How Programming Languages Affect Design Patterns

138 Pages·2016·5.2 MB·English

How Programming Languages
Affect Design Patterns
A comparative study of programming languages and
design patterns
Vladislav Georgiev Alfredov
Master’s Thesis Autumn 2016

Abstract
This thesis is an empirical study of the affects that Language Features,
provided by Programming Languages on Design Pattern implementa-
tions. The set of Design Patterns is mostly based on the ones described
byfirstbooktodocumentDesignPatterns,namelytheGangofFourbook
[31]. It examines comparatively two Programming Languages, Java and
Python. In terms of comparing Language Features and Design Pattern
implementationsinacrossthetwoProgrammingLanguages. Theexamin-
ation is based on the Programming Languages’ documentation as well as
theliteratureavailablewithregardstoDesignPatternimplementationsin
these Programming Languages. Such cross language study, has not been
conductedbeforeandthusitisanapproachtothetopicofDesignPatterns
fromanovelperspective. Thethesisproposesaclassificationschemewith
regards to Language Features in relation to Design Pattern. In addition
tothatitproposesacategorizationschemeofLanguageFeatures,thatim-
plement Design Patterns in Programming Languages. It also assesses the
dependenceofDesignPatternsonspecificLanguageFeatures.
This thesis also examines some of the observed effects of Design
PatternsonProgrammingLanguages,bycomparativeexaminationoftwo
languages. It also catalogs related Language Features’ development over
time. LeadingtothedefinitionoftherelationshipbetweenDesignPatterns
andProgrammingLanguagesasbidirectional. Andthetheory,explaining
the consequences of changes to either Design Patterns or Programming
Languages.
2
Contents
I Introduction 1
1 Introduction 3
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 BackgroundandDefinitionsofTherms . . . . . . . . . . . . 4
1.2.1 ProgrammingLanguage . . . . . . . . . . . . . . . . . 4
1.2.2 LanguageFeatures . . . . . . . . . . . . . . . . . . . . 4
1.2.3 DesignPattern . . . . . . . . . . . . . . . . . . . . . . 4
1.2.4 UMLExtension . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 LanguageChoiceCriteria . . . . . . . . . . . . . . . . . . . . 6
1.6 WorkDone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.7 RelevantLiterature . . . . . . . . . . . . . . . . . . . . . . . . 7
1.8 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.9 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.10 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.11 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 Background 11
2.1 ResourcesOverview . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 DesignPatternsandLanguageFeaturesScope . . . . . . . . 12
2.3 EvaluationCriteria . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 DesignPatternsbeingmissingLanguageFeatures . . . . . . 13
2.5 RelatedWork . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.5.1 Annotations . . . . . . . . . . . . . . . . . . . . . . . . 14
2.5.2 Metaprogramming . . . . . . . . . . . . . . . . . . . . 15
2.5.3 Programming Paradigm Affects on Design Pattern
Implementations . . . . . . . . . . . . . . . . . . . . . 15
2.5.4 SerializationTechniques . . . . . . . . . . . . . . . . . 16
2.5.5 ModelingvsTypingAsTopicSuggestion . . . . . . . 16
2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3
II Analysis 17
3 ProgrammingLanguagesandDesignPatterns 21
3.1 Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.1 Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.2 Python . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.3 OtherCandidates . . . . . . . . . . . . . . . . . . . . . 23
3.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 Python 25
4.1 PythonEnhancementProposals . . . . . . . . . . . . . . . . . 25
4.2 PythonMagicMethods . . . . . . . . . . . . . . . . . . . . . . 25
4.3 Metaclasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.3.1 Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.3.2 UsingMetaclassestoImplementDesignPatterns . . 28
4.3.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.4 AbstractBaseClasses . . . . . . . . . . . . . . . . . . . . . . . 29
