Identifier

Identifier: A name in the java program is called an identifier. It may be a class name, method name, variable name and label name.
Example:

Rules to define java identifiers:

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

1) a to z

2) A to Z

3) 0 to 9

4) _

5) $

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

Example:

1) total_number-------valid

2) Total#------------------invalid

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

Example:

1) ABC123---------valid

2) 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 Test

                  {

                        public static void main(String[] args){

                        int String=10;

                        System.out.println(String);

                   }}

Output:

10

Example 2:

               class Test

                   {

                         public static void main(String[] args){

                         int Runnable=10;

                         System.out.println(Runnable);

                    }}

Output:

10

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?