What is the difference between an interface and abstract class?

Question

What exactly is the difference between an interface and abstract class?

Answer 1

You can find clear difference between interface and abstract class.

Interface

• Interface only contains abstract methods.
• Force users to implement all methods when implements the interface.
• Contains only final and static variables.
• Declare using interface keyword.
• All methods of an interface must be defined as public.
• An interface can extend or a class can implement multiple other interfaces.

Abstract class

• Abstract class contains abstract and non-abstract methods.

• Does not force users to implement all methods when inherited the abstract class.

• Contains all kinds of variables including primitive and non-primitive

• Declare using abstract keyword.

• Methods and members of an abstract class can be defined with any visibility.

• A child class can only extend a single class (abstract or concrete).