Observer پترن در جاوا (Observer Pattern)

public class Subject {



     private List<Observer> observers = new ArrayList<Observer>();

     private int state;



     public int getState() {

          return state;

     }



     public void setState(int state) {

          this.state = state;

          notifyAllObservers();

     }



     public void attach(Observer observer) {

          observers.add(observer);

     }



     public void notifyAllObservers() {

          for (Observer observer : observers) {

              observer.update();

          }

     }

}

public abstract class Observer {

     protected Subject subject;



     public abstract void update();

}

public class BinaryObserver extends Observer {



     public BinaryObserver(Subject subject) {

          this.subject = subject;

          this.subject.attach(this);

     }



     @Override

     public void update() {

          System.out.println("Binary String: "

                   + Integer.toBinaryString(subject.getState()));

     }

}

public class OctalObserver extends Observer{



   public OctalObserver(Subject subject){

      this.subject = subject;

      this.subject.attach(this);

   }



   @Override

   public void update() {

     System.out.println( "Octal String: " + Integer.toOctalString( subject.getState() ) );

   }

}

public class HexaObserver extends Observer {



     public HexaObserver(Subject subject) {

          this.subject = subject;

          this.subject.attach(this);

     }



     @Override

     public void update() {

          System.out.println("Hex String: "

                   + Integer.toHexString(subject.getState()).toUpperCase());

     }

}

public static void main(String[] args) {

          Subject subject = new Subject();



          new HexaObserver(subject);

          new OctalObserver(subject);

          new BinaryObserver(subject);



          System.out.println("First state change: 15");

          subject.setState(15);

          System.out.println("Second state change: 10");

          subject.setState(10);

     }

First state change: 20

Hex String: 14

Octal String: 24

Binary String: 10100

Second state change: 40

Hex String: 28

Octal String: 50

Binary String: 101000