Avoiding Overdesign and Underdesign

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BT6

Concurrent!Session!
11/14/2013!2:15!PM!
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"Avoiding Overdesign and
Underdesign"
!
!
!

Presented by:
Ken Pugh
Net Objectives
!
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!
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Brought(to(you(by:(
!

!
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340!Corporate!Way,!Suite!300,!Orange!Park,!FL!32073!
888C268C8770!E!904C278C0524!E!sqeinfo@sqe.com!E!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
ken.pugh@netobjectives.com!

info@netobjec+ves.com000
www.netobjec+ves.com
0

Avoiding(Over(and(
Under(Design(
In"Agile"Projects"
"
Ken"Pugh"
Fellow"Consultant"
Net"Objec6ves"

1"

"Copyright"©"2008"Net"Objec6ves."All"Rights"Reserved.""

"6"November"2013"

Agenda"

!  Emergent"Design"
–  Code"Quali6es"
–  Refactoring"

!  Case"Study"
!  Advice"from"the"Gang"of"Four"
!  Emergent"Design"In"Ac6on"
"
"

2"


"6"November"2013"

Ken"Pugh"
Photo
Size:
Height: 2.25
Position:
from top left corner
Horizontal 0.75
Vertical 1.
Picture Style: Simple Black
Frame

!  Fellow"Consultant"
!  OOA&D,"Design"PaSerns,"Lean,"Scrum,"TestVDriven"
Development"

!  Over"2/5"century"of"soYware"development"
experience"

!  Author"of"seven"books,"including:"
ken.pugh"
@netobjec6ves.com"

–  0Prefactoring:0Extreme0Abstrac+on,0Extreme0
Separa+on,0Extreme0Readability00(2006"Jolt"Award)"
–  0Interface0Oriented0Design0
–  Lean0Agile0Acceptance0TestFDriven0Development:0
BeHer0SoIware0Through0Collabora+on0

No code goes in till the test goes on.
A journey of two thousand miles begins with a single step.
3"


"6"November"2013"

Lean for Executives
Product Portfolio
Management
Business Product Owner
Scaled Agile Framework

Business"

ASSESSMENTS"
CONSULTING"
T RAINING "
COACHING"

Lean"
Enterprise"
Manag
ement"

Team"
technical"

process"

Kanban / Scrum
ATDD / TDD / Design Patterns
Emergent Design

4"

Lean Management
Project Management


"6"November"2013"

Emergent(Design(
3(Code(Quali8es(

5"

"""

"6"November"2013"

Predictability"

!  Can’t"predict"how"requirements"going"to"change"
!  Can"predict"how"code"will"adapt"to"unpredictable"

requirements"changes"
!  How"to"increase"predic6on"abili6es"of"code"quality?"

6"


"6"November"2013"

Ques6on"to"Ask"

!  When"working"on"a"mature"system"consider"when"
adding"a"new"func6on…"

""""""which"task"area"takes"more"6me"
""
"–"wri6ng"the"new"func6on"or""
""
"–"integra6ng"it"into"the"system?"

7"


"6"November"2013"

8"


"6"November"2013"

Creeping"Changes"
function()
{
Do_this;
Do_that;
Do_something_else;
}

9"


"6"November"2013"

Creeping"Changes"(2)""
function()
{
if (a) {
Do_another_thing:
//…
}
else {
Do_this;
Do_that;
Do_something_else;
}
}

10"


"6"November"2013"

Creeping"Changes"(3)""
function()
{
if (a) {
if (b) {
Do_another_thing:;
//…
}
else {
Do_one_more_thing;
//..
}
}
else {
Do_this;
Do_that;
Do_something_else;
}
}

11"


"6"November"2013"

Cohesion"
!  Cohesion""
–  How"“closely"the"opera6ons"in"a"rou6ne"[or"class]"are"related.”""
–  Cohesion"as"“clarity”""
!  Because"the"more"opera6ons"are"related"in"a"rou6ne"[or"class]"the"easier"it"is"to"
understand"the"code"and"what"it's"intended"to"do."*"

!  Strong"cohesion"related"to"clarity"and"understanding."
!  “No"schizophrenic"classes”"

*"Steve(McConnell,"Code0Complete,"1993,"p."81."Note:"This"concept"was"ﬁrst"
described"by"Larry"Constan6ne"in"1975,"but"we"like"McConnell’s"deﬁni6on"best."

12"


"6"November"2013"

Coupling"
!  Coupling""
–  Strength"of"a"connec6on"between"two"rou6nes"[or"classes].""
–  Coupling"is"a"complement"to"cohesion."""
!  Cohesion"describes"how"strongly"the"internal"contents"of"a"rou6ne"[or"class]"are"related"
to"each"other.""
!  Coupling"describes"how"strongly"a"rou6ne"is"related"to"other"rou6nes.""

–  Goal"is"to"create"rou6nes"[and"classes]"with"internal"integrity"
(strong"cohesion)"and"small,"direct,"visible,"and"flexible"
rela6ons"to"other"rou6nes"[and"classes]"(loose"coupling).”*"
!  Tight"coupling"is"related"to"highly"interconnected"code."
*"Steve(McConnell,"Code0Complete,"1993,"p."81."Note:"This"concept"was"first"
described"by"Larry"Constan6ne"in"1975,"but"we"like"McConnell’s"defini6on"best."

