Inheritance and Interfaces

Inheritance and interfaces are core pillars of object-oriented programming in C#. They enable code reuse, polymorphism, and the design of flexible, extensible systems.

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Inheritance

A class can inherit from a single base class:

public class Animal
{
    public string Name { get; set; }

    public void Eat()
    {
        Console.WriteLine($"{Name} is eating.");
    }
}

public class Dog : Animal
{
    public void Bark()
    {
        Console.WriteLine($"{Name} says: Woof!");
    }
}

var dog = new Dog { Name = "Rex" };
dog.Eat();   // Inherited from Animal
dog.Bark();  // Defined in Dog

Important: C# supports single inheritance only — a class can inherit from one base class, but can implement multiple interfaces.

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Virtual and Override Methods

Use virtual and override for runtime polymorphism:

public class Shape
{
    public virtual double Area() => 0;
    public virtual string Describe() => "I am a shape.";
}

public class Circle : Shape
{
    public double Radius { get; set; }

    public override double Area() => Math.PI * Radius * Radius;
    public override string Describe() => $"Circle with radius {Radius}";
}