So, you might be wondering what the difference between an abstract class and an interface is. It basically comes down to where you want your implementation. If you need to share functionality between derived classes, then an abstract class is the best fit for your needs. In other words, we had specific things that were common to all cats (lions, tigers, and cheetahs) such as hunting, eating, and sleeping. This is then best used within an abstract class.

If your implementation is specific to a class or several classes (but not all classes), then your best course of action would be to use an interface. In this case, the IPurrable interface can be applied to several classes (for example, cheetahs and domestic cats) but can't be applied to all cats (such as lions and tigers), because not all cats can purr.

Knowing this difference and where you need to place your implementation will aid you in deciding whether you need to use an abstract class or an interface.