Johan Fabry: Language-Independent Detection of Object-Oriented Design Patterns (ESUG 2003, Bled)

1. Language-Independent
Detection of Object-Oriented
Design Patterns
Johan Fabry
Vrije Universiteit Brussel, Programming Technology Lab
johan.fabry@vub.ac.be
25 Aug 2003 Lang-Indep Detection of OO DP 1

2. Overview
ß Research Goal
ß DMP and Soul
ß Soul to SoulJava
ß Base-Level Reification
ß Design Pattern Detection
ß Conclusion & Future Work
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3. Research Goal
ß Language-agnostic reasoning about OO
programs
ß Validate research in different OO -
languages
ß Soul: Reasoning about Smalltalk (coding
conventions, DP, bad smells, …)
ß Clear separation language indep / dep
ß Validation: ST + Java detect BPP, DP
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4. DMP and Soul
ß DMP:
ß Declarative language at meta-level
ß OO language at base level
ß Meta-level programs reason about structure of
base-level
ß Soul:
ß Meta-level prolog-like programming language
ß Smalltalk code can be embedded in prolog code
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5. Soul Layering
‘Uses’ Layering:
Inference Code
LiCoR MLI
Engine Repository
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6. Inference engine
ß Logic query with a variable:
If class(?x)
Inference Code
LiCoR MLI
Engine Repository
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7. LiCoR
ß Appropriate rule is triggered:
class(?c) if variable(?c),
generate(?c,[ExplicitMLI
current allClasses)])
Inference Code
LiCoR MLI
Engine Repository
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8. Meta Level Interface
ß Link to the base-level:
allClasses
^Smalltalk allClasses
Inference Code
LiCoR MLI
Engine Repository
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9. Code Repository
ß Investigate the code:
allClasses
…
Inference Code
LiCoR MLI
Engine Repository
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10. Soul to SoulJava
We discuss changes in inverse order.
Inference Code
LicoR MLI
Engine Repository
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11. Java Code Repository
ß Use Frost to parse Java Code
ß Assume correct java code !
ß Java 1.0 (+epsilon) parser
ß Java Code = parse trees
ß .java ‘File in’ in File Browser
ß Java Code Browser
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12. Java Code Browser
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13. MLI For Java
ß Uses Java Code Repository
ß Implements
ß all methods of ST MLI
ß methods for interface support
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14. Base-Level Reification
ß Namespace [name|super|sub|classes]
ß ->Through MLI
ß Class [name|super|sub|ns|methods|iv]
ß ->Through MLI
ß InstVar [name|inClass|type]
ß ->Through MLI
ß Method [name|arglist]
ß ->Through MLI
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15. Method Body Reification
ß Method bodies = logic parse tree form
ß Smalltalk: count set: 0 =
send(variable([#count])),[#set:],<[0]>)
ß Java: count.set(0) =
send(variable([#count])),[#set],<[0]>)
ß Allows for easy verification:
isMessageSend(send(?receiver,
?message,?arguments))
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16. Method Body Reification
ß But Java has more PT elements!
ß if-then-else, while, for, …
ß Introduce new logic functor for each
ß Logic Java Parse trees have different form!
ß No transformation to ‘ST-compatible’ form
ß Logic PT as similar as possible to Java code
ß Needed for later work: Java PT manipulations
ß Users of parse tree must take this into
account
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17. Parse Tree Traversal Layer
ß PTT: Specific layer in LiCoR
ß Recursively traverses parse trees
ß Called with:
ß ?found predicate
ß ?process predicate
ß ?env for results
ß Provide lang-spec implementation
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18. Parse Tree Traversal Layer
ß PTT: Specific layer in LiCoR
ß RecursivelyisMessageSend trees
traverses parse
ß Called with:
ß ?found predicate
ß ?process predicate
ß ?env for results
ß Provide lang-spec implementation
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19. Parse Tree Traversal Layer
ß PTT: messageSendMessage(
Specific layer in LiCoR
ß Recursively traverses parse trees
send(?rec,?msg,?args),
?args)
ß Called with:
ß ?found predicate
ß ?process predicate
ß ?env for results
ß Provide lang-spec implementation
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20. Parse Tree Traversal Layer
ß PTT: Specific layer in LiCoR
ß Recursively traverses parse trees
ß Called with:
ß ?found predicate
ß ?process predicate
ß ?env for results
ß Provide lang-spec implementation
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21. Idioms
ß Lang specific naming and coding
conventions
ß Accessor method name:
ß Smalltalk: var name
ß Java: ‘get’ + capitalized var name
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22. Pattern Detection
ß 4 patterns in 4 apps
Smalltalk Java
HotDraw Drawlets
RefactoringBrowser JRefactory
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23. Best Practice Patterns
Double Dispatch
ß One language-independent rule
ß Two idiom rules
ß selfReference
ß varName
ß HotDraw: 0, Drawlets:3
ß RefactoringBrowser: 17, JRefactory 174
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24. Best Practice Patterns
Getting Method
ß One language-independent rule
ß Two idiom rules
ß methodSelector
ß gettingMethodName
ß HotDraw: 35/75, Drawlets:33/270
ß RBrowser: 125/531, JRefactory 134/721
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25. Design Patterns
Template Method
ß Three language-independent rules
ß Three idiom rules
ß abstractSelector, abstractMethod
ß selfReference
ß HotDraw Fig: 3, Drawlets Fig: 42 (19 I)
ß RBrowser: 43, JRefactory: 50
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26. Design Patterns
Template Method
ß Three language-independent rules
ß Three idiom rules
ß abstractSelector, abstractMethod
ß selfReference
Takes care of interfaces in Java
ß HotDraw Fig: 3, Drawlets Fig: 42 (19 I)
ß RBrowser: 43, JRefactory: 50
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27. Design Patterns
Template Method
ß Three language-independent rules
ß Three idiom rules
ß abstractSelector, abstractMethod
ß selfReference
ß HotDraw Fig: 3, Drawlets Fig: 42 (19 I)
ß RBrowser: 43, JRefactory: 50
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28. Design Patterns
Visitor
ß Two language-independent rules
ß Use double-dispatch rule
ß Zero idiom rules
ß HotDraw: 0, Drawlets: 0
ß RBrowser: 14, JRefactory: 174
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29. Conclusion
ß Feasible to reason about OO software in a
language-independent way
ß Soul to SoulJava
ß Source Code Repository (Parser & Storage)
ß Meta-level Interface (Implement API)
ß Parse tree & traversal (Convertor & Logic Rules)
ß Idiom layer (As Needed)
ß Growth Idiom Layer < growth Detection
layer
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30. Future Work
ß More pattern detection rules
ß Easy / Tricky / Too language-specific
ß New languages
ß Small impact on current language-indep rules
ß New language versions
ß Reasoning about Java Bytecodes
ß Type inferencing
ß Language-Independent code generation
ß From UML, pattern descriptions
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31. FAQ
ß Static Typing vs Dynamic Typing
ß No Type Inferencing (Yet)
ß Types in var declarations: 1 idiom rule
ß Interfaces
ß Not widely used in patterns: 1 idiom rule
ß Accuracy of detection
ß No false positives, no false negatives
ß Similar limitations as other approaches
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32. LiCoR Structure
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33. public void getFoo(){
if (foo == null)
foo = factory.boot();
return foo;}
public void getFoo() {
foo = factory.boot(foo == null);
return foo;}
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