Chapter 6 - Design Patterns

Question 1

Design patterns

Answer 1

descriptions of communicating objects and classes that are customized to solve a general design problem in a particular context

Question 2

design for change

Answer 2

when designing a system we should also plan for inevitable changes.

Question 3

Creational

Answer 3

patterns proposing flexible solutions for creating objects. They include Abstract Factory (6.2), Factory Method, Singleton (6.3), Builder (6.12), and Prototype.

Question 4

Structural

Answer 4

patterns proposing flexible solutions for composing classes and objects. They include Proxy (6.4), Adapter (6.5), Facade (6.6), Decorator (6.7), Bridge, Composite, and Flyweight.

Question 5

Behavioral

Answer 5

patterns proposing flexible solutions for interaction and division of responsibilities among classes and objects. They include Strategy (6.8), Observer (6.9), Template Method (6.10), Visitor (6.11), Chain of Responsibility, Command, Interpreter, Iterator (6.12), Mediator, Memento, and State.

Question 6

Singleton

Answer 6

This design pattern ensures that a class, as the name suggests, has at most one instance

Question 7

Factory

Answer 7

(1) creates and returns objects of a particular class; and (2) hides the type of these objects behind an interface

Question 8

Proxy

Answer 8

advocates the use of an intermediary object, also known as a proxy, between a base object and its clients

Question 9

stubs

Answer 9

facilitate remote communication.

Question 10

Adapter

Answer 10

This pattern is recommended when we need to convert one class interface into another.

Question 11

Facade

Answer 11

a class that offers a simplified interface to a complex system. The objective is to shield users from the need to understand the internal classes of this system.

Question 12

Decorator

Answer 12

Instead of using inheritance, it employs composition to dynamically add these functionalities to base objects.

Question 13

Strategy

Answer 13

aims to parameterize the algorithms used by a class, encapsulating a family of algorithms and making them interchangeable

Question 14

Observer

Answer 14

defines a way to implement a one-to-many relationship between subject and observer objects. When the state of a subject changes, all its observers are notified.

Question 15

Template Method

Answer 15

specifies how to implement the template of an algorithm in an abstract class, which we’ll call X, while deferring some steps or methods for implementation in the subclasses of X. In summary, a Template Method allows subclasses to customize an algorithm without changing its fundamental structure, which is defined in the base class

Question 16

double dispatch

Answer 16

the types of the target object and one argument are used to determine the method that will be invoked. (only available in a few languages)

Question 17

Visitor

Answer 17

This pattern provides a way to add an operation to a family of objects without modifying the classes themselves.

Designed to function effectively even in languages with single dispatching, such as Java.

Question 18

Iterator

Answer 18

a design pattern that standardizes an interface for traversing a data structure

Question 19

Builder

Answer 19

a design pattern that simplifies the instantiation of objects with several attributes, some of which may be optional

Question 20

patternitis

Answer 20

an inflammation associated with the premature or excessive use of design patterns