24/01/25
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Q)Java program on "private access modifier".
class Student{
	int rollno;
	String name;
	private int marks;
	private char grade;
	Student(int rollno,String name,int marks){
		this.rollno=rollno;
		this.name=name;
		this.marks=marks;
	}//parameterised constructor
	 void displayStudentDetails(){
              System.out.println("ROLLNO:"+rollno);
              System.out.println("NAME:"+name);
              System.out.println("MARKS:"+marks);
              System.out.println("GRADE:"+grade);
	 }//instance method
         void calculateGrade(){
		 if(marks>=80){
			 grade='A';
		 }
		 else if (marks>=60 && marks<80) {
			 grade='B';
		 }
		 else{
			 grade='C';
		 }
	 }//instance method
}
class StudentApplication{
	public static void main(String[] args){
		Student s=new Student(101,"Rama",76);
		s.calculateGrade();
		s.displayStudentDetails();
	}
}
                                  
Q)What is the output of the following program?
class Employee{
        int emp_count;
	Employee(){
		emp_count++;
	}
	void displayEmpCount(){
		System.out.println("Total Number of emps appointed:"+emp_count);
	}
}
class  EmpCountApplication{
	public static void main(String[] args){
		Employee e1=new Employee();
		e1.displayEmpCount();
		Employee e2=new Employee();
		e2.displayEmpCount();
	}
}

Ans:- 
Total Number of emps appointed:1
Total Number of emps appointed:1
Note:- "Reason for the unexpected output is", the kind of variable
used to keep track of total number of employees appointed.

                                     static modifier
				     ----------------          
Q) What is the purpose of "static" modifier?
    =>We can create
               1)static variables
	       2)static methods
	       3)static initializer/block
Q)What is a class variable?
       =>If "static" modifier is applied to an instance variable of a class,
       it becomes a (per) class variable.I.e. static variable is nothing but a 
       class variable.
Q)What are the differences between static variables and instance variables?
instance  variables                          static variables
  ----------------------------------------------------------------
  1)per object                             per class only one copy
  one seperate copy.                     irrespective of the 
                                                 number of objects.

 2)meant for representing            meant for representing 
 individual object information.       entire class level information.


3)contributes to the size              doesn't contribute.
of the object.


4)owned by an object.                 shared by every object of the class.


5)memory is allocated                 memory is allocated to the
only when the object                    static variable as soon as
is created.                                 the class is loaded into memory
                                                 and before any object is created.

6)memory is allocated                memory is allocated in the method
in the HEAP area.                       area.

7)using the reference                  can be referenced using
(explicit/implicit reference)          class name.
only, instance variable
can be referenced in the program.