The document discusses the application of design principles in software development, emphasizing the importance of a well-educated mindset in design over specific technologies. It covers the SOLID principles, practical applications through examples, and techniques for recognizing and refactoring 'design smells' to improve code quality. Key takeaways include the proactive use of enabling techniques, refactoring, and employing design analysis tools.

1. How to Apply Design
Principles in Practice?
Ganesh Samarthyam
Entrepreneur; Author; Conf. speaker
ganesh@codeops.tech
www.designsmells.com; www.codeops.tech

2. "The critical design tool for software development
is a mind well educated in design principles.
It is not the UML or any other technology"
- Craig Larman

3. Why care about design quality and
design principles?

4. "We thought we were just programming on an airplane”
- Kent Beck

5. SOLID principles
• There&should&never&be&more&than&one&reason&for&a&class&to&
change&&
Single'Responsibility'
Principle'(SRP)'
• So6ware&en88es&(classes,&modules,&func8ons,&etc.)&should&
be&open&for&extension,&but&closed&for&modifica8on&
Open'Closed'Principle'
(OCP)'
• Pointers&or&references&to&base&classes&must&be&able&to&use&
objects&of&derived&classes&without&knowing&it&
Liskov’s'Subs<tu<on'
Principle'(LSP)'
• Depend&on&abstrac8ons,&not&on&concre8ons&
Dependency'Inversion'
Principle'(DIP)'
• Many&clientGspecific&interfaces&are&beHer&than&one&
generalGpurpose&interface&
Interface'Segrega<on'
Principle'(ISP)'

6. Booch’s fundamental principles
Principles*
Abstrac/on*
Encapsula/on*
Modulariza/on*
Hierarchy*

7. How to apply principles in practice?
Principles
Code
How to bridge
the gap?

8. Proactive application: enabling techniques

9. Discussion example
Violates Single
Responsibility
Principle (SRP)

10. Completeness: Example

11. Discussion Example

12. Principle of Least Astonishment: Example

13. Discussion Example

14. Use “enabling techniques” to apply
design principles in practice
Key-takeaway
#1

15. Design smells: example

16. 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!

17. “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?

18. Refactoring for Date
Replace inheritance
with delegation

19. java.time package!

20. 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!

21. 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]

22. More classes in Date/Time API

23. What’s that smell?
switch'(transferType)'{'
case'DataBuffer.TYPE_BYTE:'
byte'bdata[]'='(byte[])inData;'
pixel'='bdata[0]'&'0xff;'
length'='bdata.length;'
break;'
case'DataBuffer.TYPE_USHORT:'
short'sdata[]'='(short[])inData;'
pixel'='sdata[0]'&'0xffff;'
length'='sdata.length;'
break;'
case'DataBuffer.TYPE_INT:'
int'idata[]'='(int[])inData;'
pixel'='idata[0];'
length'='idata.length;'
break;'
default:'
throw' new' UnsupportedOperaQonExcepQon("This' method' has' not' been' "+' "implemented'
for'transferType'"'+'transferType);'
}'

24. Don’t repeat yourself (DRY) principle
protected(int(transferType;! protected(DataBuffer(dataBuffer;!
pixel(=(dataBuffer.getPixel();(
length(=(dataBuffer.getSize();!
switch((transferType)({(
case(DataBuffer.TYPE_BYTE:(
byte(bdata[](=((byte[])inData;(
pixel(=(bdata[0](&(0xff;(
length(=(bdata.length;(
break;(
case(DataBuffer.TYPE_USHORT:(
short(sdata[](=((short[])inData;(
pixel(=(sdata[0](&(0xffff;(
length(=(sdata.length;(
break;(
case(DataBuffer.TYPE_INT:(
int(idata[](=((int[])inData;(
pixel(=(idata[0];(
length(=(idata.length;(
break;(
default:(
throw( new( UnsupportedOperaRonExcepRon("This( method(
has( not( been( "+( "implemented( for( transferType( "( +(
transferType);(
}!

25. Refactor “bad smells” to apply
design principles in practice
Key-takeaway
#2

26. Tool driven approach for design
quality

27. Comprehension tools
STAN
http://stan4j.com

28. Comprehension tools
Code City
http://www.inf.usi.ch/phd/wettel/codecity.html

29. Comprehension tools
Imagix 4D
http://www.imagix.com

30. Critique, code-clone detectors, and metric tools
Infusion
www.intooitus.com/products/infusion

31. Critique, code-clone detectors, and metric tools
Designite
www.designite-tools.com

32. Critique, code-clone detectors, and metric tools
PMD Copy Paste Detector (CPD)
http://pmd.sourceforge.net/pmd-4.3.0/cpd.html

33. Critique, code-clone detectors, and metric tools
Understand
https://scitools.com

34. Technical debt quantification/visualization tools
Sonarqube
http://www.sonarqube.org

35. Refactoring tools
ReSharper
https://www.jetbrains.com/resharper/features/

36. Use design analysis tools to apply
design principles in practice
Key-takeaway
#3

37. Key take-aways
❖ Thee effective ways to apply design principles in
practice:
❖ Use “enabling techniques”
❖ Refactoring “bad smells”
❖ Use design analysis tools

38. Proactive application: enabling techniques

39. Reactive application: refactoring smells

40. Enablers: tools for refactoring
Jhawk&
(Java)&
CodeCity&&
(C++,&Java,&C#)&&
CppDepend&
(C++)&
Sotograph&
(C++,&Java,&C#)&
Imagix&4D&&
(C,&C++,&Java)&
La?x&
(C/C++,&Java,&C#)&&
SolidSX&&
(C++,&Java,&C#)&
Bauhaus&
(C/C++,&Java,&C#)&
Structure101&&
(Java,&C#)&
Understand&&
(C/C++,&Java,&C#)&
Simian&
(C/C++,&Java,&C#,&…)&
Jarchitect&
(Java)&
Ndepend&
(C#)&
Stan4J&
(Java)&
InFusion&
(C/C++,&Java)&
InCode&
(C/C++,&Java)&

41. Our upcoming workshops
Modern Software Architecture - July 2
Modern Programming with Java 8 - July 16
Software Refactoring in Practice - July 23

42. www.codeops.tech
www.designsmells.com
ocpjava.wordpress.com
ganesh@codeops.tech
bit.ly/sgganesh
@GSamarthyam