13"


"6"November"2013"

Coupling"To"Data"
Class
Global Data

Attributes

Function
One
Function
Two
Function Three

14"

Method One
Method Two
Method Three


"6"November"2013"

No"Redundancy"

!  "One"Rule"in"One"Place""
!  Redundancy"is"not"just:"
–  Redundant"state"
–  Redundant"func6ons"

!  It"can"also"be"redundant"rela+onships0

15"


"6"November"2013"

Encapsula6on"
Usual"encapsula6on""
!  Data"

–  Hide"from"other"en66es."

!  Implementa6on"

–  How"par6cular"func6on"is"implemented"or"whether"it"delegates"to"other"objects"

Also:"

!  Object"Type"

(

–  Abstract"classes"and"interfaces"hide"implemen6ng"classes."

!  Design"

–  Assembling"collabora6ng"classes"with"factory"keeps"clients"decoupled"from"design"

!  Construc6on"

–  Encapsula6on"of"construc6on""V"wrap""new"""in"getInstance()"method""

"

16"


"6"November"2013"

Abstrac6on"

!  Abstrac6on"encompasses"encapsula6on"
–  Think"about"what"you"want"done,"not"how"you"want"it"done""

!  “When"You’re"Abstract,"Be"Abstract"All"the"Way”"
–  Never"use"a"primi6ve"

!  Example:"

–  double"GetCost();""
–  AddToOrder(double"price);"

!  Versus"

–  Dollar"GetCost();"
–  AddToOrder(Dollar"price);""

""

17"


"6"November"2013"

Observa6on"

!  Reversible"changes"are"oYen"not"equal"in"diﬃculty"
!  Usually"easier"to"deobjec6vey"for"performance"than"it"
is"to"objec6vey"for"code"quality""
!  Example:"

–  double"GetCost()""""Dollar"GetCost()"
–  Dollar"GetCost()"""double"GetCost()""

18"


"6"November"2013"

Testability"and"Design"

!  Crea6ng"tests"ﬁrst"is"a"kind"of"design"
!  Forces"look"at:"
–  Public"method"deﬁni6ons"
–  What"responsibili6es"of"object"are"

!  Easy"testability"6ghtly"correlated"to:"
–  Loose"coupling""
–  Strong"cohesion"

19"


"6"November"2013"

Testability"

!  Diﬃcult"to"unit"test""code"is"oYen:"
–  Tightly(Coupled:""
"I"cannot"test"this"without"instan6a6ng"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"mul6ple"places"to"ensure"it"works"everywhere""

20"


"6"November"2013"

Unit"Tes6ng"

!  Tests"at"low"or"granular"level"
!  Test"confirms"that"code"reflects"one"inten6on"of"system"
!  Good"test"of"our"thought"process:"
–  If"class"does"one"thing"(strong"cohesion)"
!  Then"func6onality"is"testable"
–  If"class"does"not"create"side"effects"in"other"classes,"(loose"
coupling),""
!  Then"testable"individually"

21"


"6"November"2013"

Testability"and"Contracts"

!  Contracts"
–  Seman6c"–"desired"behavior""
–  Syntac6c"–"enforced"by"language""

!  Seman6c"contract"enforced"by"syntac6c"contract"
requires"less"tes6ng"
!  Example:"
–  void"setPriority(int"priority);"
"versus"
–  void"setPriority(Priority"aPriority);"

22"


"6"November"2013"

Quali6es"and"Pathologies"
!  Strong"cohesion"

–  Goal:"classes"do"one"thing"–"easier"to"understand"
–  Pathology:"the"“God"object”"is"as"bad"as"it"gets"

!  Proper"coupling"

–  Goal:"well"defined"rela6onship"between"objects"
–  Pathology:"side"affects"when"have"improper"coupling"

!  No"redundancy"

–  Goal:"once"and"only"once"
–  Pathology:"a"change"in"one"place"must"be"duplicated"in"another"

!  Readability"

–  Goal:"coding"standards"
–  Pathology:"nonVreadable"code"

!  Encapsula6on"

–  Goal:"hide"data,"type,"implementa6on"
–  Pathology:"assump6ons"about"how"something"is"implemented"makes"it"
difficult"to"change"

23"


"6"November"2013"

Emergent(Design(
Refactoring(

24"

"""

"6"November"2013"

Refactoring"

!  Refactoring:""Improving"the"Design"of"Exis6ng"Code"*"
!  “Refactoring"is"the"process"of"changing"a"soYware"

system"in"such"a"way"that"it"does"not"alter"the"external"
behavior"of"the"code"yet"improves"its"internal"
structure.”*"

0
Mar8n(Fowler,"Refactoring:0Improving0the0Design0of0Exis+ng0Code."AddisonVWesley."1999."
*

25"


"6"November"2013"

Types"of"Refactoring"
Refactoring(Bad(Code(
!  Code""smells""
!  Improve"code"quality"
!  Clean"up"code"without"
breaking"system"

26"

Refactoring(Good(Code(
!  Code"is""6ght""
!  New"Requirement"means"
change"in"code"/"design"
!  Way"to"make"change"
without"breaking"system"


"6"November"2013"

Case(Study(
Monitoring"Microwave""
Communica6ons"Hardware"
"

27"

"""

"6"November"2013"

Complete"Requirements"
!  Need"to"monitor"both"chips"and"cards"
–  Program"requests"status"of"either"and"sends"it"""

