Identifier

• name for program for identification purpose.
• Can be classname, method name, variable name or label name also.
• is case sensitive.
• is any sequence of letters, digits, " _ " , " $ " characters that doesn't begin with a digit.

How many identifier here ?

class Hello{
    public static void main(String[] args){
        int numOne = 20;
        int numTwo = 10;
    }
}

String -> Wrapper Class
main -> Name of function/identifier args -> arguments (variable, used for passing Command Line Arguments)
numOne, numTwo -> Variable
Hello -> Class Name

username	✅
#username	❌
num1	✅
1num	❌

class Test{
    int num = 10;
    int NUM = 20;
    int Num = 30;
}

Java is case-sensitive and all three declaration of variables are valid.

Notes

• Identifier length is not limit.
• Max character - no length limit

  int while = 20; ❌
  int String = 9; ✅
  

String is class name, now reserved word.