Design Patterns Explained: From Analysis through Implementation

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MI AM!Half(day!Tutorial!

11/11/2013!8:30!AM!

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"Design Patterns Explained: From Analysis through

Implementation" !

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Presented by:

Ken Pugh

Net Objectives !

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Brought(to(you(by:(!

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340!Corporate!Way,!Suite!300,!Orange!Park,!FL!32073!

888(268(8770!H!904(278([email protected]!H!www.sqe.com

!!!!Ken!Pugh!!!Net!Objectives!!

A fellow consultant with Net Objectives, Ken Pugh helps companies transform into lean-agile organizations through training and coaching. His special interests are in communication (particularly effectively communicating requirements), delivering business value, and using lean principles to deliver high quality quickly. Ken trains, mentors, and testifies on technology topics from object-oriented design to Linux/Unix. He has written several programming books, including the 2006 Jolt Award winner Prefactoring and his latest Lean-Agile Acceptance Test Driven Development: Better Software Through Collaboration. Ken has helped clients from London to Boston to Sydney to Beijing to Hyderabad. He enjoys snowboarding, windsurfing, biking, and hiking the Appalachian Trail. Reach Ken at [email protected]!

Design'Pa*erns'Explained'

16#October#2013#Copyright#©#2007#Net#Objec8ves.#All#Rights#Reserved.#

info@netobjec+ves.com000www.netobjec+ves.com0

1# #Copyright#©#2008#Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Pa*ern'Oriented'Design''

(Design'Pa*erns'Explained)'

A#New#Perspec8ve#on#ObjectDOriented#Design#

POD#Half#Day#October#2012##

2# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Teams#

!  Great#designs#are#a#collabora8ve#effort#!  You#will#be#part#of#a#team#for#a#couple#exercises#!  Agile#teams#are#selfDorganizing##

!  Form#yourself#into#three#to#five#person#teams#




Introduc8ons#

!  Name#! What#do#you#do?#! Who#do#you#do#it#for?#

!  Languages#used?##!  Years#programming?#! What#paWerns#have#you#used?##

! Why#are#you#here?#! What#do#you#want#out#of#the#course?#


Ken#Pugh#

ken.pugh#@netobjec8ves.com#

Photo#Size:####Height:#2.25#Posi8on:####from#top#le_#corner###Horizontal#0.75####Ver8cal#1.#Picture##Style:#Simple#Black#####Frame##

No0code0goes0in0+ll0the0test0goes0on.0A0journey0of0two0thousand0miles0begins0with0a0single0step.0

!  Fellow#Consultant#!  OOA&D,#Design#PaWerns,#Lean,#Scrum,#TestDDriven#

Development#

!  Over#2/5#century#of#so_ware#development#experience#

!  Author#of#seven#books,#including:#–  0Prefactoring:0Extreme0Abstrac+on,0Extreme0

Separa+on,0Extreme0Readability00(2006#Jolt#Award)#

–  0Interface0Oriented0Design0

–  Lean0Agile0Acceptance0TestIDriven0Development:0BeKer0SoLware0Through0Collabora+on0




Lean Enterprise

Business

Management Team

ASSESSMENTS"CONSULTING"TRAINING"COACHING"

Lean for Executives Product Portfolio Management Business Product Owner

Lean Management Project Management

ILAFYT Kanban / Scrum ATDD / TDD / Design Patterns

technical process


"PaWernDOriented#Development"#

Pa*ern5oriented'development'is'matching''

'the'forces'in'the'problem'''to'the'forces'in'pa*erns'




Purpose#of#this#Course#

!  Present#a#powerful#way#of#analyzing#and#designing#so_ware#!  Incorporates:#

–  Quali8es,#Principles,#and#Prac8ces##–  Design#PaWerns#(seen#in#a#different#way)##

!  Mostly#about#design,#not#implementa8on#!  AWempts#to#change#our#paradigm#of#design#


The#Gang#of#Four#

!  Design#PaWerns##–  Gamma,#Helms,#Johnson,#Vlissides#

–  Known#as#the#Gang#of#Four#(GOF)##!  Based#on#“Timeless#Way#of#Building”#

–  Christopher#Alexander##




Logis8cs#

!  Please#phones#and#pagers#off#(or#to#vibrate)#!  Break#halfway##


Learning#Styles#

! People#have#different#learning#styles#– One#is#not#beWer#than#another#– MisDmatches#cause#communica8on#problems#

– Please#ask#ques8ons#if#examples#are#not#detailed#enough#

~2

See:#hWp://www.netobjec8ves.com/resources/teamDissues/#for#more#informa8on#




Outline#

!  Beginnings##!  Code#Quali8es##!  The#PaWerns#

#


Agenda:#PaWerns#Covered#

!  Strategy#!  Template#Method#

!  Bridge#!  Adapter#!  Façade#!  Abstract#Factory##




The#Pyramid##

Paradigm00

PaKerns0

Wisdom0

Principles0 Prac+ces0

Quali+es##


UML#Summary#

A

B

A

B

A

B

A

B

Aggregation

A aggregates B B is a member of A

A is composed of B A contains B type objects

B implements A A depends upon B A uses B

Composition

Interface Implementation Dependency

Different#ways#to#represent#classes.

Different#rela8onships#between#classes.##Don’t#worry#about#represen8ng#the#difference#between#aggrega8on#and#composi8on.#

From#Design#PaWerns#Explained:#A#New#Perspec8ve#on##ObjectDOriented#Design.#Shalloway#and#TroW#

A

B

B is derived from A A generalizes B

Inheritance




Sequence#Diagram#Summary##

16# ### #16#October#2013#

Beginnings'




Retrospec8on#

!  To#improve,##we#need#to#reflect#– What#worked#

– What#did#not#work#

!  How#can#a#design#accommodate#change?#–  Not#an+cipate#change#


Creeping#Changes##

function() { Do_this; Do_that; Do_something_else; }




Creeping#Changes#(2)##

function(a) { if (a) {

Do_another_thing: //… }

else { Do_this; Do_that; Do_something_else; }

}


Creeping#Changes#(3)##

function(a, b) { if (a) {

if (b) { Do_another_thing:; //… }

else { Do_one_more_thing; //.. }

} else {

Do_this; Do_that; Do_something_else; }

}




Spreadsheet#Conundrum#

2000#rows#10000#columns#32#MB#Flash#Drive##Access#by#individual#byte:##rowNumber#*##sizeofRow#+######columnNumber##Or##columnNumber#*#sizeofColumn##+#####rowNumber##How#will#you#store#it?###By#row?###By#column?#


How#to#organize#?#

Language / Word

ENGLISH GERMAN

NAME Name Namen

CITY City Stadt

POSTAL_CODE Zip PC




Implementa8on#(1)#

String getLabelForNAME(Language l ) { if (l == ENGLISH) return “Name”; else if (l == GERMAN) return “Namen”; else throw Exception(“No translation for language” + l); } // Same for the other words


Implementa8on#(2)#

String getLabelForGERMAN(Word w) { if (w == NAME) return “Name”; else if (w == CITY) return “Stadt”; else if (w == POSTAL_CODE) return “PC”; else throw Exception(“No German translation for word ” + w); } // Same for the other languages



25# ### #16#October#2013#

Code'QualiAes'

c#

Paradigm00PaKerns0

Wisdom0Principles0 Prac+ces0

Quali+es##


Predictability#

!  Cannot#predict#how#requirements#will#change#!  How##to#increase#predic8ve#abili8es?#

–  High#quality#code#easier#to#change#




Discussion#Exercise#

!  Imagine#someone#brings#you#code#to#evaluate#

! What#do#you#look##for#to#decide#if#it#is#easy#to#change?##

! What#recommenda8ons#would#you#make?#


Quali8es#

!  In#PaWernDOriented#Development#–  Focus#is#on:#

Cohesion#Coupling#NonDRedundancy#Encapsula8on#And,#overall,#Testability0




Cohesion#

!  Cohesion##–  “How#closely#opera8ons#in#a#rou8ne#[or#class]#are#related.”##

!  No#"schizophrenic#classes”#doing#more#than#one#thing#!  No#"12Dpage#methods"#

*#Code%Complete,#Steve#McConnell,#1993,#p.#81.#This0concept0was0first0described0by0Larry0Constan+ne0in01975,0but0we0like0McConnell’s0defini+on0best.0

c#

Paradigm00PaKerns0


Quali+es##


Strong#Cohesion##

!  Class#Cohesion##–  Class#has#a#single#responsibility#–  Everything#"about"#fulfilling#that#responsibility#

! Method#Cohesion#–  Each#method#fulfills#only#one#aspect#of#class#responsibility#–  Prac8ce:#Programming#by#inten8on#(next#slide)#

c#

Paradigm00PaKerns0


Quali+es##




Programming#by#Inten8on#

public void printReportOfEmployeesOfCustomer (String CustomerID) { Employee[] emps = getEmployees(CustomerID); if(needsSorting(emps)) sortEmployees(emps); printHeader(CustomerID); printFormattedEmployees(emps); printFooter(CustomerID); paginate(); }

"Private"* Methods

"Sergeant" Method

C#/Java/…

*Note:#These#methods#may#not#be#literally#private,#as#we#may#need#to#make#some#of#them#public#or#protected#for#tes8ng.##But#we#treat0them0as0private#from#client#objects,#to#limit#coupling.#


Alterna8ve#Methods#(Separa8on#of#Concerns)###

public void printReportOfEmployeesOfCustomer (String CustomerID) { Employee[] emps = getEmployees(CustomerID); printReport(CustomerID, emps); } private void printReport(String CustomerID, Employee [] emps) { sortEmployees(emps); printHeader(CustomerID); printFormattedEmployees(emps); printFooter(CustomerID); paginate(); } private void sortEmployees(Employee [] emps){ if(needsSorting(emps)) doSortEmployees(emps); }

C#/Java/…




Programming#by#NonDInten8on#

public void printReportOfEmployeesOfCustomer (String CustomerID) { // Get Employees Employee[] emps …Make series of calls to get employees // Sort Employees … Series of calls to sort // Print Header … Series of calls //… and so forth for lots of lines }

C#/Java/…


Programming#by#Inten8on#

void Report::printReportOfEmployeesOfCustomer (string CustomerID) { vector<Employee> emps = getEmployees(CustomerID); if(needsSorting(emps)) sortEmployees(emps); printHeader(CustomerID); printFormattedEmployees(emps); printFooter(CustomerID); paginate(); }

Private Methods

"Sergeant" Method

C++

*Note:#These#methods#may#not#be#literally#private,#as#we#may#need#to#make#some#of#them#public#or#protected#for#tes8ng.##But#we#treat0them0as0private#from#client#objects,#to#limit#coupling.#




What#Programming#by#Inten8on#Gets#You#

!  Method#Cohesion#!  Separa8on#of#concerns#

–  "Sergeant"#method#calls#other#methods#–  Private#methods##implement#details#

!  Clarity##–  Clear#code#beWer#than#comments##

!  Ease'in'finding/forming'certain'pa*erns'!  No#extra#work#is#required#


Coupling##

!  Coupling###–  “strength#of#connec8on#between#two#rou8nes#[or#classes]”#

!  Object#can#be##–  Loosely#coupled##

! No#dependence#on#other#implementa8ons#

!  (Also#called0inten+onal0coupling)0–  Tightly#coupled##

! Objects#are#interdependent;#–  Change#one#thing;#other#things#change#unpredictably#

!  (Also#called#accidental0coupling)#

c#

Paradigm00PaKerns0


Quali+es##

*#Code%Complete,#Steve#McConnell,#1993,#p.#81.#This0concept0was0first0described0by0Larry0Constan+ne0in01975,0but0we0like0McConnell’s0defini+on0best.0




Coupling#To#Data#

Global#Data#

Func8on#One#

Func8on#Two#

Func8on#Three#

AWributes#

Method#One#

Method#Two#

Method#Three#

Class#


Coupling#To#Other#Classes#

MyClass# YourClass#HerClass#

HisClass#Hard#to#test#Need#to#instan8ate#many#classes#Too#coupled##




No#Redundancy#

!  "One#Rule#in#One#Place"#!  Example#of#viola8on:##Y2K#!  Redundancy#can#be#more#than#state##

–  E.g.#.#redundant#rela8onships#!  Redundancy#causes#maintenance#problems#

!  Before#copying#and#pas8ng,#ask#why?##

c#

Paradigm00PaKerns0


Quali+es##


Redundancy#D#Shalloway’s#Law#

!  From#Al#Shalloway#(CEO#of#Net#Objec8ves)##

!  “When#N#things#need#to#change#and#N>1,#Shalloway#will#find#at#most#ND1#of#these#things.”#

#

!  Shalloway’s'Principle:#“Avoid#situa8ons#where#Shalloway’s#Law#applies”#




Encapsula8on#

!  Hide##–  Data#–  Implementa8on#

!  Other#encapsula8on:#–  Type#

!  Interfaces#hide#their#implemen8ng#classes#–  Design#

! Using#factory#decouples#clients#from#implemen8ng#classes#

!  Details#expanded#in#next#slides##

c#

Paradigm00PaKerns0


Quali+es##


Encapsulate#by#Policy,#Reveal#by#Need#

! What#is#encapsulated#is#–  Decoupled#–  Freely#changeable#

! Never#know#what#might#want#change#

!  Easier#to#deDencapsulate#than#encapsulate#later#–  So#encapsulate##

#




Abstrac8on#

!  Abstrac8on#encompasses#encapsula8on#–  Think#about#what#you#want#done,#not#how#you#want#it#done##

