The
Character
class wraps a value of the primitive
type
char
in an object. An object of type
Character
contains a single field whose type is
char
.
In addition, this class provides several methods for determining
a character's category (lowercase letter, digit, etc.) and for converting
characters from uppercase to lowercase and vice versa.
Character information is based on the Unicode Standard, version 4.0.
The methods and data of class Character
are defined by
the information in the UnicodeData file that is part of the
Unicode Character Database maintained by the Unicode
Consortium. This file specifies various properties including name
and general category for every defined Unicode code point or
character range.
The file and its description are available from the Unicode Consortium at:
The char
data type (and therefore the value that a
Character
object encapsulates) are based on the
original Unicode specification, which defined characters as
fixed-width 16-bit entities. The Unicode standard has since been
changed to allow for characters whose representation requires more
than 16 bits. The range of legal code points is now
U+0000 to U+10FFFF, known as Unicode scalar value.
(Refer to the
definition of the U+n notation in the Unicode
standard.)
The set of characters from U+0000 to U+FFFF is sometimes
referred to as the Basic Multilingual Plane (BMP). Characters whose code points are greater
than U+FFFF are called supplementary characters. The Java
2 platform uses the UTF-16 representation in char
arrays and in the String
and StringBuffer
classes. In this representation, supplementary characters are
represented as a pair of char
values, the first from
the high-surrogates range, (\uD800-\uDBFF), the
second from the low-surrogates range
(\uDC00-\uDFFF).
A char
value, therefore, represents Basic
Multilingual Plane (BMP) code points, including the surrogate
code points, or code units of the UTF-16 encoding. An
int
value represents all Unicode code points,
including supplementary code points. The lower (least significant)
21 bits of int
are used to represent Unicode code
points and the upper (most significant) 11 bits must be zero.
Unless otherwise specified, the behavior with respect to
supplementary characters and surrogate char
values is
as follows:
- The methods that only accept a
char
value cannot support
supplementary characters. They treat char
values from the
surrogate ranges as undefined characters. For example,
Character.isLetter('\uD840')
returns false
, even though
this specific value if followed by any low-surrogate value in a string
would represent a letter.
- The methods that accept an
int
value support all
Unicode characters, including supplementary characters. For
example, Character.isLetter(0x2F81A)
returns
true
because the code point value represents a letter
(a CJK ideograph).
In the Java SE API documentation, Unicode code point is
used for character values in the range between U+0000 and U+10FFFF,
and Unicode code unit is used for 16-bit
char
values that are code units of the UTF-16
encoding. For more information on Unicode terminology, refer to the
Unicode Glossary.