This presentation covers practical aspects and some of the best practices in Java class design.

1. Java Class Design Ganesh Samarthyam
ganesh@codeops.tech

2. Name the first
object oriented
programming
language

3. Simula (1965!)

6. OOP sometimes becomes
❖ Uh-oh
or
❖ Oops!

7. Guess the output
class Base {
public Base() {
foo();
}
public void foo() {
System.out.println("In Base's foo ");
}
}
class Derived extends Base {
public Derived() {
i = new Integer(10);
}
public void foo() {
System.out.println("In Derived's foo " + i.toString() );
}
private Integer i;
}
class Test {
public static void main(String [] s) {
new Derived();
}
}

8. Guess the output
abstract class Printer {
private Integer portNumber = getPortNumber();
abstract Integer getPortNumber();
public static void main(String[]s) {
Printer p = new LPDPrinter();
System.out.println(p.portNumber);
}
}
class LPDPrinter extends Printer {
/* Line Printer Deamon port no is 515 */
private Integer defaultPortNumber = 515;
Integer getPortNumber() {
return defaultPortNumber;
}
}

9. Date & time exercise
❖ Your project requires support for date and time
functionality
❖ Assume that the Java library or third-party library support is
not available for date and time related functionality
❖ Will you provide separate classes for date, time and
timezone or a single class that supports all the three? How to
support calculating differences between two date/time
values?

10. Class design problem: Example

11. 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!

12. 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?

13. java.time package!

14. 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!

15. Revisiting the 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]

16. More classes in Date/Time API

17. Avoid switch cases
public'Insets'getBorderInsets(Component'c,'Insets'insets){'
''''''''Insets'margin'='null;'
'''''''''//'Ideally'we'd'have'an'interface'defined'for'classes'which'
''''''''//'support'margins'(to'avoid'this'hackery),'but'we've'
''''''''//'decided'against'it'for'simplicity'
''''''''//'
''''''''if'(c'instanceof'AbstractBuEon)'{'
'''''''''''''''''margin'='((AbstractBuEon)c).getMargin();'
''''''''}'else'if'(c'instanceof'JToolBar)'{'
''''''''''''''''margin'='((JToolBar)c).getMargin();'
''''''''}'else'if'(c'instanceof'JTextComponent)'{'
''''''''''''''''margin'='((JTextComponent)c).getMargin();'
''''''''}'
''''''''//'rest'of'the'code'omiEed'…'

18. Interface hierarchy for polymorphism

19. Using runtime polymorphism
!!!!!!!margin!=!c.getMargin();
!!!!!!!!if!(c!instanceof!AbstractBu8on)!{!
!!!!!!!!!!!!!!!!!margin!=!((AbstractBu8on)c).getMargin();!
!!!!!!!!}!else!if!(c!instanceof!JToolBar)!{!
!!!!!!!!!!!!!!!!margin!=!((JToolBar)c).getMargin();!
!!!!!!!!}!else!if!(c!instanceof!JTextComponent)!{!
!!!!!!!!!!!!!!!!margin!=!((JTextComponent)c).getMargin();!
!!!!!!!!}

20. Assign responsibilities correctly
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);
}
}
…
}

21. Keep data members private

22. Protect from direct external mutations

23. Ensure each class has a single responsibility

24. Adhere to IS-A relationship

25. Depend on abstractions

26. SOLID Principles
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

27. Tools to explore
Jhawk
(Java)
CodeCity
(C++, Java, C#)
CppDepend
(C++)
Sotograph
(C++, Java, C#)
Imagix 4D
(C, C++, Java)
Lattix
(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)

28. Meetups
h"p://www.meetup.com/JavaScript-Meetup-Bangalore/
h"p://www.meetup.com/Container-Developers-Meetup-Bangalore/
h"p://www.meetup.com/So>ware-Cra>smanship-Bangalore-Meetup/
h"p://www.meetup.com/Core-Java-Meetup-Bangalore/
h"p://www.meetup.com/CloudOps-Meetup-Bangalore/
h"p://www.meetup.com/Bangalore-SDN-IoT-NetworkVirtualizaGon-Enthusiasts/
h"p://www.meetup.com/So>wareArchitectsBangalore/
h"ps://www.meetup.com/Mobile-App-Developers-Bangalore-Meetup/

29. ganesh@codeops.tech @GSamarthyam
www.codeops.tech slideshare.net/sgganesh
+91 98801 64463 bit.ly/ganeshsg