Identifier

A Name in Java program by default considered as an identifier. It may be a Class Name, Method Name, Variable Name or Label Name.

Example:

class Test{

public static void main(String args[]){

System.out.println("HelloWorld");

int x=10;

}

}

In this program the identifiers are:-

1.  Test -->Name of the class

2.  main -->Name of method

3.  String -->Name of a predefined java class

4.  args -->Name of Array

5.  println -->Name of method

6.  x -->Name of variable

Rules for defining an Identifier:

1. The only allowed characters for java identifier in java are { a-z,A-Z,0-9,_,$ }

If we are using any other charcter we ll get compile time error

Example:

total_number (valid)

total# (Invalid)

2. Identifiers should not start with digit.

Example:

total123 (valid)

123total (Invalid)

3. Java Identifiers are case Sensitive,Of Course Java language itself is treated as case-sensitive programming language.

Example:

class Test{

int number=10; (valid)

int Number=20; (valid)

int NUMBER=30; (valid)

}

4. There is no length limit for java identifiers. But it is not recommended to take too lengthy identifiers.

Example:

class Test{

int xhgxihihoiweflwedvbkbdvbdbvdfbvdfsbvfdlmbvfdlflegplrtkhgerugvterwh=10;

System.out.println(xhgxihihoiweflwedvbkbdvbdbvdfbvdfsbvfdlmbvfdlflegplrtkhgerugvterwh); //valid and No error,but not recommended for good programmer

}

5. We can't use reserved words(KeyWords) as identifier.

Example:

class Test{

int x=10; (valid)

int if=20; (Invalid)

}

6. All predefined java class names and interface names, we can use as identifiers.

Example:

class Test{

public static void main(String args[]){

int String =10

System.out.println(String); //valid and No error, but not recommended

int Runnable =20

System.out.println(Runnable); //valid and No error, but not recommended

}

}

Note: Even though it is valid, but it is not a good programming practice because it reduces readability and creates confusion.

Practice Question:

which of the following are valid java identifiers?

1.  max_number

2.  max#

3.  123max

4.  max123

5.  _$_$_$_$_

6.  all@hands

7.  ca$h

8.  Java2Share

9.  Integer

10. Int

11. int