chapter 6 introduction to design patterns. process phase discussed in this chapter requirements...

Chapter 6Introduction to Design Patterns

Process Phase Discussed in This ChapterRequirementsAnalysis

Design

Implementation

ArchitectureFramework Detailed Design

xKey: = secondary emphasisx = main emphasis

Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

Sample Design Goals and Ways to Accomplish Them

Reusability, Flexibility, and Maintainabilityo Reuse flexible designso Keep code at a general levelo Minimize dependency on other classes

Robustness o Reuse reliable designso Reuse robust parts

Sufficiency / Correctnesso Modularize designo Reuse trusted parts


KitchenViewer Interface

Wallcabinet

Counter

Floorcabinet

Modern Classic Antique Arts & Crafts

menu

display area

styles


KitchenViewer Example

Modern Classic Antique Arts & Crafts

Wall cabinets Floor cabinetsCountertop


Selecting Antique Style

Modern Classic Antique Arts & CraftsAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

KitchenViewer Without Design Patterns

Kitchen

ClientrenderKitchen()

FloorCabinet

ModernWallCabinet

ModernFloorCabinet AntiqueFloorCabinet

AntiqueWallCabinet

WallCabinet


Design Goal At Work: Flexibility

Our design should be flexible enough to produce any of several kitchen styles.


AntiqueKStylegetWallCabinet()getFloorCabinet()

The Abstract Factory Idea

KitchenStylegetWallCabinet()getFloorCabinet()

ModernKStylegetWallCabinet()getFloorCabinet()

WallCabinet FloorCabinet

AntiqueWallCabinet AntiqueFloorCabinet

FloorCabinet getFloorCabinet() { return new AntiqueFloorCabinet(); }

……

FloorCabinet getFloorCabinet() { return new ModernFloorCabinet(); }


Abstract Factory Design Pattern Applied to KitchenViewer

KitchenStylegetWallCabinet()getFloorCabinet()

KitchengetWallCabinet()getFloorcabinet()

ClientrenderKitchen( KitchenStyle )

ModernKStylegetWallCabinet()getFloorCabinet()

AntiqueKStylegetWallCabinet()getFloorCabinet()

WallCabinet FloorCabinet

ModernWallCabinet

ModernFloorCabinet

AntiqueWallCabinet

AntiqueFloorCabinetAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

Abstract Factory Design Pattern

StylegetComponentA()getComponentB()

ClientdoOperation( Style myStyle )

Style1getComponentA()getComponentB()


ComponentA ComponentB

Style1ComponentA

Style1ComponentB

Style2ComponentA

Style2ComponentB

Collection


Abstract Factory Design PatternAlternative

StylegetComponentA()getComponentB()

ClientdoOperation()



ComponentA ComponentB

Style1ComponentA

Style1ComponentB

Style2ComponentA

Style2ComponentB

Collection getComponentA()getComponentB()


Key Concept: Design Pattern

-- class combination and algorithm fulfilling a common design purpose.


Key Concept: Creational Design Patterns

-- used to create objects in flexible or constrained ways.


Key Concept: Structural Design Patterns

-- used to represent data structures such as trees, with uniform processing interfaces.


Example of Behavioral Design Goal: Port Traffic

berthberth

to drydock

obstacles


Design Goal At Work: Flexibility

Our design should be flexible enough to produce any of several kitchen styles.


Ship Tugboat1..n1

Harbor application

Customs application: reuse Ship alone

Ship Longshoreman

Avoiding Dependencies


Core Mediator Concept Applied to The Harbor Problem

Ship

Tugboat

LeavingPortestimateTime()


Applying the Mediator Design Pattern to The Harbor Problem

Ship Tugboat

VesselPortMissionestimateTime()

LeavingPortestimateTime()

EnteringPortestimateTime()

BeingMaintainedestimateTime()

Mediator base class


You have requested to view a luxury model

with luxury body style, and black body color.

Model

Body Style

Body color

Choose an automobile to view.

OK

A Design Problem Solvable by Chain of Responsibility

Basic Midsize Luxury SUV

Luxury Extra Basic

Black Brown Red White

This part is fixed

Display depends on model selected

Display depends on body style selected

Assume that each of these will eventually be a small, expensive animation.


Key Concept: Behavioral Design Patterns

-- to capture behavior among objects.