!  “When#You’re#Abstract,#Be#Abstract#All#the#Way”#–  Never#use#a#primi8ve#(except#in#constructors)#

!  Example#next#page##

Paradigm00PaKerns0


Quali+es##


Dollar#Abstrac8on#

!  Dollar#as#double##–  double#interestRate;##–  double#balance;#–  double##interest#=#balance#*#interestRate#;#

!  Dollar#class###–  Dollar#mul8plyBy(Percentage#p)#

–  Dollar#add(Dollar#other)#–  Dollar#mul8plyBy(Dollar#d);#

–  Dollar#add(Percentage#p);##Percentage#interestRate;#

Dollar#balance;##

Dollar#interest#=#balance.mul8plyBy(interestRate);##

#




Observa8on#

!  Reversible#changes#are#o_en#not#equal#in#difficulty#!  Usually#easier#to#deDobjec8fy#for#performance#than#it#is#to#objec8fy#for#code#quality##

!  Example:#–  Dollar#balance#"#double#balance;##

–  double#balance##"#Dollar#balance;#


Redundancy#

Class A

-Redundant Issue

Class B

-Redundant Issue

Class A and Class B:

Have redundant state or functionality

Redundant issue inside each class

How to resolve redundancy?

c#

Paradigm00PaKerns0


Quali+es##




It#Depends!*#

Depends#on#rela8onship#between#classes#–  Conceptual?###

!  Are#A#and#B#varia8ons#of#common#concept?#

or#–  Rela8onship#of#consistent#use?###

!  A#and#B#have#a#need#that#is#resolvable#in#a#common#way?#

Class A

-Redundant Issue

Class B

-Redundant Issue

*#©2007#All#Consultants#Everywhere#


Using#Inheritance#

Class A Class B

Inheritance

Classes coupled to superclass

SuperClass

#Redundant Issue Conceptual

Concrete




Using#Delega8on#

Class A

Class B

Delega+on.##

Class C

Redundant Issue


Comparing#These#Op8ons#

!  Inheritance:#– May#not#be#possible###

!  Classes#may#already#have#superclass##

– May#make#superclass#less#cohesive#

!  Delega8on:#–  Available#if#other#en88es#need#behavior#

!  Favor'delegaAon'over'inheritance''(GOF)''Paradigm00PaKerns0


Quali+es##




Testability#

! Difficult#to#unitDtest#code#is#o_en:#– Tightly#Coupled#

! “I#cannot#test#this#without#instan8a8ng#half#the#system"#

– Weakly#Cohesive#! #"This#class#does#so#much,#the#test#will#be#enormous#and#complex!"#

– Redundant#! #"I'll#have#to#test#this#in#mul8ple#places#to#ensure#it#works#everywhere"#

c#

Paradigm00PaKerns0


Quali+es##


The#Role#of#Testability#

!  Unit#tes8ng#is#good#!  If##you#don’t#do#unit#test##

–  Always#ask#"if#I#were#to#test#this,#how#would#I#do#it?"#–  If#design#is#hard#to#test##

! Ask#"why#isn't#this#more#testable?"#

!  It's#a#significant#trim#tab#(see#next#slide)#

c#

Paradigm00PaKerns0


Quali+es##




Trim#Tabs#

"If you try to change the course of a supertanker by pushing at the bow you will not see any change.

If you push on the rudder your chances of changing the course of the supertanker are guaranteed, but the amount of energy needed is still prohibitive.

To be the most effective we need to push on the trim tabs, those small fins on the end of the rudder.

By moving them, the rudder in turn moves and the tanker makes its turn.”

R. Buckminster Fuller "Critical Path"

~2 54# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Standards#for#High#Quality#Code#(Review)#

High#quality#code#(in#order#of#importance):#!  Testable''!  Contains#no#redundancy''!  Inten8onal#coupling,#strong#cohesion,#encapsulaAon'!  Clarity'

–  Inten8onDrevealing#names#

–  Adhere#to#a#coding#standard#



55# ### #16#October#2013#

A'Design'Exercise''


Exercise##

!  Exis8ng#Chip#object#–  Gets#status#of#hardware#–  Encrypts#status##–  Sends#status#to#monitoring#applica8on#

!  Now#need:#–  Different#encryp8on#algorithms##

!  For#different#customers#

! Or#perhaps#different#8me##

!  How#can#we#can#handle#this#varia8on?#

Chip

+getAndSendStatus() -getStatus() -encrypt() -send()

-ChipID:String

Note:0I0am0not0asking0for0the0best0way0to0handle0this,0just0for0the0possible0ways0

Please#don't#turn#the#page#un8l#instructed#to#do#so…#




Blank#Slide#

!  One#more#uninten8onally#blank#slide#


Blank#Slide#

!  Another#inten8onally#blank#slide#

!  Don’t#look#ahead#




Blank#Slide#

!  S8ll#another#inten8onally#blank#slide#

60# ### #16#October#2013#

AlternaAves'Approaches'To'Design'Exercise'




Different#Strategies#to#Follow#

!  Best/Worst#Case##–  Everyone#can#upgrade#to#the#new#encryp8on#

!  Copy#and#paste##–  Start#with#fresh#code,#just#make#needed#changes#

!  Use#a#switch##–  Add#switch#to#exis8ng#code#that#specifies#encryp8on#

!  Inheritance##–  Specialize##class#containing#encryp8on#code#–  Override##encryp8on#method#to#use#new#encryp8on#

!  Delega8on#–  Encryp8on#code#in#own#class##–  Different#versions#of#encryp8on#class.###–  Clients#refer#to#appropriate#encryp8on#object#

!  Func8on#pointers#in#C++;##delegates#in#C##62# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Ways#to#Handle#New#Func8on:#Switches#

! Chip#has#switch#based#on#value#given#by#Client#– Pro:##

! Simple,#obvious#implementa8on#

– Con:##! If#new#encryp8on#algorithm#

– Must#maintain#Chip#

! Cohesion#in#Chip#is#weakened#! May#get#“switch#creep”#

– Switches#are#not#a#good#longDterm#solu8on#




Switch#Creep#

switch (nation) {!!case US:!! !// us version!!case MEXICO:!! !// Mexican version!

!case CANADA:!! !// Canadian version!

!!

switch (nation) {!!case US:!! !// us version!!case MEXICO:!! !// Mexican version!!case CANADA:!! !// Canadian version!

}!!

Pseudocode


Ways#to#Handle#New#Func8on:#Inheritance#

!  Subclass#Chip:#–  Chip#has#original#encryp8on#(64#bit)#–  Subclass#is#Chip128E#

!  Or#Make#Chip#an#abstract#class#–  Implemen8ng#subclasses:#

! Encrypt#0##(no#encryp8on)#! Encrypt#64#! Encrypt#128#

– Most#func8onality#inherited#! Override#encrypt()#

Chip + getAndSendStatus() # encrypt()

Chip64E # encrypt() Chip128E

# encrypt() Chip0E

# encrypt()




Problems#With#Inheritance#

!  Inheritance#works##for#one#varia8on#–  Not#for#two#

!  E.g.#what#if#sending#also#varies?###!  Subclassing#is#sta8c##!  How#change#Chip#from#Encrypt64#to#Encrypt128?#

–  Need#to#transfer#internal#state##


Combinatorial#Explosion#


Chip64E # encrypt() Chip128E

# encrypt()

# send()

# send() # send()

Chip128ETCP Chip128EFTP # send() # send()

Chip64ETCP Chip64EFTP # send() # send()

Redundancies

Cohesion getting worse

and worse

-ChipID




Delega8on#


PGP64 +encrypt()

PGP128 +encrypt()

Encryptor +encrypt()

-myEncrypt

Paradigm00PaKerns0


Quali+es##


Delega8on#Scales#

Chip

+ getAndSendStatus() # encrypt() PGP64

+encrypt() PGP128

+encrypt()


-mySend -myEncrypt

TCPIP +send()

FTP +send()

Sender +send()

# send()




Refactoring:##The#Tradi8onal#View#

!  Refactoring#usually#is#for#legacy#code#–  Seen#as#cleaning#up#bad#code#–  True,#but#not#complete#

!  Refactor#code#to#issue#that#has#become0a0varia+on0–  Improvement#in#light#of#new#requirements#

“Adventure”# hWp://benfry.com/distellamap/# 70# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Refactoring#(1)#

public class Chip { private String chipID; public Chip(String aChipID) { this.chipID = aChipID; } public void getAndSendStatus() { String status = getStatus(chipID); String encryptedStatus = encrypt(status); send(encryptedStatus); } private String getStatus(String chipID) { // get status from the real chip } private String encrypt(String status) { // encryption algorithm here } private void send(String status) { // sending behavior here }

}

Original'code'




Refactoring#(2)#

// All elided code is unchanged from previous slide public class Chip {

private String chipID; private Encrypt myEncrypt; public Chip(String aChipID) { this.chipID = aChipID; this.myEncrypt = new PGP64(); } private String encrypt(String status) { return myEncrypt.encrypt(status); }

}

Delega8on#“Extract#Class”#

and#“Extract#Interface”#


Enhancement###

Adding'new'encrypAon'is'enhancement,'not'refactoring'




Factory###

Encryptor getEncryptor(CustomerType customer) { switch (customer)

{ case C1:

return new PGP64(); case C2:

return new PGP128(); default:

return new PGP0(); } }

//In Chip

public Chip(String aChipID, Customer customer) { this.chipID = aChipID;

this.myEncrypt = getEncryptor(customer); }


Strategy#Injec8on##(1)#

•  Constructor injection class Chip {

private Encryptor enc; public Chip(Encryptor encrypt) {

this.enc = encrypt; }

private void encrypt() { this.enc.encrypt(); } public void getAndSendStatus() { encrypt() // and other calls

}





•  Parameter injection class Chip {

public Chip() { }

public void getAndSendStatus(Encryptor enc) {

enc.encrypt(); // and other calls }

}



•  Setter injection class Chip { private Encryptor enc;

public Chip() { } public void setEncryptor(Encryptor encrypt) { enc = encrypt; } public void getAndSendStatus() {

enc.encrypt(); // and other calls }

}




Injec8on#With#Mul8ple#Strategies###

// Multiple strategies, constructor injection // Chip has constructor Chip(Encryptor e, Sender s) Chip getChip(CustomerType customer)

{ switch(customer) { case C1: return new Chip(new PGP64(), new TCPIP()); case C2: return new Chip(new PGP128(), new TCPIP()); default: return new Chip(new PGP0(), new FTP()); } }

78# ### #16#October#2013#

Advice'from'the'Gang'of'Four'




Gang#of#Four#Gives#Us#Guidelines*#

!  Open/Closed'Principle'!  Design'to'interfaces'!  Favor'delegaAon'over'class'inheritance'!  Encapsulate'concept'that'varies''

#

*'Gamma,#Helms,#Johnson,#Vlissides:#The#authors#of#Design%Pa2erns:%Elements%of%Reusable%Object<Oriented%Design%

Paradigm00PaKerns0


Quali+es##


The#OpenDClosed#Principle#

!  So_ware#en88es#should#be:#–  Open#for#extension#–  Closed#for#modifica8on##

!  In#short:#–  Design#modules#so#that#they#never#change##–  Add#new#modules#to#handle#changed#requirements#–  Not#always#achievable##

!  Bertrand#Meyer:##–  So_ware#en88es#(classes,#modules,#func8ons,#etc.)#should#be#open#for#

extension,#but#closed#for#modifica8on”#

!  Ivar#Jacobson#:###–  “All#systems#change#during#their#life#cycles.##This#must#be#borne#in#mind#

when#developing#systems#expected#to#last#longer#than#the#first#version”#A#good#ar8cle#on#the#OpenDClosed#Principle:#www.objectmentor.com/publica8ons/ocp.pdf#

c#

Paradigm00PaKerns0


Quali+es##




Design#to#Interfaces#

InterfaceA

Impl1 Impl2 Impl3

Interface B

Impl4 Impl5

Relationship

Relationship

Want#1→1#or#1→many#rela8onships#between#abstrac8on#

Not#n→m#rela8onships#between#implementa8ons#

Paradigm00PaKerns0


Quali+es##


Favor#Delega8on#Over#Inheritance#

!  Define#interface#encapsula8ng#varia8on#!  Delegate#to#concrete#class#implemen8ng#interface#

1. Decoupling concepts 2. Defer decisions until runtime 3.  Small performance hit

Delegation

The "Strategy Pattern"


PGP64 +encrypt()

PGP128 +encrypt()


-myEncrypt

Paradigm00PaKerns0


Quali+es##




Treat#Conceptually#Similar#Things#the#Same#Way#

!  Deal#with#things#at#an#abstract#level#!  Encapsulate#that#which#varies#

Impl4

AbstractionA

Impl1 Impl2 Impl3

Client

Closed is abstraction

Open are implementations

Paradigm00PaKerns0


Quali+es##


Find#What#Varies#and#Encapsulate#It#

!  GoF#meant#a#varying#anything:0–  Varying#design#–  Varying#object#crea8on#–  Varying#rela8onships#(1D1,#1Dmany)#–  Varying#sequences#and#workflows#–  Etc…#




This#Advice#Promotes#Quality#

Cohesive#

Decoupled#Reusable#

(eliminates#Redundant#Implementa8on)#

Encapsulated#


Design#PaWerns#Are#Examples0

!  Each#paWern:#–  Example#of#a#design#following#general#advice#

–  Discovered,#not#invented#–  Example#in0a0given0context#



87# ### #16#October#2013#

The'Strategy'Pa*ern'


The#Strategy#PaWern#

!  Issue:#–  Need#different#behavior#at#different#8mes#

!  GoF#Intent:##–  Define#a#family#of#algorithms,#encapsulate#each#one,#and#make#them#interchangeable##

–  Algorithm#vary#independently#from#clients#using#it#*#

#

*Design%Pa2erns,%Elements%of%Reusable%Object<Oriented%So?ware,#Gamma,#Helm,#Johnson,#Vlissides#

Paradigm00PaKerns0Wisdom0


Quali+es##




The#Canonical#Strategy#PaWern#

Java/C# // in Client: Strategy myStrategy=

Factory.getStrategy() . . . myContext.request( myStrategy) // in Context: request ( Strategy myStrategy) { myStrategy.algorithm() }

StrategyA + algorithm()

StrategyB + algorithm()

Context + request(Strategy)

Strategy + algorithm()

Client

C++ // in Client: Strategy *myStrategy=

Factory.getStrategy() . . . myContext.request( myStrategy) // in Context Context::request ( Strategy myStrategy) { myStrategy->algorithm() }


Handling#Varia8ons#

!  Factory#creates#different#objects#having#common#interface##(polymorphism)##–  Factory#is#cohesive##D##only#deals#with#instan8a8on#

!  Client#decoupled#from#actual#objects#




Strategy#PaWern#with#a#Factory#

*#


Code#Examples#for#this#Approach#

class Client () { Encryptor myEncrypt; myEncrypt= Factory.getEncryptor(); // get proper derivation to use

Chip myChip= new Chip(); myChip.getAndSendStatus(myEncrypt); } class Chip () { //... public void getAndSendStatus( Encryptor anEncrypt) {

//... anEncrypt.doEncrypt(s); // ... } } // Encrypt is an interface or abstract class with a doEncrypt method.