4.4.1 Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.4.2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.5 Decorators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.5.1 DescriptionandExampleUse . . . . . . . . . . . . . . 31
4.5.2 DecoratorsversusDecoratorDesignPattern . . . . . 33
4.5.3 UseofDecoratorstoImplementDesignPatterns . . . 34
4.5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.6 Iterator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.6.1 ImplementationDetails . . . . . . . . . . . . . . . . . 35
4.6.2 WhyusePythonIterators . . . . . . . . . . . . . . . . 36
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.8 ObjectCopying . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.8.1 DescriptionandExampleUse . . . . . . . . . . . . . . 37
4.8.2 ProblemsWiththeLanguageFeature . . . . . . . . . 39
4.8.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5 Java 41
5.1 Cloneable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.1.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.2 Iterator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2.1 Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2.2 ElementsoftheImplementation . . . . . . . . . . . . 44
5.2.3 Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.3 Observer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.3.1 Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
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5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
6 Evaluation 49
6.1 BasicDesignPatterns . . . . . . . . . . . . . . . . . . . . . . . 49
6.1.1 OverviewofBasicDesignPatternsVersusLanguage
Features . . . . . . . . . . . . . . . . . . . . . . . . . . 49
6.1.2 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.1.3 AbstractParentClass . . . . . . . . . . . . . . . . . . . 58
6.1.4 InterfaceComparedtoAbstractParentClass . . . . . 61
6.1.5 AccessorMethodsandPrivateMethods . . . . . . . . 65
6.1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 70
6.2 Decorator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
6.2.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 72
6.3 Iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6.3.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 75
6.4 Observer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.4.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 77
6.5 ObjectDuplication . . . . . . . . . . . . . . . . . . . . . . . . 77
6.5.1 CopyMethodandCopyConstructor . . . . . . . . . 77
6.5.2 ShallowandDeepCopy . . . . . . . . . . . . . . . . . 78
6.5.3 Use of Object Duplication for Design Pattern Imple-
mentation . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 80
6.6 LanguageFeaturesOverview . . . . . . . . . . . . . . . . . . 80
6.7 Resultsandcomparisonsgraphs . . . . . . . . . . . . . . . . 84
6.8 LifeCycleofaDesignPattern . . . . . . . . . . . . . . . . . . 85
6.9 ClassificationofLanguageFeatures . . . . . . . . . . . . . . . 86
6.9.1 Classification . . . . . . . . . . . . . . . . . . . . . . . 87
6.9.2 Invisible . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.9.3 Partial . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
6.9.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 88
6.10 BidirectionalRelationship . . . . . . . . . . . . . . . . . . . . 89
6.11 TheRippleEffectTheory . . . . . . . . . . . . . . . . . . . . . 89
6.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7 Conclusion 93
Appendices 101
A LanguageFeatures 103
A.0.1 PythonMetaclass . . . . . . . . . . . . . . . . . . . . . 103
A.0.2 PythonDecorators . . . . . . . . . . . . . . . . . . . . 104
A.0.3 PythonCopy . . . . . . . . . . . . . . . . . . . . . . . 111
A.0.4 JavaIterator . . . . . . . . . . . . . . . . . . . . . . . . 112
A.0.5 JavaCloneable . . . . . . . . . . . . . . . . . . . . . . 114
5
A.0.6 JavaObservable . . . . . . . . . . . . . . . . . . . . . . 117
A.0.7 Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 118
6
List of Figures
1.1 UMLdiagramdepictingtheAssociationrelationship. . . . . 5
2.1 Venndiagramofthescopeofthismasterthesiswithrelation
toDesignPatternsandLanguageFeatures. . . . . . . . . . . 12
4.1 DiagramofmetaclassesinPython . . . . . . . . . . . . . . . 27
4.2 A demonstration using Metaclasses to construct classes in
Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.3 A demonstration of the equivalent Python syntax to using
MetaclassesinPython . . . . . . . . . . . . . . . . . . . . . . 27
4.4 AdemonstrationoftheMetaclasssyntaxinPython . . . . . 27
4.5 An implementation of the Singleton design pattern using
metaclassesinPython . . . . . . . . . . . . . . . . . . . . . . 28
4.6 UsingthemetaclassinPython . . . . . . . . . . . . . . . . . . 29
4.7 UsingaMetaclass,byextendingitinPython . . . . . . . . . 29
4.8 Exception thrown, when the subclass has not implemented
allabstractmethodsandtriestocreatenewobjectsinPython 30
4.9 ExampleofinstantiatingemptyAbstractBaseClassPython 30
4.10 Pythondecorators . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.11 Functionassignment . . . . . . . . . . . . . . . . . . . . . . . 32
4.12 DecoratorDesignPatternusingpython . . . . . . . . . . . . 34
4.13 PythonDecoratorsfunctionassignment . . . . . . . . . . . . 34
4.14 Pythondecoratordefinitionforsingletonimplementation . . 35
4.15 Comparisonofiteratorusetofor-loopinPython . . . . . . . 37
4.16 AdemonstrationofobjectcopyinginPython . . . . . . . . . 38
4.17 AdemonstrationofoverridingthecopymethodinPython . 38
4.18 Cloneableexampleoverview . . . . . . . . . . . . . . . . . . 39
5.1 Javaoverridingclonemethod . . . . . . . . . . . . . . . . . . 42
5.2 Cloneableexampleoverview . . . . . . . . . . . . . . . . . . 43
5.3 Iteratoruse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.4 Equivalentforeachloop . . . . . . . . . . . . . . . . . . . . . 45
6.1 UML diagram of the Interface Design Pattern, and the Java
implementation . . . . . . . . . . . . . . . . . . . . . . . . . . 51
6.2 JavaInterfacedefinition . . . . . . . . . . . . . . . . . . . . . 52
7
6.3 JavaInterfaceuse . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.4 UML diagram of the Interface Design Pattern in Python,
usingducktyping. . . . . . . . . . . . . . . . . . . . . . . . . 54
6.5 UML diagram of the Interface Design Pattern in Python,
usinginheritance. . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.6 InterfaceProviderusingNotImplementedErrorinPython . 55
6.7 Interface Provider using NotImplementedError for init in
Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.8 InterfaceimplementationusingtheabcmoduleinPython . 57
6.9 InterfaceclientimplementationinPython . . . . . . . . . . . 58
6.10 UMLdiagramoftheAbstractParentClassDesignPattern . 59
6.11 An example implementation of the Abstract Parent Class
DesignPatterninJava . . . . . . . . . . . . . . . . . . . . . . 59
6.12 An example implementation of the Abstract Parent Class
DesignPatterninPython . . . . . . . . . . . . . . . . . . . . . 60
6.13 AnexampleimplementationusingdefaultmethodsinJava . 61
6.14 UML diagram of Interfaces used in conjunction with Ab-
stractParentClassesinJava. . . . . . . . . . . . . . . . . . . . 64
6.15 AnexampleimplementationofPrivateMethodsinJava . . . 65
6.16 AnexampleimplementationofAccessorMethodsinJava . . 65
6.17 An example implementation of the Private Method Design
PatterninPython . . . . . . . . . . . . . . . . . . . . . . . . . 67
6.18 An example implementation of the Accessor Methods
DesignPatternusingpropertyinPython . . . . . . . . . . . 68
6.19 An example of how the implementation of the Accessor
Methods Design Pattern using property in Python would
restrictaccesstovariables . . . . . . . . . . . . . . . . . . . . 69
6.20 ExtendedUMLdiagramoftheDecoratordesignpattern . . 71
6.21 UMLdiagramofPython’simplementationoftheDecorator
designpattern . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6.22 UMLdiagramoftheIteratordesignpattern . . . . . . . . . . 73
6.23 UML diagram of Java’s implementation of the Iterator
designpattern . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.24 UML diagram of Python’s implementation of the Iterator
designpattern . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.25 UMLdiagramoftheObserverDesignPattern . . . . . . . . 76
6.26 UMLdiagramoftheObserverDesignPatterninJava . . . . 76
6.27 UMLdiagramofthePrototypeDesignPattern . . . . . . . . 79
6.28 UMLdiagramofobjectduplicationinJava . . . . . . . . . . 79
6.29 UMLdiagramofthecopymethodsinPython . . . . . . . . . 79
6.30 DesignPatternadoptionpath . . . . . . . . . . . . . . . . . . 86
8