1. Working of static variables, methods
http://improvejava.blogspot.in
1

2. Objective
On completion of this period, you would be able to know :
• Static member
• Static variables
• Static methods
http://improvejava.blogspot.in

3. Recap
In the previous lesson, we have discussed
• ‘this’ pointer
• Usage of ‘this’ pointer
• Related programs
http://improvejava.blogspot.in

4. Static Member
• Normally a class member must be accessed only in
conjunction with an object of its class
• However, it is possible to create a member that can be used
by itself, without reference to a specific instance
• Such a member is called static member
http://improvejava.blogspot.in
4

5. Static Member
• To create such a member, precede its declaration with the
keyword static
• When a member is declared static, it can be accessed before
any objects of its class are created, and without reference to any
object
• The most common example of a static member is main()
• main() is declared as static because it must be called before any
object exist.
http://improvejava.blogspot.in
5

6. Static Variable
• You can declare both methods and variables to be static
• Instance variables declared as static are, essentially,
global variables
• Such variables are called as class variables
• For a class variable only one copy of memory is allotted
regardless of any number of objects created
http://improvejava.blogspot.in
6

7. Example Program : Non-Static Variable
class A {
int x; non static variable
public static void main (String args[]) {
A obj_a = new A();
obj_a.x = 10;
System.out.println (“ value of x in obj_a ”+ obj_a.x);
A obj_b = new A();
System.out.println(“value of x in obj_b ”+ obj_b.x);
}
}
Output : x value in object pointed by obj_a 10
x value in object pointed by obj_b “garbage value”
http://improvejava.blogspot.in
7

8. Example Program :Non-Static Variable
Memory allocation for the objects in the above program
• A obj_a = new A(); • A obj_b = new A();
• obj_a.x = 10;
x :10 x :gb
obj_a for non-static variables obj_b
memory is allocated for
each object individually
http://improvejava.blogspot.in
8

9. Example program :Static Variable
class A {
static int x;
public static void main (String args[]) {
A obj_a = new A();
obj_a.x = 10;
System.out.println(“value of x in obj_a ”+ obj_a.x);
A obj_b = new A();
System.out.println(“value of x in obj_b ”+ obj_b.x);
}
}
http://improvejava.blogspot.in

10. Example Program :Non-Static Variable
Memory allocation for the objects in the above program
• A obj_a = new A(); • A obj_b = new A();
• obj_a.x = 10;
x :10
For static variables memory
obj_a is allocated for each object
obj_b
in common place
not inside object
http://improvejava.blogspot.in
10

11. Static Methods
• Methods declared as static have several restrictions
• They can only call other static methods
• They must only access static data
• They cannot refer to this or super in any way
http://improvejava.blogspot.in
11

12. Example Program : Static Methods
class A {
static int x=10;
static void call (int y) {
System.out.println(“ x value is : ”+ x);
System.out.println(“ y value is : ”+ y);
}
public static void main (String args[]) {
call(20);
}
}
Output : x value is : 10
y value is : 2 call() is called without
creating object because
call() is static method
http://improvejava.blogspot.in

13. Calling Static Methods
• Normally to call a method, its object is need
• To call total_mks() of Student class we need to create student
object and then call total_mks on thaat objecxt
• Student s = new Student();
• s.total_mks();
• To call static method, there is no need to create an object of the
class
• To call it use the class name directly
• ClassName.methodName();
http://improvejava.blogspot.in
13

14. Example program : Calling Static Methods
class A {
static int a = 10;
static int b = 20;
static void callme() {
System.out.println(“ a: ”+a);
}
}
class B {
public static void main() { calling static method
A.callme(); without using object
System.out.println(“ b: ”+A.b); reference
}
}
Output:
static variable is
a: 10
Accessed without
b: 20
object reference
http://improvejava.blogspot.in
14

15. Summary
• Static member
• Static variables
• Static methods
http://improvejava.blogspot.in
15

16. Quiz
1. Static variable memory is created
a. Like instance variable
b. Separate memory for each object
c. Common memory for all object
d. None
http://improvejava.blogspot.in
16

17. Quiz contd..
2. Static variables or methods are accessed:
a. using object
b. using reference
c. using class name from outside class.
d. none
http://improvejava.blogspot.in

18. Frequently Asked Questions
1. Explain the use of static variables?
2. Explain the concept of static methods?
http://improvejava.blogspot.in
18

19. Assignment
1. Write an Employee class assuming appropriate data
and method members
Create objects for the above class, and display
how many number of objects are created by using
static member concept
http://improvejava.blogspot.in