int timeLeft;

final CounterClass timer = new CounterClass(timeLeft, 1000);

@Override
public boolean onMenuItemClick(MenuItem item) {

    switch (item.getItemId()){
        case R.id.countdownMenu1:
            timeLeft = 15000;
            timer.start();
            return true;

        case R.id.countdownMenu2:
            timeLeft = 20000;
            timer.start();
            return true;

        default:
            return false;
    }
}

public class CounterClass extends CountDownTimer  {

    public CounterClass(long millisInFuture, long countDownInterval) {
        super(millisInFuture, countDownInterval);
    }

    @Override
    public void onTick(long millisUntilFinished) {

        long millis = millisUntilFinished;
        String hms = String.format("%02d:%02d:%02d", TimeUnit.MILLISECONDS.toHours(millis),
                TimeUnit.MILLISECONDS.toMinutes(millis) - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)),
                TimeUnit.MILLISECONDS.toSeconds(millis) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));
        System.out.println(hms);
        textViewTime.setText(hms);
    }

    @Override
    public void onFinish() {
        // textViewTime.setText("Completed.");
        System.exit(0);
    }

}