import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class Clock extends Frame {
public Clock() {
setSize(400,300);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}
public void paint(Graphics g) {
int hour,minute,second,milli;

GregorianCalendar t=new GregorianCalendar();

hour = t.get(Calendar.HOUR);
minute = t.get(Calendar.MINUTE);
second = t.get(Calendar.SECOND);
milli = t.get(Calendar.MILLISECOND);

g.drawString(""+hour+"時"+minute+"分"+second+"秒"+milli,20,40);
}
public static void main(String[] args) {
Frame w=new Clock();
w.show();
}
}
こいつをリアルタイムで動くようにするにはどうしたらいいですか？