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.

What is a static keyword in Java?

Normally, if you want to access a class member in Java, you must first create an instance of the class. But, there will be cases when you have to define a class member that will be used independently without creating an instance of that class.

However, in Java it is possible to create a class members (variables and methods) that can be accessed and invoked without creating an instance of the class. In order to to create such a member, you have to use static keyword while declaring a class member.

The best use case of static class members is in Math class of package java.lang. Almost all the class members (variables and methods) of the Math class are static. Hence, these class members can be accessed without creating an instance of Math class. Let’s look at the use of Math class and its class members:

The static can be:
  1. variable (also known as class variable)
  2. method (also known as class method)
  3. block
  4. nested class
Example 1: Using the static variables and methods from builtin Math class.
public class StaticMembers { public static void main( String[] args ) { System.out.println("Absolute value of -12 = " + Math.abs(-12)); System.out.println("Value of PI = " + Math.PI); System.out.println("Value of E = " + Math.E); System.out.println("2^2 = " + Math.pow(2,2)); } }

Absolute value of -12 = 12 Value of PI = 3.141592653589793 Value of E = 2.718281828459045 2^2 = 4.0

Did you notice in above program, a new instance of Math class is not created every time its member function is called. Rather, method is invoked directly from the class itself. This is all possible because almost every class members are static in the Math class.

1) Java static variable

Like static methods, static instance variables are actually, global variables unless they aren’t explicitly declared private. Also, when the instance are created for a class, seperate copy of static variables aren’t made each time but, all instances of the class share the same static variable. For example, the instance variable PI in the Math class of java.lang package is static. Hence, it can be referenced directly from class name itself.

  • 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.

static int VAR1 = 123; // with initialization static int VAR2;// without initialization
class Student8{ int rollno; String name; static String college ="ITS"; Student8(int r,String n){ rollno = r; name = n; } void display (){System.out.println(rollno+" "+name+" "+college);} public static void main(String args[]){ Student8 s1 = new Student8(31,"Pavi"); Student8 s2 = new Student8(36,"Kiran"); s1.display(); s2.display(); } }

Output:31 Pavi ITS 36 Rama ITS
Static Variable
Program of counter without static variable

In this example, we have created an instance variable named count which is incremented in the constructor. Since instance variable gets the memory at the time of object creation, each object will have the copy of the instance variable, if it is incremented, it won't reflect to other objects. So each objects will have the value 1 in the count variable.

class Counter{ int count=0;//will get memory when instance is created Counter(){ count++; System.out.println(count); } public static void main(String args[]){ Counter c1=new Counter(); Counter c2=new Counter(); Counter c3=new Counter(); } }

1 1 1
Program of counter by static variable
class Counter2{ static int count=0;//will get memory only once and retain its value Counter2(){ count++; System.out.println(count); } public static void main(String args[]){ Counter2 c1=new Counter2(); Counter2 c2=new Counter2(); Counter2 c3=new Counter2(); } }

1 2 3
2) Java static method

Static methods are also called class methods because it belongs to the class rather than object of a class. Which means that static methods can be invoked directly from the class name itself rather than creating an instance and invoking from the instance.

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

  1. A static method belongs to the class rather than object of a class.

  2. A static method can be invoked without the need for creating an instance of a class.

  3. static method can access static data member and can change the value of it.


As you might have noticed in every Java program, the main() method is always declared as static. Hence, in order for the JVM to allow invocation of the main() method or to run the program in the initial phase where no object exists in the memory, it must be declared as static.

Example of static method
//Program of changing the common property of all objects(static field). class Student9{ int rollno; String name; static String college = "ITP"; static void change(){ college = "MAX"; } Student9(int r, String n){ rollno = r; name = n; } void display (){System.out.println(rollno+" "+name+" "+college);} public static void main(String args[]){ Student9.change(); Student9 s1 = new Student9 (31,"Pavi"); Student9 s2 = new Student9 (36,"Rama"); Student9 s3 = new Student9 (3136,"PR"); s1.display(); s2.display(); s3.display(); } }

31 Rama MAX 36 Pavi MAX 3136 Sonoo MAX
Another example of static method that performs normal calculation
//Program to get cube of a given number by static method class Calculate{ static int cube(int x){ return x*x*x; } public static void main(String args[]){ int result=Calculate.cube(10); System.out.println(result); } }

Restrictions for static method

There are two main restrictions for the static method.

  1. The static method can not use non static data member or call non-static method directly.

  2. this and super cannot be used in static context.

class A{ int a=40;//non static public static void main(String args[]){ System.out.println(a); } }

Compile Time Error
why java main method is static?

because object is not required to call static method if it were non-static method, jvm create object first then call main() method that will lead the problem of extra memory allocation.

3) Java static block
  1. Is used to initialize the static data member.

  2. It is executed before main method at the time of classloading.

Example of static block
class A5 { static{System.out.println("static block is invoked");} public static void main(String args[]){ System.out.println("Hello main"); } }

static block is invoked Hello main
Can we execute a program without main() method?

Yes, one of the way is static block but in previous version of JDK not in JDK 1.7.

class A9 { static { System.out.println("static block is invoked"); System.exit(0); } }

Output:static block is invoked (if not JDK7) In JDK7 and above, output will be: Output:Error: Main method not found in class A3, please define the main method as: public static void main(String[] args)