Utiliser le patron Observable en java

public class Tester {

	public Tester() {
	}

	public static void main(String[] args) {
		Tester tester = new Tester();

		ConcreteModel model = new ConcreteModel();

		DisplayPanel display = new DisplayPanel();
		display.setModel(model);
		MainView mainView = new MainView("Observer/Observable");
		mainView.addComponent(display);
		mainView.pack();
		mainView.setVisible(true);
	}
}

import java.util.Date;
import java.util.Observable;

public class ConcreteModel extends Observable {
	private Date now;

	public ConcreteModel() {
		now = new Date();
	}

	public void fireUpdate() {
		now = new Date();
		setChanged();
		notifyObservers(new Date());
	}

}

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Observable;
import java.util.Observer;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class DisplayPanel extends JPanel implements Observer {
	private JLabel hour;
	private ConcreteModel model;

	public DisplayPanel() {
		initialize();
	}

	private void initialize() {
		hour = new JLabel();
		JButton jb_getHour = new JButton("Mettre l'heure à jour");
		jb_getHour.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				model.fireUpdate();
			}
		});
		add(hour);
		add(jb_getHour);
	}

	public void update(Observable o, Object arg) {
		GregorianCalendar calendar = (GregorianCalendar) GregorianCalendar.getInstance();
		calendar.setTime((Date) arg);
		hour.setText(calendar.get(GregorianCalendar.HOUR) + ":" + calendar.get(GregorianCalendar.MINUTE)+":"+calendar.get(GregorianCalendar.SECOND));
		hour.validate();
	}

	public void setModel(Observable model) {
		this.model = (ConcreteModel) model;
		model.addObserver(this);
		model.notifyObservers();
	}

}

import java.awt.Component;
import java.awt.Container;
import javax.swing.JFrame;

public class MainView extends JFrame {
	private Container c;
	
	public MainView(String name){
		super(name);
		setDefaultCloseOperation(EXIT_ON_CLOSE);
		c = getContentPane();		
	}
	
	public void addComponent(Component comp){
		c.add(comp);		
	}

}