Java Static Keyword

The static keyword in Java is used for memory management mainly. We can apply static keywords with variables, methods, blocks, and nested classes. The static keyword belongs to the class than an instance of the class.

 The static can be:

1. Variable (also known as a class variable)
2. Method (also known as a class method)
3. Block
4. Nested class

1) Java static variable

If you declare any variable as static, it is known as a static variable.

• The static variable can be used to refer to the common property of all objects (which is not unique for each object), for example, the company name of employees, college name of students, etc.
• The static variable gets memory only once in the class area at the time of class loading.

Advantages of static variable

It makes your program memory efficient (i.e., it saves memory).

Example: -

//Java Program to demonstrate the use of static variable  
class Student{  
   int rollno;//instance variable  
   String name;  
   static String college ="ITS";//static variable  
   //constructor  
   Student(int r, String n){  
   rollno = r;  
   name = n;  
   }  
   //method to display the values  
   void display (){System.out.println(rollno+" "+name+" "+college);}  
}  
//Test class to show the values of objects  
public class TestStaticVariable1{  
 public static void main(String args[]){  
 Student s1 = new Student(111,"Karan");  
 Student s2 = new Student(222,"Aryan");  
 //we can change the college of all objects by the single line of code  
 //Student.college="BBDIT";  
 s1.display();  
 s2.display();  
 }  
}

2) Java static method

If you apply a static keyword with any method, it is known as the static method.

• A static method belongs to the class rather than the object of a class.
• A static method can be invoked without the need for creating an instance of a class.
• A static method can access static data members and can change the value of it.

Example: -

//Java Program to demonstrate the use of a static method.  
class Student{  
     int rollno;  
     String name;  
     static String college = "ITS";  
     //static method to change the value of static variable  
     static void change(){  
     college = "BBDIT";  
     }  
     //constructor to initialize the variable  
     Student(int r, String n){  
     rollno = r;  
     name = n;  
     }  
     //method to display values  
     void display(){System.out.println(rollno+" "+name+" "+college);}  
}  
//Test class to create and display the values of object  
public class TestStaticMethod{  
    public static void main(String args[]){  
    Student.change();//calling change method  
    //creating objects  
    Student s1 = new Student(111,"Karan");  
    Student s2 = new Student(222,"Aryan");  
    Student s3 = new Student(333,"Sonoo");  
    //calling display method  
    s1.display();  
    s2.display();  
    s3.display();  
    }  
}

3) Java static block

• Is used to initialize the static data member.
• It is executed before the main method at the time of classloading.

Example: -

class A2{  
  static{System.out.println("static block is invoked");}  
  public static void main(String args[]){  
   System.out.println("Hello main");  
  }  
}