Polymorphism vs Inheritance

Question

Suppose I have two classes: Animal and Dog. Dog is a subclass of Animal. I do the following code:

Animal a = new Dog();

Now I can call methods

Answer 1

You can have other implementations of the Animal class, such as Cat. Then you can say

Animal a = new Dog();
Animal b = new Cat();

You can call methods of the Animal class without caring which implementation it really is, and polymorphism will call the correct method. E.g.

a.speak();  // "Woof"

b.speak();  // "Meow"

Really, it's not "Polymorphism vs Inheritance" but "Polymorphism using Inheritance".