(String weatherContent) {
        this.weatherContent = weatherContent;
    }


    public String getRemindThing() {
        return remindThing;
    }


    public void setRemindThing(String remindThing) {
        this.remindThing = remindThing;
    }
    
}

Client.java 测试类

package com.asiainfo.test.observerjdk;
//测试类
public class Client {
    public  static void main(String[] args) {
        //创建目标对象
        ConcreteWeatherSubject subject = new ConcreteWeatherSubject();
        
        //创建观察者对象
        ConcreteWeatherObserver observerMum = new ConcreteWeatherObserver();
        observerMum.setObserverName(observerMum.observerMap.get("Mum"));
        observerMum.setRemindThing("去逛街");
        
        ConcreteWeatherObserver observerGril = new ConcreteWeatherObserver();
        observerGril.setObserverName(observerMum.observerMap.get("GrilFriend"));
        observerGril.setRemindThing("去约会");
        //注册观察者
        subject.addObserver(observerMum);
        subject.addObserver(observerGril);
        
        //目标对象发布状态
        subject.setWeatherContent("下雨了");
        
    }
}

 

4.可以自己定义观察者的接口和目标对象类

4.1　　WeatherSubject.java

package com.asiainfo.test.observer;

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

/**
 * 天气目标对象，知道观察自己的观察者，并且提供对观察者添加和删除的方法
 * @author luke
 *
 */
public class WeatherSubject {
    //用于保存所以的观察者
    private List<WeatherObserver> observers = new ArrayList();
    
    //提供对观察者进行添加或者删除的方法
    public void attach (WeatherObserver observer) {
        observers.add(observer);
    }
    
    public void delete(WeatherObserver observer) {
        observers.remove(observer);
    }
    
    //如果目标对象发生改变时,通知所有注册的观察者对象
    protected void notifyObservers() {
        for (int i = 0; i < observers.size(); i++) {
            WeatherObserver observer = observers.get(i);
            observer.update(this);
        }
    }
}

4.2　　ConcreteWeatherSubject.java

package com.asiainfo.test.observer;

/**
 * 
 * @author luke
 *
 */
public class ConcreteWeatherSubject extends WeatherSubject {
    //目标对象的状态
    private String weatherContent;
    
    public String getWeatherContent() {
        return weatherContent;
    }

    public void setWeatherContent(String weatherContent) {
        this.weatherContent = weatherContent;
        //通知所有的观察者
        this.notifyObservers();
    }
    
    
    
}

4.3　　WeatherObserver.java

package com.asiainfo.test.observer;

public interface WeatherObserver {
    //更新观察者的状态，传入目标对象方便获取对应的观察者的引用
    public void update(WeatherSubject subject);
}

4.4　　ConcreteWeatherObserver.java

package com.asiainfo.test.observer;

public class ConcreteWeatherObserver implements WeatherObserver {
    //观察者的名称
    private String observerName;
    //观察者的内容,从目标处获取
    private String subContent;
    //提醒的内容
    private String remindThings;
    
    /**
     * 获取目标类的状态并同步到观察者的状态中
     */
    @Override
    public void update(WeatherSubject subject) {
        ConcreteWeatherSubject concreteSub = (ConcreteWeatherSubject)subject;
        subContent = concreteSub.getWeatherContent();
        System.out.println(observerName + "收到了信息：" + subContent + "," + remindThings);
    }

    public String getObserverName() {
        return observerName;
    }

    public void setObserverName(String observerName) {
        this.observerName = observerName;
    }

    public String getSubContent() {
        return subContent;
    }

    public void setSubContent(String subContent) {
        this.subContent = subContent;
    }

    public String getRemindThings() {
        return remindThings;
    }

    public void setRemindThings(String remindThings) {
        this.remindThings = remindThings;
    }

    
}

4.4　　Client.java测试类

package com.asiainfo.test.observer;

//测试类
public class Client {
    public static void main(String[] args) {
        //1.创建目标对象
        ConcreteWeatherSubject subject = new ConcreteWeatherSubject();
        
        //2.创建观察者对象
        ConcreteWeatherObserver mum = new ConcreteWeatherObserver();
        mum.setObserverName("黄明的妈妈");
        mum.setRemindThings("适合去超市购物");
        
        ConcreteWeatherObserver gf = new ConcreteWeatherObserver();
        gf.setObserverName("黄明的女朋友");
        gf.setRemindThings("适合去谈恋爱");
        
        //3.注册观察者1
        subject.attach(mum);
        subject.attach(gf);
        subject.setWeatherContent("天气晴朗，气温28°");
        
    }
}

 

Client.java