Design Patterns (Gang of Four)

Question 1

Abstract Factory

Answer 1

Creational Pattern. Provide an interface for creating families of related or dependent objects without specifying their concrete classes.

Question 2

Builder

Answer 2

Creational Pattern. Separate the construction of a complex object from its representation so that the same construction process can create different representations.

Question 3

Factory Method

Answer 3

Creational Pattern. Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

Question 4

Prototype

Answer 4

Creational Pattern. Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.

Question 5

Singleton

Answer 5

Creational Pattern. Ensure a class has only one instance, and provide a global point of access to it.

Question 6

Adapter

Answer 6

Structural Pattern. Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces.

Question 7

Bridge

Answer 7

Structural Pattern. Decouple an abstraction from its implementation so that the two can vary independently.

Question 8

Composite

Answer 8

Structural Pattern. Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.

Question 9

Decorator

Answer 9

Structural Pattern. Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Question 10

Facade

Answer 10

Structural Pattern. Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.

Question 11

Flyweight

Answer 11

Structural Pattern. Use sharing to support large numbers of fine-grained objects efficiently.

Question 12

Proxy

Answer 12

Structural Pattern. Provide a surrogate or placeholder for another object to control access to it.

Question 13

Chain of Responsibility

Answer 13

Behavioral Pattern. Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.

Question 14

Command

Answer 14

Behavioral Pattern. Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

Question 15

Interpreter

Answer 15

Behavioral Pattern. Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.

Question 16

Iterator

Answer 16

Behavioral Pattern. Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

Question 17

Mediator

Answer 17

Behavioral Pattern. Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

Question 18

Observer

Answer 18

Behavioral Pattern. Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.

Question 19

State

Answer 19

Behavioral Pattern. Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

Question 20

Strategy

Answer 20

Behavioral Pattern. Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

Question 21

Template Method

Answer 21

Behavioral Pattern. Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure.

Question 22

Visitor

Answer 22

Behavioral Pattern. Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.