3.9
Keywords
LEXICAL STRUCTURE
A Java letter is a character for which the method
Character.isJavaLetter
( 20.5.17) returns
true
. A Java letter or digit is a character for which the method
Character.isJavaLetterOrDigit
 ( 20.5.18) returns
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 mechanically generated Java code or, rarely, to access pre 
existing names on legacy systems.
The Java digits include the ASCII digits
0 9
 (
\u0030
\u0039)
.
Two identifiers are the same only if they are identical, that is, have the same
Unicode character 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
), and
CYRILLIC SMALL LETTER A
 (
a
,
\u0430
) are all different.
Unicode composite characters are different from the decomposed characters.
For example, a
LATIN CAPITAL LETTER A ACUTE
(
A, \u00c1)
 could be considered
to be the same as a
LATIN CAPITAL LETTER A
 (
A
,
\u0041)
 immediately followed
by a
NON SPACING ACUTE
 ( ,
\u0301
) when sorting, but these are different in Java
identifiers. See
The Unicode Standard
, Volume 1, pages 412ff for details about
decomposition, and see pages 626 627 of that work for details about sorting.
Examples of identifiers are:
String
i3
     
MAX_VALUE
isLetterOrDigit
3.9   Keywords
The following character sequences, formed from ASCII letters, are reserved for
use as
keywords
 and cannot be used as identifiers ( 3.8):
Keyword: one of
abstract
default
if
private
throw
boolean
do
implements
protected
throws
break
double
import
public
transient
byte
else
instanceof
return
try
case
extends
int
short
void
catch
final
interface
static
volatile
char
finally
long
super
while
class
float
native
switch
const
for
new
synchronized
continue
goto
package
this
18






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