Static keyword in java

Static keyword in java can be used for following three scenarios:

1.       Class variables

2.       Methods

3.       Block of code

Static data members:

Static data members (variables) are the variables which are to be used at class level. These are defined in a class outside any method, block or constructors with the keyword “static”. These are common to the entire class and only one copy will be available irrespective of how many objects will be created. Static variables will be stored in static memory. These are created when the program starts and destroyed when the program stops.

Syntax:

Public static String str1;

Or

Static public String str1;

They can be accessed as beow:

ClassName.variableName;

Methods:

Just like static variable, static method is a method which is common to the entire class. Static methods are called directly using class name. These cannot be accessed using any object reference. Static methods cannot access any non static member of the class while other methods/blocks can use static methods.

Syntax:

Public static Integer getTotal()

They can be accessed as below:

ClassName.methodName();

Static Blocks:

The static block is a block of code inside a class which will be executed when a class is first loaded. Static block is used to initialize the static members of the class just as constructor helps in initializing the instance members.

Syntax:

Class Sample

{

                Static

{

// code to be written

}

}

Important point:

When to use static and when not:

Statics are used when data is not instance dependent and same state is needed for the static data for all instances to be created. Static should be used only when they are actually required reason being, as they create dependencies and references to other classes and class loaders in JVM and they stay in memory for longer time. They won’t be considered for garbage collection when they are done with current work as they have to be de-referenced with their loading classes.

Example for static variables, static method and static block:

package test;

public class StaticSample

{

            //declaring static variable to have count of objects

private static int count = 0;  

            //constructor to increase count

public StaticSample()

            {

                        count++;

            }

           

//static block which will be called at first time class is loaded

static  

            {

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

            }

            //static method

public static void printCount()

            {

                        System.out.println(" Count value : " +count);

            }          

           

}

//Main class to see how static works.

package test;

public class MainClass

{

public static void main(String[] args)

            {

                        static Sample sam1 = new StaticSample();

                        static Sample.printCount();

                        static Sample sam2 = new StaticSample();

                        static Sample.printCount();

            }

}

The result for above program would be as below:

in static block

Count value : 1

Count value : 2