Static and Instance variables 

class MyClass {

     static int x;      // class variable
            int y;      // instance variable

}

class AnotherClass {

     public static void main(String[] args)

         {
            MyClass a,b;

            a = new MyClass();
            b = new MyClass();

            a.x = 5;
            System.out.println(b.x);
            
            MyClass.x = 7;
            System.out.println(b.x);

            a.y = 10;
            b.y = 20;
            System.out.println(a.y);
          }
}


Polygons

class Polygon {

      static int polyNum;
      int numSides;

}

In some other class ...

     public static void main(String[] args) {
 
         Polygon.polyNum = 0;
         Polygon triangle, quadrilateral;

         triangle = new Polygon();
         triangle.polyNum = triangle.polyNum + 1;
         triangle.numSides = 3;

         quadrilateral = new Polygon();
         quadrilateral.polyNum = quadrilateral.polyNum + 1;
         quadrilateral.numSides = 4;
      }