观察者模式（订阅发布模式）及实例Demo

1、观察者模式，又称订阅发布模式，其架构如下：

2、实例demo——订阅天气，发布天气

1>WeatherSubject  目标类

public class WeatherSubject {      private List observers = new ArrayList();       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> 具体的目标类

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

3> 观察者

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

4> 具体的观察者

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 类

public class test {      public static void main(String[] args) {      //1.创建目标      ConcreteWeatherSubject weather = new ConcreteWeatherSubject();         //2.创建观察者      ConcreteObserver observerGirl = new ConcreteObserver();      observerGirl.setObserverName("girl");      observerGirl.setRemindThing("go shopping");           ConcreteObserver observerBoy = new ConcreteObserver();      observerBoy.setObserverName("boy");      observerBoy.setRemindThing("play football");           //3.注册观察者      weather.attach(observerGirl);      weather.attach(observerBoy);           //4.目标发布天气      weather.setWeatherContent("a nice day!");    }   }

测试结果：

girl收到了a nice day! ,go shopping
boy收到了a nice day! ,play football