Subject Interface (INewsPublisher):?

Short answer: This interface defines methods for subscribing, unsubscribing, and notifying observers. The subject manages a list of observers and notifies them when there is an update. public interface INewsPublisher

Example code

{ void Subscribe(IObserver observer); void Unsubscribe(IObserver observer); void Notify(string news); }

Real-world example (ShopNest)

When order status changes, observers update email, SMS, and analytics without the Order class knowing each one.

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.