!  Over"either"a"TCP/IP"connec6on"or"via"eVmail"(SMTP)""

!  Messages"may"be"encrypted""
–  PGP64"bit"or"PGP128"bit"

!  Chip"status"queued"for"sending"up"to"10"minutes"unless"an"error"
–  Card"status"sent"immediately"

!  Conﬁgura6on"ﬁle"gives"transmission"method"to"use"

28"


"6"November"2013"

Accommoda6ng"Change"with"Specializa6on"

!  One"way"problem"could"evolve:"
–  Start"with"Chip"and"TCP/IP"
–  Add"one"func6on"at"a"6me"
–  Accommodate"through"specializa6on"

!  Result"not"preSy"(except"as"in"preSy"common)"

29"


"6"November"2013"

Start"with"ChipTCPIP"Requirement"

Client
ChipTCPIP
+ getAndSendStatus()
# sendWithTCPIP()

30"


"6"November"2013"

Now"Get"Card"with"SMTP"

Client
ChipTCPIP
# getStatus()
# send()

CardSMTP
# getStatus()
# send()

31"


"6"November"2013"

BeSer"Way"

Client

Hardware

ChipTCPIP
# get Stat us()
# send()

32"

CardSMTP
# getStatus()
# send()


"6"November"2013"

Then"Get"Chip"with"SMTP"Requirement"

Client

Hardware

Chip
# getStatus()

ChipTCP
# send()

33"

CardSMTP
# getStatus()
# send()

ChipSMTP
# send()


"6"November"2013"

Finally"Get"Card"with"TCPIP"Requirement"

Hardware

Client


Chip
# getStatus()

ChipTCPIP
# send()

34"

Card
# getStatus()

ChipSMTP
# send()

CardTCPIP
# send()


CardSMTP
# send()

"6"November"2013"

It"Is,"Of"Course,"Worse0

!  Have"not"discussed"varia6ons"of"encryp6on"
–  Will"make"things"worse"

!  Using"switches"instead"of"inheritance""
–  Will"have"coupled"switches"instead"of"class"hierarchy"

35"


"6"November"2013"

Problems"with"This"
!  BriSle.""
–  Not"easily"allow"for"new"deriva6ons"of"Card"and"Chip"
!  Or"new"transmission"types"

!  Redundant.""
–  Changes"in"send()"in"ChipTCPIP"causes"changes"in"CardTCPIP"

!  Weak"cohesion."""
–  Concrete"classes"are"about"mul6ple"things."

!  Mul6ple"varia6ons"cause"combinatorial"(class)"explosion"
–  Increases"maintenance"problems"

!  In"Short:""
–  Using"inheritance"for"specializa6on"does0not0scale0

36"


"6"November"2013"

Combinatorial"Explosion"
Hardware

Client


Card
# getStatus()

Chip
# get Stat us()

CardTCPIP
# send()

ChipTCPIP
# send()

37"

ChipSMTP
# send()

CardSMTP
# send()

CardFTP
# send()

ChipFTP
# send()


"6"November"2013"

Tes6ng"

!  10"Varia6ons"of"sending""
!  10"Varia6ons"of"encryp6ng""
!  10"Varia6ons"of"compressing""
!  How"many"classes"if"use"inheritance?""
!  How"many"if"use"delega6on?"""

38"


"6"November"2013"

Advice(from(the(
Gang(of(Four(

39"

"""

"6"November"2013"

Gang"of"Four"Gives"Us"Guidelines*"

!  Design"to"interfaces"
!  Favor"object"delega6on"over"class"inheritance."

Gamma,(E.,(Helm,(R.,(Johnson,(R.,(Vlissides,(J."Design0PaHerns:0
Elements0of0Reusable0ObjectFOriented0SoIware,"1995,"pp."18,"20,"29."
40"


"6"November"2013"

Design"to"Interfaces"

!  Determine"interface"for"class""
–  Design"to"that,"ignoring"implementa6on"details"
!  Therefore"cannot"couple"to"them"
–  What"you"hide"you"can"change"

!  Stay"at"conceptual"level,"while"designing"
–  Promotes"Cohesion"

41"


"6"November"2013"

Find"What"Varies"and"Encapsulate"It"

!  Iden6fy"varying"behavior"
!  Deﬁne"interface"for"behavior""
–  Tailor"as"you"go"
–  Extract"varia6ons"resul6ng"from"new"requirements"
–  Put"those"into"their"own"interfaces"

42"


"6"November"2013"

Favor"Delega6on"Over"Inheritance"

!  Deﬁne"interface"encapsula6ng"varia6on""
!  Use"delega6on"to"instance"of"an"implementa6on""

Socket0
Socket_cmp1"

Socket"

Socket_cmp2"

Class0Inheritance0to0Specialize0

Compression0
Cmp1"

Cmp2"

Object0delega+on0

1.  Decouples"concepts"
2.  Can"defer"decisions"un6l"run6me"
3.  Small"performance"hit"
43"


"6"November"2013"

Interface"Oriented"Design"

!  To"save"code,"you"can"use""
–  Inheritance""
–  Delega6on"to"another"class""

!  Cannot"inherit"from"two"classes"(other"than"C++)"
!  Therefore"either""
–  Need"to"determine"the"“most"important”"rela6onship""

44"


"6"November"2013"

Interface"Oriented"Design"(2)"

