This document summarizes the findings of a tertiary review on code smells and refactoring. It analyzed 40 secondary studies on the topic. Key findings include: 1) Common refactoring topics investigated were opportunities, techniques and tools, while common smell topics were detection, descriptions and support tools. 2) Popular smell detection tools were CCFinder and Jdeodorant, while there were fewer refactoring tools. 3) The relationship between smells and refactoring is complex, as not all smells require refactoring and refactoring can sometimes negatively impact quality. The review identified implications for practitioners, researchers and educators, as well as open issues in the field.

1. 36th IEEE International Conference on Software Maintenance and Evolution
September 27-October 3, Journal First Track
Code smells and refactoring: A tertiary review of
challenges and observations
Guilherme Lacerda, Fábio Petrillo, Marcelo Pimenta, and Yann Gaël Guéhéneuc
Brazil Brazil Canada Canada

2. Published: JSS, 167 (2020)
Preprint: https://arxiv.org/abs/2004.10777

3. Introduction
and Background

4. Introduction and Background
▪ Refactoring and Smells
▪ Several secondary studies have been published on code smells and refactoring
▪ Tertiary Systematic Literature Review
▪ Surveys, secondary systematic literature reviews, and systematic mappings
▪ 40 secondary studies selected
▪ Challenges and Observations

5. Research Questions
RQ1: What refactoring-related topics have been investigated in secondary studies?
RQ2: What smells-related topics have been investigated in secondary studies?
RQ3: Which tools have been mentioned for code smell detection and refactoring support?
RQ4: Which RQs have been studied on code smells and refactoring? What are the highest
cited secondary studies?
RQ5: What are the annual trends of types, quality, and the number of primary studies
reviewed by the secondary studies?

6. Study Design

7. Study Design
Definition of
Goal and RQs
(3.1)
Identification of
Relevant Papers
and Search String
(3.2)
Selection
Criteria
(3.3)
Apply Quality
Assessment
(3.4)
Data Extraction
and Execution
(3.5, 3.6)
Lacerda, G., 2019. Online Repository for Tertiary Systematic Review about Code Smells and Refactoring (Package Replication).
https://bit.ly/2WRD1N2
Search databases
ACM (30), IEEE (65),
Scopus (58), Science
Direct (130), Springer
(89), Google Scholar
(33), AIS (40), Wiley (22)
467
1st selection of
studies
Using selection
criteria (title,
abstract, keywords)
59
Duplicated papers
and 2nd selection
of studies
Using selection criteria
(full text analysis)
33 Snowballing
40 Total of selected
studies

8. Study Design
Top-10
(Example)

9. Findings

10. RQ1
What refactoring-related topics have been
investigated in secondary studies?

11. RQ1 Summary
▪ Topics
▪ Opportunities, techniques, refactoring tools, refactoring in other contexts, and others
▪ Challenges
▪ Relationship between smells and refactoring is not a one to one
▪ Encourage researchers to improve the results most commonly used in practice
▪ Observations
▪ Extraction techniques are the most mentioned
▪ Number of techniques explored is still small (between 20 and 27 of 72)
▪ Quality metrics-oriented approach, precondition-oriented approach, and clustering-oriented
approach are most cited approaches
▪ Some refactoring, when applied, negatively affect the quality

12. RQ2
What smells-related topics have been
investigated in secondary studies?

13. RQ2 Summary
▪ Challenges
▪ Smells naming standardization is necessary
▪ Co-occurence of smells
▪ Explore and improve methods of defining, specify, and capture the smell context
▪ Observations
▪ Blob and Duplicated code/clones are most mentioned design and code smell, respectively
▪ God Class/Large Class has been the most investigated smell (Technical Debt)
▪ metrics-oriented approach and strategies/rules are most cited approaches to detection
▪ Topics
▪ Smells detection, code smell description, support tools for smell detection, and others