// Have different classes implement this, each with a doEncrypt method.

C#/Java

~2




Code#Examples#for#this#Approach#

public void main () { Encryptor * myEncrypt; myEncrypt= Factory::getEncryptor(); // get proper derivation to use Chip myChip; myChip->getAndSendStatus( myEncrypt); } // in Chip.h class Chip () { public void getAndSendStatus( Encryptor *); } // in Chip.cpp ... void Chip::getAndSendStatus( Encryptor *anEncrypt) { ... anEncrypt->doEncrypt(s); ... } } // Encrypt is an interface or abstract class with a doEncrypt method. // Have different classes implement this, each with a doEncrypt method.

C++


What#Happens#Now#with#Changing#Requirements#

!  If#new#encryp8on#requirement:##–  1.)#Create#new#class#implemen8ng#encryp8on#

–  2.)#Modify#Factory#to#return#new#class#–  3.)#Nothing#else!#




Creeping#Changes#(Review)#

function(a, b) { if (a) {

if (b) { Do_another_thing:; //… }

else { Do_one_more_thing; //.. }

} else {

Do_this; Do_that; Do_something_else; }

}


Switch#Version#(1)#enum WhatToDo {Do_original, Do_another_thing, Do_one_more_thing}; class DoSomething { static void process(WhatToDo wtd) { switch(wtd) { case Do_original: Do_this; Do_that; Do_something_else; break; case Do_another_thing:

Do_another_thing; //.. break;

case Do_one_more_thing: Do_one_more_thing; //… break;

} }




Switch#Version#(2)#

// Separate what to do from doing it WhatToDo factory(a, b) { if (a){

if (b) return Do_another_thing;;

else return Do_one_more_thing; }

else return Do_original; }

class Client {

WhatToDo wtd = factory(a, b); DoSomething.process(wtd); }


Switch#Version#with#Func8ons###class DoSomething { static void process(WhatToDo wtd) { switch(wtd) { case Do_original: DoOriginal(); break; case Do_another_thing:

DoAnotherThing(); break; case Do_one_more_thing: DoOneMoreThing(); break; } } static void doOriginal() { Do_this; Do_that; Do_something_else; } static void doAnotherThing() {

Do_another_thing; //.. } static void DoOneMoreThing() {

Do_one_more_thing; //… }




Convert#To#Strategy#

! Separate#what#to#construct#from#using#it##– Separate#policy#from#implementa8on#– Create#factory#to#return#implementa8on#of#interface#

#interface DoSomething{ void process(); };


Convert#To#Strategy#(2)#class Do_original implements DoSomething { void process()

Do_this; Do_that; Do_something_else; } };

class Do_another_thing implements DoSomething { void process() { Do_another_thing; //… } };

class Do_one_more_thing implements DoSomething { void process() { Do_one_more_thing; //… } };




Convert#To#Strategy#(2)#

DoSomething factory(a, b) { if (a){ if (b)

return new Do_another_thing(); else return new Do_one_more_thing(); } else return new Do_original();

} class Client { public void some_method() { DoSomething ds = factory(a, b); ds.process(); } }


Select#Strategy#with#a#Table#

A# B# Return##

True# true# Do_another_thing#

True# false# Do_one_more_thing#

False# true# Do_original#

False# False# Do_original#



103# ### #16#October#2013#

The'Template'Method'Pa*ern'

~2



Quali+es##


The#Template#Method#PaWern#

!  Issue:#–  Abstract#common#theme#from#cases#with#different#implementa8ons#

!  GoF#Intent:##–  Define#skeleton#of#an#algorithm#in#an#opera8on,#deferring#some#steps#to#subclasses.###

–  Template#Method#lets#subclasses#redefine#certain#steps#of#an#algorithm#without#changing#the#algorithm’s#structure*#

!  Analogy##–  Hollywood#–#“Don’t#call#us,#we’ll#call#you”##


~2




Print#Report##

class Report { public void printReportOfEmployeesOfCustomer (String CustomerID) { Employee[] emps = getEmployees(CustomerID); if(needsSorting(emps)) sortEmployees(emps); printHeader(CustomerID); printFormattedEmployees(emps); printFooter(CustomerID); paginate(); } //.. Implementation methods here }


Commonali8es#/#Variabili8es#

~2

Commonality#

Variabili8es#

printHeader(CustomerID);

printFooter(CustomerID);

printHeader(CustomerID); // Brief Header // Full Header

printFooter(CustomerID); // Brief Footer // Full Footer




Template##PaWern#

BriefHeaderReport

#printHeader();

#printFooter();

FullHeaderReport

#printHeader();

#printFooter();

Report +printReportOfEmployeesOfCustomer()

#getEmployees(CustomerID);

#sortEmployees();

#printHeader();

#printFormattedEmployees();

#printFooter();

#paginate();


Template#Method#Code#Example#

abstract class Report { public void printReportOfEmployeesOfCustomer (String customerID) { // … printHeader(customerID); printFooter(customerID); } abstract protected void printHeader(ID id); abstract protected void printFooter(ID id); } class BriefHeaderReport extends Report { protected void printHeader(ID id) { //. Code here } protected void printFooter(ID id) { //.. Code here } }




"Canonical"#Template#Method#

Client

ConcreteClassB

#Operation1() #Operation2()

TemplateMethod: … Operation1() … Operation2() …

AbstractTemplate +TemplateMethod()


~2

ConcreteClassA



Strategy##PaWern#

BriefHeader

printHeader();

printFooter();

FullHeader

#printHeader();

printFooter();

Report +printReportOfEmployeesOfCustomer()

#getEmployees(CustomerID);

#sortEmployees();

#printHeader();

#printFormattedEmployees();

#printFooter();

#paginate();

Header

printHeader();

printFooter();




Exercise#

!  There#could#be#a#separate#strategy#for#both#header#and#footer.###

! What#are#the#tradeoffs#between#the#Template#Method#and#the#two#versions#of#the#Strategy#paWern#(header/footer#in#one,#header/footer#separate)##


Template#Example#in#MFC#

Windows#System## Applica8on##ac8vate#

Window##ac8vate()##{draw();}#draw();###close()#minimize()#//#fi_y#more#(with#default#implementa8on)##

MyWindow##draw()#{#//#mydrawing;}##



113# ### #16#October#2013#

Design'Pa*erns'



Quali+es##


A#PaWern#in#Carpentry#

!  Two#carpenters#are#building#a#chest#of#drawers#!  One#says#to#the#other:#“should#we#build#the#joint#by#first#cuÑng#down,#then#cuÑng#up#at#a#45#degree#angle...”#

!  “then#back#down#and#back#up### #the#other#way,#then#back#down”#

!  “And#keep#this#up#un8l#done”#!  This#is#“doveDtail#joint”##




DoveDTail#


A#Miter#Joint#

Commonly#used#in#picture#frames#




PaWerns#Work#At#All#Levels#

Dovetail' Miter'

Forces' Strong,#HighDCost,#Decora8ve,#Humidity#Tolerant#

Weak,#Cheap,#Fast,#Good#for#Picture#Frames#

Design' Interlaced#joint# Single#AbuÑng#Cut#

ImplementaAon' Cut#teeth,#.5"#long,#.4"#deep,#match#teeth#to#gaps#

45#degree#angle#cut#aWached#with#staple#or#other#spanning#connector#


Common#Reasons#to#Study#PaWerns#

!  ReDuses#others’#experience#–  some8mes#results#in#quick#solu8on#

!  Designs#improved#for#modifiability#–  Embrace#change#

!  Use#common#terminology#–  Improve#and#elevate#communica8on#

!  PaWerns#are#great#examples#of#powerful#OO#




What#Are#PaWerns?#

!  PaWern:#–  Collec8on#of#proven#prac8ces#for#a#recurring#problem#in#a#given#context#

!  Design#paWerns##–  Describe#rela8onships#between#en88es#(objects)#in#a#problem#domain#

!  PaWerns#–  Handle#varia8ons#in#behavior#–  Use#interfaces#

!  PaWerns#have#forces##–  Contextual#forces#–#to#determine#what#paWern#to#use#–  Implementa8on#forces#–#how#to#create#the#paWern##–  Consequen8al#forces#–#what#happens#when#paWern#is#used##

!  PaWerns#emphasize#importance#of#abstrac8ons#–  …but#do#not#address#how#to#iden8fy#the#right#ones…#

120# ### #16#October#2013#

AbstracAon'

Paradigm00PaKerns0


Quali+es##




Consider#These#

Mop'''''''''''''''''''''''''Broom''''''''''''''Sponge'

The#same?##Different?#


“It0Depends!”#

!  As#specific#objects:##–  Different#

!  As#a#concept#(abstrac8on):#–  All#Cleaning#Tools#

!  Are#there#other#abstrac8ons#with#different#commonality?##

! Which#abstrac8ons#are#useful?#####




Various#Concepts#

Cleaning#Tool#cleanSomething()#

Mop#

Floor#Cleaning#Tool#cleanFloor()#

Water#Cleaning#Tool#removeWater()#

Mop#Mop#Broom# Broom#Sponge# Sponge#

ItemsToStore#size()#

Mop# Broom# Sponge#

ItemsForSale#price()#

Mop# Broom# Sponge#

All#Yellow#Items#


High#Abstrac8on##

!  Higher#abstrac8ons#are#longer#life##–  (But#can#be#less#useful)#

!  Example:#–  Abstrac8on###

!  Automobile##–  Prepare#for#following##–  Follow#a#course###

!  Implementa8ons:#–  Turn#on#with#key##/###Push#a#buWon##–  Steer#with#wheel,#speed#with#pedals#/###Use#a#joys8ck###




What#Is#the#Right#Abstrac8on?##

!  The#United#Kingdom#"could#be#seen#as#economy#by#economists,#a#society#by#sociologists,#a#threaded#chunk#of#nature#by#conserva8onists,#a#tourist#aWrac8on#by#some#Americans,#a#military#threat#by#rulers#of#the#Soviet#Union,#and#the#green,#green#grass#of#home#to#the#more#roman8c#of#us#Britons".#

!  Flood#and#Carson#!  "Why#is#a#light#bulb#like#Doonesbury?"#

–  Neither#one#can#whistle#


CommonalityDVariability#Analysis#

!  Abstrac8on##focuses#on#commonality#(general)#!  DeDemphasize#variable#details##(specifics)#.#!  Acknowledgement:##

–  Commonality#–#Variability#Analysis#in#James#Coplien’s#Mul8Dparadigm#Design#for#C++#

His#thesis#is#on#line#at#hWp://www.netobjec8ves.com/download/CoplienThesis.pdf#

c#

Paradigm00PaKerns0


Quali+es##

His#thesis#is#on#line#at:#hWp://www.netobjec8ves.com/files/CoplienThesis.pdf#(link#is#caseDsensi8ve)#




Commonali8es#and#Variability#

!  Commonali8es#can#define#basic#domain#concepts#(abstrac8ons)#–  Recognized#from#experience#–  Learned#through#analysis#(abstracted)#

!  Variability#is#varia8on#of#commonality#(abstrac8on)##

*'MulB<Paradigm%Design%in%C++,#Jim#Coplien#

128# ### #16#October#2013#

The'Bridge'Pa*ern'




The#Bridge#PaWern#

!  GoF#Intent:##–  DeDcouple#an#abstrac8on#from#its#implementa8on#so#that#the#two#can#vary#independently#*##

!  First#an#example##




Quali+es##


Rectangle#Drawing#Program#

Rectangle + draw() # drawLine(x1,y1,x2,y2)

