Manipulação de hora

import java.awt.*;
import java.awt.event.*;
import java.io.IOException;

import javax.swing.*;
import javax.swing.event.*;

public class teste extends JPanel {
    private JTextField tfMilissegundos;
    private JButton btCalcular;

    public teste() {
        //construct components
        tfMilissegundos = new JTextField (5);
        btCalcular = new JButton ("Calcular");

        //adjust size and set layout
        setPreferredSize (new Dimension (220, 88));
        setLayout (null);

        //add components
        add (tfMilissegundos);
        add (btCalcular);

        //set component bounds (only needed by Absolute Positioning)
        tfMilissegundos.setBounds (15, 15, 190, 25);
        btCalcular.setBounds (60, 45, 100, 25);
        
        btCalcular.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
			{
				conversao();				
			}
		});
        tfMilissegundos.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
			{
				conversao();				
			}
		});
    }
    
    
    public void conversao()
    {
    	int s,m,h;
		long ms,tempoMilissegundos = Long.parseLong(tfMilissegundos.getText());
		String tempoPronto;
		
		
		s = (int)tempoMilissegundos/1000;
		ms = (int)(tempoMilissegundos/1000-s);
		m = (int) s/60;
		s = (int)(s/60-m);
		h = (int)m/60;
		m = (int)m/60-h;
		System.out.println(h+"\n"+m+"\n"+s+"\n"+ms+"\nTempo total (ms): "+tempoMilissegundos);
		
		tempoPronto = String.valueOf(h)+"  :  "+String.valueOf(m).substring(1)+"  :  "+String.valueOf(s).substring(1);
		
		JOptionPane.showMessageDialog(null,"           Hora     Minutos   Segundos\nTempo: "+tempoPronto);
    }


    public static void main (String[] args) {
        JFrame frame = new JFrame ("Milissegundos");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add (new teste());
        frame.setLocationRelativeTo(null);
        frame.pack();
        frame.setVisible (true);
    }
}