Wiley patterns in java a catalog of reusable design patterns illustrated with UML volume 1 2nd edition sep 2002 ISBN 0471227293

PatternsinJava,Volume1—A
CatalogofReusableDesign
PatternsIllustratedwithUML,
SecondEdition
PatternsinJava,Volume1:ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
byMarkGrand
JohnWiley&Sons©2002


PatternsinJava,Volume1—ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
MarkGrand

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Acknowledgments
Iwouldfirstliketoacknowledgethepatienceofmywife,Nicole.
Withouthersupport,thissecondeditionofPatternsinJava,Volume1
wouldnothavebeenpossible.
IwouldalsoliketoacknowledgethefeedbackthatIhavereceived
frommanyreaderswhoseemailstomesuggestedimprovementsand
correctionsthathavegoneintothissecondedition.Iwouldliketo
singleoutEdRemmell,whoorganizedadiscussiongrouparoundmy
bookandtookthetimetosendmesummariesofthediscussions.
Otherreaderswhotookthetimeandtroubletosendmeuseful
questionsandcommentsare(inalphabeticalorder):NaderAfshar,
DerrickAmpy,BarryW.Anderson,PaulE.Andrighetti,KaushikBarot,
TedBeckett,PabloBellver,DavideDeBenedictis,DaveBusse,Mike
Carlin,MaxChandler,JohnClarke,CharlieCrook,ChristianCryder,
CarlosDevoto,CyrusDoomasia,RodrigoFigueiredo,JeffFrench,
BrentFry,SrinivasGanti,DanielL.Gleneck,SatishGupta,BartonW.
Hammond,ShannonHarvey,JudyHousman,HongHsu,Rob
Hulsebos,GaryJanes,BrianKrahmer,ErikBakKristensen,Robert
Laganière,LaureneO.Laidlaw,AllenLee,RogerLee,TimLethbridge,
CharlesMagid,KurtMatthys,PhilMcGlauchlin,BarryMiddlebrook,
SadiqMohammed,ThomasMoore,RaymondNaseef,JaimeNino,


JeffOakes,SudeshPalekar,GregPearman,JimPhipps,JohnPinto,

JonPoploskie,RajPrathinidhi,AndyPryke,TulsiRai,DamithC.
Rajapakse,StevenRanieri,JohnSargeant,RobertAllanSchwartz,
GregScott,JoeSharp,MikeShivas,EduardoSilva,Daniel
Stainhauser,SteveStephens,ChristianSvenstrup,OyvindTeig,Alan
Thompson,RichardTomlinson,BruceWallace,DieterWankmueller,
MarkWaschkowski,RichardWilliams,JoeWissmann,RobertWragg,
WayneWylupski,andHongYan.

AcknowledgmentsfromtheFirstEdition
IwanttothankCraigLarman,mymostconscientiousreviewer.He
convincedmeoftheimportanceofpatterns.Craigalsoprovidedme
withmuchinvaluablefeedbackontheuseofUMLandthe
presentationofpatterns.Hisvaluablesuggestionsgreatlyimproved
thewaythatIpresentthepatternsinthisbook.
JackHarichwasanothermanuscriptreviewerwhomademanyuseful
suggestionsabouttheorganizationofthisbook.Heconvincedmeto
expandmycoverageoffundamentalpatterns.Healsosuppliedthe
examplethatIusefortheStatepattern.
BradAppletonprovidedmewiththemostvoluminousanddetailed
comments.
TheUIUCpatternsgroupprovidedsomeinsightfuldiscussionsforthe
patternsinthisbook.Theparticipantsinthosediscussionsincluded
BrianFoote,EdPeters,DragosMalonescu,PeterHatch,Don
Roberts,JosephW.Yoder,RalphJohnson,JohnBrant,James
Overturf,JeanPierreBriot,EijiNabika,HiroNakamura,andIanChai.
Ialsowanttoacknowledgesomeofmyotherreviewers,inparticular
MichealWheatonandMichealPair.

