Difference Between Abstract Class and Interface

The discussion about the use of abstract class and interface with different programming languages is going to be a bit complex, so be attentive until you are sure you’ve got the basic ideas of each. In the present article, I will discuss the key differences between Abstract class and Interface considering four main programming languages that any programmer knows or works with including Java, C#, Python, , and PHP. Many of them are common in all four so I will not talk about them in each after pointing them out in Java which is the first and more preferable language for programming.

Basically, both abstract class and interface are used to achieve abstraction to declare the abstract method in any programming language. But what are abstraction and abstract methods?

Abstraction actually is the process of hiding the implementation details from the user only to allow them to enjoy the functionalities. While abstract method as the name suggests is a method that doesn’t contain a body in opposition to concrete methods characterized by codes.

Both abstract class and interface by the standards of their definition cannot be instantiated. However, deep in their interiors they come with certain differences, and in order to understand them, it is important for us to know what they actually are.

Abstract Class

A class having an abstract keyword in its declaration is characterized as an abstract class. We don’t provide all the implementation details when using it. An abstract class usually contains at least one method. Although when you have to instantiate a class, then there will be no method, but normally you cannot only have abstract methods, you can have regular or concrete methods as well to execute the implementation that you will find in any normal class. It helps you in defining a common interface for its subclasses while also allowing code reusability to minimize complications.


Interface is a collection of abstract methods and used to implement a class. The very basic difference between abstract class and interface is that the interface does not contain any concrete method. All the methods that you will use here will be abstract in nature, so you do not need to use the abstract keyword to declare an interface. But methods in an interface are implicitly public.

A class can implement multiple interfaces at the same time. An interface is designed to support dynamic method resolution at run time. It also allows you to detach the definition of a method with the hierarchy.

Abstract class vs Interface Java

Let’s have a look at a few points in delimiting the difference between both abstract class and interface.

The speed of abstract class is faster than an interface in terms of its parameters.

Interface is used for future enhancement, while abstract class is used for avoiding independence.

Variables that you will declare in a java interface will be final by default. An abstract class, however, can have tentative variables too.

Members of a java interface are public by default. But an abstract class can contain different other types of members such as private and protected.

The default implementation of the abstract class is accommodating and helpful in comparison to implementing newly defined stuff in an interface. But keep this also in mind that an abstract class does not support multiple inheritances while interface does.

Abstract class can provide the implementation of an interface but interface cannot do the same for an abstract class.

As mentioned earlier, an abstract class can have abstract and nonabstract methods. Interfaces can only have abstract methods. Since the launch of java 8, it can have default and static methods as well.

Because an interface is more abstract, it cannot provide any code. An abstract class can give complete and default codes to be overridden.

An abstract class can be extended by using the keyword “extends”. Similarly, an interface can be implemented by using the keyword “implement”.

Abstract class vs Interface C#

Points discussed below highlight the specific differences you will find while designing an application with interface and abstract class using C#

An interface is capable of providing full abstraction while an abstract class isn’t. In other words, a declaration and a definition is available in an abstract class but not in an interface.

An abstract class allows you to create functionalities that subclasses can implement or override. In contrast, an interface can only provide you with the definition of functionality without implementing them as it basically is a contract.

Multiple inheritance are achievable when we are using an interface in C#. In an abstract class, however, it isn’t possible. As Microsoft’s documentation of interfaces states, “you must use an interface if you want to simulate inheritance for structs, because they can’t actually inherit from another struct or class.”

An interface can also be implemented implicitly or explicitly.

We cannot declare a member field in an interface.

Abstract class vs interface Python

We did discover some similarities while differentiating abstract class with interface in Java and C#, but Python is a bit off that scale. Let’s see how it defers:

By default, Python does not provide abstract classes. There is a module by the name of ABC in Python, and it provides a base for defining abstract base classes. This ABC module works through decorating methods of the base class as abstract and then registering concrete or regular classes.

The dynamic nature of python as discussed earlier allows you to implement a formal Python interface. There is no strict enforcement.

We can use an abstract based class to define and enforce an interface.

We use abstract class when there are some common features set by all the objects as they are whereas we use interface if all the features need to be implemented differently for different objects.

Any third party vender takes the responsibility to write child class in interface. While in Abstract class, writing child class is the responsibility of the programmer.

Abstract Class vs Interface PHP

The following points indicate the differences between abstract class and interface in PHP:

Abstract class contains class properties or variables while interface doesn’t.

Abstract class also contains constructors whereas interface doesn’t. In Php, however, an interface can have an empty constructor shell.

Only complete members of abstract class can be static. Members of an interface cannot be static at all.

An interface cannot have access modifiers per definition. An abstract class can have access modifiers for the functions and properties.


These differences are very significant and worthwhile when it comes to tailoring your needs of programming. Behind each language, there is a different and a new set of differences working to functionalize and execute to achieve abstraction. Continue to visit us for a number of other articles anticipating to talk about all your needs with advanced apps upgrading every day and programming.