Digital Clock in java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

///////////////////////////////////////////////////////////// TextClock2
public class TextClock2 extends JApplet {

    //====================================================== constructor
    public TextClock2() {
        add(new Clock());
    }

    //============================================================= main
    public static void main(String[] args) {
        JFrame window = new JFrame("Time of Day");
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        window.setContentPane(new Clock());

        window.pack();
        window.setVisible(true);
        System.out.println(window.getContentPane().size());
    }
}

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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Calendar;

///////////////////////////////////////////////////////////// Clock
class Clock extends JTextField {
    javax.swing.Timer m_t;

    //================================================== constructor
    public Clock() {
        //... Set some attributes.
        setColumns(6);
        setFont(new Font("sansserif", Font.PLAIN, 48));

        //... Create a 1-second timer.
        m_t = new javax.swing.Timer(1000, new ClockTickAction());
        m_t.start();  // Start the timer
    }

    /////////////////////////////////////////// inner class listener
    private class ClockTickAction implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //... Get the current time.
            Calendar now = Calendar.getInstance();
            int h = now.get(Calendar.HOUR_OF_DAY);
            int m = now.get(Calendar.MINUTE);
            int s = now.get(Calendar.SECOND);
            setText("" + h + ":" + m + ":" + s);
        }
    }
}