IDENTIFIERS

IDENTIFIERS:

A name in java program is called identifier. It may be class name, method name, variable name and label name.  

Example:

           

       Class Collegetak

{

    publc static void main (String [] args)

{

 int x=20;

}

}

            

     In this code there are 5 identifiers

1. Collegetak
2. main
3. String
4. args
5.  x

Rules to define java identifiers:

Rule 1: The only allowed characters in java identifiers are:

•   a to z 
•  A to Z 
•  0 to 9 
•  _ (underscore) 
•  $ 

Rule 2: If we are using any other character we will get compile time error.

Example:

1) total_number-------valid

 2) Total#------------------invalid

 Rule 3:  identifiers are not allowed to starts with digit.

 Example:

•  ABC123---------valid
•  123ABC---------invalid 

Rule 4: java identifiers are case sensitive up course java language itself treated as case sensitive language. 

Example:

 class Test

{

 int number=10;

 int Number=20; 

int NUMBER=20; we can differentiate with case. 

int NuMbEr=30; 

}

Rule 5: There is no length limit for java identifiers but it is not recommended to take more than 15 lengths. 

Rule 6: We can't use reserved words as identifiers.

 Example: 

int if=10; --------------invalid

 Rule 7: All predefined java class names and interface names we use as identifiers. 

Example 1: 

class Collegetak

 {

 public static void main(String[] args)

{ 

int String=15; System.out.println(String);

 }

}

 Output: 15

Example 2:

class CollegeTak

{ 

public static void main(String[] args)

{

int Runnable=20;

 System.out.println(Runnable);

}

} 

 output: 20

Even though it is legal to use class names and interface names as identifiers but it is not a good programming practice. 

Which of the following are valid java identifiers? 

1. _$_   (valid)
2. Ca$h (valid)
3. Java2shre  (valid)
4. all@hands  (invalid)
5. 123abc (invalid)
6. Total# (invalid)
7. Int ( valid)
8. Integer (valid)
9. int   (valid)

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