Presentation on Agile Evolutionary Design and SOLID principles given at Agile NCR.

1. Agile Evolutionary Design & SOLID Principles

3. Agile Design Process

4. SOLID principles

5. And coding time :)

6. Questions anytime.

7. Typical Evolution of System Dream system designed to perfection and beauty. Meaning of beauty and perfection are subjective. What do those mean for you?

8. Typical Evolution of System Adding features

9. Typical Evolution of System Changing features

10. Birth of Legacy System Somewhere in near future

11. Agile Design Process

12. Beautiful System Beautiful System

13. Adding a feature

14. Clean the mess We will see some of the techniques which will help us to keep the system clean in this presentation.

15. After a period of time Beautiful System.

17. Not doing an anticipatory design

19. XP Practices

20. But at code level what helps to create simple and evolutionary design?

22. ReadFile

23. Extract Data

24. FormatReport Reporter App File

25. SOLID Principles

27. Open Closed Principle

28. Liskov Substitution Principle

29. Interface Segregation Principle

30. Dependency Inversion Principle

31. Single Responsibility Principle

33. Or a class should not handle more than one responsibility

34. Design smell – Class changed when unrelated responsibilities change. High afferent coupling? Or multiple classes changed when a responsibility changes. High Efferent Coupling?

35. Shotgun surgery and divergent change

36. If it is not possible to separate the responsibilities at least show the presence of multiple roles played by the object.

37. Applies not just for classes but also for modules, functions as well

38. Better cohesion, encapsulation and less coupled design

40. May be will add more report formats (Graphical etc..) Reporter App Report Data Extractor Report Formatter CSV Format JSON Format

41. Open Closed Principle

43. Design smell - Change ripples through code base.

44. Abstraction and polymorphism are the key.

45. Chain of responsibility, Strategy pattern, Aspects...

46. Separate creation from usage of objects.

47. No module is 100% closed (Open/Closed/Open principle)

48. Easy to lead to anticipatory design. Better to burn finger at least once.

49. Service and framework interface follow OCP. Open for extension, closed for modification

50. Better design applying OCP Report Data Extractor CSV Format JSON Format Report Data Extractor Service Reporter App (UI + Formatter)

51. Liskov Substitution Principle

54. Used when inheritance was a main form of reuse.

55. Design smell – Type checking in client code and changing the behavior for a specific type in client.

56. Due to forcing an unrelated object into an inheritance hierarchy

57. Prefer composition over inheritance whenever possible

58. LSP Violation Data Extractor CSV Format JSON Format Data Extractor Service Reporter (UI + Formatter) Database New Requirement - Adding Database as a data source for report data. Adding it to File Reader Service as it is conveniently there

59. Better design confirming to LSP File Reader CSV File JSON File File Data Extractor Service Reporter (UI + Formatter) Database Database Data Extractor Service Keep Database separate as it doesn't fit in File Data Extractor Service

60. Interface Segregation Principle

62. Design smell – NotImplementException thrown for some methods (which are really not needed by the client)

63. Flat and non cohesive interface problem - SRP?

64. Role based interface design – Intent Revealing Interfaces by Udi Dahan ( IExtractReportData )

65. ISP Violation

67. ReadFile

69. Dependency Inversion Principle

71. Abstractions should not depend upon details. Details should depend upon abstractions

72. Design smell – Unable to change the choice of implementation & code untestable in isolation

74. Less coupled design

75. DIP Violation Stuck with Text Format and Text Report Formatter implementations !!! Arrows are Dependency Text Report Formatter Reporting App Text Format JSON Format

76. Fixing for DIP Text Report Formatter Reporting App CSV Format JSON Format IFormatReport IExtractReportData

77. Design confirming to DIP IExtractReportData CSV Data Extractor JSON Data Extractor Data Extractor Service Reporter Writer Database Reader Service XML Data Extractor Reporting Application Report Data

79. Uncle Bob for consolidating these principles and his books Agile Software Development: Principles, Practices and Patterns and Clean Code

80. Presentation is under Creative Commons Attribution-Share Alike 2.5 India License

82. Interested in OO, DDD, Functional Programming languages, Agile, Lean, TDD, Mocks, Automated Testing, ATDD.....

83. Author and maintainer of ChromeWatir and FireDriver

85. http://twitter.com/sai_venkat

86. http://github.com/saivenkat

87. Thank you