!  Lean"principle""
–  Make"commitment"at"the"last"possible"moment""
–  (Or"not"at"all"if"possible)""

!  Prefactoring"guideline"
–  Avoid"premature"hierarchiliza6on""
–  Don’t"make"hierarchy"unless"it"is"necessary"""

45"


"6"November"2013"

Separate"Use"From"Construc6on"

!  An"object"should"construct"another"object"or"use"
another"object"
–  But"not"both"

!  Implement"construc6on"with"a"factory""

46"


"6"November"2013"

Concept"/"Varia6ons"
Encryption
E128

TCP

E64

FTP

E0

47"

Send

UDP


"6"November"2013"

"
Factory"Example""
// Client Selection
enum EncryptionType {Strong, Weak, None};
Encrypt getEncryptInstance(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”);
} }

48"


"6"November"2013"

Factory"For"Two"Strategies"
enum ChipType {ForCommercial, ForUS,
ForImportantCustomer};
Chip getChip(ChipType ct) {
switch (ct) {
case ForCommercial:
return new Chip(GetEncryptInstance(Weak),
GetSendInstance(TCP));
case ForUS:
return new Chip(GetEncryptInstance(Strong),
GetSendInstance(FTP));

case ForImportantCustomer:
return new Chip(GetEncryptInstance(Weak),
GetSendInstance(FTP);
}}
// Or use table

49"


"6"November"2013"

Emergent(Design(
In"Ac6on"

50"

"""

"6"November"2013"

Emergent"Design"

!  TestVDriven"Development,"integrated"with:"
–  High"quality"code"
–  Knowledge"of"design"paSerns"
–  A~tude"of"building"only"what"you"need"(Agile,"YAGNI)"

!  Allows"for"designs"to"emerge"
!  Can"take"advantage"of"what"we"know"
–  Without"overbuilding"or"overVdesigning."

51"


"6"November"2013"

Requirements"as"“Stories”"
!  Story(1:"Request"the"status"of"a"chip,"encrypt"it"with"PGP64"bit"

encryp6on"and"send"that"status"out"via"TCP/IP"
!  Story(2:"Allow"for"not"encryp6ng"the"status"or"using"either"
PGP64"bit"or"PGP128"bit"encryp6on.""A"configura6on"file"will"
determine"what"(if"any)"encryp6on"is"needed"
!  Story(3:"Support"transmission"via"an"eVmail"connec6on.""A"
configura6on"file"will"determine"which"type"of"transmission"to"
use"
!  Story(4:"Support"ge~ng"and"sending"the"status"for"a"card"as"well"

52"


"6"November"2013"

Emergent"Design:"Star6ng"with"Story"1"

!  Request"status"of"a"chip,"encrypt"it"with"PGP64"bit"
encryp6on"and"send"that"status"out"via"TCP/IP"
!  Implement"simplest"solu6on"possible:"
–  No"extra"func6on"
–  Design"for"full"system"will"emerge"via"refactoring"

53"


"6"November"2013"

Thinking"from"a"Testability"Perspec6ve"

!  What"do"we"need"to"test?"
–  Ge~ng"status"
–  Encryp6ng"a"string"
–  Sending"an"encrypted"string"

!  Straighorward"to"write"tests"for"individual"methods"
!  Where"should"the"methods"lie?"
!  What’s"the"easiest"way?"

54"


"6"November"2013"

TestVFirst"Development"Steps"

1.  Write"a"test"that"expresses"an"intent"of"a"class"in"
system"

– 

Stub"out"class"(enough"to"allow"the"test"to"compile)"

– 

Change"class"just"enough"to"pass"test"

2.  Fail"the"test"(don't"skip"this)"

3.  Pass"the"test"
4.  Examine"class"for"coupling,"cohesion,"redundancy,"and"
clarity"problems."""

– 

Refactor."

5.  Pass"the"test"
6.  Return"to"#1"un6l"all"inten6ons"are"expressed"
55"


"6"November"2013"

Solu6on"Diagrammed"

Client

Chip
# getStatus()
# encrypt()
# send()

Encrypt
+ encrypt()

TCPIP
+ transmit()

56"


"6"November"2013"

Why"Is"this"BeSer?"

!  Clear"what"pieces"do"and"how"they"relate"
–  Increases"extensibility"
–  Eases"maintainability"

!  Some6mes"requirements"misVlead"us"

57"


"6"November"2013"

Transi6on"

!  Remember:"Two"Kinds"of"Refactoring"
1.  Refactoring0Bad0Code:""
!  To"improve"code"quality"
2.  Refactoring0Good0Code:"
!  To"implement"new/changed"requirement,"
–  Now"going"to"do"the"second"

58"


"6"November"2013"

Story"2:"Mul6ple"Encryp6ons"

!  Allow"for"using"no"encryp6on,"PGP64"bit"encryp6on"or"
PGP128"bit"encryp6on"

59"


"6"November"2013"

Refactoring"Says"to"Restructure"Before"Adding"

!  Refactoring:""
–  Change"code"before"adding"new"func6on."
–  Keep"func6on"same,"but"restructure"code"to"improve"it"

!  Advantages:"
–  If"upVfront"tes6ng,"tests"don’t"need"to"change"
!  Doing"same"things"
–  Always"have"something"that"works"
–  If"one"step"at"a"6me"and"something"breaks"
!  More"likely"to"know"what"caused"it""

60"


"6"November"2013"

How"Can"We"Most"Easily"Test"Things?"

