You can keep a running timer using this on init:
Timer updateTimer = new Timer("update");
updateTimer.scheduleAtFixedRate(new TimerTask() {
public void run() {
updateGUI();
}
}, 0, 1000);
long startTime = System.currentTimeMillis();
Then in a Thread:
//Clock update
currentTime = System.currentTimeMillis() - startTime;
SimpleDateFormat sdf = new SimpleDateFormat("mm:ss");
clock.setText(sdf.format(currentTime));
clock.invalidate();
You could stop the Thread with a boolean inside or outside as you please?