{
  public static int fromDigit(char c)  {    if (c >= '0' && c <= '9')      {        return c - '0';      }    else if (c >= 'A' && c <= 'F')      {        return c - 'A' + 10;      }    else if (c >= 'a' && c <= 'f')      {        return c - 'a' + 10;      }    else      throw new IllegalArgumentException("Invalid hexadecimal digit: " + c);  }