SOLID: Interface Segregation Principle in C#

The Interface Segregation Principle (ISP) is a design principle in object-oriented programming that states that a class should not be forced to implement interfaces that it does not use. It suggests that a class should only be required to implement the methods that are relevant to its intended behavior, and not be burdened with implementing unnecessary methods.

In C#, we can achieve ISP by creating multiple small interfaces, each with a specific purpose, instead of one large interface that covers everything. Let's take a look at an example to understand this principle better.

Suppose we have an interface IVehicle that contains two methods Drive() and Fly(). We have a Car class that implements this interface, but it doesn't need to implement the Fly() method because it doesn't have the capability to fly.

public interface IVehicle
{
    void Drive();
    void Fly();
}

public class Car : IVehicle
{
    public void Drive()
    {
        Console.WriteLine("Car is driving.");
    }

    public void Fly()
    {
        throw new NotSupportedException("Car cannot fly.");
    }
}

Here, the Fly() method is not relevant to the Car class, but it still needs to implement it because it's part of the IVehicle interface. This violates the ISP because the Car class is forced to implement a method that it doesn't need.

To fix this, we can create two separate interfaces: IDrivable and IFlyable, each with their respective methods. We can then implement only the relevant interface(s) in our Car class.

public interface IDrivable
{
    void Drive();
}

public interface IFlyable
{
    void Fly();
}

public class Car : IDrivable
{
    public void Drive()
    {
        Console.WriteLine("Car is driving.");
    }
}

Now, the Car class only implements the IDrivable interface, and doesn't have to implement the Fly() method. If we have a Plane class that can both drive and fly, we can implement both interfaces in it.

public class Plane : IDrivable, IFlyable
{
    public void Drive()
    {
        Console.WriteLine("Plane is driving.");
    }

    public void Fly()
    {
        Console.WriteLine("Plane is flying.");
    }
}

Here, the Plane class implements both the IDrivable and IFlyable interfaces because it can do both.

In conclusion, the Interface Segregation Principle suggests that we should create small, specific interfaces that contain only the methods relevant to the implementing class, instead of creating one large interface that covers everything. By doing so, we can reduce the burden on the implementing classes and make our code more maintainable and extensible.

SOLID: Interface Segregation Principle in C#

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