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When it comes to .NET development the two most crucial concepts that stand out are interfaces and abstract classes. Though both seem to share similarities each serves a distinct purpose in helping with code organization and enhancing extensibility. In this blog post, we will explain their functionality and outline the differences between the two to gain a better understanding of both.

Introduction To Abstract Class vs Interface

Let us compare comprehensive knowledge of the two Abstract Class vs Interface. Let us first start with the Interface.

Interface in .NET refers to the definition of a group of related functionalities that a non-abstract class or struct should implement. Interfaces serve as contracts defining a set of methods or property signatures the classes should implement. They offer a blueprint for functionality without dictating how it should be implemented. This flexibility makes interface powerful tools for achieving polymorphism and enabling loose coupling between components.

Abstract class often referred to as incomplete class or special class cannot be instantiated. The core purpose of an abstract class is to offer a blueprint for derived classes and set some rules that the derived class should implement when inheriting the abstract class. It is generally used as the base class and the other derived classes must implement the abstract definitions.

Abstract Class vs Interface - When To Use What?

The abstract class offers you the flexibility to have certain substantial methods along with several other methods that the derived classes should implement. Contrary to this using interfaces, you need to implement all methods in the class that extends the interface. Abstract class is a significant choice when you aim for future expansion i.e. if a future expansion is likely in the class hierarchy. If you aim to offer support for future expansion when using interfaces, you need to extend the interface and create a new one.

On the other hand, you can easily add a new interface to the hierarchy if needed. If you have an abstract class in the hierarchy, you cannot add another meaning you can add the abstract class only if there is no one available. You can use an interface when looking for a contract on some behavior or functionality. It is not preferable to use an interface if you need to write the same code for the interface methods. Therefore under such circumstances, you should use the abstract class, define the method one, and reuse it as needed. Also, you can use an interface to decouple your application code from precise implementations of it or to restrict access to members of a certain type.

Abstract Class vs Interface - Comparison Table

When it comes to .NET software development, it is crucial to understand the difference between Abstract Class vs Interface on a circumferential level let us move ahead with it.

Feature Abstract Class Interface
Inheritance You can inherit it from one class You can implement multiple interfaces
Access Modifiers Supports multiple access modifiers such as public, protected, private, and more By default all members are public
Default Implementation Can offer the default implementation Needs C# 8.0 or above for default implementation as the default methods are allowed
Constructors Possible Not Possible
Fields Possible Not Possible
Method Definition Can have defined, abstract, or virtual methods Only contains method signatures (until C# 8.0)
Inheritance vs Implementation Inherits from another class (abstract or concrete) Implements an Interface
Type of Methods Can have statics, abstract, virtual methods Only abstract methods (until C# 8.0)
Compatibility Apt for classes with closely related functionality Apt for classes with unrelated functionalities
Versioning Simple adding new methods without breaking existing implementations Adding new methods can break existing implementations
Class Usage Can inherit only from one abstract class Can implement multiple interfaces
Implementing Keyword Uses the “extends” keyword for implementation Uses the “implements” keyword for implementation

Abstract Class vs Interface - Example

The abstract classes are declared using the keyword “abstract” that presents them these cannot be instantiated directly. They need at least one abstract method along with the “abstract” modifier which lacks the implementation details and is meant for overridden by derived classes. Generally, we use abstract classes to define base class within a class hierarchy.

// Abstract class 'Shape'
public abstract class Shape {
	// Abstract method 'CalculateArea()'
	public abstract void CalculateArea();
// Class 'Rectangle' inherits from 'Shape'
public class Rectangle : Shape {
	// Implementation of 'CalculateArea()' specific to 'Rectangle'
	public override void CalculateArea()
    	// Calculation logic for area of a rectangle
// Class 'Circle' inherits from 'Shape'
public class Circle : Shape {
	// Implementation of 'CalculateArea()' specific to 'Circle'
	public override void CalculateArea()
    	// Calculation logic for area of a circle

// Usage
public class Program {
	public static void Main() {
    	Shape shape;

    	shape = new Rectangle();
    	shape.CalculateArea(); // Calls Rectangle's implementation

    	shape = new Circle();
    	shape.CalculateArea(); // Calls Circle's implementation

Here the “Shape” is an abstract where the abstract method is “CalculateArea()”. The derived classes such as “Rectangle” and “Circle” offer their specific implementations of “CalculateArea()” following the specifics of their shapes.

Now, for interfaces, they define the contract for classes to follow by declaring methods, properties, events, and indexers without offering implementation details. You can implement a class and then implement one or more interfaces, which offer the implementation for the members of the interface.

// Interface 'IPrintable'
interface IPrintable {
	void Print();

// Class 'Document' implementing 'IPrintable'
class Document : IPrintable {
	public void Print() {
    	// Implementation for printing a document

// Class 'Image' implementing 'IPrintable'
class Image : IPrintable {
	public void Print() {
    	// Implementation for printing an image

// Usage
class Program {
	static void Main() {
    	IPrintable printable;

    	printable = new Document();
    	printable.Print(); // Prints a document

    	printable = new Image();
    	printable.Print(); // Prints an image

Here, the “IPrintable” is an interface along with the method “Print()”. Both “Document” and “Image” classes implement “IPrintable”, offering their specific set of implementations for the “Print()” method. When using instances of these classes with the interface reference, the apt implementation is invoked based on the object’s actual type.


We can infer that interfaces vs abstract classes are crucial tools when it comes to .NET development. Both have their own set of strengths and weaknesses. Utilizing the right way to use these tools, it is easier and more effective to create performant applications that make your development project stand out. If you are still confused about Interface or Abstract Class can benefit the development of your .NET app development, get in touch with a leading .NET development company and take your first step to bring your vision to reality.

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