Java Identifiers

Identifiers in Java are symbolic names used for identification. They can be a class name, variable name, method name, package name, constant name, and more. However, In Java, There are some reserved words that can not be used as an identifier.

Rules for Identifiers in Java

There are some rules and conventions for declaring the identifiers in Java. If the identifiers are not properly declared, we may get a compile-time error. Following are some rules and conventions for declaring identifiers:

• A valid identifier must have characters [A-Z] or [a-z] or numbers [0-9], and underscore(_) or a dollar sign ($). for example, @mybcaclass is not a valid identifier because it contains a special character which is @.
• There should not be any space in an identifier. For example, my bcaclass is an invalid identifier.
• An identifier should not contain a number at the starting. For example, 123mybcaclass is an invalid identifier.
• An identifier should be of length 4-15 letters only. However, there is no limit on its length. But, it is good to follow the standard conventions.
• We can't use the Java reserved keywords as an identifier such as int, float, double, char, etc. For example, int double is an invalid identifier in Java.
• An identifier should not be any query language keywords such as SELECT, FROM, COUNT, DELETE, etc.

 

Example of Valid and Invalid Identifiers

Valid identifiers:

Following are some examples of valid identifiers in Java:

• TestVariable
• testvariable
• a
• i
• Test_Variable
• _testvariable
• $testvariable
• sum_of_array
• TESTVARIABLE
• Test123
• testVariable
  
• test123

Invalid identifiers:

Below are some examples of invalid identifiers:

• Test Variable ( We can not include a space in an identifier)
• 123Variable ( The identifier should not begin with numbers)
• Test+Variable ( The plus (+) symbol cannot be used)
• Test-variable ( Hyphen symbol is not allowed)
• test_&_variable ( ampersand symbol is not allowed)
• test'variable (we can not use an apostrophe symbol in an identifier)