What happens if both interface and abstract class have the same method signature?

Short answer: Implementing class must provide implementation once. Explicit interface implementation can resolve ambiguity. interface IDriveable { void Start(); } abstract class Vehicle { public abstract void Start(); } class Car : Vehicle, IDriveable

Example code

{
public override void Start() => Console.WriteLine("Car started"); }

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.