Open Closed Principle in C#

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Implementing Open Closed Principle in C# - Example | C# Master

In the world of software development, adhering to design principles is crucial for creating maintainable, scalable, and robust applications. One such fundamental principle is the Open Closed Principle (OCP), which is a part of the SOLID principles. The Open Closed Principle states that software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. In other words, the behavior of a module can be extended without modifying its source code. In this article, we will explore how to implement the Open Closed Principle in C# with a practical example.

What is the Open Closed Principle?

The Open Closed Principle (OCP) is one of the five SOLID principles proposed by Bertrand Meyer. The idea behind OCP is to make systems more maintainable and flexible by allowing them to adapt to changing requirements without altering existing code. This is achieved by extending the system's behavior through inheritance, interfaces, or composition rather than changing the existing codebase.

Benefits of OCP

Enhanced Maintainability: By adhering to OCP, developers can add new features or modify existing behavior without altering existing code, reducing the risk of introducing bugs.

Increased Flexibility: Systems designed with OCP in mind are easier to extend, allowing for new functionalities to be added with minimal effort.

Improved Testability: Since new behavior is introduced via extensions rather than modifications, existing tests remain valid, and new tests can focus on the extended functionality.

Implementing OCP in C#

To illustrate how to implement the Open Closed Principle in C#, let's consider a scenario where we have a simple application that calculates the area of different shapes. Initially, we may have a class that handles only rectangles:

 

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public class Rectangle

{

    public double Width { get; set; }

    public double Height { get; set; }

}

 

public class AreaCalculator

{

    public double CalculateArea(Rectangle rectangle)

    {

        return rectangle.Width * rectangle.Height;

    }

}

This implementation works well for rectangles, but what if we need to add support for circles? According to OCP, we should not modify the AreaCalculator class directly. Instead, we can extend its behavior by introducing new classes.

 

Step-by-Step Implementation

Step 1: Define a Shape Interface

 

First, we define a common interface for shapes. This interface will declare a method for calculating the area, which will be implemented by all concrete shape classes.

 

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public interface IShape

{

    double CalculateArea();

}

Step 2: Implement Shape Classes

 

Next, we implement the IShape interface for different shapes. Here’s how we can implement the Rectangle and Circle classes:

 

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public class Rectangle : IShape

{

    public double Width { get; set; }

    public double Height { get; set; }

 

    public double CalculateArea()

    {

        return Width * Height;

    }

}

 

public class Circle : IShape

{

    public double Radius { get; set; }

 

    public double CalculateArea()

    {

        return Math.PI * Radius * Radius;

    }

}

Step 3: Update the AreaCalculator Class

 

Finally, we update the AreaCalculator class to work with the IShape interface. This allows the AreaCalculator class to remain closed for modification but open for extension.

 

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public class AreaCalculator

{

    public double CalculateArea(IShape shape)

    {

        return shape.CalculateArea();

    }

}

Using the Extended System

With the new design, adding support for additional shapes in the future is straightforward. Here’s how you can use the updated system:

 

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class Program

{

    static void Main(string[] args)

    {

        IShape rectangle = new Rectangle { Width = 5, Height = 10 };

        IShape circle = new Circle { Radius = 7 };

 

        AreaCalculator calculator = new AreaCalculator();

 

        Console.WriteLine("Area of Rectangle: " + calculator.CalculateArea(rectangle));

        Console.WriteLine("Area of Circle: " + calculator.CalculateArea(circle));

    }

}

Conclusion

Implementing the Open Closed Principle in C# ensures that your codebase remains flexible and maintainable as it evolves. By designing your system to be open for extension but closed for modification, you can add new functionality with minimal risk of introducing bugs. In this article, we demonstrated how to adhere to OCP by defining a common interface for shapes and extending the AreaCalculator class to support different shapes without modifying its core logic. For more detailed tutorials and examples on C# and .NET Core, visit C# Master.

 

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