How do you implement a Factory pattern in C#?

Short answer: A simple example of Factory Method: // Product interface public interface IAnimal

Example code

{ void Speak(); } // Concrete Products public class Dog : IAnimal
{
public void Speak() => Console.WriteLine("Woof");
}
public class Cat : IAnimal
{
public void Speak() => Console.WriteLine("Meow");
} // Factory public class AnimalFactory
{
public static IAnimal CreateAnimal(string animalType)
{
return animalType.ToLower() switch
{ "dog" => new Dog(), "cat" => new Cat(), _ => throw new ArgumentException("Invalid animal type") }; }
} Usage: var dog = AnimalFactory.CreateAnimal("dog"); dog.Speak(); // Outputs: Woof

Real-world example (ShopNest)

ShopNest payment fees use Strategy: IFeeCalculator with UPI/Card implementations chosen at runtime.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.