Introduction

Boy : How can i identify you ?
Girl : My name is "Priya", you can identify by my name.

• Just as "Priya" is a name used to identify the girl; in programming, identifiers are names used to identify variables, classes, methods, interfaces or other elements in the code.
• In simple words we can say, Ientifiers is any name, it can be variable, methods or class name in our program.
• They are unique names that help us recognize elements like variables, methods, and classes in our program.
• For example :
  • String name = "Deepak"; // here name is identifier
  • int rollno = 101; // here rollno is identifier
  • class Test {-} // here Test is identifier

Rules for Identifiers:

1. Spaces cannot be used in an identifier.
   • Identifiers must not contain any whitespace.
   • Invalid Examples:

     int roll no;  // Error: Spaces are not allowed
     String user name; // Error: Spaces are not allowed

   • Valid Examples:

     int rollno;
     String username;

2. Only two symbols (_ and $) can be used in an identifier.
   • Identifiers can include underscores (_) or dollar signs ($), but other special symbols like @, # or ! are not allowed.
   • Invalid Examples:

     int roll-no;   // Error: '-' is not allowed
     double @price;   // Error: '@' is not allowed

   • Valid Examples:

     int roll_no;
     double $price;

3. Integer values cannot be used at the first position.
   • Identifiers cannot begin with a digit (0-9) but may include digits after the first character.
   • Invalid Examples:

     int 1rollno;   // Error: Cannot start with a digit
     double 3value;   // Error: Cannot start with a digit

   • Valid Examples:

     int rollno1;
     double _123value;

4. Reserved words cannot be used as an identifier.
   • Reserved keywords in Java (like class, public, if, etc.) cannot be used as identifiers.
   • Invalid Examples:

     int class;   // Error: 'class' is a reserved keyword
     String public; // Error: 'public' is a reserved keyword

   • Valid Examples:

     int my_class;
     String _if;

5. Must Not Conflict with Built-in Methods.
   • Avoid using names that conflict with commonly used built-in methods or library functions to prevent confusion.
   • Valid Examples:

     int println = 5; // Valid but confusing, as 'println' is used in System.out.println()

Points for Identifiers:

1. Case Sensitivity.
   • Java identifiers are case-sensitive. For example, MyVariable and myVariable are treated as distinct identifiers.
   • Valid Examples:

     int MyVariable = 10;
     int myVariable = 20; // Different from 'MyVariable'

2. No Length Limit.
   • There is no specific limit on the length of an identifier, but it is recommended to keep names concise and meaningful.
   • Valid Examples:

     int thisIsAnExtremelyLongVariableName = 100; // Valid but not recommended

3. Use Meaningful Names.
   • Choose names that describe the purpose of the variable or method to improve code readability.
   • Valid Examples:

     int x = 10; // Valid but not descriptive
     int age = 10; // Better: Descriptive and meaningful