Observer Pattern(观察者模式)

观察者模式应用比较广泛，写一个简单的示例，扩展了一下Head First上面例子的应用范围，进一步降低Observer与Subject之间的耦合度。

简单例子，直接给代码：

 package test;
 public interface Subject {
     public void registerObserver(Observer observer);
     public void unRegisterObserver(Observer observer);
     public void notifyAllObservers();
     public void notifyObserver(Observer observer);
 }

 package test;
 public interface Observer {
     public void registerSubject(Subject subject);
     public void unRegisterSubject(Subject subject);
     public void update(Subject subject);
 }

 package test;
 import java.util.ArrayList;
 import java.util.List;
 public class WeatherDataSubject implements Subject {

     List<Observer> observers = new ArrayList<Observer>();
     private float temperature;
     private float humidity;
     private float pressure;

     public float getTemperature() {
         return temperature;
     }
     public void setTemperature(float temperature) {
         this.temperature = temperature;
     }
     public float getHumidity() {
         return humidity;
     }
     public void setHumidity(float humidity) {
         this.humidity = humidity;
     }
     public float getPressure() {
         return pressure;
     }
     public void setPressure(float pressure) {
         this.pressure = pressure;
     }

     @Override
     public void registerObserver(Observer observer) {
         // TODO Auto-generated method stub
         if(!observers.contains(observer))
             observers.add(observer);
     }
     @Override
     public void unRegisterObserver(Observer observer) {
         // TODO Auto-generated method stub
         if(observers.contains(observer))
             observers.remove(observer);
     }
     @Override
     public void notifyAllObservers() {
         // TODO Auto-generated method stub
         for(Observer o:observers)
             o.update(this);
     }
     @Override
     public void notifyObserver(Observer observer) {
         // TODO Auto-generated method stub
         if(observers.contains(observer))
             observer.update(this);
     }

     public void setWeatherDataParameters(float temperature,float humidity,float pressure)
     {
         this.setTemperature(temperature);
         this.setHumidity(humidity);
         this.setPressure(pressure);
         this.notifyAllObservers();
     }
 }

 package test;
 public class DisplayPanel implements Observer {

     private float temperature;
     private float humidity;
     private float pressure;

     public float getTemperature() {
         return temperature;
     }
     public void setTemperature(float temperature) {
         this.temperature = temperature;
     }
     public float getHumidity() {
         return humidity;
     }
     public void setHumidity(float humidity) {
         this.humidity = humidity;
     }
     public float getPressure() {
         return pressure;
     }
     public void setPressure(float pressure) {
         this.pressure = pressure;
     }
     @Override
     public void registerSubject(Subject subject) {
         // TODO Auto-generated method stub
         subject.registerObserver(this);
     }
     @Override
     public void unRegisterSubject(Subject subject) {
         // TODO Auto-generated method stub
         subject.unRegisterObserver(this);
     }
     @Override
     public void update(Subject subject) {
         // TODO Auto-generated method stub
         if(subject instanceof WeatherDataSubject)
         {
             WeatherDataSubject s = (WeatherDataSubject)subject;
             this.setTemperature(s.getTemperature());
             this.setHumidity(s.getHumidity());
             this.setPressure(s.getPressure());
         }

         this.display();
     }
     public void display() {
         System.out.println("Temperature:"+this.getTemperature());
         System.out.println("Humidity:"+this.getHumidity());
         System.out.println("Pressure:"+this.getPressure());
     }
 }

 package test;
 public class Driver {
     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         WeatherDataSubject subject1=new WeatherDataSubject();
         WeatherDataSubject subject2=new WeatherDataSubject();

         Observer panel1 = new DisplayPanel();
         Observer panel2 = new DisplayPanel();
         panel1.registerSubject(subject1);
         panel1.registerSubject(subject2);
         panel2.registerSubject(subject2);

         subject1.setWeatherDataParameters(15.0f, 0.32f, 1076.23f);
         subject2.setWeatherDataParameters(13.5f, 0.42f, 1087.11f);
         System.out.println("Subject1:======================");
         subject1.notifyAllObservers();
         System.out.println("Subject2:======================");
         subject2.notifyAllObservers();
     }
 }