Identifiers

Identifier: A name in java program is called identifier. It may be 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 compile time error.
Example:
1) total_number——-valid
2) Total#——————invalid

Rule 3: identifiers are not allowed to starts with 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

Note: 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) Java2share  (valid)
4) all@hands  (invalid)
5) 123abc           (invalid)
6) Total#           (invalid)
7) Int                  (invalid)
8) Integer          (valid)