MainActivity.java

    // Tag used for logging
    private static final String TAG = "MyActivity";

    // Declare a countdown timer
    private CountDownTimer countDownTimer;

    // Declare and initialize length for timer to run and set total equal to it
    private long length = 30000;
    private long total = length;

    // Declare TextView and ProgressBar to update view
    private TextView timeRemaining;
    private ProgressBar progressBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        // Initialize timeRemaining and progressBar views
        timeRemaining = (TextView) findViewById(R.id.time_remaining_text_view);
        progressBar = (ProgressBar) findViewById(R.id.progress_bar);
        // Set progress bar max value equal to length
        progressBar.setMax((int) length);

    }

    // Define onClick method for Start button
    public void startTimer(View v) {

        // Instantiate new CountDownTimer and assign to countDownTimer variable
        countDownTimer = new CountDownTimer(total, 1) {
            @Override // Implement required methods (onTick and onFinish)
            public void onTick(long millisUntilFinished) {

                // Update total with remaining time left
                total = millisUntilFinished;

                // Update TextView and ProgressBar
                timeRemaining.setText("seconds remaining: " + millisUntilFinished / 1000);
                progressBar.setProgress((int) (progressBar.getMax() - millisUntilFinished));

            }

            @Override
            public void onFinish() {

                // Update TextView
                timeRemaining.setText("done!");

                // Reset total to length so Start begins at beginning
                total = length;
            }
        };

        // Start countDownTimer
        countDownTimer.start();
    }

    public void stopTimer(View v) {
        countDownTimer.cancel();
        Log.v(TAG, "stopped");
    }