Inheritance

Inheritance allows you to extend the functionality of an existing class by creating a new class that derives from the inherited class.

The following code illustrates inheritance.

using System;

namespace LearnCSharp
{
    class Program
    {
        static void Main(string[] args)
        {
            Cylinder myCylinder = new Cylinder();
            myCylinder.Radius = 5;
            myCylinder.Height = 12;

            Console.WriteLine($"The radius of the cylinder is {myCylinder.Height}");
        }
    }
}

public class Circle
{
    public int Radius { get; set; }
}

public class Cylinder : Circle
{
    public int Height { get; set; }
}

The radius of the cylinder is 12

The Circle class has a property named Radius of type integer.

The Cylinder class inherits from the Circle class. We use the colon (:) to define the inheritance.

The Cylinder class , because it inherits from the Circle class, will also have a property named Radius.

Method Overrides

The override modifier is required to extend or modify the virtual implementation of an inherited method.

using System;

namespace LearnCSharp
{
    class Program
    {
        static void Main(string[] args)
        {
            Cylinder myCylinder = new Cylinder();
            myCylinder.Radius = 2;
            myCylinder.Height = 3;
            decimal surfaceArea = myCylinder.CalculateSurfaceArea();

            Console.WriteLine($"The surface area of the cylinder is {surfaceArea}");
        }
    }
}

public class Circle
{
    public int Radius { get; set; }

    public virtual decimal CalculateSurfaceArea()
    {
        return 2 * 3.14M * Radius;
    }
}
public class Cylinder : Circle
{
    public int Height { get; set; }

    public override decimal CalculateSurfaceArea()
    {
        return (2 * 3.14M * Radius * Height) + (2 * 3.14M * Radius * Radius);
    }
}

The Circle class has a virtual method called CalculateSurfaceArea() that calculates the surface area of a circle. The ‘virtual’ keyword is used to declare that this method is a virtual method and can be overridden.

The Cylinder class inherits from the Circle class, however, the function to calculate the area of a circle is different from the function to calculate the area of a cylinder.

Therefore, in the Cylinder class, we can override the method to provide a function to calculate the surface area of a cylinder (as shown in the code). We use the keyword ‘override’ to override the method.