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

Normally the question you've asked is more similar to Inheritance vs Composition :) More "real life" example of why it's good to use polymorphism is for example usage of strategy design pattern. You can have many TaxPolicy implementation: UsaTaxPolicy, CanadaTaxPolicy, EuTaxPolicy, etc. If you have method calculateFinalPrice, which have to also calculate tax, then you inject the proper implementation and good calculation is executed, no matter you've passed Usa, Canada or Eu implementation.