Abstract Classes and Interfaces in C#

Abstract classes and interfaces are two important concepts in object-oriented programming in C#. Both of them are used to define contracts that specify what a class can do, but they differ in their implementation details. In this article, we will discuss abstract classes and interfaces in C# and their differences.

Abstract Classes in C#

An abstract class is a class that cannot be instantiated directly. It serves as a base class for other classes and provides a common set of methods and properties that derived classes can use. Abstract classes are typically used when you want to create a base class that cannot be used on its own but provides a common interface for other classes.

An abstract class is defined using the “abstract” keyword in C#. Here’s an example of an abstract class:

abstract class Animal
{
    public abstract void MakeSound();

    public void Eat()
    {
        Console.WriteLine("The animal is eating");
    }
}

class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("The dog barks");
    }
}

In the above code, the “Animal” class is defined as an abstract class using the “abstract” keyword. It defines an abstract method called “MakeSound”, which must be implemented by any derived class. The “Dog” class is a derived class that inherits from the “Animal” class and implements the “MakeSound” method.

Interfaces in C#

An interface is a contract that specifies a set of methods and properties that a class must implement. An interface does not provide any implementation details, but it defines a set of rules that a class must follow. An interface is typically used when you want to define a common set of methods and properties that can be implemented by different classes.

An interface is defined using the “interface” keyword in C#. Here’s an example of an interface:

interface IShape
{
    double Area();
}

class Rectangle : IShape
{
    private double Length;
    private double Width;

    public Rectangle(double length, double width)
    {
        Length = length;
        Width = width;
    }

    public double Area()
    {
        return Length * Width;
    }
}

class Circle : IShape
{
    private double Radius;

    public Circle(double radius)
    {
        Radius = radius;
    }

    public double Area()
    {
        return Math.PI * Radius * Radius;
    }
}

In the above code, the “IShape” interface defines a single method called “Area”, which must be implemented by any class that implements the interface. The “Rectangle” and “Circle” classes both implement the “IShape” interface and provide their own implementation of the “Area” method.

Differences between Abstract Classes and Interfaces

While abstract classes and interfaces may seem similar, there are some important differences between them:

1. Implementation – Abstract classes can provide implementation details for some or all of their methods and properties, while interfaces only define the rules that must be followed. This means that abstract classes can provide more functionality than interfaces.
2. Inheritance – A class can only inherit from one abstract class, but it can implement multiple interfaces. This means that interfaces are more flexible than abstract classes.
3. Accessibility – Abstract classes can have private, protected, or public members, while interfaces can only have public members. This means that abstract classes can have more fine-grained control over member accessibility.

Conclusion

Abstract classes and interfaces are both important concepts in object-oriented programming in C#. While they both define contracts that specify what a class can do, they differ in their implementation details. Abstract classes are used to provide a common set of methods and properties that derived classes can use, while interfaces are used to define a common set of methods and properties that can be implemented by different classes. Understanding the concepts of abstract classes and interfaces is important for writing modular, flexible and extensible code in C#.