Presentation for Automated Software Engineering - ASE 2019 technical track paper https://2019.ase-conferences.org/details/ase-2019-papers/14/Empirical-Study-of-Programming-to-an-Interface

1. EMPIRICAL STUDY OF PROGRAMMING TOEMPIRICAL STUDY OF PROGRAMMING TO
AN INTERFACEAN INTERFACE
B. Verhaeghe1, Christopher Fuhrman2,
L. Guerrouj2, N. Anquetil3 and S. Ducasse4
1Berger-Levrault, France
2École de technologie supérieure, Montreal, Canada
3University of Lille, CRIStAL
4RMoD - Inria Nord Europe
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Empirical study of programming to an interface
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2. MOTIVATIONMOTIVATION
Heuristic from Design Patterns book (GoF 1994).
Clients are less fragile if implementations change.
We have been teaching this to students for decades,
but is there any empirical evidence to support it?
“Program to an interface, not an
implementation.”
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3. RELATED PRINCIPLESRELATED PRINCIPLES
Protected Variation (C. Larman)
Open-Closed Principle (B. Meyer)
Information Hiding (D. Parnas)
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4. WHAT IT LOOKS LIKEWHAT IT LOOKS LIKE
Beginner design in Java
Client
«interface»
List
ArrayList TreeList
Coupling to
implementation
ArrayList myList = new ArrayList();
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5. WHAT IT LOOKS LIKEWHAT IT LOOKS LIKE
Improved design…
Client
«interface»
List
ArrayList TreeList
Coupling to
interface
«creates»
Coupling to
implementation
List myList = new ArrayList();
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6. WHAT IT LOOKS LIKEWHAT IT LOOKS LIKE
Factory design decouples client from implementation
Client
«interface»
List
ArrayList
TreeList
ListFactory
Coupling
to interface
creates
creates
uses
List myList = ListFactory.create("...");
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7. CONSEQUENCES OF PTICONSEQUENCES OF PTI
Protect clients changing implementation(s)
Favor extensions to implementations
Simplify the API, overcome single-inheritance
limitation
Speculative Generality (code smell)
Additional level of hierarchy
Factories decouple clients from implementations
Changed interface breaks clients and
implementations
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8. EMPIRICAL STUDY OF THE CONSEQUENCESEMPIRICAL STUDY OF THE CONSEQUENCES
Human studies: qualities such as
understandability, ease of extensibility, etc.
Observational studies: Code repositories to see if
client code is protected (change propagation), fault
location, etc.
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9. OBSERVATIONAL STUDY: PROTECTED VARIATIONOBSERVATIONAL STUDY: PROTECTED VARIATION
Cochange in Java projects (GitHub)
Static analysis identi es cochange pairs (client,
implementation)
Unprotected pairs (direct coupling)
Protected pairs (no coupling)
Client A Client B
«interface»
ISomething
Implementation
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10. RESEARCH QUESTIONRESEARCH QUESTION
Do unprotected pairs cochange more often than
protected pairs?
Client A Client B
«interface»
ISomething
Implementation
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11. COCHANGE HISTORYCOCHANGE HISTORY
H is the history of commits.
Cochanged Protected Dependencies ratio
CPD(%) =
|H∩P|
|P|
Cochanged Unprotected Dependencies ratio
CUD(%) =
|H∩U|
|U|
.
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12. RESULTSRESULTS
126 (popular) Java projects on GitHub
Ratios of CPD and CUD
p < 0.001 and effect size (Cliff’s) d = 0.32 (small)
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13. FUTURE WORKFUTURE WORK
Observational studies with more context
Classify projects (abstractness)
Microarchitectures (e.g., factories)
Natural experiments for quality aspects
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