DP1 + draw_a_line(x1,y1, x2,y2) + draw_an_arc(x, y, r, a1, a2)

Client

V1Rectangle # drawLine(x1,y1 x2,y2)

V2Rectangle # drawLine(x1,y1 x2,y2)

DP2 + drawline(x1,x2,y1,y2) + drawarc(r, x, y, a1, a2)




Code#Example#abstract class Rectangle { private double_x1, _y1, _x2, _y2; public Rectangle(double x1, double y1, double x2, double y2){ .. } void public Draw () { DrawLine(_x1,_y1,_x2,_y1); DrawLine(_x2,_y1,_x2,_y2); DrawLine(_x2,_y2,_x1,_y2); DrawLine(_x2,_y1,_x1,_y1); } abstract void DrawLine( double x1, double y1, double x2, double y2); } class V1Rectangle : Rectangle { void override DrawLine( double x1, double y1, double x2, double y2) { DP1.draw_a_line( x1,y1,x2,y2); } } class V2Rectangle : Rectangle { void override DrawLine(double x1, double y1, double x2, double y2) { DP2.drawline( x1,x2,y1,y2); } }

C#


Code#Example#

abstract class Rectangle { private double_x1, _y1, _x2, _y2; public Rectangle(double x1, double y1, double x2, double y2){ .. } void public draw () { drawLine(_x1,_y1,_x2,_y1); drawLine(_x2,_y1,_x2,_y2); drawLine(_x2,_y2,_x1,_y2); drawLine(_x2,_y1,_x1,_y1); } abstract void drawLine( double x1, double y1, double x2, double y2); } class V1Rectangle extends Rectangle { drawLine( double x1, double y1, double x2, double y2) { DP1.draw_a_line( x1,y1,x2,y2); } } class V2Rectangle extends Rectangle { drawLine(double x1, double y1, double x2, double y2) { DP2.drawline( x1,x2,y1,y2); } }

Java




Code#Example#

class V1Rectangle : public Rectangle { … } class V2Rectangle : public Rectangle { … } void Rectangle::draw () { drawLine(_x1,_y1,_x2,_y1); drawLine(_x2,_y1,_x2,_y2); drawLine(_x2,_y2,_x1,_y2); drawLine(_x1,_y2,_x1,_y1); } void V1Rectangle::drawLine (double x1, double y1, double x2, double y2) { DP1::draw_a_line( x1,y1,x2,y2); } void V2Rectangle::drawLine (double x1, double y1, double x2, double y2) { DP2::drawline( x1,x2,y1,y2); }

C++


Get#New#Requirements#

!  Now#have#Circles#!  Handle#similarly##

– Make##V1Circle#and##V2Circle#

!  Decouple#client#from#specific#shapes##–  Derive#specific#shapes#from#base#class#




Handling#New#Shape#Class#

Rectangle +draw()

Shape +draw()

Client

Circle + draw()

V1Rectangle # drawLine(x1, y1, x2, y2)


V1Circle #drawArc(x,y,r,a1,a2)

V2Circle # drawArc(x,y,r,a1,a2)

DP2 + drawline(x1, x2, y1, y2) + drawarc( r,x, y, a1,a2)

DP1 + draw_a_line(x1, y1, x2, y2) + draw_an_arc(x, y, r, a1, a2)


Code#Example#

interface Shape { public void draw(); } abstract class Rectangle : Shape { private double _x1,_y1,_x2 _y2; public override void draw() { drawLine(_x1, _y1, _x2, _y1); drawLine(_x2, _y1, _x2, _y1); drawLine(_x2, _y2, _x1, _y2); drawLine(_x1, _y2, _x1, _y1); } abstract void drawLine( double x1, double y1, double x2, double y2); } } class V1Rectangle : Rectangle { public override void drawLine( double x1, double y1, double x2, double y2){ DP1.draw_a_line(x1,y1, x2, y2); } }

class V2Rectangle : Rectangle { public override void drawLine( double x1, double y1, double x2, double y2){ DP2.drawline(x1, x2, y1, y2); } } abstract class Circle : Shape { private double _x, _y, _r; public override void draw () { drawArc( _x, _y, _r, 0, 360); } abstract void drawArc( double x, double y, double r, double a1, double a2); } class V1Circle : Circle { protected override void drawArc(double x, double y, double r, double a1, double a2){ DP1.draw_an_arc(x,y,r,a1,a2); } } class V2Circle : Circle { protected override void drawArc(double x, double y, double r, double a1, double a2){ DP2.drawarc(_r,_x,_y,a1,a2); } }

C#




Code#Example#

interface Shape { public void draw(); } abstract class Rectangle implements Shape { private double_x1,_y1,_x2,_y2; public void draw() { drawline(_x1, _y1, _x2, _y1); drawline(_x2, _y1, _x2, _y1); drawline(_x2, _y2, _x1, _y2); drawline(_x1, _y2, _x1, _y1); } abstract void drawline( double x1, double y1, double x2, double y2); } class V1Rectangle extends Rectangle { public void drawline( double x1, double y1, double x2, double y2){ DP1.draw_a_line(x1, y1, x2, y2); } }

class V2Rectangle extends Rectangle { public override void drawLine( double x1, double y1, double x2, double y2){ DP2.drawline(x1, x2, y1, y2); } } abstract class Circle implements Shape { private double _x, _y, _r; public draw () { drawArc( _x, _y, _r, 0, 360); } abstract void drawArc( double x, double y, double r, double a1, double a2); } class V1Circle extends Circle { protected void drawArc( double x, double y, double r, double a1, double a2){ DP1.draw_an_arc(x,y,r,a1,a2); } } class V2Circle extends Circle { protected void drawArc( double x, double y, double r, double a1, double a2){ DP2.drawarc(_r,_x,_y,a1,a2); } }

Java


Code#Example#

void Shape::draw () {} void Rectangle::draw () { drawLine(_x1,_y1,_x2,_y1); drawLine(_x2,_y1,_x2,_y2); drawLine(_x2,_y2,_x1,_y2); drawLine(_x1,_y2,_x1,_y1); } void V1Rectangle::drawLine ( double x1, double x2, double y1, double y2) { DP1::draw_a_line(x1,y1,x2,y2); } void V2Rectangle::drawLine ( double x1, double x2, double y1, double y2) { DP2::drawline(x1,x2,y1,y2); }

void Circle::draw () { drawArc( _x, _y, _r, 0, 360); } void V1Circle::drawArc( double x, double y, double r, double a1, double a2) { DP1::draw_an_arc(x, y, r, a1,a2); } void V2Circle::drawArc ( double x, double y, double r, double a1, double a2) { DP2::drawarc( r, x, y, a1, a2); }

C++




Redundant#Rela8onships#

Rectangle +draw()

Shape +draw()

Client

Circle + draw()



V1Circle #drawArc(x,y,r,a1,a2)

V2Circle # drawArc(x,y,r,a1,a2)

DP2 + drawline(x1, x2, y1, y2) + drawarc( r,x, y, a1,a2)

DP1 + draw_a_line(x1, y1, x2, y2) + draw_an_arc(x, y, r, a1, a2)

6264#


Did#We#Resolve#the#Redundancy?#




Problems#with#this#Approach#

!  Doesn’t#scale#well#–  Another#Shape#"#3#*#2#implementa8ons#–  Number#implementa8ons#=#########number#of#Shape#types#8mes#number#of#drawing#programs#

!  Redundant#–  Drawing#with#each#shape#involves#duplica8on#–  Redundancies#between#V1Rectangle#and#V2Rectangle,#etc…#

!  Confusing#and#complex#–  Poor#cohesion#makes#classes#hard#to#follow#


Intent#Makes#Sense#Now#

!  GoF#Intent:##–  DeDcouple#an#abstrac8on#from#its#implementa8on#so#that#the#two#can#

vary#independently#*##!  Abstrac8on:##

–  Main#enAty#that#client#is#aware#of.#–  E.g.#Shape#

!  Implementa8on:##–  Way#that#main#en8ty#fulfills#one#aspect#of#its#responsibili8es.##–  E.g.##drawing#behavior#–#Drawing#

!  In#other#words:#–  Way#to#add#new#Shapes#OR#new#Drawing#Programs#without#affec8ng#the#

other#





Discovering#the#Bridge#PaWern#

!  Discover#the#Bridge#paWern#by:#–  Find#commonali8es#and#how#they#vary##–  Represent#common#concepts#with#abstrac8ons#(interfaces)#– Make#concrete#class#for#each#varia8on##

!  Then:#–  Observe#how#abstrac8ons#relate#–  Pick#rela8onship#with#beWer#code#quali8es#


We#Have#the#Following#Commonali8es#

!  Shape#class#=#abstrac8on#with#varying#behavioral#implementa8ons#

!  Commonality#Variably#Analysis#separates#issues#into#isDa#rela8onships#

Shape

+draw()

Drawing

+drawLine()+drawCircle()+drawArc()0




Derive#Varia8ons0

Shape

+draw()

Rectangle

+draw()

Drawing

+drawLine()+drawCircle()

V2Drawing


V1Drawing


Circle

+draw()

+drawArc()0

+drawArc()# +drawArc()#


Determine#Remaining#Rela8onships0

Shape

+draw()

Rectangle

+draw()

Drawing


V2Drawing


V1Drawing


Circle

+draw()

Each side should "Design to Interfaces”

Which Way?




Use#Quali8es#to#Define#Rela8onship#

! Ways#the#two#sides#can#relate:#–  Shapes#use#drawing#programs#

–  Drawing#programs#draw#shapes#–  Third#object##gets#shape#and#drawing#program##

! Which#way#is#beWer?#–  Score#with#quali8es#–  BeWer#quali8es#"#beWer#design##


Another#Quality#D#Asser8veness##

!  Asser8veness###–  Don’t#ask#ques8ons#of#an#object##–  Assert#that#an#object#should#do#something#

!  Example#on#next#slide#

c#

Paradigm00PaKerns0


Quali+es##




Inquisi8ve#

class Date { int getMonth(); int getDay(); int getYear(); }

Date d = new Date(); String output = d.getMonth() + “/” + d.getDay() + “/” +

d.getYear();


Asser8ve#

class Date { String getAsString() { ] }

Date d = new Date(); String output = d.getAsString();

#




Scoring#–#Fill#It#In#

Shapes#use#DP# DP#given#Shape# 3rd#Module#

Loose#Coupling#

Strong#Cohesion#

No#Redundancy#

Encapsula8on#

Testable#

Asser8ve#

Focus#


Shapes#Using#Drawing#Programs#

: Client : Rectangle : DP1

1: draw

2: drawLine

3: drawLine

4: drawLine5: drawLine




Drawing#Programs#Using#Shapes#

: Rectangle : Client : DP1

1: draw( Shape s)

2: What kind of shape?

3: I'm a rectangle

4: Give me your line 1 info

5: Draw it


7: Draw it


9: Draw it


11: Draw it


Control#Program#Using#Shapes#

: Client : ControlPrgm

: Rectangle : DP1

1: draw( Shape, DP)

2: what kind of shape?

3: I'm a rectangle

4: give me your line 1 info

5: drawLine


7: drawLine


9: drawLine


11: drawLine




Scoring#

Shapes#use#DP# DP#given#Shape# 3rd#Module#

Loose#Coupling# Yes# DPs#coupled#to#Shapes#

Module#coupled#to#Shapes#

Strong#Cohesion# Yes# DPs#concerned#with#Shapes#

Weak:#Shape#and#Draw#stuff#

No#Redundancy# Yes# Knowledge#of#shapes#duplicated#in#DPs#

Knowledge#of#shapes#duplicated#in#CP#

Encapsula8on# implementa8on#and#type#

implementa8on#only# implementa8on#only#

Testable# N#+#M# N#*#M# N#+#M#

Asser8ve# Yes# No# No#

Focus# Yes# Shapes#spread#out#a#liWle#

Yes#

Shapes using DPs wins! 156# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Add#the#Rela8onship#

Shape

+draw()

Rectangle

+draw()

Drawing

+drawLine()+drawArc()

1..1

1

DP2

+drawline()+drawarc()

V2Drawing

+drawLine()drawArc()

DP1

+draw_a_line()+draw_an_arc()

V1Drawing


Circle

+draw()

drawing.drawLine()##




Illustra8ng#the#Separa8on#

Shape

+draw()

Rectangle

+draw()

Drawing


1..1

1

DP2

+drawline()+drawarc()

V2Drawing


DP1

+draw_a_line()+draw_an_arc()

V1Drawing


Circle

+draw()

Abstraction

Implementation


Example#Implementa8on##class Client { public static void Main (String argv[]) { Shape s1; Shape s2; Drawing dp; // See comments below to see // what gets returned dp= Factory.getDP(); s1= Factory.getShape(dp); dp= Factory.getDP(); s2= Factory.getShape(dp); s1.draw(); s2.draw(); } } // Factory: // 1st call: getDP returns V1Drawing // 1st call: getShape returns // new Rectangle(dp,1,1,2,2); // 2nd call: getDP returns V2Drawing // 2nd call: getShape returns // new Circle( dp,2,2,4);

interface Shape { public void draw(); } class Rectangle : Shape { private Drawing _dp; Rectangle (Drawing dp, double x1, double y1, double x2, double y2) { _dp = dp; _x1= x1; _y1= y1; _x2= x2; _y2= y2;} public override void draw () { _dp.drawLine(_x1, _y1, _x2, _y1); _dp.drawLine(_x2, _y1, _x2, _y2);

