Identifiers

Identifiers:

                                    A name in java program is called identifier, which can be used for identification purposes. It can be a method name, variable name, class name, or label name.

Rules for defining java identifiers:

1. The only allowed characters in java identifiers are a - z, A - Z, 0 - 9, $, and _. If we are using other characters, we will get a compile-time error.
2. Identifiers can't start with digits.
3. Java identifiers are case sensitive. Of course, java is treated as case sensitive programming language.
4. There is no limit for java identifiers but it is not recommended to take too lengthy identifiers.
5. We can't use reserved words as identifiers.
6. All predefined java class name and interface name we can use as identifiers.

                    e.g.

                        int String = 888;

                        int Runnable = 999;

                        Even this is valid, but it is not good programming practice.

Examples

Que 1) How many identifiers in the following program?

                            

                                class Test{

                                            public static void main(String args[]){

                                                    int x = 10;

                                            }

                                }

Ans:      Five

               They are Test, main, String, args, x.

Que 2) Which of the following are valid java identifiers?

1.   tot_num                        Valid
2. total#                              Invalid
3. 123totoal                        Invalid
4. total123                          Valid    
5. ca$h                                Valid 
6. _$_$_$_$_                     Valid
7. arr@share                      Invalid
8. Java2share                     Valid
9. Integer                           Valid
10. Int                                  Valid
11. int                                  Invalid