Static Keyword

Static Keyword

• Static means class level. static can be applied to variable method and block.
• static variables , static methods , static blocks.
• makes your program memory efficient 
  

Static variables 

• If you declare any variable as static, it is known static variable.
• The static variable can be used to refer the common property of all objects (that is not unique for each object) e.g. company name of employees,college name of students etc.
• The static variable gets memory only once in class area at the time of class loading.

Example program:

package com.instanceofjava.snippets.basics;


public class StaticDemo {

    // static variable - the same on all instances of a class
    static int X = 10;

    // non static variable
    int Y = 5;
   
    public static void main(String[] args) {




  StaticDemo o1= new StaticDemo();

  StaticDemo o2= new StaticDemo();


  System.out.println("o1.X = " + o1.X + " o1.Y = " + o1.Y);

  System.out.println("o2.X = " + o2.X + " o2.Y = " + o2.Y);

 

  instance1.X = 15;

  instance1.Y = 10;

 

  System.out.println("After updating X value to 15 and Y value to 10 from o1:");

  System.out.println("o1.X = " + o1.X + " o1.Y = " + o1.Y);

  System.out.println("o2.X = " + o2.X + " o2.Y = " + o2.Y);

    }

}

Output:

instance1.X = 10 o1.Y = 5
instance2.X = 10 o2.Y = 5
After updating X value to 15 and Y value to 10 from o1:
instance1.X = 15 o1.Y = 10
instance2.X = 15 o2.Y = 5 


Static methods:

• Static method belongs to the class rather than object of a class
• Static methods can be called without creating an object of class
• Static method can access static data member and can change the value of static data
• You can define as many static methods. These methods are independent, except that they may refer to each other through calls
• Any static method can call any other static method in the same file or any static method in a Java library like Math. 

Example program:

1. class Student{  
2.      int rollno;  
3.      String name;  
4.      static String college = "SBIT";  
5.        
6.      static void change(){  
7.      college = "SBCE";  
8.      }  
9.   
10.      Student9(int r, String n){  
11.      rollno = r;  
12.      name = n;  
13.      }  
14.   
15.      void show(){
16.      System.out.println(rollno+" "+name+" "+college);
17.    }  
18.   
19.     public static void main(String args[]){  
20.     Student.change();  
21.   
22.     Student s1 = new Student (37,"indhu");  
23.     Student s2 = new Student (38,"sindhu");  
24.     Student s3 = new Student (39,"swathi");  
25.   
26.     s1.show();  
27.     s2.show();  
28.     s3.show();  
29.     }  
30. } 

OutPut:

indhu SBCE
sindu SBCE
swathi SBCE

Static Blocks:

• Whenever class loads these static blocks will be exeuted.
• Static blocks are also called Static initialization blocks . A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword.
• we can use static blocks to assign static variables.

Example program:
class staticBlockDemo{

    static int i;

    int j;

    

    // start of static block

    static {

        i = 20;

        System.out.println("static block called ");

    }

    // end of static block

}

class Main {

    public static void main(String args[]) {

        // Although we don't have an object of staticBlockDemo, static block is

        // called because i is being accessed in following statement.

        System.out.println(staticBlockDemo.i);

    }

}

      Output:

static block called

20