_dp.drawLine(_x2, _y2, _x2, _y1); _dp.drawLine(_x2, _y1, _x1, _y1); } }

C#




Example#Con8nued#

class Circle : Shape { private Drawing _dp; Circle (Drawing dp, double x, double y, double radius) { _dp = dp; _x= x; _y= y; _radius= radius; } public override void draw () { _dp.drawArc(_x,_y,_radius, 0, 360); } }

interface Drawing { void drawLine ( double x1, double y1, double x2, double y2); void drawArc(double x, double y,double radius, double fromAngle, doubletoAngle);} class V1Drawing : Drawing { public override void drawLine ( double x1, double y1, double x2, double y2) { DP1.draw_a_line( x1, y1, x2, y2); } public override void drawArc ( double x, double y, double radius, double fromAngle, double toAngle){ DP1.draw_an_arc( x, y,radius, fromAngle,toAngle); } }

C#


Example#Con8nued#

class Rectangle : Shape { Rectangle : base(dp) ( Drawing dp, double x1, double y1, double x2, double y2) { _x1= x1; _y1= y1; _x2= x2; _y2= y2; } public override void draw () { drawLine(_x1, _y1, _x2, _y1); drawLine(_x2, _y1, _x2, _y2); drawLine(_x2, _y2, _x2, _y1); drawLine(_x2, _y1, _x1, _y1); } }

C#

// With abstract base class abstract class Shape { private Drawing _dp; Shape (Drawing dp) { _dp= dp; } abstract void draw (); protected void drawLine ( double x1, double y1, double x2, double y2) { _dp.drawLine( x1, y1, x2, y2);} protected void drawArc ( double x, double y, double radius, double fromAngle, double toAngle){ _dp.drawArc( x,y,radius, fromAngle, toAngle); } }




Example#Con8nued#

class V2Drawing : Drawing { public override void drawLine (double x1,double y1, double x2, double y2){ DP2.drawline( x1, x2, y1, y2);} public override void drawArc ( double x, double y, double radius, double fromAngle, double toAngle) { DP2.drawarc(radius, x, y, fromAngle, toAngle); } } class DP1 { static void draw_a_line ( double x1, double y1, double x2, double y2) { // draw_a_line implementation given to us} static void draw_an_arc( double x, double y, double radius, double from_angle, double to_angle) {

// draw_an_arc implementation given to us } } class DP2 { static void drawline ( double x1, double y1, double x2, double y2) { // drawline implementation given to us } static void drawarc( double radius, double x, double y, double fromangle, double toangle) { // drawarc implementation given to us } }

C#


Example#Implementa8on##class Client { public static void main (String argv[]) { Shape s1; Shape s2; Drawing dp; // See comments below to see // what gets returned dp= Factory.getDP(); s1= Factory.getShape(dp); dp= Factory.getDP(); s2= Factory.getShape(dp); s1.draw(); s2.draw(); }} // Factory: // 1st call: getDP returns V1Drawing // 1st call: getShape returns // new Rectangle(dp,1,1,2,2); // 2nd call: getDP returns V2Drawing // 2nd call: getShape returns // new Circle( dp,2,2,4);

interface class Shape { void draw (); }

class Rectangle implements Shape{ private Drawing _dp; Rectangle (Drawing dp, double x1, double y1, double x2, double y2) { _dp = dp; _x1= x1; _y1= y1;

_x2= x2; _y2= y2;} public void draw () { _dp.drawLine(_x1,_y1,_x2,_y1); _dp.drawLine(_x2,_y1,_x2,_y2); _dp.drawLine(_x2,_y2,_x2,_y1); _dp.drawLine(_x2,_y1,_x1,_y1); } }

Java




Example#Con8nued#interface Drawing { void drawLine ( double x1, double y1, double x2, double y2); void drawArc(double x, double y, double radius, double fromAngle,double toAngle);} class V1Drawing implements Drawing { public void drawLine ( double x1, double y1, double x2, double y2) { DP1.draw_a_line(x1,y1,x2,y2); } public void drawArc ( double x,double y,double radius, double fromAngle, double toAngle){ DP1.draw_an_arc( x, y,radius, fromAngle, toAngle); } }

Java

class Circle implements Shape { private Drawing _dp; Circle (Drawing dp, double x, double y, double radius) {

_dp = dp; _x= x; _y= y;

_radius= radius; } public void draw () { _dp.drawArc(_x,_y,_radius, 0, 360); } }


Example#Implementa8on##With#Abstract#

// with abstract class abstract class Shape { private Drawing _dp; Shape (Drawing dp) { _dp= dp; } abstract void draw (); protected void drawLine ( double x1, double y1, double x2, double y2) { _dp.drawLine( x1, y1, x2,

y2); } protected void drawArc ( double x, double y, double radius, double

fromAngle, double toAngle){ _dp.drawArc( x, y,

radius, fromAngle, toAngle); } }

Java

class Rectangle extends Shape { Rectangle (Drawing dp, double x1, double y1, double x2, double y2) { super( dp); _x1= x1; _y1= y1; _x2= x2; _y2= y2; } public void draw () { drawLine(_x1, _y1, _x2, _y1); drawLine(_x2, _y1, _x2, _y2); drawLine(_x2, _y2, _x2, _y1); drawLine(_x2, _y1, _x1, _y1); } } class Circle extends Shape { Circle (Drawing dp, double x, double y, double radius) { super( dp); _x= x; _y= y; _radius= radius; } public void draw () { drawArc(_x,_y,_radius, 0, 360); } }




Example#Con8nued#

class V2Drawing implements Drawing { public void drawLine ( double x1, double y1, double x2, double y2) { DP2.drawline( x1, x2, y1, y2);} public void drawArc ( double x, double y, double radius, double fromAngle, double toAngle) { DP2.drawarc(radius, x, y, fromAngle, toAngle); } }

class DP1 { static void draw_a_line ( double x1, double y1, double x2, double

y2) { // draw_a_line implementation given to us } static void draw_an_arc( double x, double y, double radius, double from_angle, double to_angle) {

// draw_an_arc implementation given to us } } class DP2 { static void drawline ( double x1, double y1, double x2, double y2) { // drawline implementation given to us } static void drawarc( double radius, double x, double y, double fromangle, double toangle) { // drawarc implementation given to us } }

Java


Example#Implementa8on#

void main (String argv[], int arc) { Shape *s1; Shape *s2; Drawing *dp; dp= Factory::getDP(); s1= Factory::getShape(dp); dp= Factory::getDP(); s2= Factory::getShape(dp); s1->draw(); s2->draw(); } NOTE: Memory management has not been tested and the INCLUDE statements are not being shown.

class Shape { public: Shape (Drawing *dp); virtual void draw(); protected: drawLine( double x1, double y1, double x2, double y2); drawArc( double x, double y, double rad, double fromAngle, double toAngle); private: Drawing *_dp; }; Shape::Shape (Drawing *dp) { _dp= dp; } void Shape::drawLine( double x1, double y1, double x2, double y2) { _dp->drawLine( x1, y1, x2, y2); } void Shape::drawArc( double x, double y, double radius, double fromAngle, double toAngle){ _dp->drawArc( x, y, radius, fromAngle, toAngle); } !!

C++




Example#Con8nued#

class Rectangle : public Shape { public: Rectangle (Drawing *dp, double x1, double y1, double x2, double y2); private: double _x1, _y1, _x2, _y2; }; Rectangle::Rectangle (Drawing *dp, double x1, double y1, double x2, double y2) : Shape(dp) { _x1=x1; _y1=y1; _x2=x2; _y2=y2; } void Rectangle::draw () { drawLine(_x1, _y1, _x2, _y1; drawLine(_x2, _y1, _x2, _y2); drawLine(_x2, _y2, _x2, _y1); drawLine(_x2, _y1, _x1, _y1); }

class Circle : public Shape { public: Circle ( Drawing *dp, double x, double y,

double radius); private:

double _x, _y, _radius;

}; Circle::Circle (Drawing *dp, double x, double y,

double radius) : Shape(dp) { _x= x; _y= y; _radius= radius; }

void Circle::draw () { Shape::drawArc( _x,_y,_radius,0,360);

}

C++


Example#Con8nued#

###

class V2Drawing : public Drawing { public: void drawLine ( double x1, double y1,

double x2, double y2); void drawArc ( double x, double y, double radius, double fromAngle,

double toAngle); }; void V2Drawing::drawLine ( double x1,double y1,

double x2,double y2){ DP2::drawline( x1, x2, y1, y2); }

void V2Drawing::drawArc ( double x,double y, double radius, double fromAngle, double toAngle){ DP2::drawarc( radius, x, y, fromAngle, toAngle); }

class V1Drawing : public Drawing { public: void drawLine ( double x1, double y1, double x2, double y2);

void drawArc ( double x1, double y1, double radius, double fromAngle,

double toAngle); }; void V1Drawing::drawLine (double x1, double y1, double x2, double y2) {

DP1::draw_a_line( x1, y1, x2, y2); } void V1Drawing::drawArc ( double x, double y, double radius, double fromAngle, double toAngle){ DP1::draw_an_arc(x,y,radius, fromAngle, toAngle);

}

C++

class Drawing { public: virtual void drawLine (double x1,double y1, double x2,double y2) =0; virtual void drawArc (double x1, double y1, double radius, double fromAngle,

double toAngle)=0; };




Example#Con8nued#

class DP1 { public: static void draw_a_line ( double x1, double y1, double x2, double y2); static void draw_an_arc( double x, double y, double radius, double fromAngle, double toAngle); }; class DP2 { public: static void drawline ( double x1, double x2, double y1, double y2); static void drawarc ( double radius, double x, double y, double fromAngle, double toAngle); }; // Implementations given to us

C++


Where#is#varia8on#coming?#

Drawing Program/ Shape

DP1 DP2

Line

Rectangle

Circle




Look#For#Abstrac8ons#

!  Commonali8es#could#be##–  Func8ons#–  Data##

!  Alterna8ve#interfaces#may#produce#different#design##

!  Example#on#next#slide##


Drawing#Another#Way#

Line#

DrawingPrimi8ve##

Arc#

Shape#

DrawingPrimi8ve[]#getPrimi8ves();##

In#DrawingProgram:####

draw(Shape#s)#{#

##DrawingPrimi8ve#[]#dp#=#s.getDrawingPrimi8ves();##

##//#Now#draw#each#one##

##}#

#

What#are#advantages#/#disadvantages?#




Drawing#Another#Way#(2)#

interface Shape { DrawingPrimitive [] getPrimitives(); } class Rectangle implements Shape { double x1; double y1; double x2; double y2; DrawingPrimitive [] getPrimitives() {

DrawingPrimitive [] dp = { new Line(x1,y1,x1,y2), new Line(x1,y1,x2,y1), new Line(x2,y1,x2,y2), new Line(x1,y2,x2,y2)}

return dp; }


Drawing#Another#Way#–#One#Class##(3)#

class Shape { Shape (DrawingPrimitive [] primitives)

{ this.primitives = primitives;

} DrawingPrimitive [] primitives; DrawingPrimitive [] getPrimitives() { return primitives }; } // Each object has its own primitives Shape rectangle({ new Line(x1,y1,x1,y2), new Line(x1,y1,x2,y1), new Line(x2,y1,x2,y2), new Line(x1,y2,x2,y2)});




How#Drawing#Usually#Works#(op8onal)#

Drawing#(Graphics#Device#Interface)#draws#specific#shapes#(not#derived#from#a#Shape)##

interface GDI { drawRectangle(Rectangle r) drawCircle(Circle c) drawLine(Line l) drawPolyline(Line [ ] lines ) }

class Screen implements GDI //What are advantages / disadvantages?


