How do abstract classes relate to abstract factories or strategy patterns?

Short answer: Abstract classes often define base contracts or template methods for patterns: Abstract Factory: Defines abstract methods to create families of objects. Strategy Pattern: Abstract class defines a common interface for interchangeable algorithms. abstract class PaymentStrategy {

Example code

public abstract void Pay(decimal amount);
}
class CreditCardPayment : PaymentStrategy
{
public override void Pay(decimal amount) => Console.WriteLine($"Paid {amount} by credit card"); }

Real-world example (ShopNest)

Checkout calls IPaymentGateway.Charge(). Razorpay and Stripe adapters implement the same interface, so ShopNest can switch gateways without rewriting the order service.

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.