!  Need"to"test"every"encryp6on"
!  Want"to"deal"with"encryp6ons"same"way."
!  Easy"if"have"a"common"interface"for"encryp6ons"
!  If"interfaces"aren’t"the"same,"then"either:"
–  Chip"has"to"deal"with"diﬀerences""
–  Use"design"paSerns"to"hide"varia6ons"
!  Requires"wrapping"diﬀerences"

61"


"6"November"2013"

OpenVClosed"Principle"
!  Ivar"Jacobson"said:""
–  “All"systems"change"during"their"life"cycles.""This"must"be"borne"in"mind"
when"developing"systems"expected"to"last"longer"than"the"ﬁrst"version”"

!  Bertrand"Meyer"summarized"this"as:""

–  SoYware"en66es"(classes,"modules,"func6ons,"etc.)"should"be"open"for"
extension,"but"closed"for"modiﬁca6on"

!  In"short:"

–  Design"modules"so"that"they"never"change."""
–  When"requirements"change,"add"new"modules"to"handle"things"

For"a"good"ar6cle"on"the"OpenVClosed"Principle,"see"www.objectmentor.com/publica6ons/ocp.pdf""

62"


"6"November"2013"

Refactoring"to"OpenVClosed"

!  First"refactor"code"so"can"add"new"func6on"following"
OCP"
!  Then"add"new"code"

63"


"6"November"2013"

First,"Add"Needed"Interface"and"Factory"

Client

Used by Client
or Chip
Config

Chip

Encrypt

# getStatus()
# encrypt()
# send()

+ encrypt()

Encrypt64

TCPIP
+ transmit()

+ getEncrypt()

64"


"6"November"2013"

Now,"Can"Put"in"the"New"Func6on"
! 
! 
! 
! 
! 
! 

Someone"must"determine"which"encryp6on"to"use"
Maybe"configura6on"object"can"do"that""
Client"object"asks"configura6on"object"what"to"use"
Chip"object"given"needed"behavior""
Now"add"encrypt128"and"no"encrypt"op6ons"
Note:""
–  Chip"object"could"talk"to"configura6on"object"
–  Then"Client"must"give"Chip"informa6on"configura6on"object"needs"

"

65"


"6"November"2013"

Then,"Add"New"Implementa6ons"

Chip

Used by Client
or Chip

+ encrypt()

TCPIP

EncryptNull

Encrypt64

Encrypt128

+ transmit()

Config
+ getEncrypt()

66"

Encrypt

+ get AndSendS tatus()
# get Stat us()
# enc rypt ()
# send()

Client

makes one of these


"6"November"2013"

Story"3"

!  Support"transmission"via"an"eVmail"connec6on.""A"
conﬁgura6on"ﬁle"will"determine"which"type"of"
transmission"to"use"
!  Testability"suggests"concept"of"Transmission"
–  Don’t"have"to"test"all"combina6ons"

!  Design"PaSerns"tell"us"same"thing"

67"


"6"November"2013"

Want"to"Follow"Gang"of"Four"Advice"

!  Because"transmission"will"vary,"
–  Encapsulate"it"and"delegate"to"it"from"Chip"

!  To"implement"
–  First"pull"out"exis6ng"transmission"func6onality"into"own"class"""

!  No"extra"cost"by"doing"this"now"instead"of"when"
possibility"ﬁrst"no6ced"

68"


"6"November"2013"

Refactor"First"
Client

Used by Client
or Chip

Chip

Encrypt

# getStatus()
# encrypt()
# send()

+ encrypt()

EncryptNull

Encrypt64

Transmit
+ transmit ()

Encrypt128

Config
+ getEncrypt()
+ getTransmit()

makes this

TCPIP

makes one of these

69"


"6"November"2013"

Add"Other"TransmiSers"
Client

Used by Client
or Chip

Chip

Encrypt

# getStatus()
# encrypt()
# send()

+ encrypt()

EncryptNull

Encrypt64

Transmit
+ transmit()

Encrypt128

Config
+ get Encrypt()
+ get Transmit()

TCPIP

SMTP

makes one of these
makes one of these

70"


"6"November"2013"

Story"4:"Support"Cards"

!  For"tes6ng"reasons"
–  Don’t"want"to"have"to"handle"diﬀerent"func6onal"test"cases"
when"we"have"Cards"or"Chips"
–  Want"to"handle"them"together"

!  Want"Cards"and"Chips"to"appear"to"be"the"same"to"the"
Client"
!  Implement"with"twoVstep"RefactorVOCP"shuﬄe"

71"


"6"November"2013"

First,"Refactor"So"OCP"Can"Apply"
Hardware"

+ getAndSendStatus()"
# getStatus()"
# encrypt()"
# send()"

Encrypt"

Client"

+ encrypt()"

Chip"

EncryptNull"
Used by Client "
or Hardware"

Encrypt64"

Transmit"

+ transmit()"

Encrypt128"

Config"

+ getEncrypt()"
+ getTransmit()"
+getHardware()"

TCPIP"

SMTP"

makes one of these"
makes one of these"
72"


"6"November"2013"

Then,"Add"New"Func6on"
Hardware"
+ getAndSendStatus()"
# getStatus()"
# encrypt()"
# send()"

Encrypt"

Client"

+ encrypt()"

Card"

Used by Client "
or Hardware"

Chip"