Who’s#In#Charge?##

!  Class#PhoneNumber#–  Dial#(Phone)#

!  Class#Phone#–  Dial(PhoneNumber)#

#




Who’s#In#Charge#(2)?##

!  One#more#thing#to#dial:###

!  Class#AccountNumber#–  Dial#(Phone)#

!  Class#Phone#–  Dial(PhoneNumber)#

–  Dial(AccountNumber)##

#178# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Who’s#In#Charge#(3)#?#

!  Interface#Dialable##–  DialableString#getStringToDial();#

!  Class#AccountNumber#implements#Dialable#{##DialableString#getStringToDial()#{##//..##}###}#

!  Class#PhoneNumber#implements#Dialable##

!  Class#Phone#–  Dial(Dialable)#

#

#




Canonical#Bridge#PaWern#

Concrete1ImpA

+ opImp1()+ opImp2()

ImpB+ opImp1()+ opImp2()

Abstraction+ operation()

Implementation+ opImp1()+ opImp2()

operat ion() { imp.opImp1()}

Concrete2

operation() { imp.opImp2()}


Bridge#PaWern#as#an#Example##of#the#GoF#Approach#

Concrete1ImpA

+ opImp1()+ opImp2()

ImpB+ opImp1()+ opImp2()

Abstraction+ operation()

Implementation+ opImp1()+ opImp2()

operat ion() { imp.opImp1()}

Concrete2

operation() { imp.opImp2()}

(1)'(2)'encapsulates'variaAon'

(3)'

(1)'

(1)  Find0what0varies0(the0abstrac+ons0and00implementa+ons)0and##(2)  Encapsulate0it.0(3)  Favor00object0delega+on0over0classIinheritance0#

(2)'encapsulates'variaAon'



181# ### #16#October#2013#

The'Adapter'Pa*ern'


The#Adapter#PaWern#

!  Issue:#–  Class#has#right#stuff##

!  But#wrong#interface#!  GoF#Intent:#

–  #Convert#class#interface#into#the#one#client#expects##–  #Allows#classes#with#incompa8ble#interfaces#to#work#together#




Quali+es##




Our#Problem#

Shape + setLocation() + getLocation() + display() + fill() + setColor() + undisplay()

Point + display() + fill() + undisplay()

Line + display() + fill() + undisplay()

Square + display() + fill() + undisplay()


What#We#Have#

XX_Circle

+ set_location() + get_location() + display_it() + fill_it() + set_its_color() + undisplay_it()




What#We#Want#

! Want#XX_Circle#to#behave#like#a#Shape#–  No#polymorphism#with#XX_Circle:#

!  Author#of#XX_Circle#not#willing#or#able#to#change#XX_Circle’s#interface#

Shape

XX_CIRCLE

=


How#to#Implement#the#PaWern#

Shape + setLocation() + getLocation() + display() + fill() + setColor() + undisplay()

Point + display() + fill() + undisplay()

Line + display() + fill() + undisplay()

Square + display() + fill() + undisplay()

XX_Circle + set_location() + get_location() + display_it() + fill_it() + set_its_color() + undisplay_it()

Circle + display() + fill() + getLocation() + setLocation() + setColor() + undisplay()




Example#

class Circle : Shape { … private XX_circle pxc; … public Circle () { pxc= new XX_circle(); } public void override display() { pxc.display_it(); } }

C#


Example#

class Circle extends Shape { … private XX_circle pxc; … public Circle () { pxc= new XX_circle(); } public void display() { pxc.display_it(); } }

Java




Example#

IN HEADER class Circle : public Shape { private: XX_circle *pxc; } IN CONSTRUCTOR instantiate and initialize XX_circle. Have it refer to pxc IN CODE void Circle::display () { pxc->display_it(); }

C++


Adap8ng#

// May have some state to keep class Circle implements Shape { private XX_circle pxc; private Color color; setColor(Color c)

{ this.color = c; }

fill() { pxc.fill_it(color):; }

}




General#Approach#

!  Client#works#with#other#classes#without#"knowing"#which#one#–  Create#an#interface#–  Adapt#each#class#to#implement#that#interface#

!  Adap8ng##is#also#called#"wrapping"#

192# ### #16#October#2013#

The'Façade'




The#Façade#PaWern#

! Want#:#–  To#use#a#subDset#of#a#complex#system#

–  Or#to#provide#OO#access#to#a#nonDOO#system#

!  GoF#Intent*:##–  Provide#a#unified#interface#to#a#set#of#interfaces#in#a#subsystem##

–  Facade#defines#a#higherDlevel#interface#that#makes#the#subsystem#easier#to#use#




Quali+es##


Using#a#Complex#System#

!  If#your#group#had#to#use#parts#of#a#complex#system,#would#you:#A.  Have#everyone#learn#how#to#use#it?#B.  Have#one#person#create#an#interface#to#use?#

!  If#you#picked#B,#what#that#person#created#would#be#a#Façade#




Insula8ng#Ourselves#From#the#Complex#System#

Façade

#


Façade#Example#(1)#

!  #Example#StoreStringInFile(String filename, String data); // calls open, write, close String RetrieveStringFromFile(String filename); // calls open, read, close

!  Error#handling#(try,#catch,#etc.)#in#the#implementa8on#code#!  Allows#easy#mock##

–  Read/write#to#memory,#rather#than#a#file##

#




Façade#Example#(2)#

SimpleFileStorageFacade#####SelectStorageDirectory(String#directory)######StoreStringInFile(String#filename,#String#data)#:#boolean#####RetrieveStringfromFile(String#filename)#:#String#

File#//#Read,#write,#open,#close#//#Excep8on#handling##

Directory#//#change#working#directory#

SimpleFileStorageFacadeMock####SelectStorageDirectory(String#directory)#####StoreStringInFile(String#filename,#String#data)#:#boolean#

#//#stores#in#memory#–#maybe#a#map#?#####RetrieveStringfromFile(String#filename)#:#String#

#//#retrieves#from#memory##

LiWle#more#complete#


Standard#Façade#vs.#Encapsula8ng#Facade#

!  Standard#Façade#provides#interface#–  Clients#may#use#underlying#

system#directly#

!  Encapsula8ng#Façade#restricts#access#to#the#underlying#system##–  Clients#must#use#Façade#




Comparing#Façade#With#Adapter#

Client Pre-Existing?which pattern?

Façade# Adapter#Pre5ExisAng,'or'Foreign'classes?'

Yes# Yes#

Is'there'an'exisAng'interface'we'must'adhere'to?'

No# Yes#

Are'we'trying'to'enable'polymorphism?'

No# Usually#

Are'we'creaAng'a'new'interface'for'simplificaAon?'

Yes# No#

Is'statefullness'a'concern?' Yes,#Façades#tend#to#be#large#

Not#usually#


Adapter#and#Façade#

!  Use##Adapter#and#Façade#–  Defer#Worrying#About#Your#Interface#

– Make#interfaces#of#classes#to#be#the#way#you#want#

!  Design#by#context#–  #First#figure#out#what#you#want##–  Then#adapt#(or#simplify#with#a#Facade)#the#interface#to#that#




Microso_#Founda8on#Classes#(MFC)#Façade##

MFC#Classes#####Window#####Dialog##

Windows#SDK#####Win#98##

Windows#SDK#####Windows#7##

Windows#SDK#####Windows#2000#

Applica8on#

Note:#NonDencapsula8ng#facade#


Façade###Usage##

Your#system#

Façade##

Third#party#library##



203# ### #16#October#2013#

The'Abstract'Factory'


Strategy#Revisited#

!  Abstract#Factory#is#strategy#of#strategies##!  Here’s#an#example#




Switch#to#Strategy(1)#

// Just a switch, not a strategy enum Country {USA, MEXICO, CHINA}; functionOne (Country c){ switch(c) { case USA: doOneUSA(); break; case MEXICO: doOneMexico(); break; case CHINA: doOneChina(); break; } };

Switch#in#one#func8on#


Switch#to#Strategy#(2)#

//FACTORY Strategy getStrategy(Country c){ switch(c) case USA: return new USAStrategy(); case MEXICO: return new MexicoStrategy(); case CHINA: return new ChinaStrategy(); break; } }; // USAGE: void functionOne (Country c){ Strategy s = getStrategy(c); s.doFunctionOne();}

interface Strategy { void doFunctionOne(); }; class USAStrategy implements Strategy { void doFunctionOne() { doOneUSA(); }}; class MexicoStrategy implements Strategy { void doFunctionOne(){ doOneMexcio(); } }; // .. And so on

To#a#strategy#





functionTwo (Country c){ switch(c) { case USA: doTwoUSA(); break; case MEXICO: doTwoMexico(); break; case CHINA: doTwoChina(); break; } };

Now#a#2nd#switch##


How#to#organize#?#

County/ Function

USA

MEXICO

FunctionOne

FunctionTwo

FunctionThree





class MexicoStrategy implements Strategy { void doFunctionOne() { doOneMexcio(); } void doFunctionTwo() { doTwoMexcio(); } }; // .. And so on void functionTwo (Country c){ Strategy s = getStrategy(c); s.doFunctionTwo();}

interface Strategy { void doFunctionOne(); void doFunctionTwo(); }; class USAStrategy implements Strategy { doFunctionOne() { doOneUSA(); } doFunctionTwo() { doTwoUSA(); };

Add#to#strategy#



interface Strategy { void doFunctionOne(); void doFunctionTwo(); //…. void doFunctionNintyNine(); }; class USAStrategy implements Strategy { void doFunctionOne() { doOneUSA(); } void doFunctionTwo() { doTwoUSA(); }; //…. void doFunctionNinetyNine() {

Now#99##func8ons##added#to#strategy#





interface StrategyFactory { StrategyA getStrategyA(); StrategyB getStrategyB(); ///… StrategyZ getStrategyZ(); }; class USAStrategyFactory() implements StrategyFactory { StrategyA getStrategyA() { return new USAStrategyA(); } StragegyB getStrategyB(){ return new USAStrategyB(); } //.. And so forth };

interface StrategyA { { // Related functions void doFunctionOne(); void doFunctionTwelve(); }; class USAStrategyA implements StrategyA { void doFunctionOne() { doOneUSA(); } void doFunctionTwelve() { doTwelveUSA(); } };

Break#into#related#strategies#



StragetyFactory getInstanceStrategyFactory(Country c){ switch(c) { case USA: new USAStrategyFactory( (); break; case MEXICO: new MexicoStrategyFactory( (); break; case CHINA: new ChinaStrategyFactory( (); break; } };

Now#get#the#strategy#factory#





void functionTwelve(Country c) { StrategyFactory sf = getInstanceStrategyFactory(c); StrategyA sa = sf.getStrategyA(); sa.doFunctionTwelve(); } // Instead of previous operation void functionTwelve(Country c){ Strategy s = getStrategy(c); s.doFunctionTwelve();}

Usage:#


The#Abstract#Factory#PaWern#

!  GoF#Intent:##–  Need#to#create#families#of#objects#for#par8cular#situa8ons.##

–  Provide#interface#for#crea8ng#families#of#related#or#dependent#objects##! Without#specifying#their#concrete#classes#

Design0PaKerns:0Elements0of0Reusable0ObjectIOriented0SoLware#by#Gamma,#Helm,#Johnson,#Vlissides.#AddisonDWesley#Professional.#1995.#




Abstract#Factory:#Contextual#Forces#

! Mo8va8on:##–  Instan8ate#families#of#objects#

!  Encapsula8on:##–  Number#of#cases#

–  Concrete#types#of#all#services#–  Issue#that#case#varies##

216# ### #16#October#2013#

Not'an'Ending,'But'a'Beginning'




Purpose#of#this#Course#(Revisited)#

!  Present#a#powerful#way#of#designing#applica8on#architectures#!  Incorporates:#

–  Code#Quali8es##–  Design#PaWerns#–  CommonalityDVariability#Analysis#–  Contextual#Design#(a#la#Alexander)#


Summary#

!  Design#in#context##!  Code#quali8es##as#basis#for#paWerns##!  Favor#delega8on#over#inheritance#!  Encapsulate#variability#! What#else?##




Thank#You##

Please#Fill#Out#Evalua8ons#

info@netobjec+ves.com000www.netobjec+ves.com0


Supplemental'



221# ### #16#October#2013#

Factories'

Paradigm00PaKerns0


Quali+es##


Another#Issue#of#Perspec8ve#

!  PaWerns,#e.g.#strategy,#bridge##–  Create#context#for#factory##

!  Factories##–  Only#construct#objects,#do#not#use#

objects#Shape +centerX:int +centerY:int

Circle +diameter:int

Square +width:int +height:int

Factory +make():Shape

Client

~2




The#Use#of#Factories#

!  Factories#decouple#object#being#used#from#client##!  Factories#promote#encapsula8on#of#design#

–  1st##Determine#interfaces#and#interac8ons#of#objects##!  Conceptual#and#specifica8on#perspec8ves#

–  2nd##Get#right#objects#with#factory#!  Implementa8on#perspec8ve##


How#do#Factories#Make#Decisions?#

!  "Extrinsic"#(to#the#client)#–  Example:#

!  Configura8on#file#or#device#iden8fica8on#(e.g.#version#of#Windows)#

–  Only#factory#couples#to#configura8on#file##!  "Intrinsic"#(to#the#client)##

–  Client#decides#and#passes#a#parameter##

!  "Rule#Based“#–  Based#on#a#rule#–  Example##

!  If#user#is#administrator,#create#object#with#write#privileges##

–  Only#factory#couples#to#rule##




#Factory#Example##

// Client Selection enum EncryptionType {Strong, Weak, None}; Encryptor getEncryptorInstance(EncryptionType et)

{ switch(et) { case Strong: return new E128(); case Weak: return new E64(); case None: return new E0(); default: throw new Exception( “Look at the EncryptionType”); } }


#Factory#Alterna8ves#

enum EncryptionType {Strong, Weak, None}; // Table (struct, array, etc.)

Type Class Strong E128 Weak E64 None E0

Encryptor getEncryptorInstance(EncryptionType et) { for (i = 0; i < table.size; i++) { if (et == table[i].type) // return new object of table[i].class

} throw new Exception(“Look at the EncryptionType”); }

// Or array indexed by enum Encrypt [] encrypt= {new E128(), new E64(), new E0()}; return encrypt[et];




Factory#Alterna8ve#D#Service#Locator#PaWern#

class Chip { private Encryptor myEncryptor; Chip () {

myEncryptor = ServiceLocator.getEncryptor(); } } // Service locator checks a configuration file for type of encryptor to return


Concept#/#Varia8ons#

Encryption

E128

E64

E0

Send

TCP

FTP

UDP




Factory#For#Two#Strategies#

enum ChipType {ForCommercial, ForUS, ForImportantCustomer}; Chip getChip(ChipType ct) {

switch (ct) { case ForCommercial:

return new Chip(GetEncryptorInstance(Weak), GetSendInstance(TCP));

case ForUS: return new Chip(GetEncryptorInstance(Strong), GetSendInstance(FTP));

case ForImportantCustomer: return new Chip(GetEncryptorInstance(Weak), GetSendInstance(FTP);

}} // Or use table


#Discussion#Exercise#

!  You#have#exis8ng#Account#object#–  You#need#to#log#all#access#to#its#

public#methods#!  But#only#for#certain#accounts#and/or#at#certain#8mes#of#the#day#

–  You#don’t#want#client#code#to#change#a#lot##!  (or#at#all,#if#possible)#

!  What#would#you#do?#

Please#Don’t#Turn#the#Page#Un8l#Instructed#to#Do#So#

~2

Account + Account(AccountID id) + AddMoney(Dollar d) + TakeOutMoney(Dollar d)




Workspace#


Workspace#




Workspace#


Workspace#




One#Approach:#An#Intervening#Class#

Client Logger Account

Writes to a log file, then delegates


Account#Logger#(Proxy)##

Account

+ addMoney() + takeOutMoney()

Account_Impl LoggingAccount

Client

Call#logger#before#calling#original#method##

.