AbouttheAuthor

MarkGrandisanAtlanta-basedconsultantwithover23yearsof
experiencespecializingindistributedsystems,object-orienteddesign,
andJava.Hewasthearchitectforthefirstcommercialbusiness-tobusiness(B2B)e-commerceproductfortheInternet.Heiscurrently
workingonanopensourceframeworkforgluingcomponentsand
programsintoanapplication.
MarkGrandismostwidelyknownforhisbest-sellingPatternsinJava
books.InadditiontoteachingJavaforSunandothertraining
organizations,Markhasbeeninvolvedinseverallarge-scale
commercialJavaprojects.
PriortohisinvolvementwithJava,Markspentover11yearsasa
designerandimplementeroffourth-generationlanguages(4GLs).His
mostrecentroleinthatveinwasasthearchitectandprojectmanager
foranelectronicdatainterchangeproduct.Markhasworkedwitha
numberofinformationtechnology(IT)organizationsincapacitiessuch
assoftwarearchitect,databasearchitect,networkdesignerand
administrator,andSunSystemadministrator.Hehasbeeninvolved
withobject-orientedprogramminganddesignsince1982.


PatternsinJava,
Volume1:A
Catalogof
ReusableDesign
Patterns
Illustratedwith
UML,Second
Edition
ISBN:0471227293
by

Mark
Grand
JohnWiley&Sons
2002(580pages)

In-depthcoverage
offorty-sevenJava
designpatterns.

TableofContents BackCover
TableofContents
PatternsinJava,Volume1—ACatalogofReusable
DesignPatternsIllustratedwithUML,SecondEdition
Chapter1 - IntroductiontoSoftwarePatterns


Chapter2 - OverviewofUML
Chapter3 - TheSoftwareLifeCycle
Chapter4 - FundamentalDesignPatterns
Chapter5 - CreationalPatterns
Chapter6 - PartitioningPatterns
Chapter7 - StructuralPatterns
Chapter8 - BehavioralPatterns
Chapter9 - ConcurrencyPatterns
OverviewofPatternsinJava,Volumes1
Appendix through3
Bibliography
Index
ListofFigures
ListofTables

ListofSidebars



Chapter1-Introductionto
SoftwarePatterns
PatternsinJava,Volume1:ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
byMarkGrand
JohnWiley&Sons©2002


Chapter1:IntroductiontoSoftwarePatterns


Overview
Softwarepatternsarereusablesolutionstorecurringproblemsthat
weencounterduringsoftwaredevelopment.Becausethisbookisall
aboutsoftwarepatterns,theyaresimplyreferredtoaspatterns
throughout.
Whatmakesabright,experiencedprogrammermuchmoreproductive
thanabright,butinexperiencedprogrammer?Experience.
Experiencegivesprogrammersawealthofwisdom.Asprogrammers
gainexperience,theyrecognizethesimilarityofnewproblemsto
thosetheyhavesolvedinthepast.Withevenmoreexperience,they
recognizethatsolutionstosimilarproblemsfollowrecurringpatterns.
Withknowledgeofthesepatterns,experiencedprogrammerscan
recognizeaproblemtowhichspecificpatternsapplyandimmediately
determinethesolutionwithouthavingtostoptoanalyzetheproblem

first.
Whenaprogrammerdiscoversapattern,it’sjustaninsight.Inmost
cases,togofromanunverbalizedinsighttoawell-thought-outidea
thattheprogrammercanclearlyarticulateissurprisinglydifficult.It’s
alsoanextremelyvaluablestep.Whenweunderstandapatternwell
enoughtoputitintowords,weareabletointelligentlycombineitwith
otherpatterns.Moreimportant,onceputintowords,apatterncanbe
usedindiscussionsamongprogrammerswhoknowthepattern.Such
discussionsallowprogrammerstomoreeffectivelycollaborateand
combinetheirwisdom.Theycanalsohelpavoidthesituationinwhich
programmersargueoverdifferentsolutionstoaproblembutfindthat
theywereactuallythinkingofthesamesolution,onlyexpressingitin
differentways.
Puttingapatternintowordshasanadditionalbenefitforless
experiencedprogrammerswhohavenotyetdiscoveredthepattern.
Onceapatternhasbeenputintowords,moreexperienced
programmerscanteachittoprogrammerswhoaren’tfamiliarwiththe
pattern.


