How does a subject notify its observers of changes?

The correct answer involves understanding the observer design pattern, which enables a subject to notify its observers when there are changes in its state. This notification process often begins with a registration mechanism, where observers express their interest in being notified about changes to the subject.

When observers register for notifications, they typically provide a way for the subject to reach out to them, either via a callback method, event handler, or similar mechanism. This registration step is critical, as it establishes the connection between the subject and its observers, ensuring that observers can receive updates whenever changes occur.

On the other hand, while other options might describe aspects of notification methods in various contexts, they do not fully capture how the observer pattern is implemented. For example, a direct method call implies a more synchronous and tightly coupled approach rather than the loose coupling that the observer pattern allows. The pull mechanism refers to instances where observers may need to request updates, which does not align with the typical design of an observer that is meant to be more passive and receive notifications automatically. Broadcasting event messages can be related but doesn't emphasize the need for the initial registration process, which is fundamental to establishing observer relationships.

Thus, the registration process for subscriptions is the mechanism that enables observers to be effectively notified of