Abstract Class vs Interface

In this post, we will learn the difference between abstract class and interface in Java. This is a frequently asked question in Java interviews for beginners. Let's dive into it.

Difference between abstract class and interface in Java

Features Abstract Class Interface
Multiple Inheritance An abstract class doesn't support multiple inheritance. An interface supports multiple inheritance.
Default Implementation An abstract class can have methods with default implementation. Before Java 8, interfaces could not have methods with default implementations. From Java 8 onwards, interfaces can have default and static methods.
Instance Variables An abstract class can have instance variables. An interface can have only static and final variables (constants).
Constructors An abstract class can have constructors. An interface cannot have constructors.
Type of methods An abstract class can have abstract, non-abstract, static, final or non-final methods. Before Java 8, an interface could only have abstract methods. From Java 8 onwards, interfaces can have default and static methods.
Access Modifiers Abstract classes can have public, protected and default methods. Interface methods are implicitly public and abstract (if not static or default).
Keyword 'abstract' keyword is used to declare abstract class. 'interface' keyword is used to declare interface.
Sub Class A class extending an abstract class has to provide implementation to its abstract methods. A class implementing an interface has to provide implementation to all of its methods.


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