Which design pattern lets observers subscribe to changes in another object?

Which design pattern lets observers subscribe to changes in another object?

• A. Singleton pattern
• B. Factory pattern
• C. Observer pattern
• D. Adapter pattern

Answer: (C)

The key idea here is that one object can notify others about its changes through a subscription mechanism. In this pattern, a subject keeps a list of observers that have expressed interest, and whenever the subject’s state changes, it sends out a notification to all registered observers. Observers can subscribe or unsubscribe at runtime, and their responses are triggered by those notifications. This decouples the subject from the observers, so the subject doesn’t need to know who’s watching or what they’ll do with the update. That dynamic, broadcast-style relationship is what makes this pattern the right fit for letting observers subscribe to changes in another object. A practical example is a model in a UI: when the model changes, it notifies all registered views, and each view updates accordingly. The other patterns aren’t about notifying dependents: a Singleton ensures a single instance, a Factory focuses on creating objects, and an Adapter translates interfaces between components.