Theintendedvalueofthisbookisthatitprovideexperienced
programmerswithacommonvocabularytodiscusspatterns.Itshould
alsoallowprogrammerswhohavenotyetdiscoveredapatternto
learnaboutthepattern.
Althoughthisbookincludesasubstantialbreadthofpatterns,youmay
discoveradditionalpatternsyourself.Somepatternsthatyoudiscover
maybehighlyspecializedandofinterestonlytoasmallnumberof
people.Otherpatternsmaybeofbroadinterestandworthyof
inclusioninafuturevolumeofthisbook.Ifyouwishtocommunicate
suchapatterntothisbook’sauthor,youmaysendanemailto

Thepatternscatalogedinthisbookconveyconstructivewaysfor
organizingpartsofthesoftwaredevelopmentcycle.Thereare,
however,nonconstructivepatternsthatcanrecurinprograms.These
arecalledAntiPatternsbecausetheycancanceloutthebenefitsof
patterns.ThisbookdoesnotattempttocatalogAntiPatterns,forthe
subjectiswellcoveredinotherbooks.
PatternsandAntiPatternsaresimilarbutfundamentallydifferent.The
pointofapatternistorecognizewhenyouhavetheopportunityto
applyagoodsolutiontoaproblem.ThepointofanAntiPatternisto
recognizethenatureofabadsituationandsuggestsolutions.


Chapter1-Introductionto
SoftwarePatterns
PatternsinJava,Volume1:ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
byMarkGrand
JohnWiley&Sons©2002


PatternsDescription
Patternsareusuallydescribedusingaformatthatincludesthe
followinginformation:
Anamethatiscommonlyusedforthepattern.Alternative
namesaregivenincaseswherethepatternisknownbymore
thanonename.
Adescriptionoftheproblemthatincludesaconcreteexample
andasolutionspecifictotheconcreteproblem.

Asummaryoftheconsiderationsthatleadtotheformulation
ofageneralsolutionortheavoidanceofthesolution.
Ageneralsolution.
Theconsequences––goodandbad––ofusingthegiven
solutiontosolveaproblem.
Alistofrelatedpatterns.
Patternbooksdifferinhowtheypresentthisinformation.Theformat
usedinthissetofbooksvarieswiththephaseofthesoftwarelife
cyclethatthepatternaddresses.Thepatternsinthisvolumeareall
relatedtothedesignphase.Thedescriptionsofdesign-phase-related
patternsinthisvolumeareorganizedintosectionswiththefollowing
headings:

PatternName
Theheadingofthissectionconsistsofthenameofthepattern.Most
patternsdon’thaveanyadditionaltextunderthisheading.Forthose
thatdo,thissectioncontainsalternatenamesforthepatternor
informationaboutthederivationorgeneralnatureofthepattern.

Synopsis
Thissectioncontainsabriefdescriptionofthepattern.Thesynopsis


conveystheessenceofthesolutionprovidedbythepattern.The
synopsisisprimarilydirectedatexperiencedprogrammerswhomay
recognizethepatternasonetheyalreadyknowbutforwhichthey
maynothavehadaname.
Don’tbediscouragedifyoudon’trecognizeapatternfromitsname
andsynopsis.Instead,carefullyreadthroughtherestofthepattern
descriptiontounderstandit.

Context
Thissectiondescribestheproblemthatthepatternaddresses.For
mostpatterns,theproblemisintroducedintermsofaconcrete
example.Afterpresentingtheproblemintheexample,theContext
sectionsuggestsadesignsolutiontotheproblem.

