Abstract Class vs Interface in Object-Oriented Programming

In object-oriented programming, both abstract classes and interfaces are used to achieve abstraction. However, they have key differences:

Abstract Class

An abstract class in Java is a class that contains one or more abstract methods, which must be implemented by its subclasses. It can also have non-abstract methods. An abstract class cannot be instantiated directly but can be extended by other classes.

Interface

An interface in Java is a blueprint of a class that consists of abstract methods without any implementation. A class can implement multiple interfaces but can only extend one class. Interfaces are used to achieve multiple inheritances in Java.

Differences

• An abstract class can have both abstract and non-abstract methods, while an interface can only have abstract methods.
• A class can extend only one abstract class but can implement multiple interfaces.
• An abstract class can have constructor, member variables, and normal methods, while an interface cannot.
• Interfaces are used for achieving multiple inheritances, while abstract classes are used for defining the base class.

Understanding these differences is crucial when designing object-oriented systems and can be a common interview question in the field of computer science.