Introduction

The final pillar of object-oriented programming that we’ll explore is polymorphism.

Polymorphism

Polymorphism is an object-oriented mechanism that allows for objects of different types to be used in the same way.

We’ve already encountered polymorphism made possible by inheritance when talking about casting with our Cat and HouseCat classes. In that case, we stored an object of type HouseCat in its compatible type, Cat.

Let’s take a closer look at how polymorphism might work in our cat-centric application.

Example

Suppose we had a CatSitter class like the one below:

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   public class CatSitter
   {
      public Cat Pet { get; set; }

      public CatSitter(Cat pet) {
         Pet = pet;
      }

      public void FeedTheCat() {

         // ...code to prepare the cat's meal...

         Pet.Eat();
      }
   }

The method FeedTheCat uses the property Pet, which is of type Cat. Since a HouseCat is a Cat via inheritance, it is perfectly acceptable to use an instance of HouseCat to fill the Pet property.

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   HouseCat suki = new HouseCat("Suki", 12);
   CatSitter annie = new CatSitter(suki);

   annie.FeedTheCat();

Similarly, FeedTheCat can accept Tiger instances as well. This is because the only thing that the method requires is that the input parameter has the methods defined within Cat. Via inheritance, both HouseCat and Cat satisfy this requirement.

In addition to using classes to code in a polymorphic way, we can use interfaces.