!(
aRern
e(p
EncryptNull" Encrypt64"
(bridg
his(is(a
T
Transmit"
+ transmit()"

Encrypt128"

Config"

+ getEncrypt()"
+ getTransmit()"
+getHardware()"

TCPIP"

SMTP"

makes one of these"
makes one of these"
73"


"6"November"2013"

"A"Few"Comments"

!  Not"coincidence"or"good"luck"change"is"easy"
!  Happened"because"
–  No"redundancy""
–  Unrelated"things"in"different"classes"

!  Low"level"dis6nc6ons"easy"to"see"
–  Even"if"immediate"benefit"is"not"

!  Use"them"because"they"represent"very"low"cost"
–  Will"result"in"significant"gains"if"things"change"(which"they"
almost"certainly"will)"

74"


"6"November"2013"

Code(Quali8es((
As(A(Guide(

75"

"""

"6"November"2013"

Using"Coding"Quali6es"

!  Could"arrive"by"following"coding"quali6es.""
!  TDD,"DPs"and"CVA"(Commonality/Variability"
Analysis)"are"related"to"code"quali6es""
–  Easy"to"use,"so"use"them""

!  However,"to"illustrate,"say"started"with:"
Client
ChipTCPIP
# sendWithTCPIP()

!  and"then"got"another"transmiSer."

76"


"6"November"2013"

Handling"This"in"Chip"Weakens"Cohesion"
!  Handle"varia6on"as:"
private void sendStatus(String anInfo) {
if (transType== TCPIP) sendStatusTCPIP(anInfo);
else sendStatusSMTP(anInfo);
}

!  Requires"Chip"class"to"remember"more"detail"about"
transmission."

–  More"than"how"TCP/IP"works"
–  Now""SMTP"stuﬀ""
–  This"erodes"cohesion""

!  So"split"out"TransmiSer."

77"


"6"November"2013"

Using"Encapsula6on"

!  Consider"how"to"break"up"func6onality"into"classes"
–  Where"as"much"as"possible"is"encapsulated""

!  Implementa6on"encapsula6on"implies""
–  Pull"out"encryp6on"

!  Design"encapsula6on"means""
–  Chip"should"not"know"about"mul6ple"encryp6ons"
–  Hence"polymorphism"and"factory"

78"


"6"November"2013"

Diﬀerent"Approaches"for"Diﬀerent"Situa6ons"

!  Emergent"Design"allows"forward"mo6on:"
–  When"certainty"
!  PaSern"Oriented"Design"
–  When"a"lack"of"certainty"
!  TestVDriven"Development,"supported"by"
–  Refactoring"

!  PaSerns"help"us"see""leading"edge""of"new"designs"

"

79"


"6"November"2013"

Not(An(Ending,(
But(a(Beginning(
"
"

80"

"""

"6"November"2013"

Conclusions(1)"

!  Design"emerges"from:"
–  Concepts"and"varia6ons"(Commonality/Variability"Analysis)""
–  Abstrac6ons"(and"encapsula6on)"
–  Refactoring,"with"adherence"to"good"principles"
–  Thinking"about"paSerns,"which"reﬂect"past"adherence"to"
good"principles"

81"


"6"November"2013"

Conclusions"(2)"

!  Agility"requires"ﬂexibility"
!  Flexibility"comes"from:"
–  Adherence"to"Good"Principles,"
–  Maintaining"awareness"of"emergent"design,"
–  Understanding"the"forces"of"change"
–  Recognizing"applicable"paSerns"in"a"design"

"

!  We"can"create"maintainable"code!"

82"


"6"November"2013"

!  Thank"you"
!  Please"ﬁll"out"evalua6ons""

83"


"6"November"2013"

0

Supplemental
(

84"


"6"November"2013"

Designing(with(
PaRerns(

85"

"""

"6"November"2013"

The"Bridge"PaSern"
!  GoF(Intent:"“DeVcouple"an"abstrac6on"from"its"implementa6on"
so"that"the"two"can"vary"independently”*"
!  In"example:"

–  Abstrac6on"is"Hardware"V"Chips"and"Cards)"
–  Implementa6on"is"oneaspect"of"its"responsibility"(TCP/IP"communica6on"
and"eVmail"communica6on)"

!  All"implementa6ons"must"look"same"to"abstrac6on"

Gamma, E., Helm, R., Johnson, R., Vlissides, J. Design
Patterns: Elements of Reusable Object-Oriented Software, 1995.
86"


"6"November"2013"

An"Abstrac6on"(Hardware)"Tightly"Coupled"
to"Its"Implementa6on"(Transmission)"

Hardware

Client


Chip

Card



ChipTCPIP

ChipSMTP

+ getAndSendStatus() + getAndSendStatus()
# sendWithTCPIP()
# sendWithSMTP()

87"

CardTCPIP

CardSMTP

# sendWithTCPIP()
# sendWithSMTP()


"6"November"2013"

Bridge"Would"Tell"Us"to"Build"It"This"Way"

Client

Transmit

Hardware

+ sendInfo(string)
+ start()
+ done()


Chip

Card



TCPIP
+ sendInfo(string)
+ start()
+ done()

88"


SMTP
+ sendInfo(string)

"6"November"2013"

Refactoring(a(
Poor(Design
(

89"

"""

"6"November"2013"

Poor"Design"as"a"Result"of"Using"En66es""
and"Behaviors"/"Specializa6on"

