Concrete Subject (NewsPublisher):?

• The NewsPublisher class is the concrete implementation of the subject. It

maintains a list of observers and provides methods to subscribe, unsubscribe, and

notify them when a new news article is available.

public class NewsPublisher : INewsPublisher

private readonly List<IObserver> _observers = new

List<IObserver>();

public void Subscribe(IObserver observer) =>

_observers.Add(observer);

public void Unsubscribe(IObserver observer) =>

_observers.Remove(observer);

public void Notify(string news)

foreach (var observer in _observers)

observer.Update(news);

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