class Animal {
  public void eat() { System.out.println(this + " is eating"); }
  public String toString () { return "Animal"; }
}

class Mammal extends Animal {
  public void suckMilk() { System.out.println(this + " is sucking"); }
  public String toString () { return "Mammal"; }
}

class Dog extends Mammal {
  public void bark() { System.out.println(this + " is barking"); }
  public String toString () { return "Dog"; }
}

public class Zoo {
  public static void main(String a[]) {
    Animal a1 = new Animal();
    Animal a2 = new Mammal();
    Animal a3 = new Dog();
    System.out.println(a1);
    System.out.println(a2);
    System.out.println(a3);
    a1.eat();
    a2.suckMilk();
    a2.eat();
    Dog d1 = a3;
    Dog d2 = new Dog();
    Mammal m1 = d2;
    d2.bark();
    m1.suckMilk();
    d2.suckMilk();
    Dog d3 = (Dog)a3;
    a3.bark();
    d3.bark();
    Dog d4 = (Dog)a2;
  }
}