Detecting and Removing Bad Code Smells from Source Code

Fabio Palomba

A review of my first PhD year

PhD Symposium 2014

Technical Debt is...“Not quite right code which we

postpone making it right.”

W. Cunningham

Technical Debt is...“Not quite right code which we

postpone making it right.”

W. Cunningham

Documentation DebtCode Smell

Test debt

Coding Style Violation

Structural DebtArchitectural Debt

Low Internal Quality

Code Complexity

Bad Code Smells

[Abbes et al. CSMR 2011]

[Abbes et al. CSMR 2011]

Bad Smells hinder code comprehensibility

[Khomh et al. EMSE 2012]

[Khomh et al. EMSE 2012]

Bad Smells increase change and fault proneness

[Banker et al. Comm. of the ACM 1993]

[Banker et al. Comm. of the ACM 1993]

Bad smells increase maintenance costs

F. Palomba, A. De Lucia, G. Bavota, R. Oliveto. “Anti-Pattern Detection: Methods, Challanges, and Open Issues”

Advances in Computers, vol. 95 (to appear)

Many detection techniques use structural analysis

Many bad smells are intrinsically characterized by how code elements change over time, rather

than by structural properties

HIST

Historical Information for Smell deTection

Historical Information for Smell deTection

HIST

Historical Information for Smell deTection

HISTChange History Extractor

Historical Information for Smell deTection

HISTChange History Extractor

log download

Historical Information for Smell deTection

HISTChange History Extractor

log download code analyzer

Historical Information for Smell deTection

HISTChange History Extractor

log download code analyzer

method getUser has been

added

Historical Information for Smell deTection

HISTChange History Extractor

log download code analyzer

method getUser has been

added

method getData has been modified

Historical Information for Smell deTection

HISTChange History Extractor

log download code analyzer

method getUser has been

added

method getData has been modified

method getLogin has been moved

Historical Information for Smell deTection

HISTChange History Extractor

log download code analyzer

method getUser has been

added

method getData has been modified

method getLogin has been moved

class User

has been added

Historical Information for Smell deTection

HISTChange History Extractor

log download code analyzer

method getUser has been

added

method getData has been modified

method getLogin has been moved

class User

has been added

...

...

...

...

Historical Information for Smell deTection

HISTChange History Extractor

Code Smells Detector

log download code analyzer

method getUser has been

added

method getData has been modified

method getLogin has been moved

class User

has been added

...

...

...

...

Historical Information for Smell deTection

HISTChange History Extractor

Code Smells Detector

log download code analyzer

method getUser has been

added

method getData has been modified

method getLogin has been moved

class User

has been added

...

...

...

...

Association rule discovery to capture co-changes between entities

Historical Information for Smell deTection

HISTChange History Extractor

Code Smells Detector

log download code analyzer

method getUser has been

added

method getData has been modified

method getLogin has been moved

class User

has been added

...

...

...

...

Association rule discovery to capture co-changes between entities

Analysis of change frequency of some specific entities

Historical Information for Smell deTection

HISTCode Smell DetectorFive different smells considered

Divergent ChangeShotugun SurgeryParallel Inheritance

Historical Information for Smell deTection

HISTCode Smell DetectorFive different smells considered

Three code smells, by definition, to consider as “historical” smells

Divergent ChangeShotugun SurgeryParallel Inheritance

Historical Information for Smell deTection

HISTCode Smell DetectorFive different smells considered

Three code smells, by definition, to consider as “historical” smells

Divergent ChangeShotugun SurgeryParallel Inheritance

BlobFeature Envy

Historical Information for Smell deTection

HISTCode Smell DetectorFive different smells considered

Three code smells, by definition, to consider as “historical” smells

Two code smells generally detected by structural analysis, where the historical analysis can aid in the identification of complementary information

Divergent ChangeShotugun SurgeryParallel Inheritance

BlobFeature Envy

Code Smells Detectordivergent change

Code Smells Detectordivergent change

A class is changed in different ways for different reasons

Code Smells Detectordivergent change

A class is changed in different ways for different reasons

Solution: Extract Class Refactoring

Code Smells Detectordivergent change

A class is changed in different ways for different reasons

Solution: Extract Class Refactoring

DetectionClasses containing at least two sets of methods such that:

(i) all methods in the set change together as detected by the association rules

(ii) each method in the set does not change with methods in other sets

Code Smells Detectorblob

Code Smells Detectorblob

A class implementing several responsibilities, having a large size, and dependencies with data classes

Code Smells Detectorblob

A class implementing several responsibilities, having a large size, and dependencies with data classes

Solution: Extract Class refactoring

Code Smells Detectorblob

A class implementing several responsibilities, having a large size, and dependencies with data classes

Solution: Extract Class refactoring

DetectionBlobs are identified as classes frequently modified in commits involving at least another class.

