Pattern Design Basic Design Pattern 3

Question 1

In the Observer pattern, what are the two main roles?

Accepted Answer

Subject and Observer

Answer

The Observer pattern defines a Subject that maintains a list of Observers and notifies them automatically when its state changes.

Question 2

Which pattern allows you to add responsibilities to objects dynamically without modifying their class?

Accepted Answer

Decorator

Answer

The Decorator pattern wraps an object in decorator objects to attach new behaviors at runtime, as a flexible alternative to subclassing.

Question 3

The Command pattern converts requests into objects primarily to support which feature?

Accepted Answer

Undo/redo operations

Answer

Encapsulating requests as Command objects allows you to parameterize, queue, log, and reverse operations, making undo/redo straightforward to implement.

Question 4

Which design pattern uses a 'virtual' object as a placeholder to control access to another object?

Accepted Answer

Proxy

Answer

The Proxy pattern provides a surrogate or placeholder for another object to control access, add logging, or perform lazy initialization.

Question 5

What distinguishes a class-based (compile-time) Adapter from an object-based (runtime) Adapter?

Accepted Answer

Class Adapter uses multiple inheritance; object Adapter uses composition

Answer

A class Adapter inherits from both the target and adaptee (requiring multiple inheritance), while an object Adapter holds a reference to the adaptee via composition.

Pattern Design Practice Test

Pattern Design Practice Test

Pattern Design Basic Design Pattern 3