public void init() {
    //TODO generate general init
    //String.format() cannot be used in GWT
    for (int i = 0; i < 10000; i ++) {
      String digits = String.valueOf(i);
      StringBuilder sb = new StringBuilder();
      for (int j = 0; j < 4-digits.length(); j ++) {
        sb.append('0');
      }
      sb.append(digits);
      possibleAnswer.add(sb.toString());
    }
  }