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

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

Abstract classes and interfaces are both used to define contracts in programming, but they have key differences. An abstract class can have both abstract methods (without implementation) and concrete methods (with implementation), while an interface can only have abstract methods (until Java 8, which introduced default methods). Additionally, a class can inherit from only one abstract class but can implement multiple interfaces.

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

Sure! Use an abstract class when you have a base class that should provide some common functionality to derived classes. For example, if you have a base class Animal with a method makeSound(), you can define it in the abstract class and let subclasses like Dog and Cat provide their specific implementations. Use an interface when you want to define a contract that multiple classes can implement, regardless of their position in the class hierarchy.

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

Generally, there are no significant performance differences between abstract classes and interfaces. The choice between them should be based on design and functionality rather than performance. However, using interfaces can sometimes lead to more flexible and maintainable code, especially in large systems.

Can a class implement multiple interfaces?

Yes, a class can implement multiple interfaces. This is one of the key advantages of using interfaces, as it allows for a form of multiple inheritance. For example, a class Smartphone can implement both Camera and Phone interfaces, inheriting behaviors from both.