ISO/IEC JTC 1/SC22/Java SG

ISO/IEC JTC 1/SC22/Java SG   N 3-12

DATE: 1998-10-17

REPLACES: N/A

DOC TYPE: Plain DOS Text

TITLE: Requirements for supporting non-BMP planes in UCS-4

SOURCE: Japan (Kazuhiro Kazama)

PROJECT: N/A

STATUS: This document is circulated to National Bodies of JTC
1/SC22/Java SG for review and consideration at the October 1998
SC22/Java SG meeting in Tokyo.

ACTION ID: FYI

DUE DATE:

DISTRIBUTION: P and L Members

MEDIUM:

DISKETTE NO.:

NO. OF PAGES: 1

Text of contribution:

ISO Java standard should support non-BMP planes in UCS-4.  For
example, additional ideographs will be added to plane 2 in ISO/IEC
10646. Those characters are necessary for reading/writing Japanese
documents.

The current Java specification has some problems in non-BMP plane
support. The primitive character data type "char" can't store UCS-4
data directly because its values are 16-bit unsigned
integers. Although the Unicode Standard 2.0 supports surrogate pairs
(UTF-16), there are the following problems in the Java specification.

* Unicode escapes (ex. \uFFFF) don't support UCS-4 representation.
* Almost all methods in java.lang.Character class don't process
surrogate pairs as one character.
* Because The "CONSTANT_Utf8" format in class files isn't the standard
UTF-8 format, surrogate pairs don't convert correctly.

This document has reported only requirements of non-BMP planes, and
doesn't specify methods to support those planes.