Java Identifiers
In programming languages, identifiers are used for identification purpose. In Java, an identifier can be a class name, method name, variable name or a label. For example :
public class Test { public static void main(String[] args) { int a = 20; } }
In the above java code, we have 5 identifiers namely :
- Test : class name.
- main : method name.
- String : predefined class name.
- args : variable name.
- a : variable name.
Rules for defining Java Identifiers
There are certain rules for defining a valid java identifier. These rules must be followed, otherwise we get compile-time error. These rules are also valid for other languages like C,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 contain ‘@’ special character.
- Identifiers should not start with digits([0-9]). For example “123geeks” is a 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 while is a reserved word. There are 53 reserved words in Java.
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 characterjava java tutorials learn java study java