An identifier is an unlimited-length sequence of Java letters and Java digits, the first of which must be a Java letter. An identifier cannot have the same spelling (Unicode character sequence) as a keyword, boolean literal, or the null literal.

Identifier:
IdentifierChars but not a Keyword or BooleanLiteral or NullLiteral

IdentifierChars:
JavaLetter
IdentifierChars JavaLetterOrDigit

JavaLetter:
any Unicode character that is a Java letter (see below)

JavaLetterOrDigit:
any Unicode character that is a Java letter-or-digit (see below)

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.
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) 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 source code or, rarely, to access preexisting 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), CYRILLIC SMALL LETTER A (a, \u0430) and MATHEMATICAL BOLD ITALIC SMALL A (a, \ud835\udc82) are all different.

Unicode composite characters are different from the decomposed characters. For example, a LATIN CAPITAL LETTER A ACUTE (Á, \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 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



Rajanikant

Hi friend,

Identifiers are the names of variables, methods, classes, packages and interfaces. In the HelloWorld program, HelloWorld, String, args, main and println are identifiers.

Identifiers must comply with these rules:

* The first character of an identifier must be a letter, an underscore(_), or a dollar sign($).
* The rest of the characters in the identifier can be a letter, underscore, dollar sign, or digit. Note that spaces are NOT allowed in identifiers.
* Identifiers are case-sensitive. This means that age and Age are different identifiers.
* Identifiers cannot match any of Java's reserved words.

Examples:

These identifiers are valid:

MyClass
$amount
totalGrades;
TotalGrades;
TAX_RATE
one

These identifiers are NOT valid:

My Class // spaces are not allowed
numberOf*s // the asterisk cannot be used
final // final is a reserved word
1Way // identifiers cannot start with a digit


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Amardeep.