returns whether the given byte array slice is a well-formed utf-8 byte sequence , as defined by #iswellformed byte . note that this can be false even when iswellformed bytes is true . concode_field_sep PlaceHolder placeHolder concode_field_sep int encodedLength concode_elem_sep boolean isWellFormedSlowPath concode_elem_sep String unpairedSurrogateMsg concode_elem_sep int encodedLengthGeneral