What is the difference between interfaces and abstract classes in programming?

What is the difference between interfaces and abstract classes in programming?

Interfaces and abstract classes are both used to define contracts for classes, 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).

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

Sure! Use an interface when you want to define a contract that multiple classes can implement, especially when those classes are not related. For example, if you have different classes like 'Car' and 'Boat', both can implement an interface 'Vehicle' to ensure they have methods like 'start' and 'stop'.

What about the use of multiple inheritance? How does that relate to interfaces?

Great question! In languages like Java, a class can implement multiple interfaces, allowing for a form of multiple inheritance. This means a class can inherit behaviors from multiple sources, which is not possible with abstract classes since a class can only extend one abstract class.

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

Generally, the performance difference is negligible. However, using abstract classes can be slightly more efficient since they can provide default implementations. Interfaces, on the other hand, may require more overhead due to the need for implementing all methods in the implementing class.