Up and down transitions in polymorphism

/* * *  Up transformation and down transformation in polymorphism : * *  Conversion between reference types  *  Upward transformation  *  From small to large ( Child type to parent type ) *  Move down  *  From big to small  *  Conversion of basic data types  *  Automatic type conversion  *  From small to large  * byte short char --- int --- long --- float --- double *  Cast  *  From big to small  * * * */
public class PoymorphicDemo3{
    
    public static void main(String[] args) {
    
        Animal2 a = new Dog();// Upward transformation 
        //a.eat();

        Dog d = (Dog)a;// Move down 
        d.swim();

    }
}

class Animal2 {
    
    public void eat() {
    
        System.out.println(" Eat something ");
    }
}


class Dog extends Animal2 {
    
    public void eat() {
    
        System.out.println(" Gnaw at the bone ");
    }

    public void swim() {
    
        System.out.println(" Dogplane ");
    }
}