import java.util.Observable;
import java.util.Observer;

import javax.swing.JFrame;
import javax.swing.JTextField;

public class ObserverClass {
    public static void main(String[] args) {
        new Erzaehler();
    }
}

class Erzaehler extends Observable {
    
    public Erzaehler(){
        this.addObserver(new Zuhoerer_1());
        this.addObserver(new Zuhoerer_2());
        tell("hoihoi!");
    }

    
    public void tell(String info){
        if(countObservers()>0){
            setChanged();
            notifyObservers(info);
        }
    }
}

class Zuhoerer_1 implements Observer{
    
    private JTextField field1;
    
    public Zuhoerer_1(){
        JFrame frame = new JFrame("Zuhoerer 1");
        field1 = new JTextField("a");
        frame.add(field1);
        
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 50);
        frame.setLocation(400, 400);
        frame.setVisible(true);
    }
    
    public void update(Observable o, Object arg) {
        field1.setText((String) arg);
    }
}

class Zuhoerer_2 implements Observer{
    
    private JTextField field2;
    
    public Zuhoerer_2(){
        JFrame frame = new JFrame("Zuhoerer 2");
        field2 = new JTextField("b");
        frame.add(field2);
        
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 50);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
    
    public void update(Observable o, Object arg) {
        field2.setText((String) arg);
    }
}