237# ### #16#October#2013#

The'Family'of'Proxy'Pa*erns'



Quali+es##


The#Proxy#PaWern#

!  Issue:#–  Need#to#add#func8onality#before#or#a_er#accessing#an#object#

!  Client#should#not#know#it#is#talking#to#a#different#object#!  GoF#Intent:##

–  Provide#a#surrogate#or#placeholder#for#another#object*#!  Summary:#

–  Proxy#acts#on#behalf#of#another#class#–  Proxy’s#interface#must#be#same#as#class#it#is#duplica8ng#





The#Proxy#PaWern#

! Many#uses#for#proxy#paWern#!  Some#are:#

–  Access#protec8on#!  Protec+on0proxy#provides#security#for#another#object#

–  Caching#!  Cache0proxy#provides#caching#for#accessing#another#object#

–  Virtualiza8on#!  Virtual0proxy##provides#holding#point#for#another#object##


The#Protec8on#Proxy#PaWern#

!  Need#to#control#access#to#exis8ng#object##!  Don’t#want#to#change#exis8ng#data#object##

–  Or#how#it#is#referred#to##!  Follows#openDclosed#principle#

–  Closed#=#exis8ng#object##–  Open#=#adding#access#control#




The#Protec8on#Proxy#PaWern#

!  Example:#–  Teachers#place#test#problems#and#answers#in#database#

!  Access#through#Problem#with:#–  String#getQues8on#(int#problem_number)#D#returns#ques8on#as#string#–  String#getAnswer#(int#problem_number)#D#returns#answer#as#string#

!  Now#give#students#access#to#the#ques8on#–  But#not#the#answers#

!  User#class#has#method#–  Boolean#isTeacher()#–#returns#if#User#is#teacher##


Possible#Solu8ons#

!  Could#add#isTeacher()#call#before#every#getAnswer()#call#–  Problem:##

!  #Have#to#change#Client#code#wherever#getAnswer()#is#used##! Make#Problem#class#smarter#

–  Add#isTeacher()#to#getAnswer#(int#problem_number)##–  Problems:#

!  Breaks#open/closed#! May#have#side#effects#for#other#Client#using#Problem##




Protec8on#Proxy#Solu8on#

!  Create#a#Problem#interface#–  Both#original#Problem#and#a#new#class#(SecurityProblem)#implement#it#

!  SecurityProblem#checks#user#before#passing#back#answers#–  Uses#Problem#to#do#real#work#

!  Client#gets#SecurityProblem,#not#Problem#to#use##–  Can’t#tell#the#difference#


Protec8on#Proxy#Looks#Like#

Problem

+ getAnswer() + getQuestion()

Problem_Impl


SecurityProblem


Client

getAnswer checkis type of client calls Problem_Impl's getAnswer. getQuestion just calls Problem_Impl's getQuestion.




Protec8on#Proxy##

class SecurityProblem implements Problem { Problem original; SecurityProblem() { original = new Problem_Impl(); } String getQuestion(int which) { return original.getQuestion(which); } String getAnswer(int which) { if (User.isTeacher()) return original.getAnswer(which); else return “I can't give you answer”; } // Could also have SecurityProblem(Problem p); }


How#It#Works# : Client : Security

Problem : Problem _Impl Problem

_Factory

2: Instantiate

5: Request question 6: Request question 7: Return question

8: Return question 9: Request answer

10: Do I have a teacher? 11: If no, say can't give you answers

12: If yes, ask for answer 13: Return answer

14: Return answer

1: Get Problem

3: Instantiate (pass in Problem_Impl) 4: Return Object




Common#Characteris8cs#of#All#Proxies#

!  Proxy#paWern#characteris8cs:#–  Client#uses#proxy#class#instead#of#original#class#–  Proxy#and#original#class#have#same#interface##

–  Proxy#calls#original#class#for#services#! No#duplica8on#of#func8onality#


The#Proxy#PaWern#Generalized:#Class#Diagram#

Original + Request()

Proxy + Request()

Interface + Request()

Client

Request() calls Original’s Request()




The#Proxy#PaWern#Generalized:#Interac8ve#Diagram#

Client Proxy Original

1: Request

2 : do necessary pre-processing

3: request

5: do necessary post-processing

6: Respond to client

4: respond to request


The#Cache#Proxy#PaWern#Example#

!  Needs:#–  Improve#performance#in#accessing#data#

–  No#change#in#exis8ng#object#!  Example#Situa8on:##

–  Applica8on#makes#read0only0use#of#sta8c#data#through#Table#class#!  Table#data#resides#on#disk#

!  Problem:#–  Performance#is#slow#– Many#accesses#to#table#are#for#the#same#data##




Cache#Proxy#Looks#Like#

Cache_Table

+ read_data()

Table

+ read_data()

Table_Impl

+ read_data()

Client

read_data() calls Table_Impl read data() if info isn't cached


The#Virtual#Proxy#PaWern#Example#

!  Needs:#–  Exis8ng#object#uses#many#system#resources##

–  Client#doesn’t#reference#object#immediately#! Don’t#want#to#use#system#resources#un8l#necessary#

! Need#a#placeholder#for#it#!  Example:##

–  Applica8on#contains#many#graphic#images#! Only#shows#a#few#of#them#at#a#8me#

!  Problem:##–  If#all#of#the#images#instan8ated,#run#out#of#memory##




Virtual#Proxy#Looks#Like#

Image

+ display()

Image_Impl

+ display()

VirtualImage

+ display()

Client

display is implemented by instantiating the corresponding Image and displaying

- filename


The#Remote#Proxy#PaWern#

!  Remote#proxy##–  Access#object#on#remote#machine#

–  Local#proxy#looks#like#that#object##!  Almost#transparent#

–  Client#may#have#to#deal#with#network#unavailability#issues#

Local#Proxy# Remote#Object#

Client# Server#Somewhere#




Other#Proxies#

!  Smart'reference'proxy*.#–  Replaces#“bare”#reference##–  Adds#func8onality,#for#example:#

!  Counts#number#of#references##

!  SynchronizaAon'proxy*#–  Coordinates#mul8ple#simultaneous#accesses#to#a#component#

–  Locks/unlocks#the#object# ##

!  Firewall'proxy*.##–  Protects#local#clients#from#the#outside#world##

*Pa2ern<Oriented%So?ware%Architecture,#Buschmann,#et.#al.##256# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Browser#Proxy##

Browser## Remote#Web#Server##

Proxy##




What#the#Proxy#Teaches#Us#

!  Use#interfaces#for#objects#whose#behavior#or#use#may#change#

!  Proxies###– Accommodate#changes#that#require#preD#and#postDprocessing#

– Separate#op8onal#behavior#from#"always“#behavior###! Thus,#improved#cohesion#

258# ### #16#October#2013#

The'Decorator'Pa*ern'



Quali+es##




The#Decorator#PaWern#

Mo8va8on#–  Change#func8onality#of#an#object#of#a#class#

!  Rather#than#the#en8re#class#–  Dynamically#add#addi8onal#func8onality#–  Pick#from#addi8onal#behaviors#

!  Add#desired#ones#for#a#par8cular#case#!  Analogy#

–  Electrical#connectors##! One#with#on/off#"#One#with#fuse#"#One#with#UPS##

!  GoF#Intent:##–  AWach#addi8onal#responsibili8es#to#an#object#dynamically.##



Decorator#PaWern#for#Streaming#IO#

Client

TCPIPStream + flush()

FileStream + flush()

U128 + flush()

CompressStream + flush()

Stream + output() + flush()

StreamDecorator




Encapsula8on#

FileStream#

Compress#

U128#

Client#

Convert#to#U128#and#then#flush#

Compress#and#then#flush#

Send#

Each#circle#encapsulates#(hides)#what#is#within#from#what#is#without.###

Each#en8ty#(U128,#Compress,#FileStream)#also#does#not#know#if#it’s#the#outer#circle#or#not#

Construc8on:###Stream#s#=#new#U128(#####new#Compress#(#######new#FileStream(“name”)));#Use:####s.output();####s.flush();##


Comparing#Adapter,#Façade,#Proxy#and#Decorator#

Adapter Facade Proxy Deco-rator

Have pre-existing stuff? Yes Yes Yes Yes Is the client expecting a particular interface?

Yes No Yes Yes

Want to make a new interface to simplify things?

No Yes No No

Modifying interface to what clients expect?

Yes No No No

Want some new function before or after the normal action?

Maybe, but not intent

Maybe, but not intent

Yes (sta-

tically)

Yes (dyna-

mically)

Client Pre-Existing?which pattern?




Object#Diagram#of#Decorator#/#Proxy#

Decorator''B'

Decorator'A'

Client'

Original'

Proxy'

Client'

Original'

Decorator' Proxy' !  Proxy##–  Func8onality#usually#added#sta8cally##

–  Usually#knows#original#object#

!  Decorator#–  Func8onality#usually#added#dynamically##

–  Does#not#know#original#object##

264# ### #16#October#2013#

Chain'of'Responsibility'



Quali+es##




The#Chain#of#Responsibility#PaWern#

!  Issue:#–  Any#of#a#set#of#objects#can#perform#a#task#–  Requestor#of#task#does#not#want#to#know#which#one#does#it#

!  GoF#Intent:##–  Decouple#sender#of#a#request#to#its#receiver##

!  By#giving#more#than#one#object#a#chance#to#handle#the#request#

–  Chain#receiving#objects#!  Request#passed#along#the#chain#un8l#an#object#handles#it*##

!  Example:#Have#a#message#to#decode#–  Chain#decoders#together#–  Pass#message#to#each#one#un8l#one#decodes#it#



Chain#of#Responsibility#Object#Diagram##

Decoder1

Decoder3

Decoder2

Decoder4

return computedvalue or given




2: decode ifpossible



4: decode ifpossibleClient

Requestto decode




Example#CoR#Diagrammed#

Client

Decoder1 + decode()

Decoder2 + decode()

Decoder3 + decode()

Decoder + decode()

1#

0..1#


Who#Knows#How#to#Build#the#Chain?#

!  Have#to#decide#somewhere:#– Which#decoders#belong#in#the#chain#– What#order#they#should#be#in#–  How#the#Chain#will#end##

!  Request%execuBon%not%guaranteed%–  Possible#it#not#handled#at#all#

! Good#to#have#default#"always"#en8ty#at#end#of#chain#–  Either#default#behavior#or#error#signaling##

!  Op8ons#included:#–  Hard#code#chain#in#Client#–  Client#gets#chain#from#factory##

!  Factories##usually#less#likely#to#grow#in#number#than#clients#




Code#Example#of#Chain#of#Responsibility#

class Client { public string Decode( string message, Decoder aDecoder) { return aDecoder.Decode( message); } } abstract class Decoder {

private Decoder trailer; public Decoder ( Decoder nextDecoder) { trailer= nextDecoder; } public string Decode ( string message) { if (MyAction(message))

return DecodeString( message); if (trailer!= null) return trailer.Decode(message); return "Cannot decode"; } abstract protected bool MyAction( string message); abstract protected string DecodeString( string message); }

C#



class Decoder1 : Decoder { protected override bool MyAction( string message) { // see if I can do this. // if I can: // return true // if I can’t // return false } protected override string DecodeString( string message) {

String decodedMessage; //Decode the message

return decodedmessage; } } // other decoders follow this format as well.

C#





class Client { public String decode( String message, Decoder aDecoder) { return aDecoder.decode( message); } } abstract class Decoder { private Decoder trailer; public Decoder ( Decoder nextDecoder) { trailer = nextDecoder; } public String decode ( String message) { if (myAction(message))

return decodeString( message); if (trailer!= null) return trailer.decode( message); return "Cannot decode"; } abstract protected boolean myAction( String message); abstract protected String decodeString( String message); }

Java



class Decoder1 extends Decoder { protected override boolean myAction( String message) { // see if I can do this. // if I can: // return true // if I can’t // return false } protected String decodeString( String message) {

String decodedMessage; //Decode the message

return decodedmessage; } } // other decoders follow this format as well.

Java





bool Client::decode ( SubString message, Decoder aDecoder) { return aDecoder.decode( message); } class Decoder { public: Decoder(Decoder*); ~Decoder(); bool decode(string); protected: virtual bool myAction( string)= 0; private: Decoder *trailer; } Decoder::Decoder (Decoder* aDecoder) { trailer= aDecoder; } bool Decoder::decode ( string message) { if (myAction(message)) return(true); if (trailer!= null) return trailer->decode(message); else return false; } }

C++



class Decoder1 : public Decoder { public: protected: bool myAction( string message); } bool Decoder1::myAction( string message) { // see if can do this. // if can: // do it here // // return true // if can’t // return false } } // other decoders follow this format as well.

