1.01 Identifiers

Definition of Identifiers

Identifier: A name in Java program is called Identifier, which can be used for identification purpose.
It can be any of the following:

• Variable Name
• Class Name
• Label Name

Q. In the following code identify number of Identifiers present and highlight them -

class Test {
    public static void main(String[] args) {
        int x = 10;
    }
}

Identifiers:

• Test - class name
• main - method name
• String - predefined java class name
• args - name of array
• x - name of variable

Total 5 identifiers in above example

---

Rules for defining Java identifiers

1. Characters we can use: The only allowed characters are-
   a-z, A-Z, 0-9, '$', '_'
   Examples:
   1. total_Num -
   2. totalNum# -
      If we are using any other character we’ll get compile time error.
2. Identifier should mot start with digit As the rule name suggest an Identifier can’t start with digit.
   Examples:
   1. total123 -
   2. 123total -
      If we are using any other character we’ll get compile time error.

3. Case-Sensitive: Not just Identifiers, whole Java language is treated as Case-Sensitive programming language. Q. Is following code valid?

    class Test {
        public static void main(String[] args) {
            int number = 10;
            int Number = 20;
            int NUMBER = 30;
        }
   

   

4. Length Limit: Even though there is no limit for java identifiers, it is not recommended to take too lengthy identifiers. Examples:
   1. int JavaSupportsReallyReallyLongLongIdentifier = 0; -
5. We can’t use reserved words as identifiers:: In Java we can’t use reserved words as identifiers. Examples:
   1. int a = 10; -
   2. int if = 0; -

6. Pre-Defined Java class names and interface as Identifiers All pre-defined Java classnames and interface can be used as Identifiers. Even though it is valid, but it is not a good programming practice, because it reduces Readability and creates confusion.

    class Test {
        public static void main(String[] args) {
            int String = 888;
            System.out.println(String);
        }
   

   

    class Test {
        public static void main(String[] args) {
            int Runnable = 999;
            System.out.println(Runnable);
        }
   

   

---

TEST

Q. Which of the following are valid Java identifiers?

Sr. No.	Identifier	Answer
1.	total_number
2.	total#	Rule No.1
3.	123total	Rule No.2
4.	total123
5.	ca$h
6.	_$_$_$_$_
7.	all@hands	Rule No.1
8.	Integer
9.	Int
10.	int	Rule No.5

---

Next Topic: 1.02 Reserved Words