Abstract Classes and Interfaces

Introduction to Abstract Classes and Interfaces in C#

When learning C#, you'll quickly come across two crucial concepts - abstract classes and interfaces. These are fundamental building blocks for designing complex applications. This tutorial will guide you through both concepts, helping you understand their importance and how to use them in your programming.

Abstract Classes

An abstract class in C# is a class that cannot be instantiated. It's designed to act as a base class for other classes. Abstract classes can have abstract methods, which are methods without a body. These methods must be overridden (i.e., implemented) in any non-abstract class that directly inherits from the abstract class.

public abstract class Animal
{
    public abstract void MakeSound();
}

In the above example, Animal is an abstract class with an abstract method MakeSound(). Any class inheriting from Animal must provide an implementation for MakeSound().

public class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Woof!");
    }
}

In this case, Dog is a non-abstract class that inherits from Animal and provides an implementation for MakeSound().

Remember, an abstract class can contain both abstract methods and normal methods with a body. The normal methods will have their behavior in the abstract class itself while the abstract methods will only have their behavior in the derived class.

Interfaces

An Interface in C# is a blueprint of a class. It's like an abstract class because it can have abstract methods, properties, indexers, or events. However, the key difference is that an interface cannot have any implementation. All the methods inside an interface are implicitly abstract.

public interface IAnimal
{
    void MakeSound();
}

In the above example, IAnimal is an interface with a method MakeSound(). Any class implementing this interface must provide an implementation for this method.

public class Cat : IAnimal
{
    public void MakeSound()
    {
        Console.WriteLine("Meow!");
    }
}

In this case, Cat is a class that implements IAnimal and provides an implementation for MakeSound().

Remember, a single class can implement multiple interfaces. This is useful because C# does not support multiple inheritance (a class cannot inherit from more than one class), but it does allow multiple implementation of interfaces.

Abstract Classes vs. Interfaces

While abstract classes and interfaces seem similar, there are key differences:

An abstract class can provide complete, default code and/or just the details that have to be overridden.
An interface cannot provide any code at all, just the signature.
In case of inheritance, a class can derive from one base class only, but can implement multiple interfaces.

Use an abstract class when you want to provide common, implemented functionality among all implementations of your component, and use an interface when you want to guarantee a certain API for the implementer but not provide any implementation for it.

Conclusion

Both abstract classes and interfaces are powerful tools in C#. They provide a way to enforce certain properties or methods to be implemented in derived classes. While they can seem similar, they are best used in different scenarios. Abstract classes are best when providing shared implemented functionality, while interfaces are best when requiring a specific API but not implementation.

Abstract Classes and Interfaces

Introduction to Abstract Classes and Interfaces in C#​