Hardware

Client


Chip

Card



ChipTCPIP

ChipSMTP

# sendWithTCPIP()
# sendWithSMTP()

90"

CardTCPIP

CardSMTP

# sendWithTCPIP()
# sendWithSMTP()


"6"November"2013"

Pull"Out"Duplica6on"of"Transmission"
Hardware

Client


Chip

Card



ChipTCPIP

ChipSMTP

CardTCPIP

CardSMTP

+ getAndSendStatus() + getAndSendStatus() + getAndSendStatus() + getAndSendStatus()

TCPIP
+ sendTCPIP(string)
+ start()
+ done()

91"

SMTP
+ sendSMTP(string)


"6"November"2013"

Create"Trans0Class"to"Simplify"Things"
Hardware

Client


Chip

Card



ChipTCPIP

CardTCPIP

ChipSMTP

CardSMTP

+ getAndSendStatus() + getAndSendStatus() + getAndSendStatus() + getAndSendStatus()

Transmit
+ sendInfo(string)
+ start()
+ done()

TCPIP
+ sendInfo(string)
+ start()
+ done()

92"

SMTP
+ sendInfo(string)


"6"November"2013"

Derived"Classes"Now"Not"Needed"
Hardware

Client


Chip

Card



Transmit
+ sendInfo(string)
+ start()
+ done()

TCPIP
+ sendInfo(string)
+ start()
+ done()

93"

SMTP
+ sendInfo(string)


"6"November"2013"

Can"Keep"Reference"in"Hardware"

Client

HWComp

Transmit
Chip

Card


+ sendInfo(string, int)
+ start()
+ done()

TCPIP
+ start()
+ done()

94"


SMTP

"6"November"2013"

Technical(
Solu8ons(to(Aid(
Scaling(

95"

"""

"6"November"2013"

Keep"Technical"Dependencies"Low"

!  Ways"minimize"dependencies"of"different"projects"on"
each"other"

–  Design"PaSerns"
–  APIs"to"return"Value"Objects"
–  Mocks"to"provide"layering""
!  And"to"avoid"scheduling"dependencies"

!  Difficul6es"when"one"project"uses"another"
–  Use"component"tes6ng"as"a"method"of"decoupling"components"
–  Implement"with"up"front"testVspecifica6on"and"mocks"

!  Minimize"impacts"that"do"occur"with"Test"Driven"
Development"

96"


"6"November"2013"

Using"Design"PaSerns"

!  Design"paSerns"
–  How"to"deal"with"implementa6ons"at"the"conceptual"level,"
i.e.,"through"an"API"
–  If"added"or"changed"implementa6on""
!  Using"code"does"not"change"
–  Handles"varia6on"

!  DP"can"be"used"in"agile"projects"eﬀec6vely.""

97"


"6"November"2013"

Decoupling"Projects"
!  4"Groups"(A,"B,"C,"D)"
–  All"use"a"network"maintained"by"E"
–  These"groups"all"need"informa6on"from"each"other"
–  They"stated"what"info"was"needed"at"start"of"project"

Group"B"

Group"A"

Group"E"

Group"C"
98"

Group"D"

"6"November"2013"

Good"Start,"Bad"Finish"

!  New"informa6on"becomes"needed."
–  Group"A"needs"something"from"Group"B"
–  Group"B"is"busy"and"not"par6cularly"helpful"
–  Group"B"will"not"allow"group"A"to"touch"their"code"

!  How"could"we"have"set"it"up"to"resolve"these"issues?"
–  While"not"requiring"us"to"be"preVcogni6ve?"

!  Use"the"ValueVObject"PaSern"

99"


"6"November"2013"

Value"Object"PaSern"
!  Have"each"group"have"an"API"that"has:"

–  setUp("flag,"GetInfo"useThis)"–"used"to"say"which"value"object"to"use."
–  ValueObject"getInfo(flag)"

!  Calling"program"knows"

–  Type"of"value"object"to"use""
!  and"the"rou6ne"to"fill"it"out"
–  Knows"what"it"gets"back"
!  Can"use"that"par6cular"informa6on"

100"


"6"November"2013"

Shown"in"the"UML"
Group"A"

Group"B"

Group"C"

+setUp(ﬂag,"GetInfo"useThis)"
"""
""""
+getInfo(ﬂag)"

Group"D"
ValueObject"

GetInfo"
+ValueObject"getInfo()"

ValueObjectA"

ValueObjectC"

ValueObjectD"

GetInfoForA"

GetInfoForC"



GetInfoForD"
101"


"6"November"2013"

How"This"Works"
Group"A"

Group"B"

Group"C"

+setUp(ﬂag,"useThis)"
"""
""""
+getInfo(ﬂag)"

Group"D"
ValueObject"

GetInfo"

ValueObjectA"

ValueObjectC"

ValueObjectD"

GetInfoForA"

GetInfoForC"



GetInfoForD"
102"


"6"November"2013"

0

103"

Mocks(on(a(Large(
Scale(


"6"November"2013"

Managing"Dependencies"

!  Let’s"say"group"A"needs"to"use"the"system"built"by"

group"B""
!  Group"A"speciﬁes"to"Group"B"what"group"B"needs"to"
provide"
!  Group"A’s"and"Group"B’s"understanding"is"changing"as"
6me"goes"by"
!  How"can"we"manage"this?"

