Difference Between Interface and Abstract Class in Java

In this post, we will understand the difference between abstract class and interface in Java and C#.

Abstract Class

• It contains the declaration and definition part.

• Multiple inheritance can’t be implemented using abstract class.

• It contains the constructor.

• It can also contain some static members.

• It can contain multiple types of access modifiers such as public, private, protected.

• The performance of an abstract class is very good, because it is quick.

• It is used to implement the core identity/functionality of a class.

• A class can use only one abstract class.

• If many implementations are same, and they have a common behaviour, it is suggested to use an abstract class.

• Abstract classes contain methods, fields, constants.

• It can be fully implemented, partially implemented or not even implemented.

Interface

• It contains a declaration part only.

• Multiple inheritance can be achieved using interface.

• It doesn’t contain a constructor.

• It doesn’t contain static members.

• It contains public access modifier since everything in an interface is considered public.

• The performance of interface is not good.

• It is slow since it needs time to search for an actual method in the respective class.

• It is used to implement peripheral abilities of a class.

• It can use multiple interface.

• If multiple implementations share methods, then the ‘Interface’ can be used.

• Interface can contain methods only.

• It needs to be fully implemented.