Identifiers in Java

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)

$ (Doller)

Rule 2:

we Can not use any other character

Example :

total_number   - ✔

Total#  - ✘

Rule 3:

identifiers are not allowed to starts with digit.

Example :

feelfreetocode123   - ✔

123feelfreetocode  - ✘

Rule 4:

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

Example :

    class HelloWorld {
        int age=10;
        int Age=10;
        int aAE=10;
        int AGE=10;
    }
                                

All Age Varibale are different

Rule 5:

There is no length limit for java identifiers

Rule 6:

We can't use reserved words as identifiers.

Example :

int break=10;   - ✘

int else=10;  - ✘

Rule 7:

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

Example :

class Test {
    public static void main(String[] args){
        int Integer=10;
        System.out.println(Integer);
    }
}
                                

Let's Practice

---

VALID   - ✔
INVALID  - ✘

MyVariable   - ✔

myvariable   - ✔

My Variable  - ✘

9pins  - ✘

MYVARIABLE   - ✔

a+c  - ✘

xi_my variable
  - ✔


testing1-2-3  - ✘

$myvariable
  - ✔

_9pins
  - ✔

andro
  - ✔

O'Reilly  - ✘
This_is_an_insanely_long_variable_name_that_just_keeps_going_and_going_and_going_and_well_you_get_the_idea_The_line_breaks_arent_really_part_of_the_variable_name_Its_just_that_this_variable_name_is_so_ridiculously_long_that_it_won't_fit_on_the_page_I_cant_imagine_why_you_would_need_such_a_long_variable_name_but_if_you_do_you_can_have_i
  - ✔