Java Reference
In-Depth Information
any Unicode character that is a Java letter (see below)
JavaLetterOrDigit:
any Unicode character that is a Java letter-or-digit (see below)
A “Java letter” is a character for which the method
Character.isJavaIdentifierStart(int)
returns
true.
A “Java letter-or-digit” is a character for which the method
Character.isJavaIdentifierPart(int)
re-
turns true.
The “Java letters” include uppercase and lowercase ASCII Latin letters
A-Z
(
\u0041-
\u005a
), and
a-z
(
\u0061-\u007a
), and, for historical reasons, the ASCII underscore (
_
, or
\u005f
) and dollar sign (
$
, or
\u0024
). The
$
character should be used only in mechanic-
ally generated source code or, rarely, to access pre-existing names on legacy systems.
The “Java digits” include the ASCII digits
0-9
(
\u0030-\u0039
).
Letters and digits may be drawn from the entire Unicode character set, which supports most
writing scripts in use in the world today, including the large sets for Chinese, Japanese, and
Korean. This allows programmers to use identifiers in their programs that are written in
their native languages.
An identifier cannot have the same spelling (Unicode character sequence) as a keyword
(§
3.9
)
, boolean literal (§
3.10.3
)
, or the null literal (§
3.10.7
), or a compile-time error occurs.
Two identifiers are the same only if they are identical, that is, have the same Unicode char-
acter for each letter or digit. Identifiers that have the same external appearance may yet be
different.
For example, the identifiers consisting of the single letters LATIN CAPITAL
LETTER A (
A
,
\u0041
), LATIN SMALL LETTER A (
a
,
\u0061
), GREEK CAPITAL
LETTER ALPHA (
A
,
\u0391
), CYRILLIC SMALL LETTER A (
a
,
\u0430
) and
MATHEMATICAL BOLD ITALIC SMALL A (
a
,
\ud835\udc82
) are all different.
Unicode composite characters are different from their canonical equivalent decom-
posed characters. For example, a LATIN CAPITAL LETTER A ACUTE (
Á
,
\u00c1
) is
different from a LATIN CAPITAL LETTER A (
A
,
\u0041
) immediately followed by a
NON-SPACING ACUTE (
´
,
\u0301
) in identifiers. See The Unicode Standard, Section
3.11 “Normalization Forms”.
Examples of identifiers are:
•
String
