Object Oriented Programming 1. Cohesion and coupling 2. Single Responsibility Principle 3. Dependency Inversion Principle 4. Interface Segregation Principle

1. Object Oriented Programming
in Swift
Ch 3
Single Responsibility Principle
Dependency Inversion Principle
Interface Segregation Principle
Sai Li @ Yowoo Tech.
2016/1/9

2. References
• Agile Software Development: Principles, Patterns,
and Practice ( : )
by Robert C. Martin
• Fundamental Object Oriented Programming
by Hsuan-Tien Lin
•
by Teddy Chen
• Essential Object-Oriented Programming
by Josh Ko

3. Cohesion & Coupling

4. Cohesion
• Degree to which the elements of a module belong
together
• The force that cause a module or a class to change

5. Coupling
• Degree of interdependence between software
modules

6. Cohesion & Coupling

7. Cohesion & Coupling
Goal: high cohesion, low coupling

8. S.O.L.I.D
• SRP: Single Responsibility Principle
• OCP: Open Closed Principle
• LSP: Liskov Substitution Principle
• ISP: Interface Segregation Principle
• DIP: Dependency Inversion Principle

9. Single Responsibility Principle
“A class should have one,
and only one, reason to change.”

10. SRP

11. SRP

12. Responsibility
• A reason for change
• More than one responsibility
• coupled responsibilities
• Fragile Design

13. Example

14. Needless Complexity?
When?

15. Persistence
TDD

16. Single Responsibility Principle
• One of the simplest and hardest principle
• Software Design: The art of separating responsibility

17. S.O.L.I.D
• SRP: Single Responsibility Principle
• OCP: Open Closed Principle
• LSP: Liskov Substitution Principle
• ISP: Interface Segregation Principle
• DIP: Dependency Inversion Principle

18. Dependency Inversion Principle
1. High-level modules should not depend on low-
level modules.
Both should depend on abstractions
2. Abstractions should not depend on details. Details
should depend on abstractions.

19. Inversion of Control
low level change -> high level change

20. Hollywood Principle: Don’t call me, I’ll call you
Inversion of Control
What they need

21. Switch
+ switch()
SwitchableDevicePolicy

23. – Robert C. Martin
“Depend on abstractions,
not on concretions.”

24. - Design Pattern , GoF
“Program to an interface,
not an implementation.”

25. S.O.L.I.D
• SRP: Single Responsibility Principle
• OCP: Open Closed Principle
• LSP: Liskov Substitution Principle
• ISP: Interface Segregation Principle
• DIP: Dependency Inversion Principle

26. Interface Pollution

27. Interface Pollution

28. Adaptor

29. Interface Segregation Principle
“Client should NOT be forced to depend
upon interfaces that they do not use”

30. Glass door
Separate Clients == Separate Interfaces

33. “Fat” Interface
• More than one responsibility
• Coupled responsibilities
• Fragile Design
• Clients depend on what they need only

34. Recap
• SRP: A class should have one, and only one, reason to change.
• DIP: Depend on abstractions, not on concretions.
• ISP: Make fine grained interfaces that are client specific

35. Recap Liskov Violation

36. Liskov Substitution Principle
Subtypes must be substitutable for their base
types.

37. Rectangle & Square Problem

39. Segment
Line
Ray

40. Line: isOn(point: Intercept) == true
LineSegment: isOn(point: Intercept) == ?

43. It’s the end
of the beginning

44. – Sai Li
“Live for interfaces, not implementations,
except Lovers”

45. References
• https://en.wikipedia.org/wiki/Cohesion_(computer_science)
• https://drive.google.com/file/d/0ByOwmqah_nuGNHEtcU5OekdDMkk/view?pli=1
• http://teddy-chen-tw.blogspot.tw/2011/12/1.html
• http://www.cs.utexas.edu/users/downing/papers/DIP.1996.pdf
• http://howard-lyrics.blogspot.tw/2011/04/test.html
• http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod
• https://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Laptop-hard-drive-exposed.jpg/220px-Laptop-hard-drive-
exposed.jpg
• http://sce2.umkc.edu/BIT/burrise/pl/design/cohesion-coupling-abstract.gif
• http://freefeast.info/wp-content/uploads//2013/08/cohesion-vs.-coupling.jpg
• http://cdn.mos.cms.futurecdn.net/7047e9b7bfca2b3b6f352495885e77c2.jpg
• https://upload.wikimedia.org/wikipedia/commons/8/8d/DIPLayersPattern.png
• http://flylib.com/books/4/444/1/html/2/images/11_3.jpg
• http://flylib.com/books/4/444/1/html/2/images/11_4.jpg
• http://stg-tud.github.io/sedc/Lecture/ws13-14/Images/DIP-RegulatorBase.png
• http://stg-tud.github.io/sedc/Lecture/ws13-14/Images/DIP-RegulatorDIPCompliant.png
• http://www.coolmath.com/sites/cmat/files/images/03-lines-01.gif
• http://flylib.com/books/4/444/1/html/2/images/12_2.jpg
• http://flylib.com/books/4/444/1/html/2/images/12_1.jpg