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Observer Pattern - Description

publish date: 2026/06/12 10:18:11.612824 UTC

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The Observer pattern is one of the most widely used design patterns. Which of the following correctly describes what problem it solves and how?

It provides a standard way to traverse a collection of objects without exposing the underlying collection implementation

It provides a single unified interface to a set of interfaces in a subsystem, reducing coupling between subsystems

It allows functionality to be added to an individual object at runtime without affecting other objects

It separates the display of the state of an object from the object itself, allowing alternative displays; when the object state changes, all displays are automatically notified and updated

Correct Answer

It separates the display of the state of an object from the object itself, allowing alternative displays; when the object state changes, all displays are automatically notified and updated

Explanation

The Observer pattern separates the display of the state of an object from the object itself and allows alternative displays to be provided. When the object state changes, all displays are automatically notified and updated to reflect the change. It is used when multiple displays of state information are required and when it is not necessary for the object maintaining the state to know the specific display formats used.

Reference

Software Engineering, Ian Sommerville, 10th edition

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