C++




A#Focused#Example:#Poker#

Hand HandEvaluator

+eval(card[]):int

RoyalFlush

+eval(card[]):int

StraightFlush

+eval(card[]):int

4ofaKind

+eval(card[]):int

Flush

+eval(card[]):int

FullHouse

+eval(card[]):int

Straight

+eval(card[]):int

3ofaKind

+eval(card[]):int

Pair

+eval(card[]):int

HiCard

+eval(card[]):int

Encapsulated#Rules#


At#Run8me#

Hand RF

SF

4K

FH

FL

ST

3K

PR

HC



277# ### #16#October#2013#

Vector'Forces'Discussion'


Design##

! We#need#to#store#some#related#numbers.#!  Let’s#store#them#in#consecu8ve#memory#loca8ons#

– What#do#we#call#it?###A#vector#

!  Alternate#way#of#storing##–  Store#a#number#along#with#a#reference#to#the#next#number.#

– What#do#we#call#it?##A#linked#list##

#




Forces#

Array Vector Linked List

Random Access Quick Quick Slow

Insert Client needs to make copy

Need to copy memory

Quick

Size per element Size of data Size of data

Size of data plus the reference

Cost of insert Allocate and copy Allocate and copy

Same every time


Design#

!  Vector##–  Consecu8ve#memory#addresses#

–  Use#index#to#select#element##

!  Linked#list##–  NonDconsecu8ve#memory#addresses##–  Reference#to#next#element#in#list##




Implementa8on##

!  Vector##–  Allocate#memory#big#enough#to#hold#ini8al#elements#

–  Ini8alize#each#element#to#null#or#0##

!  Linked#List#–  Set#ini8al#reference#to#null#–  As#add#element,#update#the#reference##

– Make#sure#don’t#go#off#end#when#traversing##– Maybe#allocate#from#block#of#storage#to#avoid#severe#memory#block#use##

282# ### #16#October#2013#

Architectural'Pa*erns'




Architectural#PaWerns#

! Model#View#Controller#– Model#–#handles#data#and#rela8onships#

–  View#–#displays#the#model#–  Controller#–#interface#to#changing#the#model#

Controller#

Model#

View#


Architectural#PaWerns#

!  Pipes#and#Filters#(Unix)#–  Document#to#spell#check##–  Input#"#WordBreaker#"#Sorter#"#Unique#"#Dic8onaryCompare##

–  Note:##Can#be#Decorator#paWern#on#lower#level#

!  Cat#filename#|#sort#|#uniq#!  Filter#/#pipe#/#filter#/#pipe###

A#B#C#A#A##

Becomes##A#

A#A#

B#

C##Becomes##

A#B#

C##



285# ### #16#October#2013#

Inheritance'Versus'Interface'


Inheritance#Issues##

!  Inheritance#combines#two#perspec8ves#–  Common#interface#(specifica8on)#

! Derived#classes#play#same#role#as#base#class##

–  Common#implementa8on##!  Inherited#methods,#aWributes#

!  O_en#mix#up#these#perspec8ves###




Changing#Base#versus#Changing#Interface#

Base#Class#

MethodOne()#

AddedMethod()#//New#

Interface#

MethodOne()#

AddedMethod()#//#New#

Derived#Class#

Does#AddedMethod()#need#overriding#?##

Implemen8ng#Class#

AddedMethod()#needs#implementa8on#


Inheritance#Versus#Interface#

BaseClass#Method();#

DerivedClass# AnotherDerivedClass#Method()#{#anotherWay;}##

How#to#avoid#redundancy?#

OneMore##DerivedClass#

Fourth#DerivedClass#Method()####{#anotherWay;}##




Inheritance#

BaseClass#Method();#

DerivedClass#

AnotherDerivedClass#

Create#hierarchy##


Fourth#DerivedClass##

AnotherDerivedClass#Method()#{#anotherWay;}##


Inheritance#

BaseClass#Method();#NewMethod();#

DerivedClass#NewMethod()#{someWay;}##

AnotherDerivedClass#

NewMethod()##Two#classes#need#same#override#


Fourth#DerivedClass#NewMethod()#{someWay;}##

AnotherDerivedClass#Method()#{#anotherWay;}##




Interface#

Interface#Method();#

Implemen8ngClass#

AnotherImplemen8ngClass#InterfaceHelper#Method();#AnotherWay();##

OneMoreImplemen8ngClass#

FourthImplemen8ngClass#


Inheritance#Versus#Interface#

Interface#Method();#NewMethod():#

Implemen8ngClass#

AnotherImplemen8ngClass#InterfaceHelper#Method();#AnotherWay();##NewMethod();#SomeWay();#

OneMoreImplemen8ngClass#

FourthImplemen8ngClass#




Prefactoring#Guideline#

!  Avoid#premature#hierarchaliza8on##–  Don’t#create#hierarchies#un8l#you#really#need#them##

!  Easier#to#create#right#hierarchy#than#to#deDhierarchalize#the#wrong#one#

294# ### #16#October#2013#

Code'Notes'




Interfaces#and#Abstract#Classes#

!  An#interface#–  Defines#methods#and#their#signatures#

!  An#abstract#class#–  Defines#methods#and#their#signatures#–  Can#include##

!  Data#members#(aWributes)#! Method#implementa8ons#

!  Class#can:#–  Derive#from#abstract#class##

!  O_en#only#from#one#class#(Java,#C#)#

–  Implement#interface##!  Can#implement#numerous#interfaces#


Interface#and#Abstract#Classes#(2)#

!  Interface#cannot#contain#sta8c#method#–  So#some#examples#use#abstract#class##

–  If#sta8c#method#is#in#another#class#(for#example#a#factory#class),#then#could#use#interface##

interface#MyInterface#####void#method();#

class#MyInterfaceHelper#####sta8c#MyInterface#getInstance();##

abstract#class#MyInterface#####void#method();#####sta8c#MyInterface#getInstance();###

class#MyClass####

class#MyClass####



297# ### #16#October#2013#

Naming'


Naming(1)#

!  Six#character#names#(FORTRAN)###–  CMPORB#,#ORBCMP##

–  STRCMP##–  Needs#comments##

!  But#now?##– What’s#the#limit?### ##




Naming#(2)#

Class BfsSwsTpidConfigTable { BfsSwsTpidConfig TrySEHPBfsSwsTpidConfig() { try { int iRec = 0; int dwRecs = CountRecs(sizeof(BfsSwsTpidConfig)); while(iRec < dwRecs) { BfsSwsTpidConfig pbstc = (BfsSwsTpidConfig ) Pv() + iRec; if(pbstc.m_dwTPID == _dwTPID) { return pbstc; } ++iRec; } } }

300# ### #16#October#2013#

Commonality5Variability'Analysis'




CommonalityDVariability#Analysis#

!  Abstrac8on##focuses#on#commonality#(general)#!  DeDemphasize#variable#details##(specifics)#.#!  Acknowledgement:##

–  Commonality#–#Variability#Analysis#in#James#Coplien’s#Mul8Dparadigm#Design#for#C++#

His#thesis#is#on#line#at#hWp://www.netobjec8ves.com/download/CoplienThesis.pdf#

c#

Paradigm00PaKerns0


Quali+es##

His#thesis#is#on#line#at:#hWp://www.netobjec8ves.com/files/CoplienThesis.pdf#(link#is#caseDsensi8ve)#


Commonali8es#and#Variability#

!  Commonali8es#can#define#basic#domain#concepts#–  Recognized#from#experience#

–  Learned#through#analysis#(abstracted)#!  Variability#is#varia8on#of#commonality##

!  From#an#architectural#perspec8ve:#–  Commonality#analysis#gives#architecture#its#longevity;##–  Variability#analysis#drives#its#fitness#for#use”*#

*'MulB<Paradigm%Design%in%C++,#Jim#Coplien#




Abstrac8on#Longevity##

Longevity###Interface#Car#####turn()####speedUp()####slowDown()#

Implementa8on#VW#####turn()####speedUp()####slowDown()#

Implementa8on#BMW####turn()####speedUp()####slowDown()#

Implementa8on#Yugo####turn()####speedUp()####slowDown()#


Steps##

!  Steps#to#follow:#– Pick#something#in#problem#domain#– Ask#is#it?#

! A#par8cular#way#of#doing#something#(a#varia8on)?#–  If#so,##what#concept#is#it#a#varia8on#of?# # ##

! Or#! A#way#of#conceptually#thinking#about#different#ways#to#do#things?#

–  If#so,#iden8fy#as#a#concept#!  If#neither##

–  (just#a#standalone#func8on)#,#iden8fy#it#as#an#en8ty#

not in sem




Commonality–Variability#Analysis#Exercise#

!  Have#to#handle#European#date#formats#as#well#as#US#date#format#

!  US#Tax#!  Canadian#PST,#GST#!  European#VAT#!  German#Shipping#Rates#!  French#Freight#Rules#!  Verifica8on#of#valid#addresses#

in#different#countries#

!  Max#Weight#in#US#is#70#lbs#!  Canadian#Freight#Rules#!  US#Freight#Rules#!  US#Phone##s#!  European#Phone##s#!  Max#Weight#in#Germany#is#40#

kg#!  Euros#in#Europe,#Dollars#in#

US,#etc…#

Say#we’re#given#the#following#requirements#for#an#eDcommerce#system:#

#


CVA#and#OO#Rela8onships#

! CVA#does#not#deal#with#rela8ng#concepts#– E.G.#US$#in#US,#Euro#in#Germany.###

! Money#and#country0are#“related”#

– US$##and#Euro#varia8on#of#money##! Not#of#country##

! CVA#says:#– First#find#Commonali8es#and#Variability's#

! Limit#to#isDa#rela8onship#

– Then#iden8fy#interDrela8onships#later#! Will#use#paWerns#to#implement#rela8onships##




Discussion#Exercise#

!  For#the#eDcommerce#system##–  Iden8fy#commonali8es#and#variability's#present#in#the#problem#domain#

–  First#iden8fy#commonali8es#!  Then#iden8fy#varia8ons#within#these#commonali8es#

not in sem 308# #Copyright#©#2013##Net#Objec8ves.#All#Rights#Reserved.## #16#October#2013#

Work#Space#




Work#Space#


Work#Space#




Work#Space#


Some#Commonali8es#and#Variabili8es#

!  Con8nents#–  European#–  North#American#

!  Countries#–  France#–  Germany#–  Canada#–  US#

!  Taxes#–  European#–  Canadian#–  US#

!  Money#–  US#$#–  Canadian#$#–  Euro#

!  Phone###Formats#–  European#–  US/Canadian#

!  Shipping#Rules#–  French#–  German#–  Canadian#

!  Date#Formats##–  yyyy/mm/dd#–  dd/mm/yyyy#–  mm/dd/yyyy#

!  Freight#Rates#–  German#Rates#–  French#Rates#–  Canadian#Rates#

!  Shipping#–  Truck#–  Plane#–  Rail#–  Ship#

!  Max#Weights#–  German##D#40#kg#–  French#–#none#–  Canada#–#none#–  US#D#70#lbs#

!  Address#Verifica8on#–  French#–  German#–  Canadian#–  US# Note:#If#Units#are#abstracted,#

perhaps#Max0Weights0can#simply#be#an#aWribute/value#




Notes#about#Commonali8es#and#Their#Varia8ons#

!  CVA#is#just#a#star8ng#point.##Suggests:##–  Concepts#D>#abstract#interfaces#–  Varia8on#D>#concrete#types#

!  Not#all#commonali8es#and#varia8ons#are#useful#–  Some#describe#varia8ons#implementable#by#changing#an#aWribute#value#(e.g.,#finance#charge#rate)#


Ways#To#Handle#Varia8on#

!  PaWerns#–#Strategy,#others#!  Tables#–#Lookup#value##!  Pass#in#values#

Concept / Variation US Canada Germany

Max weight 70 lbs none 40 kg




Exercise#D#Which#Way?#

Varia8ons#(e.g.#Countries)#

Concepts#(e.g.)#Address#Verifica8on##


Handling#Varia8ons##D#(1)##

int getMaximumWeight(Locale locale) { switch(locale)

{ case US:

return 70; case Canada

return UNLIMITED; //…

// Or a table lookup }

String getDateAsString(Locale locale, Date date)

{ switch(locale)

{ case US:

return date.FormattedAs(locale); //…..




Handling#Varia8ons#(2)##

interface Details { int getMaximumWeight(); getDateAsString(Date date); }; class US implements Details { int getMaximumWeight() { return 70; } String getDateAsString) Date date){ return date.FormattedAs(US);} } class Canada implements Details { int getMaximumWeight() { return UNLIMITED; } String getDateAsString) Date date){ return date.FormattedAs(CANADA);} }


Using#CommonalityDVariability##Analysis#to#Design#Class#Structures#

Commonalityanalysis

Variabilityanalysis

Conceptualperspective

Specificationperspective

Implementationperspective

Interface

Operations

Concreteclass

Operations

Concreteclass

Operations




How#Do#Abstrac8ons#/#CVA#Relate#to#PaWerns?#

!  PaWerns#reflect#separa8on#that#good#abstrac8ons#create#in#design#

!  PaWerns#proceed#from#CVA#!  CVA#can#be#used#to#discover#paWerns#(to#be#shown#shortly)##

Technology

Design Patterns Explained: From Analysis through Implementation