Countdown Timer in Java

[Shmoil]

i have a school assignment where I need to create a countdown timer to attach to a scoreboard i made. the code that is attached is a program i found that is a stopwatch and will count up. im looking to get the timer count down from 2 minutes and go:

Minutes : Seconds : Milisecond in 02:00:0 format

How would i go about doing this?

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

public class Stopwatch extends JFrame implements ActionListener, Runnable
    {
     private long startTime;
     private final static java.text.SimpleDateFormat timerFormat = new java.text.SimpleDateFormat("mm : ss.SSS");
     private final JButton startStopButton= new JButton("Start/stop");
     private Thread updater;
     private boolean isRunning= false;
     private final Runnable displayUpdater= new Runnable()
         {
         public void run()
             {
             displayElapsedTime(System.currentTimeMillis() - Stopwatch.this.startTime);
         }
     };
     public void actionPerformed(ActionEvent ae)
         {
         if(isRunning)
             {
             long elapsed= System.currentTimeMillis() - startTime;
             isRunning= false;
             try
                 {
                 updater.join();
                 // Wait for updater to finish
             }
             catch(InterruptedException ie) {}
             displayElapsedTime(elapsed);
             // Display the end-result
         }
         else
             {
             startTime= System.currentTimeMillis();
             isRunning= true;
             updater= new Thread(this);
             updater.start();
         }
     }
     private void displayElapsedTime(long elapsedTime)
         {
         startStopButton.setText(timerFormat.format(new java.util.Date(elapsedTime)));
     }
     public void run()
         {
         try
             {
             while(isRunning)
                 {
                 SwingUtilities.invokeAndWait(displayUpdater);
                 Thread.sleep(50);
             }
         }
         catch(java.lang.reflect.InvocationTargetException ite)
             {
             ite.printStackTrace(System.err);
             // Should never happen!
         }
         catch(InterruptedException ie) {}
         // Ignore and return!
     }
     public Stopwatch()
         {
         startStopButton.addActionListener(this);
         getContentPane().add(startStopButton);
         setSize(100,50);
         setVisible(true);
     }
     public static void main(String[] arg)
         {
         new Stopwatch().addWindowListener(new WindowAdapter()
             {
             public void windowClosing(WindowEvent e)
                 {
                 System.exit(0);
             }
         });
     }
}

[gunjannigam]

This will Reset Your button to two minutes everytime you pressed it and it will count backwards.

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

public class Stopwatch extends JFrame implements ActionListener, Runnable
    {
     private long startTime;
     private final static java.text.SimpleDateFormat timerFormat = new java.text.SimpleDateFormat("MM : ss : SSS");
     private final JButton startStopButton= new JButton("Start/stop");
     private Thread updater;
     private boolean isRunning= false;
     private final Runnable displayUpdater= new Runnable()
         {
         public void run()
             {
             displayElapsedTime(Stopwatch.this.startTime - System.currentTimeMillis());
         }
     };
     public void actionPerformed(ActionEvent ae)
         {
         if(isRunning)
             {
             long elapsed= startTime - System.currentTimeMillis() ;
             
             isRunning= false;
             try
                 {
                 updater.join();
                 // Wait for updater to finish
             }
             catch(InterruptedException ie) {}
             displayElapsedTime(elapsed);
             // Display the end-result
         }
         else
             {
             startTime= 2*60*1000+System.currentTimeMillis();
             isRunning= true;
             updater= new Thread(this);
             updater.start();
         }
     }
     private void displayElapsedTime(long elapsedTime)
         {
         startStopButton.setText(timerFormat.format(new java.util.Date(elapsedTime)));
     }
     public void run()
         {
         try
             {
             while(isRunning)
                 {
                 SwingUtilities.invokeAndWait(displayUpdater);
                 Thread.sleep(50);
             }
         }
         catch(java.lang.reflect.InvocationTargetException ite)
             {
             ite.printStackTrace(System.err);
             // Should never happen!
         }
         catch(InterruptedException ie) {}
         // Ignore and return!
     }
     public Stopwatch()
         {
         startStopButton.addActionListener(this);
         getContentPane().add(startStopButton);
         setSize(100,50);
         setVisible(true);
     }
     public static void main(String[] arg)
         {
         new Stopwatch().addWindowListener(new WindowAdapter()
             {
             public void windowClosing(WindowEvent e)
                 {
                 System.exit(0);
             }
         });
     }
}

[Shmoil]

Gunjannigam, thanks for your help!

It works great now that it will count down.

However, it seems to start at 13 minutes for some reason. When I let it run, it will count down a minute perfectly but as soon as the minute is up, instead of changing from 12:00:000 to 11:59:999 it resets automatically back up to 13 minutes. Also how would we go about changing this to 2:00:0 instead of the 13?

Thanks.

[gunjannigam]

Gunjannigam, thanks for your help!

It works great now that it will count down.

However, it seems to start at 13 minutes for some reason. When I let it run, it will count down a minute perfectly but as soon as the minute is up, instead of changing from 12:00:000 to 11:59:999 it resets automatically back up to 13 minutes. Also how would we go about changing this to 2:00:0 instead of the 13?

Thanks.

Sorry in Line No 8 should be

private final static java.text.SimpleDateFormat timerFormat = new java.text.SimpleDateFormat("mm : ss : SSS");

And this will adjust the time as per your time zone.
If your time zome is like 5hours 30 minutes ahead of GMT, then you might have to subtract 30 minutes from startime so that it set to zero.
You can do this by making line 37 as

startTime= 2*60*1000+System.currentTimeMillis()-30*60*1000;

[Shmoil]

 private final static java.text.SimpleDateFormat timerFormat = new java.text.SimpleDateFormat("mm : ss : SSS");

And this will adjust the time as per your time zone.
If your time zome is like 5hours 30 minutes ahead of GMT, then you might have to subtract 30 minutes from startime so that it set to zero.
You can do this by making line 37 as

startTime= 2*60*1000+System.currentTimeMillis()-30*60*1000;

Thanks gunjannigam, this works perfectly now. :)