Forces
TheForcessectionsummarizestheconsiderationsthatleadtothe
generalsolutionpresentedintheSolutionsection.Itmayalsopresent
reasonstonotusethesolution.Thereasonstouseornotusethe
solutionarepresentedasabulletedlist:
J

Reasonstousethesolutionarebulletedwithahappyface.

L

Reasonstonotusethesolutionarebulletedwithasadface.

Solution
TheSolutionsectionisthecoreofthepattern.Itdescribesageneralpurposesolutiontotheproblemthatthepatternaddresses.

Implementation
TheImplementationsectiondescribesimportantconsiderationswhen
usingthesolution.Itmayalsodescribesomecommonvariationsor
simplificationsofthesolution.

Consequences

TheConsequencessectionexplainstheimplications––goodand
bad––ofusingthesolution.Mostconsequencesareorganizedinto
bulletpointsasfollows:
J

Goodconsequencesarebulletedwithahappyface.

l

Neutralconsequencesarebulletedwithadot.

L

Badconsequencesarebulletedwithasadface.

JavaAPIUsage
WhenthereisanappropriateexampleofthepatterninthecoreJava
API,it’spointedoutinthissection.Thosepatternsthatarenotusedin
thecoreJavaAPIdonothavethissectionintheirdescription.

CodeExample
Thissectioncontainsacodeexamplethatshowsasample
implementationforadesignthatusesthepattern.Inmostcases,this
designisdescribedintheContextsection.

RelatedPatterns
Thissectioncontainsalistofpatternsthatarerelatedtothepattern
described.

Chapter1-Introductionto
SoftwarePatterns
PatternsinJava,Volume1:ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
byMarkGrand
JohnWiley&Sons©2002


ABriefHistoryofPatterns
Theideaofsoftwarepatternsoriginallycamefromthefieldof
architecture.ChristopherAlexander,anarchitect,wrotetwo
revolutionarybooksthatdescribepatternsinbuildingarchitectureand
urbanplanning:APatternLanguage:Towns,Buildings,Construction
(OxfordUniversityPress,1977)andTheTimelessWayofBuilding
(OxfordUniversityPress,1979).Theideaspresentedinthosebooks
areapplicabletoanumberoffieldsoutsideofarchitecture,including
softwaredevelopment.
In1987,WardCunninghamandKentBeckusedsomeofAlexander’s
ideastodevelopfivepatternsforuser-interfacedesign.They
publishedapaperontheuser-interfacepatternsatOOPSLA-87
entitled“UsingPatternLanguagesforObject-OrientedPrograms.”
Intheearly1990s,ErichGamma,RichardHelm,JohnVlissides,and
RalphJohnsonbeganworkononeofthemostinfluentialcomputer
booksofthelastdecade:DesignPatterns.Publishedin1994and
oftencalledthe“GangofFour,”orGoF,book,itpopularizedtheidea
ofpatternsandwasthegreatestsingleinfluenceonthisbook.
Thisbookisasecondedition.Additionalpatternshavebeenadded
thatwerenotinthefirstedition.Manyimprovementssuggestedby

readersofthefirsteditionhavebeenincorporatedintothepatterns.
ExampleshavebeenchangedtoreflectmorerecentversionsofJava.
Botheditionsofthisbookrepresentanevolutionofpatternsand
objectssincetheGoFbookwaspublished.TheGoFbookusedC++
andSmalltalkforitsexamples.ThisbookusesJavaandtakesa
ratherJava-centricviewofmostthings.WhentheGoFbookwas
written,theUnifiedModelingLanguage(UML)didnotexist;now,itis
widelyacceptedasthepreferrednotationforobject-orientedanalysis
anddesign,anditisthenotationusedinthisbook.


