How to Design Classes. Data: Structure and Organization

666 Pages·2012·2.711 MB·English

by  Matthias Felleisen, Matthew Flatt, Robert Bruce Findler, Kathryn E. Gray, Shriram Krishnamurthi, Viera K. Proulx

How to Design Classes
D : June 15, 2012
RAFT

How to Design Classes
Data: Structure and Organization
Matthias Felleisen
Matthew Flatt
Robert Bruce Findler
Kathryn E. Gray
Shriram Krishnamurthi
Viera K. Proulx
c 2003,2004, 2005,2006,2007,2008Felleisen,Flatt,Findler,Gray,
(cid:13)
Krishnamurthi,Proulx
Howtodesignclass: object-orientedprogrammingandcomputing
MatthiasFelleisen,MatthewFlatt,RobertBruceFindler,KathrynE.Gray,
ShriramKrishnamurthi,VieraK.Proulx
p. cm.
Includesindex.
ISBN0-262-06218-6 (hc.: alk.paper)
1. ComputerProgramming. 2. Electronicdataprocessing.
QA76.6 .H697 2001
005.1’2—dc21 00-048169
CONTENTS v
Contents
Preface xii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
I The Varietiesof Data 7
1 PrimitiveFormsofData 8
2 Classes 9
2.1 FingerExercisesonPlainClasses . . . . . . . . . . . . . . . . 15
2.2 DesigningClasses . . . . . . . . . . . . . . . . . . . . . . . . . 18
3 ClassReferences, ObjectContainment 19
3.1 FingerExercisesonObjectContainment . . . . . . . . . . . . 25
3.2 DesigningClassesthatRefertoClasses . . . . . . . . . . . . 26
4 UnionsofClasses 27
4.1 TypesvsClasses . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2 FingerExercisesonUnions . . . . . . . . . . . . . . . . . . . 32
4.3 DesigningUnionsofClasses . . . . . . . . . . . . . . . . . . . 35
5 Unions,Self-References andMutualReferences 37
5.1 ContainmentinUnions,Part1 . . . . . . . . . . . . . . . . . 37
5.2 ContainmentinUnions,Part2 . . . . . . . . . . . . . . . . . 44
5.3 FingerExercisesonContainmentinUnions . . . . . . . . . . 49
6 DesigningClassHierarchies 50
6.1 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
6.2 CaseStudy: FightingUFOs . . . . . . . . . . . . . . . . . . . 56
Intermezzo1: Classesand Interfaces 64
VocabularyandGrammar . . . . . . . . . . . . . . . . . . . . . . . 64
Meaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
SyntaxErrors,TypeErrors,andRun-timeErrors . . . . . . . . . . 69
II Functional Methods 83
vi CONTENTS
8 Expressions1,ComputingwithPrimitiveTypes 83
9 Expressions2,MethodCalls 85
10 MethodsforClasses 87
10.1 DesignsthroughTemplates . . . . . . . . . . . . . . . . . . . 87
10.2 FingerExercises . . . . . . . . . . . . . . . . . . . . . . . . . . 93
10.3 DesigningMethodsforClasses . . . . . . . . . . . . . . . . . 95
10.4 ConditionalComputations . . . . . . . . . . . . . . . . . . . . 96
10.5 Composingmethods . . . . . . . . . . . . . . . . . . . . . . . 104
11 MethodsandObjectContainment 107
11.1 FingerExercises . . . . . . . . . . . . . . . . . . . . . . . . . . 113
11.2 DesigningMethodsforClassesthatContainClasses . . . . . 113
12 MethodsandUnionsofClasses 114
12.1 Example: PlainGeometricShapes. . . . . . . . . . . . . . . . 115
12.2 SignalingErrors . . . . . . . . . . . . . . . . . . . . . . . . . . 127
13 Types,Classes, andHowMethodCallsCompute 128
13.1 MethodDispatch . . . . . . . . . . . . . . . . . . . . . . . . . 128
13.2 TheRoleofTypes . . . . . . . . . . . . . . . . . . . . . . . . . 132
14 MethodsandUnionsofClasses(Continued) 135
14.1 HowLibrariesWork,Part1: DrawingGeometricShapes . . 135
14.2 FingerExercises . . . . . . . . . . . . . . . . . . . . . . . . . . 140
14.3 DesigningMethodsforUnionsofClasses . . . . . . . . . . . 142
15 MethodsandClasseswithMutualReferences 142
15.1 Example: ManagingaRunner’sLogs. . . . . . . . . . . . . . 142
15.2 Example: Sorting . . . . . . . . . . . . . . . . . . . . . . . . . 150
15.3 Example: OverlappingShapes. . . . . . . . . . . . . . . . . . 153
15.4 Example: RiverSystems . . . . . . . . . . . . . . . . . . . . . 163
15.5 FingerExercises . . . . . . . . . . . . . . . . . . . . . . . . . . 171
16 DesigningMethods 173
