code: private CharSequence transform(FormatToken token, Object argument) {
      this.formatToken = token;
      this.arg = argument;
  
      // There are only two format specifiers that matter: "%d" and "%s".
      // Nothing else is common in the wild. We fast-path these two to
      // avoid the heavyweight machinery needed to cope with flags, width,
      // and precision.
      if (token.isDefault()) {
        switch (token.getConversionType()) {
          case 's':
            if (arg == null) {
              return "null";
            }
            // fall through
          case 'd':
            if (arg instanceof Integer
                || arg instanceof Long
                || arg instanceof Short
                || arg instanceof Byte) {
              String result = arg.toString();
              return result;
            }
        }
      }
  
      formatToken.checkFlags(arg);
      CharSequence result;
      switch (token.getConversionType()) {
        case 'B':
        case 'b':
          result = transformFromBoolean();
          break;
        case 'H':
        case 'h':
          result = transformFromHashCode();
          break;
        case 'S':
        case 's':
          result = transformFromString();
          break;
        case 'C':
        case 'c':
          result = transformFromCharacter();
          break;
        case 'd':
        case 'o':
        case 'x':
        case 'X':
          result = transformFromInteger();
          break;
        case 'A':
        case 'a':
        case 'E':
        case 'e':
        case 'f':
        case 'G':
        case 'g':
          result = transformFromFloat();
          break;
        case '%':
          result = transformFromPercent();
          break;
        case 'n':
          result = transformFromLineSeparator();
          break;
        case 't':
        case 'T':
          result = transformFromDateTime();
          break;
        default:
          throw token.unknownFormatConversionException();
      }
  
      if (Character.isUpperCase(token.getConversionType()) && result != null) {
        result = Ascii.toUpperCase(result.toString());
      }
      return result;
    }
docs: /*
  Gets the formatted string according to the format token and the
  argument.