t1 t3t2 t4 t6t5 t7 t9t8

Evaluationdetection accuracy

Evaluationdetection accuracy

20 open source systems

Evaluationdetection accuracy

Comparing HIST with static code analysis technique on a manually

built oracle20 open source

systems

Evaluationdetection accuracy

20 open source systems

Shotgun Surgery

Parallel Inheritance

Divergent Change

Blob

Feature Envy

HIST F-Measure CA technique F-Measure92%

71%

82%

64%

77%

0%

9%

11%

48%

68%

Comparing HIST with static code analysis technique on a manually

built oracle

Evaluationdetection accuracy

HIST and the CA techniques

are highly complementary

20 open source systems

Comparing HIST with static code analysis technique on a manually

built oracle

F. Palomba, G. Bavota, M. Di Penta, R. Oliveto, A. De Lucia, and D. Poshyvanyk. “Detecting Bad Smells in Source Code using Change History Information” - Distinguished Paper Award

International Conference on Automated Software Engineering (ASE 2013)

F. Palomba, G. Bavota, M. Di Penta, R. Oliveto, A. De Lucia, and D. Poshyvanyk. “Detecting Bad Smells in Source Code using Change History Information” - Distinguished Paper Award

International Conference on Automated Software Engineering (ASE 2013)

F. Palomba, G. Bavota, M. Di Penta, R. Oliveto, D. Poshyvanyk and A. De Lucia. “Mining Version Histories for Detecting Code Smells”

Transactions on Software Engineering (TSE) - 2015

F. Palomba, D. Di Nucci, M. Tufano, G. Bavota, M. Di Penta, R. Oliveto, D. Poshyvanyk and A. De Lucia. “Landfill: an Open Dataset of Code Smells with Public Evaluation”

Submitted to the International Conference on Software Engineering (ICSE 2015)

http://www.sesa.unisa.it/landfill

HIST

Historical Information for Smell deTection

Mar

16 The tool is coming soon...

Do They Really Smell Bad? A Study on Developers’ Perception of Bad Code SmellsFabio Palomba, Gabriele Bavota, Massimiliano Di Penta, Rocco Oliveto, Andrea De Lucia

ICSME 2014Victoria - CanadaOctober 1st, 2014

“We don’t see things as they are, we see things as we are” Anais Nin

Investigating the developers’ point of view

Investigating the developers’ point of view

RQ1: To what extent do bad smells reflect developers‘

perception of design problems?

Investigating the developers’ point of view

RQ1: To what extent do bad smells reflect developers‘

perception of design problems?

RQ2: What are the bad smells that developers feel

as the most harmful?

Smells generally not Perceived as Design or Implementation Problems

THEORical

problems

Smells generally Perceived and Identified by Respondents

THEY SHOULD BE

CAREFULLY ANALYZED

THEY SHOULD BE

studied more

Smells whose Perception may Vary dependently by Their Intensity

On the Innate Relationship between Quality and Refactoring

Refactoring is...“Refactoring is a disciplined technique for restructuring an

existing body of code, improving its non-functional attributes without changing its external behavior.”

Studying if quality metrics / bad smells capture

refactoring operations

3 open source systems

Studying if quality metrics / bad smells capture

refactoring operations

3 open source systems

11 quality metrics

Studying if quality metrics / bad smells capture

refactoring operations

3 open source systems

11 quality metrics11 bad smells

Studying if quality metrics / bad smells capture

refactoring operations

3 open source systems

11 quality metrics11 bad smells

12,922 refactoring operations manually validated

G. Bavota, A. De Lucia, M. Di Penta, R. Oliveto and F. Palomba. “An Experimental Investigation on the Innate Relationship between Quality and Refactoring”

Submitted to Transactions on Software Engineering and Methodology (TOSEM)

F. Palomba, M. Tufano, G. Bavota, R. Oliveto, A. Marcus, D. Poshyvanyk, and A. De Lucia. “Extract Package Refactoring in ARIES”

Submitted to the International Conference on Software Engineering (ICSE 2015)

http://www.sesa.unisa.it/tools/aries.jsp

Moving Forward

M. Tufano, F. Palomba, G. Bavota, R. Oliveto, M. Di Penta, A. De Lucia, and D. Poshyvanyk“When and Why Your Code Starts to Smell Bad”

Submitted to the International Conference on Software Engineering (ICSE 2015)

F. Palomba“Textual Analysis for Code Smell Detection”

Submitted to the International Conference on Software Engineering (ICSE 2015)

Learning from the past for prioritizing bad code smells

Technical Debt is...“Not quite right code which we

postpone making it right.”

W. Cunningham

Documentation DebtCode Smell

Test debt

Coding Style Violation

Structural DebtArchitectural Debt

Low Internal Quality

Code Complexity

Fabio Palombafpalomba.unisa.itdibt.unimol.it/fpalomba

Research is a work of