Identifiers

A name in the program is an identifier,it may be class name or method name or variable name or label name.

public class IdentifierDemo{
          public static void main(String[] args){
             int age;   
          }
}

In the above program IdentifierDemo,main,String,args and age are the identifiers.

Rules for defining Identifiers

  1. An identifier consists of a sequence of characters, where each character is a letter from a-z or A-Z or a digit form 0-9 or currency symbol $ or connecting punctuation _(underscore), if we are using any other symbol we will get Compile time error saying “IllegalCharacter”.
  2. The first character in a identifier should not be a digit.
    Example:
    total123 is a valid identifier
    891total is not a valid identifier
  3. There is no length limit for java identifiers,but it is not recommended to take more than 15 character length.
  4. The java identifiers are case sensitive
    Example:

    class Test{
     int number=10;
     int NUMBER=20;
     int NuMbEr=30 
      
    }
    

    All the above identifiers are valid.

  5. keywords/reserved words are not allowed to used as a identifiers
  6. We can use all predefined java class names and interface names as identifiers

Example:

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

Output: 10
In the above program String is class.