java static keyword | java static class as variable

Java static keyword

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

static keyword in java programming

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 of static variable

   //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();  

   }  

}  

Output:

111 Karan ITS

222 Aryan ITS

2) Java static method

If you apply static keyword with any method, it is known as 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 member and can change the value of it.

Example of static method

    //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();  

      }  

}  

Output:

111 Karan BBDIT

222 Aryan BBDIT

333 Sonoo BBDIT

  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 of static block

   class A2{  

    static{System.out.println("static block is invoked");}  

    public static void main(String args[]){  

   System.out.println("Hello main");  

  }  

}  

Output:

static block in invoked

Hello main

static keyword in java class methods