觀察者模式（訂閱釋出模式）及執行個體Demo

1、觀察者模式，又稱訂閱釋出模式，其架構如下：

2、執行個體demo——訂閱天氣，釋出天氣

1>WeatherSubject  目标類

public class WeatherSubject {    private List<Observer> observers = new ArrayList<Observer>();    public void attach(Observer observer){      observers.add(observer);    }    public void detach(Observer observer){      observers.remove(observer);    }    protected void notifyObservers(){      for(Observer observer : observers){         observer.update(this);      }    } }

2> 具體的目标類

public class ConcreteWeatherSubject extends WeatherSubject {    private String weatherContent;    public String getWeatherContent() {      return weatherContent;    }    public void setWeatherContent(String weatherContent) {      this.weatherContent = weatherContent;      this.notifyObservers();    } }

3> 觀察者

public interface Observer {    public void update(WeatherSubject subject); }

4> 具體的觀察者

public class ConcreteObserver implements Observer {    private String observerName;    private String weatherContent;    private String remindThing;    @Override    public void update(WeatherSubject subject) {      weatherContent = ((ConcreteWeatherSubject)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;    } }

5> test 類

public class test {    public static void main(String[] args) {      //1.建立目标      ConcreteWeatherSubject weather = new ConcreteWeatherSubject();      //2.建立觀察者      ConcreteObserver observerGirl = new ConcreteObserver();      observerGirl.setObserverName("girl");      observerGirl.setRemindThing("go shopping");      ConcreteObserver observerBoy = new ConcreteObserver();      observerBoy.setObserverName("boy");      observerBoy.setRemindThing("play football");      //3.注冊觀察者      weather.attach(observerGirl);      weather.attach(observerBoy);      //4.目标釋出天氣      weather.setWeatherContent("a nice day!");    } }

測試結果：

girl收到了a nice day! ,go shopping

boy收到了a nice day! ,play football