Use of Static keyword

Static keyword in java is mainly used for memory management.this is mainly used for variable,methods and blocks.

• Java static variable : It is used to refer common property of all the objects. As name of city which is common for all the entity.
• Static variable gets memory at time of class load.

This explain you how static variable works , if you have some more time just see it.

For videos in hindi click here 

Simple Static example

public class studentdetails {

int age ;
String name;
static String city="fremont";
studentdetails(int age,String name)
{
this.age=age;
this.name=name;
}

public static void hello(){ //this is a static method
     city = "foster";
System.out.println("My city is "+city);// Static method can use only static variable
}

public void test(){
System.out.println("My Name is -->"+name);
System.out.println("My age is -->"+age);
System.out.println("City is -->"+city);

}
// static method can use only static variable 

public static void main(String[] args) {
studentdetails obj1 = new studentdetails(22,"Ram");
studentdetails obj2 = new studentdetails(19,"krishna");  
obj1.test();//variable city is loaded only once in class so memory
obj2.test();//second time also when object is called static variables memory remains same
hello();
}
}

Output:-

My Name is -->Ram
My age is -->22
City is -->fremont
My Name is -->krishna
My age is -->19
City is -->fremont
My city is foster

Static method is used by putting a static keyword after access modifier  in method as seen in above example.

• Static method uses static variable and can also change value of it.
• Static method can be call without creating instance of class,as it belongs to class

Static method is used in counter of website as when object is created the value is add rather creating instance of object.

Example : this program shows difference of creating object with static and non-static variable, expense of  room mates total and personal for different students.

program

public class Room {

static double totalExpense;

double localexpence=0;

Room(){

}

public void addExpense(double amount){

totalExpense=totalExpense+amount; // method use static variable to add total expense 

       System.out.println("total is "+totalExpense);

}

public void addnewexpence(double amount){

localexpence=localexpence+amount; // it uses non-static variable to add personal expense

System.out.println("personal expence is "+localexpence);

}

//every time when object is created new memory is allocated to non-static variable 

       // static variable shares common memory , so not invoked when instance is created

public static void main(String[] args) {

 
      Room obj1=new Room();

obj1.addExpense(20d);

obj1.addnewexpence(40d);

Room obj2=new Room();

obj2.addExpense(50d);

obj2.addnewexpence(60d);

Room obj3=new Room();

obj3.addExpense(40d);

obj3.addnewexpence(70d);

}

}

Output:-

total is 20.0

personal expence is 40.0

total is 70.0

personal expence is 60.0

total is 110.0

personal expence is 70.0