Dynamic Clock in java

Question

I want to implement a clock within my program to diusplay the date and time while the program is running. I have looked into the getCurrentTime() method and

Answer 1

You have to update the text in a separate thread every second.

Ideally you should update swing component only in the EDT ( event dispatcher thread ) but, after I tried it on my machine, using Timer.scheduleAtFixRate gave me better results:

java.util.Timer http://img175.imageshack.us/img175/8876/capturadepantalla201006o.png

The javax.swing.Timer version was always about half second behind:

javax.swing.Timer http://img241.imageshack.us/img241/2599/capturadepantalla201006.png

I really don't know why.

Here's the full source:

package clock;

import javax.swing.*;
import java.util.*;
import java.text.SimpleDateFormat;

class Clock {
    private final JLabel time = new JLabel();
    private final SimpleDateFormat sdf  = new SimpleDateFormat("hh:mm");
    private int   currentSecond;
    private Calendar calendar;

    public static void main( String [] args ) {
        JFrame frame = new JFrame();
        Clock clock = new Clock();
        frame.add( clock.time );
        frame.pack();
        frame.setVisible( true );
        clock.start();
    }
    private void reset(){
        calendar = Calendar.getInstance();
        currentSecond = calendar.get(Calendar.SECOND);
    }
    public void start(){
        reset();
        Timer timer = new Timer();
        timer.scheduleAtFixedRate( new TimerTask(){
            public void run(){
                if( currentSecond == 60 ) {
                    reset();
                }
                time.setText( String.format("%s:%02d", sdf.format(calendar.getTime()), currentSecond ));
                currentSecond++;
            }
        }, 0, 1000 );
    }
}

Here's the modified source using javax.swing.Timer

    public void start(){
        reset();
        Timer timer = new Timer(1000, new ActionListener(){
        public void actionPerformed( ActionEvent e ) {
                if( currentSecond == 60 ) {
                    reset();
                }
                time.setText( String.format("%s:%02d", sdf.format(calendar.getTime()), currentSecond ));
                currentSecond++;
            }
        });
        timer.start();
    }

_{Probably I should change the way the string with the date is calculated, but I don't think that's the problem here}

I have read, that, since Java 5 the recommended is: ScheduledExecutorService I leave you the task to implement it.