Error: "Unfortunately Crystal Ball has stopped working" in the emulator

private CrystalBall mCrystallBall = new CrystalBall();

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //Declare our view variables and assign them the view from the layout file
    final TextView answerLabel  = (TextView) findViewById(R.id.textView1);
    Button getAnswerButton = (Button)findViewById(R.id.button1);

    getAnswerButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            String answer = mCrystallBall.getAnswer();

            //Update the label with our dynamic answer
            answerLabel.setText(answer);        
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}