Inheritance And Polymorphism In C# Complete Guide

Inheritance Example

Step 1: Understand Basic Inheritance

In C#, inheritance allows a class to inherit fields and methods from another class. The class inheriting is called a derived or child class, and the class being inherited from is called a base or parent class.

Step 2: Define Base Class

Let's start by defining a base class Animal which will have some common properties and methods:

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

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

    public void Sleep()
    {
        Console.WriteLine($"{Name} is sleeping.");
    }
}

Here, the Animal class has two properties (Name and Age) and two methods (Eat and Sleep).

Step 3: Define Derived Class

Next, we define a derived class Dog which inherits from the Animal class:

public class Dog : Animal
{
    public string Breed { get; set; }

    public void Bark()
    {
        Console.WriteLine($"{Name} the {Breed} dog is barking.");
    }
}

The Dog class inherits the Name and Age properties, as well as the Eat and Sleep methods from the Animal class. It also has an additional property Breed and a method Bark.

Step 4: Use Inheritance in a Program

Let's create a simple program to demonstrate using our Animal and Dog classes.

using System;

class Program
{
    static void Main()
    {
        // Creating an instance of Animal
        Animal myAnimal = new Animal();
        myAnimal.Name = "Generic Animal";
        myAnimal.Age = 5;
        myAnimal.Eat();   // Output: Generic Animal is eating.
        myAnimal.Sleep(); // Output: Generic Animal is sleeping.

        // Creating an instance of Dog
        Dog myDog = new Dog();
        myDog.Name = "Buddy";
        myDog.Age = 3;
        myDog.Breed = "Golden Retriever";
        myDog.Eat();         // Inherited method, Output: Buddy is eating.
        myDog.Sleep();       // Inherited method, Output: Buddy is sleeping.
        myDog.Bark();        // Dog-specific method, Output: Buddy the Golden Retriever dog is barking.

        // Using Dog object as an Animal
        Animal myAnimalDog = myDog; // Upcasting
        myAnimalDog.Eat();          // Output: Buddy is eating.
        myAnimalDog.Sleep();        // Output: Buddy is sleeping.
        // Cannot call myAnimalDog.Bark(); because myAnimalDog is treated as an Animal
    }
}

Polymorphism Example

Polymorphism means many shapes or forms. In C#, it allows us to perform a single action in different ways. We can achieve polymorphism through method overriding and method overloading.

Method Overriding Example

Step 1: Understand Method Overriding

Method overriding allows a derived class to provide a specific implementation of a virtual method defined in its base class.

Step 2: Define Virtual Methods

First, modify the Animal class to make Eat and Sleep methods virtual:

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

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

    public virtual void Sleep()
    {
        Console.WriteLine($"{Name} is sleeping.");
    }
}

Step 3: Override Methods in Derived Class

Now, override these methods in the Dog class:

public class Dog : Animal
{
    public string Breed { get; set; }

    public override void Eat()
    {
        Console.WriteLine($"{Name} the {Breed} dog is eating dog food.");
    }

    public override void Sleep()
    {
        Console.WriteLine($"{Name} the {Breed} dog is sleeping in its crate.");
    }

    public void Bark()
    {
        Console.WriteLine($"{Name} the {Breed} dog is barking.");
    }
}

Step 4: Demonstrate Method Overriding

Update the Main method to show how polymorphism works with method overriding:

using System;

class Program
{
    static void Main()
    {
        Animal myAnimal = new Animal();
        myAnimal.Name = "Generic Animal";
        myAnimal.Age = 5;
        myAnimal.Eat();   // Output: Generic Animal is eating.
        myAnimal.Sleep(); // Output: Generic Animal is sleeping.

        Animal myDog = new Dog(); // Upcasting
        myDog.Name = "Buddy";
        myDog.Age = 3;
        ((Dog)myDog).Breed = "Golden Retriever"; // Downcasting to access Dog-specific properties

        myDog.Eat();         // Overridden method, Output: Buddy the Golden Retriever dog is eating dog food.
        myDog.Sleep();       // Overridden method, Output: Buddy the Golden Retriever dog is sleeping in its crate.
        ((Dog)myDog).Bark(); // Downcasting required to call Dog-specific method, Output: Buddy the Golden Retriever dog is barking.

        Dog myRealDog = new Dog();
        myRealDog.Name = "Max";
        myRealDog.Breed = "Poodle";

        myRealDog.Eat();  // Output: Max the Poodle dog is eating dog food.
        myRealDog.Sleep(); // Output: Max the Poodle dog is sleeping in its crate.
        myRealDog.Bark(); // Output: Max the Poodle dog is barking.
    }
}

Method Overloading Example

Step 1: Understand Method Overloading

Method overloading allows multiple methods to have the same name but different parameters.

Step 2: Introduce Method Overloading in Animal Class

Add overloaded methods in the Animal class:

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

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

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

    public virtual void Sleep()
    {
        Console.WriteLine($"{Name} is sleeping.");
    }
}

Step 3: Override and Overload Methods in Dog Class

Override the methods in the Dog class and add method overloading as well:

public class Dog : Animal
{
    public string Breed { get; set; }

    public override void Eat()
    {
        Console.WriteLine($"{Name} the {Breed} dog is eating dog food.");
    }

    public override void Eat(string foodType)
    {
        Console.WriteLine($"{Name} the {Breed} dog is eating {foodType}.");
    }

    public override void Sleep()
    {
        Console.WriteLine($"{Name} the {Breed} dog is sleeping in its crate.");
    }

    public void Bark()
    {
        Console.WriteLine($"{Name} the {Breed} dog is barking.");
    }
}

Step 4: Demonstrate Method Overloading

Update the Main method to demonstrate method overloading: