Design Patterns & Architecture Flashcards

Which pattern is best suited for implementing undo/redo functionality in an application?

Answer: Command

The Command pattern encapsulates operations as objects with execute/undo methods, making undo/redo straightforward.

In the Flyweight pattern, what is the key distinction between intrinsic and extrinsic state?

Answer: Intrinsic state is shared across instances; extrinsic state is context-specific

Flyweight stores intrinsic (invariant) state internally and receives extrinsic (varying) state from the client at runtime.

Which architectural pattern divides an application into Model, View, and Presenter components?

Answer: MVP

MVP (Model-View-Presenter) replaces the Controller with a Presenter that mediates between View and Model with no direct View-Model connection.

What is the primary intent of the Null Object pattern?

Answer: Represent missing objects with a no-op implementation to avoid null checks

Null Object provides a default do-nothing implementation, eliminating the need for null checks scattered throughout client code.

In the Visitor pattern, what is 'double dispatch' and why is it needed?

Answer: Two virtual calls that resolve the concrete types of both the visitor and the element

Double dispatch uses two polymorphic calls — one on the element to accept a visitor, and one on the visitor to act on the concrete element type.

Which principle does the Dependency Inversion Principle (DIP) state?

Answer: High-level modules should not depend on low-level modules; both should depend on abstractions

DIP states that both high-level and low-level modules should depend on abstractions, reducing coupling between layers.

Which pattern defines an object that encapsulates how a set of objects interact, promoting loose coupling?

Answer: Mediator

The Mediator pattern centralizes complex communications between objects, so they interact through the mediator rather than directly.