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Design PatternsDesign Patterns

Object-Oriented DesignObject-Oriented Design

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Design Patterns

Reuse of design knowledge and experience

Common in many engineering disciplines

Avoids “reinventing the wheel” Design Patterns, Gamma, Helm,

Johnson, Vlissides (GoF) Architecture: Christopher Alexander

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Elements of a Design Elements of a Design PatternPattern

name - simple, descriptive term

intent - brief description of aim

motivation - concrete example

applicability - where is it useful?

structure - “blueprint” diagram

participants - each class in pattern

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Elements of a Design Elements of a Design Pattern (cont’d)Pattern (cont’d)

collaborations - relationships among participants

consequences - implications of use

implementation - general implementation

sample code - code for a particular application

known uses - applications where used

related patterns - to combine or substitute

problemareas

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Example Pattern: CompositeExample Pattern: Composite

Structural pattern Represent part-whole relationships

in tree hierarchy Uniform treatment of individual

objects

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Composite: Application

Piece PartType GetType()int GetIdentifier()int GetTime()float GetQuality()int GetNumberOfRejections()SetRejectStatus(bool)bool GetRejectStatus()

CompoundPart AddPart(Part)int GetNumberOfParts()Part * Decompose()PartType GetType()int GetIdentifier()int GetTime()float GetQuality()int GetNumberOfRejections()SetRejectStatus(bool)bool GetRejectStatus()

sub-parts *

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Composite: Application

Part PartType GetType()int GetIdentifier()int GetTime()float GetQuality()int GetNumberOfRejections()SetRejectStatus(bool)bool GetRejectStatus()

CompoundPart AddPart(Part)int GetNumberOfParts()Part * Decompose()

sub-parts *

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Composite Pattern Example: Simulation Components

SimComponent

PartType GetType()int GetIdentifier()int GetTime()float GetQuality()int GetNumberOfRejections()SetRejectStatus(bool)bool GetRejectStatus()

Composite

all of ops() ...AddPart(Part)int GetNumberOfParts()Part * Decompose()

Piece

PartType GetType() ...all of the ops()...

Inheritance

Contains 1 ormore Components

in a variablecalled sub-pieces

sub-pieces

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Composite Pattern Example: A Graphic

Graphic

Draw()Add(Graphic)Remove(int)GetChild(int)

Picture

Draw()Add(Graphic)Remove(int)GetChild(int)

Text

Draw()

Rectangle

Draw()

Line

Draw()

Inheritance

Contains 1 ormore Graphicsin a variable

called graphics

graphics

for all g in graphicsg.Draw()Add/Remove Graphic

to/from list of graphics

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Composite Pattern Example: A Graphic

MailBody

Disp()Add(Attch)Remove(int)GetChild(int)

Attachments

Disp()Add(Attch)Remove(int)GetChild(int)

Pic

Disp()

Image

Disp()

Text

Disp()attchs

for all m in attchsm.Disp()

Alternatively:Display a list of attachments

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Composite:Composite:General StructureGeneral Structure

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Observer

Behavioral pattern When changed, Subject notifies

Observers

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Observer: Structure

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Observer: Sequence Diagram

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Observer: Application

Unit AddPart(Part *)GetNumberFinalParts()Part * GetFinalPart()SetTypesRequired(PartType *, int num)AddUnitObserver(UnitObserver *) NotifyObservers()

UnitObserver Update()Update(Unit *)

ProductRemovalObserver Update(Unit *)

Observer Update()

// called when unit completes a partfor all o in observers o.Update(this)

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Creational Patterns

Abstract Factory Builder Factory Method Prototype Singleton

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Structural Patterns

Adapter Bridge Composite Decorator Facade Flyweight Proxy

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Behavioral Patterns

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