Chapter1-Introductionto
SoftwarePatterns
PatternsinJava,Volume1:ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
byMarkGrand
JohnWiley&Sons©2002


OrganizationofThisBook
Thisbookisthefirstvolumeofathree-volumesetthatcoversawider
rangeofpatternsthanpreviouslypublishedworks.
Thisfirstvolumefocusesexclusivelyondesignpatternsthatareused
atthemicro-architecturallevel.Thesecondvolumeincludespatterns
usedduringuserinterfacedesign,codingandtesting.Thethird
volumefocusesonarchitecturalanddesignpatternsusefulfor
enterpriseanddistributedapplications.
AllthreevolumesbeginwithadescriptionofthesubsetofUMLused
inthatvolume.Thefollowingchaptercontainsanoverviewofthe

softwarelifecycle,toprovidethecontextinwhichthepatternsare
used.Thischaptergoesontoprovideacasestudythatincludes
examplesofusingpatternsinthatvolume.Theremainingchapters
describedifferentsortsofpatterns.
TherewillbeaWebsiterelatedtothisbookat
.TheWebsitewillcontain
synopsisofthepatternsthatappearinthisbook.TheWebsitewill
alsocontainthecodeexamplesinthisvolume.
TheJavaexamplesthatappearinthisbookarebasedonJava
version1.4.


Chapter2-OverviewofUML
PatternsinJava,Volume1:ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
byMarkGrand
JohnWiley&Sons©2002


Chapter2:OverviewofUML


Overview
TheUnifiedModelingLanguage(UML)isanotationthatyoucanuse
forobject-orientedanalysisanddesign.Thischaptercontainsabrief
overviewofUMLthatintroducesyoutothesubsetofUMLandthe
extensionstoUMLusedinthisbook.Foracompletedescriptionof
UML,seewww.omg.org/technology/documents/formal/uml.htm.
BooksthatarespecificallyaboutUMLcallthepiecesofinformation

storedininstancesofaclassattributes;theycallaclass’s
encapsulationsofbehavioroperations.Thoseterms,aswithUML,are
notspecifictoanyimplementationlanguage.Thisbookisnot
languageneutral;itassumesthatyouuseJavaasyour
implementationlanguage.ItalsousesJava-specifictermsinmost
placesratherthantermsthatarelanguageneutralbutlessfamiliarto
Javaprogrammers.Forexample,itusesthewordsattributeand
variableinterchangeably,withpreferencefortheJava-specificterm
variable.Thisbookalsousesthewordsoperationandmethod
interchangeably,withpreferencefortheJava-specifictermmethod.
UMLdefinesanumberofdifferentkindsofdiagrams.Therestofthis
chapterisorganizedintosectionsthatdescribedifferentkindsofUML
diagramsandtheelementsthatappearinthem.
Ifyouareexperiencedwithobject-orienteddesign,youwillfindmost
oftheconceptsunderlyingtheUMLnotationtobefamiliar.Ifyoufind
manyconceptsunfamiliar,readonlyasmuchofthischapterasyou
feelcomfortablewith.WhenyouseeaUMLdiagraminlaterchapters
thatcontainssomethingthatyouwantexplained,comebacktothis
chapterandfindadiagramthatcontainstheUMLelementthatyou
wantexplained.


Chapter2-OverviewofUML
PatternsinJava,Volume1:ACatalogof
ReusableDesignPatternsIllustratedwith
UML,SecondEdition
byMarkGrand
JohnWiley&Sons©2002

ClassDiagram
Aclassdiagramisadiagramthatshowsclasses,interfaces,andtheir
relationships.Themostbasicelementofaclassdiagramisaclass.
Figure2.1providesanexampleofaclass,showingmanyofthe
featuresthataclasscanhavewithinaclassdiagram.

Figure2.1:Basicclass
diagram
Classesaredrawnasrectangles.Therectanglescanbedividedinto
twoorthreecompartments.TheclassrectangleshowninFigure2.1
hasthreecompartments:thetopcompartmentcontainsthenameof
theclass;themiddlecompartmentliststheclass’svariables;andthe
bottomcompartmentliststheclass’smethods.
Thesymbolsthatprecedeeachvariableandmethodarecalled
visibilityindicators.Thepossiblevisibilityindicatorsandtheir
meaningsareshowninTable2.1
Table2.1:VisibilityIndicators
VisibilityIndicators

Meaning

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Public

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Protected