code: private static String intToString(int value, int digit) {
          StringBuilder stringBuilder = new StringBuilder(digit);
          stringBuilder.append(Integer.toString(value));
          while (stringBuilder.length() < digit) {
              stringBuilder.insert(0, "0");
          }
          return stringBuilder.toString();
      }
docs: Create String representation of integer. Preceding 0 will be add as
  needed.
  
  @param value is the value.
  @param digit is the digit should be shown.
  @return the String representation of int value.