No onCreate com um button mostra os segundos passando

final EditText editText = (EditText) findViewById(R.id.editText1);

Timer timer = new Timer();
timer.scheduleAtFixedRate(new TimerTask() {
    @Override
    public void run() {
        Calendar c = Calendar.getInstance();
        int seconds = c.get(Calendar.SECOND);
        final String time = String.valueOf(seconds);
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                editText.setText(time);
            }
        });
    }
}, 0, 1000);