Object Oriented Design Patterns

Question 1

Abstract Factory

Answer 1

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

Purpose: Creational
Scope: Object

Question 2

Adapter

Answer 2

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

Purpose: Structural
Scope: Class and Object

Question 3

Bridge

Answer 3

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

Purpose: Structural
Scope: Object

Question 4

Builder

Answer 4

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

Question 5

Decorator

Answer 5

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

Purpose: Structural
Scope: Object

Question 6

Facade

Answer 6

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

Purpose: Structural
Scope: Object

Question 7

Factory Method

Answer 7

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

Purpose: Creational
Scope: Class

Question 8

Flyweight

Answer 8

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

Purpose: Structural
Scope: Object

Question 9

Chain of Responsibility

Answer 9

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.

Purpose: Behavioral
Scope: Object

Question 10

Command

Answer 10

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

Purpose: Behavioral
Scope: Object

Question 11

Composite

Answer 11

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

Purpose: Structural
Scope: Object

Question 12

Visitor

Answer 12

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.

Purpose: Behavioral
Scope: Object

Question 13

Template Method

Answer 13

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 algorithmʼs structure.

Purpose: Behavioral
Scope: Class

Question 14

Strategy

Answer 14

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

Purpose: Behavioral
Scope: Object

Question 15

State

Answer 15

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

Purpose: Behavioral
Scope: Object

Question 16

Singleton

Answer 16

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

Purpose: Creational
Scope: Object

Question 17

Proxy

Answer 17

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

Purpose: Structural
Scope: Object

Question 18

Prototype

Answer 18

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

Purpose: Creational
Scope: Object

Question 19

Interpreter

Answer 19

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

Purpose: Behavioral
Scope: Class

Question 20

Iterator

Answer 20

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

Purpose: Behavioral
Scope: Object

Question 21

Mediator

Answer 21

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.

Purpose: Behavioral
Scope: Object

Question 22

Memento

Answer 22

Without Violating encapsulation, capture and externalize an objectʼs internal state so that the object can be restored to this state later

Purpose: Behavioral
Scope: Object

Question 23

Observer

Answer 23

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

Purpose: Behavioral
Scope: Object