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Java Identifiers - GeeksforGeeks

Java Identifiers

Last Updated : 17 Jul, 2025

An identifier in Java is the name given to Variables, Classes, Methods, Packages, Interfaces, etc. These are the unique names used to identify programming elements. Every Java Variable must be identified with a unique name.

Example:

Java


 public class Test
{
    public static void main(String[] args)
    {
        int a = 20;
    }
}

In the above Java code, we have 5 identifiers as follows:

Test: Class Name
main: Method Name
String: Predefined Class Name
args: Variable Name
a: Variable Name

Rules For Naming Java Identifiers

There are certain rules for defining a valid Java identifier. These rules must be followed, otherwise, we get a compile-time error. These rules are also valid for other languages like C and C++.

The only allowed characters for identifiers are all alphanumeric characters([A-Z],[a-z],[0-9]), '$'(dollar sign) and '_' (underscore). For example, "geek@" is not a valid Java identifier as it contains a '@', a special character.
Identifiers should not start with digits([0-9]). For example, "123geeks" is not a valid Java identifier.
Java identifiers are case-sensitive.
There is no limit on the length of the identifier, but it is advisable to use an optimum length of 4 - 15 letters only.
Reserved Words can't be used as an identifier. For example, "int while = 20;" is an invalid statement as a while is a reserved word.

Note: Java has 53 reserved words (including 50 keywords and 3 literals), that are not allowed to be used as identifiers.

Examples of Valid Identifiers

MyVariable
MYVARIABLE
myvariable
x
i
x1
i1
_myvariable
$myvariable
sum_of_array
geeks123

Examples of Invalid Identifiers

My Variable // contains a space
123geeks // Begins with a digit
a+c // plus sign is not an alphanumeric character
variable-2 // hyphen is not an alphanumeric character
sum_&_difference // ampersand is not an alphanumeric character

Reserved Words in Java

Any programming language reserves some words to represent functionalities defined by that language. These words are called reserved words. They can be briefly categorized into two parts:

Keywords (50): Keywords define functionalities. The below table shows list of 50 keywords.
literals (3): Literals define value. The three literals are, true, false and null.

Identifiers are stored by symbol tables and used during the lexical, syntax, and semantic analysis phase of compilation.

List of Java Reserved Words abstract continue for protected transient Assert Default Goto public Try Boolean Do If Static throws break double implements strictfp Package byte else import super Private case enum Interface Short switch Catch Extends instanceof return void Char Final Int synchronized volatile class finally long throw Date const float Native This while

Note: The keywords const and goto are reserved, even though they are not currently used in Java. In place of const, the final keyword is used. Some keywords like strictfp are included in later versions of Java.

Java Keywords

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