What are the differences between interfaces and abstract classes?

What are the differences between interfaces and abstract classes?

Interfaces and abstract classes are both used to define contracts in object-oriented programming, but they have key differences. An interface can only declare methods without any implementation, while an abstract class can have both abstract methods (without implementation) and concrete methods (with implementation). Additionally, a class can implement multiple interfaces but can only inherit from one abstract class.

Can you give me an example of when to use an interface?

Sure! Use an interface when you want to define a contract for classes that can be implemented in different ways. For example, if you have different types of payment methods (like CreditCard, PayPal, etc.), you can create a PaymentMethod interface that requires a method like processPayment(). Each payment class can then implement this interface in its own way.

What about abstract classes? When should I use them?

Abstract classes are useful when you have a base class that should provide some common functionality to derived classes. For instance, if you have a base class called Animal with a method makeSound(), you can define it as abstract. Then, subclasses like Dog and Cat can provide their specific implementations of makeSound() while still inheriting shared properties from Animal.

Are there any performance differences between using interfaces and abstract classes?

Generally, the performance difference is negligible and should not be a primary concern. The choice between using an interface or an abstract class should be based on design needs rather than performance. However, interfaces can lead to more flexible designs since they allow multiple inheritance.