code: private int read2Digits(CharSequenceScanner scanner) throws IllegalDateFormatException {
  
      int highDigit = scanner.readDigit();
      if (highDigit == -1) {
        return -1;
      }
      int lowDigit = scanner.readDigit();
      if (lowDigit == -1) {
        throw new IllegalDateFormatException(scanner.getOriginalString());
      }
      return (highDigit * 10) + lowDigit;
    }
docs: This method reads two digits from the given {@code scanner}.
  
  @param scanner is the scanner potentially pointing to the digits.
  @return {@code -1} if the {@code scanner} does NOT point to a digit or the number represented by the two
  digits consumed from the {@code scanner}.
  @throws IllegalDateFormatException if the {@code scanner} only contained a single digit.