static keyword in java...

•  When a variable is declared with the static keyword, its called a class variable. All instances share the same copy of the variable. A class variable can be accessed directly with the class, without the need to create an instance.
• Without the “static” keyword, it's called instance variable, and each instance of the class has its own copy of the variable.
• Static block are execute even before the constructors are execute.
• When the class is first loaded static blocks can be called once.
• Static members can be execute without object creation.The following example
  illustrates about the static variables, static methods and static blocks.

Ex:-

 public class Test

{  

    public static void main(String[] args)

    {

        StaticDemo sd = new StaticDemo();

        StaticDemo.staticMethod();

    }

}

class StaticDemo

{

    public static final int x=10;

    public static final int y;

    static

    {

        y=20;

        System.out.println("X value is = "+x+" \nY value is = "+y);

    }

    public static void staticMethod()

    {

        System.out.println("Inside the static method of StaticDemo class");

    }

    StaticDemo()

    {

        System.out.println("Inside the constructor of staticDemo class");

    }

}

Output::

X value is = 10

Y value is = 20

Inside the constructor of staticDemo class

Inside the static method of StaticDemo class

          In the above example demonstrates that the order of execution is.

          >>  static variables initialize first then static block will be executed and then static

                 method will be  executed.

          >> Here constructor is called finally . This reveals that all static content can be
                execute before object  creation.

          >> The static method can access only static data

          >> It is illegal to refer a instance variable inside the static method or static block, that

                means it will be compilation error.

          >> static methods and static variables can be called  y using class name with "."

                operator like

                 Test.x;
                 Test.staticMethod();

                 Here "Test" is the class which contains the static variable "x" and static method
                 "staticMethod()"

• Methods can also be declared with the static keyword. When a method is declared static, it can be called/used without having to create a object first. For example, you can define a collection of math functions in a class, all static, using them like functions
• Static methods can only call the other static methods
• Methods declared with “static” keyword are called “class methods”. Otherwise they are “instance methods”.
• There's no such thing as static classes. “static” in front of class creates compilation error, but inner classes can be declared as static 

Static Inner Classes

• A class itself is not a static class . But we can declare a nested class as static. Here the static keyword    in the class says that the nested class is a static member of the outer class which contains the inner class  . For example

Ex:-

      class Outer

{

    static class InnerCls {

        void hi()

        {

            System.out.println("Hi");

        }

    }

}

public class InnerDemo

{

    static class InnerDC {

        void dcHi()

        {

            System.out.println("DC HI");

        }

    }

    public static void main(String[] args)

    {

        Outer.InnerCls inner = new Outer.InnerCls();

        inner.hi();

        InnerDC innerdc = new InnerDC();

        innerdc.dcHi();

    }

}

 Output::

    Hi

    DC HI