What is the primary purpose of the Observer design pattern?

Question

BlackTom AI · Accepted Answer

Consider the question about the Observer pattern's main purpose and evaluate each option in turn.
Option 1: 'To allow multiple objects to be notified when the state of another object changes.' This aligns with the core idea of the Observer pattern, where observers register with a subject and are informed automatically when the subject’s state changes. It enables decoupling: the subject doesn’t need to know details about observers, only that they should be notified.
Option 2: 'To ensure an object has only one instance.' This describes the Singleton pattern, not the Observer pattern. It focuses on controlled instantiation rather than event notification.
Option 3: 'To provide a way to compose objects into tree structures.' This is characteristic of the Composite pattern, which allows treating individual objects and compositions uniformly, not about notifying state changes.
Option 4: 'To add responsibilities to objects dynamically.' This describes the Decorator pattern (or sometimes the concept of the Proxy/Decorator family), which extends behavior without modifying the original object, rather than publishing changes to observers.
In summary, option 1 accurately captures the essence of the Observer pattern, while options 2, 3, and 4 point to other well-known design patterns with different intents.

SOFT3202 COMP9202 (ND) Quiz 4

What is the primary purpose of the Observer design pattern?

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