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 :
In the above java code, we have 5 identifiers namely :
- Customer : class name.
- main : method name.
- String : predefined class name.
- args : variable name.
- customerId : variable name.
Rules for defining Java Identifiers
1. 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++.
2. The only allowed characters for identifiers are all alphanumeric characters([A-Z],[a-z],[0-9]), ‘$‘(dollar sign) and ‘_‘ (underscore).For example “java@” is not a valid java identifier as it contain ‘@’ special character.
3. Identifiers should not start with digits([0-9]). For example “123java” is a not a valid java identifier.
4.Java identifiers are case-sensitive.
5.There is no limit on the length of the identifier but it is advisable to use an optimum length of 4 – 15 letters only.
6. 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 :
employeeId
EmployeeId
EMPLOYEEID
_employeeId
$employeeId
_1employeeId