观察者模式

目标对象（Subject）

 

观察者对象(Observer)

 

将观察者对象注册到目标对象上，当目标对象的状态发生改变时推送给观察者(推/拉模型)

以天气预报为例：

/**目标对象*/
public class WeatherSubject {
   
    private String weatherContent;
    
    private List<WeatherObserver> list = new ArrayList<WeatherObserver>();
    
    public void addObserver(WeatherObserver observer) {
        this.list.add(observer);
    }

    public void setWeatherContent(String weatherContent) {
        this.weatherContent = weatherContent;
        for(WeatherObserver observer : list) {
　　　　　　//  observer.update(this);  拉模型
　　　　　　//  observer.update(weatherContent);推模型
        }
    }

    public String getWeatherContent() {
        return weatherContent;
    }
}

 

/**观察者对象*/
public class WeatherObserver {

    private String observerName;
    
    public WeatherObserver(String observerName) {
        this.observerName = observerName;
    }

    public void update(WeatherSubject subject) {
        System.out.println(this.observerName +"收到的天气是："+subject.getWeatherContent());
    }
}

public class Main {
    public static void main(String[] args) {
        WeatherObserver girl = new WeatherObserver("女朋友");
        
        WeatherObserver monther = new WeatherObserver("monther");
        
        WeatherSubject subject= new WeatherSubject();
        subject.addObserver(girl);
        subject.addObserver(monther);
        
        subject.setWeatherContent("小雨");
    }
}

 

用jdk中提供的工具实现

/**
 * 目标对象 ，将观察者注册到目标对象上，当目标对象的状态发生变化时，通知到每个观察者 
 */
public class WeatherSubject extends Observable {
    
    private String weatherContent;//需要通知的内容

    public String getWeatherContent() {
        return weatherContent;
    }

    public void setWeatherContent(String weatherContent) {
        this.weatherContent = weatherContent;
        
        //设置变更内容时 
        setChanged();
        
        //推模型
        notifyObservers(weatherContent);
        
        //拉模型
        //notifyObservers();
    }
}

//观察者
public class WeatherObserver implements Observer {

    private String observerName;
    
    public WeatherObserver(String observerName) {
        this.observerName = observerName;
    }
    //目标对象通知过来的更新 
    @Override
    public void update(Observable o, Object arg) {
        System.out.println(observerName+"：收到的天气预报是："+arg);
        
    }
}

public class Client {
    public static void main(String[] args) {
        Observer monther = new WeatherObserver("老妈");
        
        Observer girlFriend = new WeatherObserver("女朋友");
        
        WeatherSubject observable = new WeatherSubject();//目标对象 即可以被观察的对象
        
        observable.addObserver(monther);
        observable.addObserver(girlFriend);
        
        observable.setWeatherContent("下雨天");
    }
}