how can i make test if else on Timer?

Question

i make this a Timer that makes me check the correct answer every time user compose a word so it's working if user submit correct answer but when i made else test for wrong answer it couldn't work and app crashed,
plz help me i want to check if answer wrong

//to check the whole answer

    final Timer timer = new Timer();
    timer.scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            //answer button get text to string
            final StringBuilder str = new StringBuilder();
            for (int i = 0; i < btnanswer.length; i++) {

                str.append(String.valueOf(btnanswer[i].getText()));
                Log.d("asdf", "run:   " + str);
                gamefinished = true;
            }

            //check answer button with the button
            if (answer.toLowerCase().equals(String.valueOf(str).toLowerCase())) {
                startActivity(new 
                 Intent(MainActivity.this,SecondActivity.class));
                timer.cancel();
            }

        }

    }, 0, 10);