Design Pattern - Observer - Sample Case

(Observer) README.txt

(Observer) Langkah pembuatan : 
1. Subject.java 
2. Abstract Observer.java
3. BinaryObserver.java, OctalObserver.java, dan HexaObserver.java

BinaryObserver.java

public class BinaryObserver extends Observer {
    public BinaryObserver(Subject subject) {
        super(subject);
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Hex String : "+Integer.toBinaryString(subject.getState()));
    }
}

HexaObserver.java

public class HexaObserver extends Observer {

    public HexaObserver(Subject subject) {
        super(subject);
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Hex String : "+Integer.toHexString(subject.getState()).toUpperCase());
    }
}

Observer.java

public abstract class Observer {
    protected Subject subject;

    public Observer(Subject subject) {
        this.subject = subject;
    }

    public abstract void update();
}

ObserverPatternDemo.java

public class ObserverPatternDemo {
    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 15");
        subject.setState(10);

    }
}

OctalObserver.java

public class OctalObserver extends Observer {

    public OctalObserver(Subject subject) {
        super(subject);
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Octal String : "+Integer.toOctalString(subject.getState()));
    }
}

Subject.java

import java.util.ArrayList;
import java.util.List;

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();
        }
    }
}