code: private static String longToPaddedString(long v, int digitsColumnWidth) {
      int digitWidth = numDigits(v);
      StringBuilder sb = new StringBuilder();
      appendSpaces(sb, digitsColumnWidth - digitWidth);
      sb.append(v);
      return sb.toString();
    }
docs: Converts 'v' to a string and pads it with up to 16 spaces for
  improved alignment.
  @param v The value to convert.
  @param digitsColumnWidth The desired with of the string.