Usage of Static in Java in SIMPLE

class A {
static int x = 100;
int y = 200;

void m1(){
//int Z; //this is wrong; a method local variable cannot be kept uninitialized.
int z = 300;
System.out.println(z);
}

static void m2(){
System.out.println("A");
}
public static void main(String[] args) {

A a = new A();

A b = null;//default value of object reference

System.out.println(a.x); //prints 100

System.out.println(a.y); //prints 200

a.m1();//prints 300

a.m2();//prints A

System.out.println(A.x);//prints 100 because int x is a static int

/*System.out.println(A.y);// compile error cannot referenced by the class name because its not static*/

/*A.m1();// compile error because it can not be referenced by the class name because its not static*/

A.m2(); //prints A

System.out.println(b.x);//prints 100

System.out.println(b.y);/*compies well but gives a run time error called nullObjectPointerException

* it also happens because y and m1() are not static. the reference of b is A*/

b.m1();//same as previous line

b.m2();//prints A

System.out.println(x);

// System.out.println(y);//compilation error

//m1();//compilation error

m2();//prints A

}

}


/*to understand this I recommend you to compile it and run then compare results with the code.:)*/