14. RQ3
Which tools have been mentioned for code
smell detection and refactoring support?

15. RQ3 Summary
▪ Challenges
▪ To develop tools that support more than one programming languages
▪ To expand the studies and experiments, improving the accuracy of the smell detection tools
and refactoring support
▪ Limitations and lack of maturity of tools
▪ Observations
▪ Several aspects characterize tools (license, supported languages, degree of automation, and
others)
▪ Java is the platform/programming language most used
▪ Large number of smell detection tools, detecting only a tiny amount of smells
▪ Number of refactoring tools is small
▪ CCFinder and Jdeodorant are the most cited tools

16. RQ4
Which RQs have been studied on code smells and
refactoring? What are the highest
cited secondary studies?

17. Top 5 selected studies
▪ Sorted by the number of citations by year
▪ Sorted by the number of citations of Google Scholar

18. RQ4 Summary
▪ Challenges
▪ Need for studies that contain more sophisticated RQs
▪ Studies covering RQs about Casuality and Design, describing situations of efficacy and
efficiency about methods, practices, and tools
▪ Observations
▪ 181 RQs in the 40 selected secondary studies
▪ One study is the most comprehensive work, with 13 RQs
▪ Some studies did not follow a defined protocol
▪ Scope of the study is related to the scope of the RQ

19. RQ5
What are the annual trends of types, quality, and
the number of primary studies reviewed by the
secondary studies?

20. Summary
Distribution of studies types cited
Type of referenced projects
Number of primary studies referenced per year

21. RQ5 Summary
▪ Challenges
▪ Lack of validation by experts on tool analysis
▪ Lack of benchmarks to support improvements of techniques and tools for both smells
and refactorings
▪ Observations
▪ Growth of secondary studies in recent years
▪ Vast majority of studies are SLR (65%), and 75% of studies are published in journals

22. Relationship between
code smells and refactoring

23. Smells and Refactoring connected by Quality
Primitive Refactorings
(renames, extracts, etc)
Composite Refactorings
(Replace conditional with, etc)
Approaches to Opportunities
(metrics, strategies/rules, search, etc )
Support Tools
Refactorings
Simple Smells
(magic numbers, long parameter list, etc)
Composite Smells
(God Class/Large Class, Blobs, etc)
Approaches to Detect
(metrics, strategies/rules, etc )
Support Tools
Code Smells
Internal Quality Attributes
Cohesion, Coupling, Size...
External Quality Attributes
Maintainability, Testability, Functionality...
Quality
Technical Debt
Management, Prioritizing, Mitigate...

24. Quality, Smells, and Refactoring

25. Implications
and Open Issues

26. Implications
▪ Practitioners
▪ Refactoring practice should be a daily habit
▪ Developers know the values of refactoring but are often prevented from applying them
▪ Code smells priorization, impact of quality attributes
▪ Instructors
▪ Include these topics in various courses
▪ Practices: Coding dojos, code review sessions, testing, and pair programming
▪ Researchers
▪ Impact of code smells and refactoring
▪ Industry-academic collaboration

27. Open Issues

28. Contributions
and Future Work

29. Contributions and Future Work
▪ Contributions
▪ We cross-reference the most frequent code smells with their detection approaches, detection
tools, suggested refactoring, and refactoring tools
▪ We report the relationships of the top 10 code smells with their refactoring and their impact
on quality
▪ We present the implications of this study from the perspective of practitioners, researchers, and
instructors
▪ We report on 13 open issues about code smells and refactoring
▪ Future works
▪ Practices and tools to mitigate the code smell and evaluate the impact on quality
▪ Goal of refactoring used by practitioners and their effect on quality
▪ Development/improvement of refactoring tools to monitor refactoring and its gains

30. 36th IEEE International Conference on Software Maintenance and Evolution
September 27-October 3, Journal First Track
Code smells and refactoring: A tertiary review of
challenges and observations
Guilherme Lacerda, Fábio Petrillo, Marcelo Pimenta, and Yann Gaël Guéhéneuc
Thank You!
Brazil Brazil Canada Canada