How to make a countdown timer in Android?

As shown in the documentation for CountDownTimer:

new CountDownTimer(30000, 1000) {

    public void onTick(long millisUntilFinished) {
        mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
        // logic to set the EditText could go here
    }

    public void onFinish() {
        mTextField.setText("done!");
    }

}.start();