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Observer Pattern - Consequences

publish date: 2026/06/12 10:18:12.207236 UTC

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Which of the following correctly describes a consequence (trade-off) of using the Observer pattern?

The subject knows the full details of all concrete observer classes, creating tight coupling

The Observer pattern guarantees that all observer updates are processed in a fixed, deterministic order

The subject only knows the abstract Observer interface, creating minimal coupling; however, optimizations that enhance display performance are impractical, and changes to the subject may cause a set of linked updates to observers, some of which may be unnecessary

Using the Observer pattern eliminates the need for a separate Model component in MVC

Correct Answer

Explanation

The consequences of the Observer pattern: the subject only knows the abstract Observer interface, so there is minimal coupling between objects (a positive consequence). However, because of this lack of knowledge, optimizations that enhance display performance are impractical. Also, changes to the subject may cause a set of linked updates to observers to be generated, some of which may not be necessary.

Reference

Software Engineering, Ian Sommerville, 10th edition

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