Characteristics of Design Patterns 1

Viewpoints – ways to describe patterns1. Static: class model (building blocks)

2. Dynamic: sequence or state diagram (operation)

Levels – decomposition of patterns1. Abstract level describes the core of the pattern

2. Concrete (= non abstract) level describes the particulars of this case

Roles – the “players” in pattern usage 1. Application of the design pattern itself

2. Clients of the design pattern application

3. Setup code initializes and controls


Characteristics of Design Patterns 21. Client role

2. Setup role

A

C

A. Static viewpoint B. Dynamic viewpoint

3. Role: Application of the design pattern

D

B (i) Abstract level

(ii) Concrete level

(class model)(sequence or

state diagram)

(class or classes)

(class or classes)

: Reference directionAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

getWallCabinet()

Abstract Factory Application Sequence Diagram

myStyle:KitchenStyleClient

myStyle:ModernKStyle

myStyle:AntiqueKStyle

renderKitchen( myStyle )

wallCabinet1:ModernWallCabinet

wallCabinet1:AntiqueWallCabinet

ModernWallCabinet()getWallCabinet()

AntiqueWallCabinet()

myStyle.getWallCabinet()

-- IF myStyle BELONGS TO ModernKStyle --

-- IF myStyle BELONGS TO AntiqueKStyle --


Key Concept: Two Viewpoints

We consider design patterns from the static viewpoint (what they are made from) and the dynamic viewpoint (how they function).


Concrete and Abstract Layers

KitchenStyle

Kitchen

Client

ModernKStyle

AntiqueKStyle

WallCabinet

FloorCabinet

ModernWallCabinet

ModernFloorCabinet

AntiqueWallCabinet

AntiqueFloorCabinet

Abstract level

Concrete level


Design Goal At Work: Correctness

We want to provide an interface to a design pattern so that its functionality is clear and separate.


Key Concept: Two Levels

Design patterns usually have an abstract level and a non-abstract (“concrete”) level.


Design Goal At Work: Correctness

To use design patterns effectively, we distinguish the roles involved.


2. Client Role 1. Design Pattern Application

Interface to the pattern

(frequently abstract; possibly

several classes)

DPClient DPInterface

Rest of thedesign pattern

application

Interacts with the design pattern only through its interface

3. Setup Role

The Three Roles Involved in Design Pattern Usage

Rest of the Application

No limitations


Key Concept: Three Roles

A part of a design either 1) applies a design pattern, 2) is a client of the pattern application, or 3) re/initializes these.


Basic Idea of Delegation

requiredFunction()

… intermediaryFunction( … ){ … requiredFunction() …}

ClientclientFunction() intermediaryFunction()

replace

… clientFunction( … ){… intermediaryFunction( … ) …}


Basic Design Pattern Form #1: Delegation

DoerBasedoIt()

DPInterfaceinterfaceMethod()

ConcreteDoer1doIt()

ConcreteDoer2doIt()

. . .

doerObject

… interfaceMethod( … ){ … doerObject.doIt() … }

Client


Basic Design Pattern Form #2: Recursion

RecursionBasedoOperation()

NonrecursiveClassdoOperation()

RecursiveClassdoOperation()

void doOperation( … ){ … aggregate … }

aggregate

Client


The Recursion Form Applied to an Organization Chart

EmployeeprintOrganization()

IndividualContributorprintOrganization()

SupervisorprintOrganization()

void printOrganization( … ){ … supervisees.printOrganization() … }

supervisees

Client


Key Concept: Two Forms

A design pattern’s form is usually a delegation of responsibility or a class that relates to itself (recursive).


Summary of This Chapter

Design Patterns are recurring designs satisfying

recurring design purposes

Described by Static and Dynamic Viewpoints o Typically class models and sequence diagrams respectively

Use of a pattern application is a Client Roleo Client interface carefully controlled

o “Setup,” typically initialization, a separate role

Design patterns Forms usually Delegation or

Recursion

Classified as Creational, Structural, or Behavioral


Observer Design Pattern

Sourcenotify()

Observerupdate()

ConcreteSubjectstate

ConcreteObserverobserverState

update()

Trigger

1..n

Initialize


chapter 6 introduction to design patterns. process phase discussed in this chapter requirements...

Documents

software design

braude wiley

design patternsprocess

sample design goals

new antiquefloorcabinet

new modernfloorcabinet

secondary emphasisx

main emphasisadapted