Another version of the Clock, still using the java.util.Observable

Clock.java

// Package :V

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.GregorianCalendar;
import java.util.Observable;

import javax.swing.Timer;

public class Clock extends Observable implements ActionListener {

	public static Timer timer;   

	public Clock(){
		// On new instances of clock, start the Clock.
		this.startClock();
	}
	
	public String getTime(){
		
		String time = "";
		
		// Better lib to handle this case
		GregorianCalendar calendario = new GregorianCalendar();   
		int h = calendario.get(GregorianCalendar.HOUR_OF_DAY);   
		int m = calendario.get(GregorianCalendar.MINUTE);   
		int s = calendario.get(GregorianCalendar.SECOND);   
		time += ((h < 10) ? "0" : "") + h + ":";
		time += ((m < 10) ? "0" : "") + m + ":";
		time += ((s < 10) ? "0" : "") + s;

		return time;
	}
	
	public void actionPerformed(ActionEvent e) {
		// Everytime the timer changes, we are performing an action and communicatin' with the Observers
		setChanged();
		notifyObservers(this.getTime());
	}
	
	public void startClock() {
		// Check if we didn't start the clock, if not, then start it.
		if (timer == null) {
			timer = new javax.swing.Timer(1000, this);
			timer.setInitialDelay(0);
			timer.start();
		}
	}
}

Form.java

// Package :V

import java.awt.*;
import java.awt.event.*;
import java.util.Observable;
import java.util.Observer;
import javax.swing.*;

public class Form implements Observer {

	private Clock clock = new Clock();
	private JLabel label = new JLabel();
	private JButton button = new JButton("Stop/Restart");
	private static JFrame frame = new JFrame("My personal Clock...");

	public Form(){
		this.mountFrameWindow();
		
		// This is an Observer for Clock
		clock.addObserver(this);
	}

	/*
	 * Mounting the JFrame/Form
	 */
	public void mountFrameWindow(){  
		JPanel panel = new JPanel();   

		panel.add(label);
		panel.add(button);
		panel.setLayout(new FlowLayout(FlowLayout.CENTER));

		label.setFont(new Font("Verdana", Font.BOLD, 30));
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   
		frame.getContentPane().add(panel);   
		frame.setBounds(200, 200, 600, 200);  
		frame.setVisible(true);
		
		button.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e){
				if (Clock.timer.isRunning()){
					Clock.timer.stop();
				} else {
					Clock.timer.restart();
				}
			}
		});
		
		label.setText(clock.getTime());

	}   
	
	/*
	 * Implementation of the observer pattern, we're listening to changes on the Object.(non-Javadoc)
	 * @see java.util.Observer#update(java.util.Observable, java.lang.Object)
	 */
	@Override
	public void update(Observable argument, Object value) {
		// Debugging
		System.out.println("Current time!: " + value);
		label.setText((String)value);
	}
}

Main.java

// Package.blabla
// This file runs everything

public class Main {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		new Form();
	}
	
}