C# Polymorphism Explained: The Hidden Pitfall of Method Hiding vs Overriding

Polymorphism is one of the core principles of object-oriented programming — and C# gives you powerful tools to work with it. But there's a subtle trap many developers fall into when dealing with method hiding vs method overriding.

Let’s break down this C# challenge to understand what’s really happening and why the output might surprise you.

👇 The Challenge:

public class Animal  // Base class (parent) 
{
    public virtual void animalSound() 
    {
        Console.WriteLine("The animal makes a sound - #");
    }
}

class Pig : Animal  // Derived class (child) 
{
    public override void animalSound() 
    {
        Console.WriteLine("The pig says: wee wee - #");
    }
}

class Dog : Animal  // Derived class (child) 
{
    public void animalSound()  // method hiding, not overriding
    {
        Console.WriteLine("The dog says: bow wow - #");
    }
}

class Program 
{
    public static void Main(string[] args) 
    {
        Animal myAnimal = new Animal();
        Animal myPig = new Pig();
        Animal myDog = new Dog();

        myAnimal.animalSound();
        myPig.animalSound();
        myDog.animalSound();
    }
}

🔍 Predict the Output

Let’s go through it line by line:

1️⃣ myAnimal.animalSound();

• Direct call to the base method.

• ✅ Output:

The animal makes a sound - #

2️⃣ myPig.animalSound();

• Object is of type Pig, which overrides the base method.

• ✅ Output:

The pig says: wee wee - #

3️⃣ myDog.animalSound();

• Object is of type Dog, but declared as Animal.

• Dog has a method named animalSound, but it’s not overriding the base method.

• So the base class method is called, because C# uses the reference type here.

• ✅ Output:

The animal makes a sound - #

✅ Final Output:

The animal makes a sound - #
The pig says: wee wee - #
The animal makes a sound - #

List<Animal> zoo = new List<Animal> { new Pig(), new Dog(), new Animal() };
foreach (var animal in zoo)
{
    animal.animalSound();  // Dog won't say "bow wow" unless overridden
}