#format java
/**
 * ObserverPattern example
 * NumberGenerator observer
 */

import java.util.Vector;
import java.util.Iterator;
import java.util.Random;

interface Observer {
    public abstract void update(NumberGenerator generator);
}

abstract class NumberGenerator {
    private Vector observers = new Vector();
    public void addObserver(Observer observer) {
        observers.add(observer);
    }
    public void deleteObserver(Observer observer) {
        observers.remove(observer);
    }
    public void notifyObservers() {
        Iterator it = observers.iterator();
        while(it.hasNext()) {
            Observer o = (Observer)it.next();
            o.update(this);
        }
    }
    public abstract int getNumber();
    public abstract void execute();
}

class RandomNumberGenerator extends NumberGenerator {
    private Random random = new Random();
    private int number;
    public int getNumber() {
        return number;
    }
    public void execute() {
        for(int i=0; i < 20; i++) {
            number = random.nextInt(50);
            notifyObservers();
        }
    }
}

class DigitObserver implements Observer {
    public void update(NumberGenerator generator) {
        System.out.println("DigitObserver:"+generator.getNumber());
        try {
            Thread.sleep(100);
        } catch(InterruptedException e) {
        }
    }
}

class GraphObserver implements Observer {
    public void update(NumberGenerator generator) {
        System.out.print("GraphObserver:");
        int count = generator.getNumber();
        for(int i=0; i < count; i++) {
            System.out.print('*');
        }
        System.out.println("");
        try {
            Thread.sleep(100);
        } catch(InterruptedException e) {
        }
    }
}

public class ObserverGenerator {
    public static void main(String[] args) {
        NumberGenerator generator = new RandomNumberGenerator();
        Observer observer1 = new DigitObserver();
        Observer observer2 = new GraphObserver();
        generator.addObserver(observer1);
        generator.addObserver(observer2);
        generator.execute();
    }
}