16.1 TheVarietiesofTemplates . . . . . . . . . . . . . . . . . . . . 174
16.2 WishLists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
16.3 CaseStudy: FightingUFOs,withMethods . . . . . . . . . . 179
CONTENTS vii
Intermezzo2: Methods 194
VocabularyandGrammarforMethods . . . . . . . . . . . . . . . . 195
TypeChecking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Meaning: EvaluatingMethodCalls . . . . . . . . . . . . . . . . . . 202
SyntaxErrors,TypeErrors,andRun-timeErrors . . . . . . . . . . 212
III Abstractingwith Classes 221
18 SimilaritiesinClasses 222
18.1 CommonFields,Superclasses . . . . . . . . . . . . . . . . . . 222
18.2 AbstractClasses,AbstractMethods. . . . . . . . . . . . . . . 226
18.3 LiftingMethods,InheritingMethods . . . . . . . . . . . . . . 228
18.4 CreatingaSuperclass,CreatingaUnion . . . . . . . . . . . . 234
18.5 DerivingSubclasses . . . . . . . . . . . . . . . . . . . . . . . . 250
19 DesigningClassHierarchieswithMethods 251
19.1 LocalVariablesandComposition . . . . . . . . . . . . . . . . 252
19.2 AbstractingwithMethods . . . . . . . . . . . . . . . . . . . . 255
19.3 AbstractingwithinUnionsofClasses . . . . . . . . . . . . . . 258
19.4 AbstractingthroughtheCreationofUnions . . . . . . . . . . 261
19.5 DerivingSubclassesfrom“Library”Classes . . . . . . . . . . 265
19.6 CreatingSubclassesforSpecialObjects . . . . . . . . . . . . . 267
19.7 HowLibrariesWork,Part2: DerivingClasses . . . . . . . . . 272
19.8 CaseStudy: FightingUFOs,AlltheWay . . . . . . . . . . . . 277
19.9 MiniProject: Worm . . . . . . . . . . . . . . . . . . . . . . . . 287
20 StateEncapsulationandSelf-Preservation 291
20.1 ThePowerofConstructors . . . . . . . . . . . . . . . . . . . . 292
20.2 OverloadingConstructors . . . . . . . . . . . . . . . . . . . . 296
20.3 EncapsulatingandPrivacy . . . . . . . . . . . . . . . . . . . . 298
20.4 GuidelinesforStateEncapsulation . . . . . . . . . . . . . . . 304
20.5 FingerExercisesonEncapsulation . . . . . . . . . . . . . . . 305
21 ExtensionalEquality,Part1 308
21.1 EqualityforPlainClasses . . . . . . . . . . . . . . . . . . . . 308
21.2 EqualityforInheritance . . . . . . . . . . . . . . . . . . . . . 313
21.3 EqualityforContainmentandUnions . . . . . . . . . . . . . 315
viii CONTENTS
Intermezzo3:AbstractClasses, Privacy 322
AbstractClassesandClassExtensions . . . . . . . . . . . . . . . . 322
PrivacyforMethods . . . . . . . . . . . . . . . . . . . . . . . . . . 323
OverloadingConstructorsandMethods . . . . . . . . . . . . . . . 323
IV Circular Objects, ImperativeMethods 327
23 CircularData 328
23.1 DesigningClassesforCircular Objects,Constructors . . . . . 337
23.2 TheTrueNatureofConstructors . . . . . . . . . . . . . . . . 340
23.3 CircularityandEncapsulation . . . . . . . . . . . . . . . . . . 340
23.4 Example: FamilyTrees . . . . . . . . . . . . . . . . . . . . . . 343
24 MethodsonCircularData 348
25 TheStateoftheWorldandHowItChanges 359
26 AssignmentsandChangesintheWorld 361
26.1 Example: DroppingBlocks . . . . . . . . . . . . . . . . . . . . 362
26.2 Example: Accounts . . . . . . . . . . . . . . . . . . . . . . . . 364
26.3 HowLibrariesWork3: AnAlternativeWorld . . . . . . . . . 367
27 DesigningStatefulClasses, ImperativeMethods 373
27.1 WhentoUseStatefulClassesandImperativeMethods . . . 375
27.2 HowtoDesignStatefulClasses,ImperativeMethods . . . . 378
27.3 ImperativeMethodsandTemplates . . . . . . . . . . . . . . 384
27.4 ImperativeMethodsandAbstraction . . . . . . . . . . . . . . 387
27.5 Danger! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
27.6 CaseStudy: MoreonBankAccounts . . . . . . . . . . . . . . 395
27.7 CaseStudyRepeated: AStatefulApproachtoUFOs . . . . . 399
27.8 CaseStudy: ADeckofCards . . . . . . . . . . . . . . . . . . 408
27.8.1 CachingandInvisibleAssignments . . . . . . . . . . 418
27.8.2 MergingListTraversals: SplittingLists . . . . . . . . 420
27.9 Endnote: WheredoWorldsComefrom? Wheredotheygo? 423
