If a charset listed in the IANA Charset
Registry is supported by an implementation of the Java platform then
its canonical name must be the name listed in the registry. Many charsets
are given more than one name in the registry, in which case the registry
identifies one of the names as MIME-preferred. If a charset has more
than one registry name then its canonical name must be the MIME-preferred
name and the other names in the registry must be valid aliases. If a
supported charset is not listed in the IANA registry then its canonical name
must begin with one of the strings "X-" or "x-".
The IANA charset registry does change over time, and so the canonical
name and the aliases of a particular charset may also change over time. To
ensure compatibility it is recommended that no alias ever be removed from a
charset, and that if the canonical name of a charset is changed then its
previous canonical name be made into an alias.
Standard charsets
Every implementation of the Java platform is required to support the
following standard charsets. Consult the release documentation for your
implementation to see if any other charsets are supported. The behavior
of such optional charsets may differ between implementations.
Charset | Description |
US-ASCII |
Seven-bit ASCII, a.k.a. ISO646-US,
a.k.a. the Basic Latin block of the Unicode character set |
ISO-8859-1 |
ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1 |
UTF-8 |
Eight-bit UCS Transformation Format |
UTF-16BE |
Sixteen-bit UCS Transformation Format,
big-endian byte order |
UTF-16LE |
Sixteen-bit UCS Transformation Format,
little-endian byte order |
UTF-16 |
Sixteen-bit UCS Transformation Format,
byte order identified by an optional byte-order mark |
The UTF-8 charset is specified by RFC 2279; the
transformation format upon which it is based is specified in
Amendment 2 of ISO 10646-1 and is also described in the Unicode
Standard.
The UTF-16 charsets are specified by RFC 2781; the
transformation formats upon which they are based are specified in
Amendment 1 of ISO 10646-1 and are also described in the Unicode
Standard.
The UTF-16 charsets use sixteen-bit quantities and are
therefore sensitive to byte order. In these encodings the byte order of a
stream may be indicated by an initial byte-order mark represented by
the Unicode character '\uFEFF'. Byte-order marks are handled
as follows:
When decoding, the UTF-16BE and UTF-16LE
charsets ignore byte-order marks; when encoding, they do not write
byte-order marks.
When decoding, the UTF-16 charset interprets a byte-order
mark to indicate the byte order of the stream but defaults to big-endian
if there is no byte-order mark; when encoding, it uses big-endian byte
order and writes a big-endian byte-order mark.
In any case, when a byte-order mark is read at the beginning of a decoding
operation it is omitted from the resulting sequence of characters. Byte
order marks occuring after the first element of an input sequence are not
omitted since the same code is used to represent ZERO-WIDTH
NON-BREAKING SPACE.
Every instance of the Java virtual machine has a default charset, which
may or may not be one of the standard charsets. The default charset is
determined during virtual-machine startup and typically depends upon the
locale and charset being used by the underlying operating system.
Terminology
The name of this class is taken from the terms used in RFC 2278. In that
document a charset is defined as the combination of a coded character
set and a character-encoding scheme.
A coded character set is a mapping between a set of abstract
characters and a set of integers. US-ASCII, ISO 8859-1,
JIS X 0201, and full Unicode, which is the same as
ISO 10646-1, are examples of coded character sets.
A character-encoding scheme is a mapping between a coded
character set and a set of octet (eight-bit byte) sequences. UTF-8, UCS-2,
UTF-16, ISO 2022, and EUC are examples of character-encoding schemes.
Encoding schemes are often associated with a particular coded character set;
UTF-8, for example, is used only to encode Unicode. Some schemes, however,
are associated with multiple character sets; EUC, for example, can be used
to encode characters in a variety of Asian character sets.
When a coded character set is used exclusively with a single
character-encoding scheme then the corresponding charset is usually named
for the character set; otherwise a charset is usually named for the encoding
scheme and, possibly, the locale of the character sets that it supports.
Hence US-ASCII is the name of the charset for US-ASCII while
EUC-JP is the name of the charset that encodes the
JIS X 0201, JIS X 0208, and JIS X 0212
character sets.
The native character encoding of the Java programming language is
UTF-16. A charset in the Java platform therefore defines a mapping between
sequences of sixteen-bit UTF-16 code units and sequences of bytes.
- Since:
- 1.4
- See Also:
CharsetDecoder
,
CharsetEncoder
,
CharsetProvider
,
Character