Virtual method dispatch mechanism in C Sharp (C#)

Introduction

Virtual method dispatch lets a program decide which version of a method to run when you have many classes connected by inheritance. It helps the program pick the right behavior at runtime.

When you want different classes to have their own version of a method but use the same method name.

When you write code that works with a general type but needs to run specific actions for each subclass.

When you want to add new classes later without changing existing code that calls the method.

When you want to use polymorphism to make your code flexible and easier to extend.

Syntax

C Sharp (C#)

class BaseClass {
    public virtual void Show() {
        Console.WriteLine("Base class method");
    }
}

class DerivedClass : BaseClass {
    public override void Show() {
        Console.WriteLine("Derived class method");
    }
}

virtual keyword marks a method that can be changed in child classes.

override keyword tells the program this method replaces the base version.

Examples

Animal has a virtual method Speak. Dog changes it to say "Bark" instead.

C Sharp (C#)

class Animal {
    public virtual void Speak() {
        Console.WriteLine("Animal sound");
    }
}

class Dog : Animal {
    public override void Speak() {
        Console.WriteLine("Bark");
    }
}

Shape has Draw method. Circle and Square each have their own Draw method.

C Sharp (C#)

class Shape {
    public virtual void Draw() {
        Console.WriteLine("Drawing shape");
    }
}

class Circle : Shape {
    public override void Draw() {
        Console.WriteLine("Drawing circle");
    }
}

class Square : Shape {
    public override void Draw() {
        Console.WriteLine("Drawing square");
    }
}

Sample Program

This program shows virtual method dispatch. The variable type is Animal, but the method called depends on the actual object type (Animal, Dog, or Cat).

C Sharp (C#)

using System;

class Animal {
    public virtual void Speak() {
        Console.WriteLine("Animal sound");
    }
}

class Dog : Animal {
    public override void Speak() {
        Console.WriteLine("Bark");
    }
}

class Cat : Animal {
    public override void Speak() {
        Console.WriteLine("Meow");
    }
}

class Program {
    static void Main() {
        Animal myAnimal = new Animal();
        Animal myDog = new Dog();
        Animal myCat = new Cat();

        myAnimal.Speak();
        myDog.Speak();
        myCat.Speak();
    }
}

Important Notes

If you forget virtual in the base class, the method cannot be overridden properly.

Virtual method dispatch happens at runtime, so the program picks the right method based on the actual object.

You can call the base method inside the override using base.MethodName() if needed.

Summary

Virtual methods let child classes provide their own version of a method.

The program decides which method to run when it runs, not when it compiles.

This helps write flexible and reusable code using inheritance and polymorphism.