104"


"6"November"2013"


Team"A:"“We"need"
this”"
“When"your"system"
does"this”"

105"

Team"B:"“How"will"
we"know"we’ve"done"
that?”"
How"should"team"B"
respond?"


"6"November"2013"


Team"B"should"build"a"mock"of"their"system"
The"mock"sa6sﬁes"the"tests"that"team"A"speciﬁes"
A’s""
System"

106"

Uses"

Mock"


"6"November"2013"

A"Mock"as"Requirements/Test"

!  Note"mock"fulfills"the"following"uses:"
–  Defines"the"requirements"for"A"
–  Can"be"used"by"A"to"run"while"team"B"builds"it"
–  Is"an"executable"specifica6on"for"team"B"
!  So"they"can"see"if"they"are"building"the"right"thing"

!  Tests"that"define"the"mock"can"be"used"as"tests"for"

team"B’s"system"
!  What"happens"if"team"A’s"or"team"B’s"understanding"
changes?"
–  The"mock"must"be"updated"

107"


"6"November"2013"

Resources"
!  Resources:"www.netobjec6ves.com/resources""

! 
! 
! 
! 
! 

– 
– 
– 
– 
– 

Webinars/Training"Videos"(PowerPoint"with"audio)"
Ar6cles"and"whitepapers"
Pre/post"course"support"Suppor6ng"materials"
Quizzes"
Recommended"reading"paths"

Blogs"and"podcasts:"blogs.netobjec6ves.com"
Annotated"Bibliography"
AYerVCourse"Support"(students"only)"
Addi6onal"Training"
Two"User"Groups"

–  hSp://tech.groups.yahoo.com/group/leanagile""
–  hSp://tech.groups.yahoo.com/group/leanprogramming""
Join"our"eVmail"list"to"receive"regular"updates"and"informa6on"
about"our"resources"and"training"of"interest"to"you"

108"


"6"November"2013"

Context"

!  How"do"you"avoid"over"and"under"design"in"agile"
projects?"

109"


"6"November"2013"

Exercise"

1.  Imagine"a"6me"you"built"something"in"2"steps"(or"

more)"and"had"significant"rework"in"later"steps"
because"of"not"looking"ahead."That"is,"this"is"the"
situa6on"you"are"concerned"about."
2.  Now,"imagine"you"can"go"back"and"do"the"first"step"
again"with"the"following"condi6ons:"
1.  You"know"everything"you"know"now"
2.  You"can"design"it"differently,"but"you"can’t"add"anything"that"
isn’t"needed"for"the"first"step"

3.  How"would"you"design"it?"
110"


"6"November"2013"

Good"Ques6ons"to"Ask"

!  How"would"you"do"your"design"if"you"knew"later"that"
whatever"you"did"now"was"wrong?""

111"


"6"November"2013"

Emergent(Design(
Design"PaSerns"and"
Refactoring"for"Agile"
Development"

112"

"""

"6"November"2013"

Test:"What"Does"It"Mean?"
!  1(a"chiefly0Bri+sh":(CUPEL"b((1)":"a"cri6cal"examina6on,"

observa6on,"or"evalua6on":(TRIAL;"specifically":"the'procedure'of'
submi1ng'a'statement'to'such'condi4ons'or'opera4ons'as'will'
lead'to'its'proof'or'disproof'or'to'its'acceptance'or'rejec4on(<a"
test"of"a"sta6s6cal"hypothesis>"(2)":"a"basis"for"evalua6on":(
CRITERION"c":"an"ordeal"or"oath"required"as"proof"of"conformity"
with"a"set"of"beliefs""

!  Test"can"be"thought"of:"
–  Specifica6on"that"says"you"are"doing"what"you"should"be"
doing"

113"


"6"November"2013"

Inheritance(
Versus(Interface
(

114"

"""

"6"November"2013"

Inheritance"Issues""

!  Combines"two"perspec6ves"
–  Common"interface"(speciﬁca6on)"
!  Derived"classes"play"the"same"role"as"base"class""
–  Common"implementa6on""
!  inherited"methods,"aSributes"

!  OYen"mix"up"these"perspec6ves"""

115"


"6"November"2013"

Changing"Base"vs"Interface"

Base Class

Interface

Methodone()

Methodone()

Addedmethod() //New

Addedmethod() // New

Derived Class
Does Addedmethod() need
overriding ?

116"

Implementing Class
Addedmethod() needs
implementation


"6"November"2013"

Inheritance"Versus"Interface"
BaseClass
Method();
NewMethod():

What happens if new method added to base class?
Is it applicable to all derived classes?
Do you know everything that is derived?
What if four derived classes and two use same override?
Need a helper class

DerivedClass AnotherDerivedClass
Method() { anotherway;}
Interface
Method();
NewMethod():

Fourth
OneMore
DerivedClass DerivedClass
Method()
{ anotherway;}

AnotherImplementingClass InterfaceHelper
ImplementingClass
Method();
NewMethod():
OneMoreImplementingClass
AnotherWay();
FourthImplementingClass
117"


"6"November"2013"

Prefactoring"Guideline"

!  Avoid"premature"hierarchiliza6on""
–  Don’t"create"hierarchies"un6l"you"really"need"them""

!  It"is"easier"to"create"the"right"hierarchy"than"to"
dehierarchalize"the"wrong"one"

118"


"6"November"2013"

Avoiding Overdesign and Underdesign

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