byte[] bytes = getBytesInternal();
    StringBuilder sb = new StringBuilder(2 * bytes.length);
    for (byte b : bytes) {
      sb.append(hexDigits[(b >> 4) & 0xf]).append(hexDigits[b & 0xf]);
    }
    return sb.toString();
  }

  private static final char[] hexDigits = "0123456789abcdef".toCharArray();

   *
   * <p>Accepts a decimal, hexadecimal, or octal number given by specifying the following prefix:
   *
   * <ul>
   *   <li>{@code 0x}<i>HexDigits</i>
   *   <li>{@code 0X}<i>HexDigits</i>
   *   <li>{@code #}<i>HexDigits</i>
   *   <li>{@code 0}<i>OctalDigits</i>
   * </ul>
   *
   * @throws NumberFormatException if the string does not contain a valid unsigned {@code int} value
   * @since 13.0

   *
   * <p>Accepts a decimal, hexadecimal, or octal number given by specifying the following prefix:
   *
   * <ul>
   *   <li>{@code 0x}<i>HexDigits</i>
   *   <li>{@code 0X}<i>HexDigits</i>
   *   <li>{@code #}<i>HexDigits</i>
   *   <li>{@code 0}<i>OctalDigits</i>
   * </ul>
   *
   * @throws NumberFormatException if the string does not contain a valid unsigned {@code long}
   *     value