28 Equality 434
28.1 ExtensionalEquality,Part2 . . . . . . . . . . . . . . . . . . . 435
28.2 IntensionalEquality . . . . . . . . . . . . . . . . . . . . . . . . 435
28.3 ExtensionalEqualitywithnull . . . . . . . . . . . . . . . . . 440
28.4 ExtensionalEqualitywithCast . . . . . . . . . . . . . . . . . 442
CONTENTS ix
28.5 Danger! ExtensionalEqualityandCycles . . . . . . . . . . . 443
Intermezzo4: Assignments 449
V AbstractingData Representations 452
30 TypesandSimilarities betweenPlainClasses 452
30.1 ClasseswithCommonStructure,DifferentTypes . . . . . . . 453
30.2 AbstractingTypesviaSubtyping . . . . . . . . . . . . . . . . 454
30.3 AbstractingTypesviaGenerics . . . . . . . . . . . . . . . . . 457
31 TypesandSimilarities betweenHierarchies 464
31.1 AbstractingTypesviaSubtyping,Part2 . . . . . . . . . . . . 465
31.2 AbstractingTypesviaSubtypingplusInterfaces . . . . . . . 471
31.3 AbstractingTypesviaGenerics,Part2 . . . . . . . . . . . . . 476
31.4 AbstractingTypesviaGenericsplusInterfaces . . . . . . . . 479
32 DesigningGeneralClassesandFrameworks 484
32.1 SubtypingSummarized . . . . . . . . . . . . . . . . . . . . . 488
32.2 GeneralizingviaSubtyping . . . . . . . . . . . . . . . . . . . 490
32.3 GeneralizingviaGenerics . . . . . . . . . . . . . . . . . . . . 500
32.4 FingerExercises: Sets,Stacks,Queues,andTreesAgain . . . 503
32.5 Errors,alsoknownasRuntimeExceptions. . . . . . . . . . . 508
33 Designing(to)Interfaces 511
33.1 OrganizingPrograms,HidingAuxiliaryMethods . . . . . . 511
33.2 Getters,Predicates,andSetters . . . . . . . . . . . . . . . . . 517
33.3 InterfacesasSpecifications . . . . . . . . . . . . . . . . . . . . 520
34 ExtensibleFrameworks: AbstractingConstructors 526
34.1 DataExtensionsareEasy . . . . . . . . . . . . . . . . . . . . . 528
34.2 FunctionExtension: ADesignthatdoesn’tQuiteWork... . 531
34.3 ... andhowtoFixit(Mostly) . . . . . . . . . . . . . . . . . . 535
34.4 FunctionExtension: Take2 . . . . . . . . . . . . . . . . . . . . 540
34.5 MiniProject: TheTowersofHanoi . . . . . . . . . . . . . . . 544
Intermezzo5: GenericClasses 548
x CONTENTS
VI AbstractingData Traversals 551
36 PatternsinTraversals 551
36.1 Example: MenusDesignedfromScratch . . . . . . . . . . . . 553
36.2 Example: MenusDesignedasLists . . . . . . . . . . . . . . . 554
36.3 MethodsasObjects . . . . . . . . . . . . . . . . . . . . . . . . 556
36.4 ListTraversalsandPolymorphicMethods . . . . . . . . . . . 561
36.5 Example: fold. . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
36.6 Example: ArithmeticExpressionsandTraversals . . . . . . . 575
37 DesigningAbstractTraversalMethods 587
37.1 MethodsasObjectsviaSubtyping . . . . . . . . . . . . . . . 587
37.2 MethodsasObjectsviaGenerics . . . . . . . . . . . . . . . . 590
37.3 AbstractingoverMethodCalls,AnonymousInnerClasses . 591
37.4 InnerClasses,AnonymousClasses . . . . . . . . . . . . . . . 594
37.5 VisitorTraversalsandDesigningVisitors . . . . . . . . . . . 596
37.6 FingerExercises: VisitingLists,Trees,Sets . . . . . . . . . . . 608
37.7 ExtendedExercise: GraphsandVisitors . . . . . . . . . . . . 610
37.8 WheretoUseTraversals,orAggregation . . . . . . . . . . . 613
37.9 Object-OrientedandFunctionalProgramming . . . . . . . . 617
38 TraversingwithEffects 619
38.1 AbstractingoverImperativeTraversals: theforEachMethod 619
38.2 UsingtheforEachMethod . . . . . . . . . . . . . . . . . . . . 621
38.3 UsingforEachwithAnonymousClasses . . . . . . . . . . . . 626
38.4 MiniProjects,includingaFinalLookat“WaroftheWorlds” 631
38.5 AbusingtheforEachMethod . . . . . . . . . . . . . . . . . . . 635
39 ExtensibleFrameworkswithVisitors 642
Intermezzo6:GenericMethods, InnerClasses 643
VII Loopsand Arrays 645
41 TheDesignFlaw 645
42 Loops 645
42.1 DesigningLoops . . . . . . . . . . . . . . . . . . . . . . . . . 645
42.2 DesigningNestedLoops . . . . . . . . . . . . . . . . . . . . . 645