Awareness of design smells - indicators of common design problems - helps developers or software engineers understand mistakes made while designing and apply design principles for creating high-quality designs. This presentation provides insights gained from performing refactoring in real-world projects to improve refactoring and reduce the time and costs of managing software projects.

1. Refactoring for
Software Design Smells
Ganesh Samarthyam
ganesh.samarthyam@gmail.com

2. “Applying design principles is the key to creating
high-quality software!”
Architectural principles:
Axis, symmetry, rhythm, datum, hierarchy, transformation

3. Who coined the
term “code
smell”?

4. Kent Beck

5. Who coined the
acronym “SOLID”?
(as in SOLID
principles)

6. Michael
Feathers
S
Single Responsibility
Principle
Every object should have a single responsibility and
that should be encapsulated by the class
O Open Closed Principle
Software should be open for extension, but closed for
modification
L
Liskov’s Substitution
Principle
Any subclass should always be usable instead of its
parent class
I
Interface Segregation
Principle
Many client specific interfaces are better than one
general purpose interface
D
Dependency Inversion
Principle
Abstractions should not depend upon details. Details
should depend upon abstractions

7. Why Care About Design Quality?
When, due to constraints, I design
quickly and dirty, my project is
loaded with technical debt

8. Tool: Sonar!
Sonarqube
http://www.sonarqube.org

9. The City Metaphor
Source: http://indiatransportportal.com/wp-content/uploads/2012/04/Traffic-congestion1.jpg

10. The City Metaphor
“Cities grow, cities evolve, cities
have parts that simply die while other
parts flourish; each city has to be
renewed in order to meet the needs of its
populace… Software-intensive systems
are like that. They grow, they evolve,
sometimes they wither away, and
sometimes they flourish…”
Grady Booch in the foreword for “Refactoring for Software Design Smells: Managing Technical Debt”, Girish Suryanarayana, Ganesh Samarthyam, Tushar Sharma, Morgan Kaufmann/Elsevier, 2014.

11. Tool: CodeCity!

12. What are Smells?
“Smells'are'certain'structures'
in'the'code'that'suggest'
(some4mes'they'scream'for)'
the'possibility'of'refactoring.”''

13. Smell Example
logger.severe(“details”)
errlog.log(“details”)logger.error(“details”)
System.err.println(“details”)
Since ROI (Return On Investment)
is not clear, how to get
management buy-in for this
refactoring?
Log4j java.util.logging custom log library SOPs

14. Granularity of Smells
Architectural+
+
Cyclic&dependencies&between&modules&
Monolithic&modules&&
Layering&viola9ons&(back&layer&call,&skip&layer&call,&ver9cal&layering,&
etc)&
Design+
+
God&class&
Refused&bequest&&
Cyclic&dependencies&between&classes&
Code+(implementa6on)++
+
Internal&duplica9on&(clones&within&a&class)&&
Large&method&&
Temporary&field&&

15. Architecture Smell Example

16. Design Smell Example

17. Code Smell Example
class%GraphicsDevice%
%public%void%setFullScreenWindow(Window%w)%{%
%%%%%%%%if%(w%!=%null)%{%
%%%%%%%%%%%%if%(w.getShape()%!=%null)%{%w.setShape(null);%}%
%%%%%%%%%%%%if%(w.getOpacity()%<%1.0f)%{%w.setOpacity(1.0f);%}%
%%%%%%%%%%%%if%(!w.isOpaque())%{%
%%%%%%%%%%%%%%%%Color%bgColor%=%w.getBackground();%
%%%%%%%%%%%%%%%%bgColor%=%new%Color(bgColor.getRed(),% %
%% %bgColor.getGreen(), %
%%%% %bgColor.getBlue(),%255);%
%%%%%%%%%%%%%%%%w.setBackground(bgColor);%
%%%%%%%%%%%%}%
%%%%%%%%}%
…%
}%
This%code%in%
GraphicsDevice%uses%
more%methods%of%
Window%than%calling%
its%own%methods!%
“Feature
envy” smell

18. Focus on Design Smells

19. Initial Journal Paper
Published in Journal of Object Technology (Vol. 12, No. 2, 2013)
S G Ganesh, Tushar Sharma, Girish Suryanarayana. Towards a Principle-based
Classifica4on of Structural Design Smells. In Journal of Object Technology, vol.
12, no. 2, 2013, pages 1:1–29.doi:10.5381/jot.2013.12.2.a1
URL: hLp://www.jot.fm/issues/issue_2013_06/arPcle1.pdf (open access)

20. … and a Conference Paper

21. Finally a Book

22. For Architects: Design is the Key!

23. Why Care About Principles?

24. Equivalent Principles in Software Design?
Architectural principles:
Axis, symmetry, rhythm, datum, hierarchy, transformation

25. Equivalent Principles in Software Design!
Principles*
Abstrac/on*
Encapsula/on*
Modulariza/on*
Hierarchy*

26. Proactive Application: Enabling Techniques

27. Reactive Application: Smells

28. Design Smells: Example #1

29. Discussion Example

30. Design Smells: Example #2

31. Discussion Example

32. Design Smells: Example #3

33. Discussion Example
// using java.util.Date
Date today = new Date();
System.out.println(today);
$ java DateUse
Wed Dec 02 17:17:08 IST 2015
Why should we get the
time and timezone details
if I only want a date? Can
I get rid of these parts?
No!

34. So What!
Date today = new Date();
System.out.println(today);
Date todayAgain = new Date();
System.out.println(todayAgain);
System.out.println(today.compareTo(todayAgain) == 0);
Thu Mar 17 13:21:55 IST 2016
Thu Mar 17 13:21:55 IST 2016
false
What is going
on here?

35. java.time package!

36. Refactored Solution
LocalDate today = LocalDate.now();
System.out.println(today);
LocalDate todayAgain = LocalDate.now();
System.out.println(todayAgain);
System.out.println(today.compareTo(todayAgain) == 0);
2016-03-17
2016-03-17
true
Works fine
now!

37. Refactored Example …
You can use only date,
time, or even timezone,
and combine them as
needed!
LocalDate today = LocalDate.now();
System.out.println(today);
LocalTime now = LocalTime.now();
System.out.println(now);
ZoneId id = ZoneId.of("Asia/Tokyo");
System.out.println(id);
LocalDateTime todayAndNow = LocalDateTime.now();
System.out.println(todayAndNow);
ZonedDateTime todayAndNowInTokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));
System.out.println(todayAndNowInTokyo);
2016-03-17
13:28:06.927
Asia/Tokyo
2016-03-17T13:28:06.928
2016-03-17T16:58:06.929+09:00[Asia/Tokyo]

38. More classes in Date/Time API

39. IMPaCT Process Model

40. Refactoring: Practical concerns
“Fear of breaking
working code”
Is management buy-in necessary for refactoring?
How to refactor code in legacy projects (no automated
tests, difficulty in understanding, lack of motivation, …)?
Where do I have time
for refactoring?

41. “Applying design principles is the key to creating
high-quality software!”
Architectural principles:
Axis, symmetry, rhythm, datum, hierarchy, transformation

42. email sgganesh@gmail.com
website www.designsmells.com
twitter @GSamarthyam
linkedin bit.ly/sgganesh
slideshare slideshare.net/sgganesh