Design PatternDesign Pattern

Dr. Zhen JiangWest Chester University

E-mail: zjiang@wcupa.eduurl: www.cs.wcupa.edu/~zjiang

OutlineOutline

IntroductionCreational PatternsStructural PatternsBehavioral Patterns

IntroductionIntroduction A design pattern names, abstracts, and identifies the

key aspects of a common design structure that make it useful for creating a reusable object-oriented design

Creational design patterns abstracts the instantiation process

Structural patterns are concerned with how classes and objects are composed to form larger structures.

Behavioral patterns are concerned with algorithms and assignment of responsibilities between objects.

Creational PatternCreational Pattern

Abstract factoryBuilderFactory MethodPrototypeSingleton

Abstract FactoryAbstract Factory

ClientWidgetFactory

Motif

Consider a user interface (client, windows and ScrollBar) that supports (creates) multiple look-and-feel standards.

PMW

Windows

PMW Motif

ScrollBar

PMW Motif

?

Abstract FactoryAbstract Factory

ClientAbstractFactory

Factory1 Factory2

ProductA

PA2 PA1

ProductB

PB2 PB1

Abstract FactoryAbstract Factory Shopping, interlibrary, …

BuilderBuilder

Reader/User

Add a new conversion?

Converter

ACS Widget

Text Picture

BuilderBuilder

Reader/User Builder

ConcreteBuilder

Product

BuilderBuilder Add a new tool, new course, new equipment, …

Factor MethodFactor Method For creating objects Drink, Drug, vegetables, gardening, …

CreatorProduct

ConcreteProduct ConcreteCreator

PrototypePrototype Provide an abstract tool for defining items like

those in the palette. Windows creation

PrototypeClient

movement

clone

Prototype1

clone

Prototype2

clone

SingletonSingleton For some classes to have exactly one instance Examples?

Structural PatternStructural Pattern

AdapterBridgeCompositeDecoratorFaçadeFlyweightProxy

AdapterAdapter For existing and unrelated classes working in an

application that expects classes with a different and incompatible interfaces (Builder?)

Unix process, file system, …

TargetClient

Adapter

request

Adaptee

implementation

BridgeBridge Inheritance binding (Builder? AbstractFactory?) Windows (their structure and implementation),

Database?

RefinedAbstraction

Abstraction Implementor

IA IB

CompositeComposite Group components

Component

Leaf Composite

CompositeComposite

aComposite (is aComponent)

aComponent aComponentaComponentaLeaf aLeaf aComposite

aComponentaComponent

aLeaf aLeaf

DecoratorDecorator Specifying the responsibility of certain group,

build an transparent interface to component’s client

Teaching, GA, and Instructor

Component

Leaf Decorator

DA DBops

ops ops

FacadeFacade Simplifying interface to more general facilities of

subsystems. (AbstractFactory, FactorMethod, Bridge)

Current screen status of Windows?

Facade

FlyweightFlyweight For sharing resource

Client

FlyWeight

ConcreteFlyWeight

FlyweightFlyweight

aClient

aClientaFlyWeight

aCF

aCF

FlyweightFlyweight

Paragraph and Keys of keyboard?

ProxyProxy Access control and reference

Subject

RealSubjectProxy

aClient

aProxy

aRS

ProxyProxy Network Service?

Behavioral PatternBehavioral Pattern Chain of Responsibility Command Interpreter Iterator Mediator Memento Observer State Strategy Template Method Visitor

Chain of ResponsibilityChain of Responsibility Decouple senders and receivers (sequence? ) Steps, courses, …

Handler

aHandleraHandler

aHandler

CommandCommand Request, command, …? Dos/Shell command, file I/O, user interface, …?

Invoker Command

ConcreteCommandReceiver

InterpreterInterpreter Grammar Composite? Formal language L=a|bC; C=e|cC. (sample

statement: a, b, bc, bcc, …

IteratorIterator Access without exposing any internal structure Interface FactorMethod

MediatorMediator Distribution of behavior among objects AbstractFactory

Mediator

ConcreteMediator

Colleague

CC1 CC2

MementoMemento Record the internal state (checkpoints) Tests of course, firewall, …?

Originator Memento Caretaker

ObserverObserver Maintain consistency Observer calls Getstatus( ) Ordering, TCP communication, …

Subject

ConcreteSubject

Observer

ConcreteObserver

StateState Conditional statements Used in Command, Memento, Observer, … Project, study, …,

Context State

ConcreteStateA

ConcreteStateB

StrategyStrategy Builder, Prototype, Bridge, Command, State. Hollywoodsquare, Chess, searching and sorting

(for example, shell), …

Context Strategy

ConcreteStrategyA

ConcreteStrategyB

Template MethodTemplate Method A template method defines an algorithm in terms

of abstract operations that subclasses override to provide concrete behavior

Inheritance (generalization), virtual function Operations (searching and sorting) in Template

class (Template Stack, Template Queue).

AbstractClass

ConcreteClass

VisitorVisitor Packaging related operations from each class in a

separate object, called a visitor, and passing it to elements of the abstract syntax tree as it’s traversed.

Visitor

ConcreteVisitorA

ConcreteAcceptAConcreteAcceptB

ConcreteAcceptA

ConcreteVisitorB

ConcreteAcceptB