Bra kod luktar inte, den doftar. Data-Tjej, Linköping Daniel Deogun

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1 Bra kod luktar inte, den doftar Data-Tjej, Linköping Daniel Deogun

2 Daniel Deogun Senior konsult & konsultchef på Omegapoint i Stockholm! Arbetat i drygt 6 år med patientkritisk mjukvara (pacemaker- och ICD-system) Arbetat med agila utvecklingsprocesser sedan 2005 (Scrum och Kanban)! Arbetat med Domain Driven Design (DDD) och Test Driven Development (TDD) i ca 9 år! En av Omegapoints kursledare i DDD och TDD! Nuvarande uppdrag! Lead developer på Hi3G Access AB

3 Bakgrund Varför uppstår... [1] [1] By lumaxart (EbonyG00052_LuMaxArt) [CC-BY-SA-2.0 ( or CC-BY-SA-2.0 ( via Wikimedia Commons

4 Bakgrund Varför uppstår... Null Pointer Exception [1] [1] By lumaxart (EbonyG00052_LuMaxArt) [CC-BY-SA-2.0 ( or CC-BY-SA-2.0 ( via Wikimedia Commons

5 Bakgrund Varför uppstår... Null Pointer Exception [1] Wrong Argument Order [1] By lumaxart (EbonyG00052_LuMaxArt) [CC-BY-SA-2.0 ( or CC-BY-SA-2.0 ( via Wikimedia Commons

6 Bakgrund Varför uppstår... Illegal Input Null Pointer Exception [1] Wrong Argument Order [1] By lumaxart (EbonyG00052_LuMaxArt) [CC-BY-SA-2.0 ( or CC-BY-SA-2.0 ( via Wikimedia Commons

7 Bakgrund Varför uppstår... Illegal Input Null Pointer Exception [1] Wrong Argument Order Oväntade beteenden [1] By lumaxart (EbonyG00052_LuMaxArt) [CC-BY-SA-2.0 ( or CC-BY-SA-2.0 ( via Wikimedia Commons

8 Bakgrund Varför uppstår... Illegal Input Null Pointer Exception [1] Wrong Argument Order Oväntade beteenden Komplex defensiv kod [1] By lumaxart (EbonyG00052_LuMaxArt) [CC-BY-SA-2.0 ( or CC-BY-SA-2.0 ( via Wikimedia Commons

9 Requirements Möte Ett möte har en titel, start- och sluttid, en sammankallande och minst en inbjuden deltagare. Ett mötesrum får inte ha multipla möten under samma tidsperiod. När ett rum bokats skall samtliga inbjudna deltagare notifieras.

10 Code Review...

11 Code Review...

12 Code Review...

13 Code Review...

14 Code Review...

15 Code Review...

16 Code Review...

17 The Parameter Order Bug If a method signature contains multiple arguments of the same type, then there s a risk that parameter values get interchanged upon method invocation Example,!! Then the following invocations are valid from a complier perspective but semantically incorrect! setname(string first, String last) setname( Daniel, Deogun ); setname( Deogun, Daniel );

18 Strongly Typed Arguments One way to avoid the parameter order bug is to use strongly typed arguments! Example,!!! Hence, invoking the method with incorrect parameter order will yield a compiler error! setname(firstname first, LastName last)

19 Let s apply Strongly Typed Arguments

20 Let s apply Strongly Typed Arguments

21 Let s apply Strongly Typed Arguments

22 Let s Take a Look At... Dependencies

23 Definition of Dependency Merriam-Webster! [de pen den cy] noun \-dən(t)-sē\ : the quality of being dependent! [de pen dent] adjective \di-ˈpen-dənt\ : needing someone or something else for support, help, etc.

24 Dependency in Code Given a class A and class B! When class A needs logic in class B to execute! Then class A has a dependency to class B! A depends on B

25 Identifying Dependencies

26 Identifying Dependencies

27 Identifying Dependencies

28 Identifying Dependencies

29 Identifying Dependencies

30 Identifying Dependencies

31 Identifying Dependencies

32 Identifying Dependencies

33 Identifying Dependencies

34 Identifying Dependencies

35 Why does one need to study dependencies? Studying dependencies helps one to understand how tightly coupled the code is! Dependencies may complicate testing and code reuse! So how should one treat dependencies?

36 Dependency Injection The basic idea of Dependency Injection (DI) is to separate the assembly of an object from the client with the dependency By this way, the client becomes unaware of the implementation and only needs to focus on the API Assembler builds Object injects Client depends on

37 Let s apply Dependency Injection

38 Let s apply Dependency Injection

39 Let s apply Dependency Injection

40 Let s apply Dependency Injection

41 Let s apply Dependency Injection

42 Let s Take a Look At... Design by Contract

43 Design By Contract The term was coined by Bertrand Meyer when designing the Eiffel programming language back in 1986! The main idea of DbC is the collaboration between software elements where mutual obligations and benefits exist! Let s look at an example...

44 Design By Contract Assume we have the following method! public void register(listener listener) What do we expect to happen when A. register(new Listener()) B. register(null)! If the call to register returns without an exception, what can be assumed?

45 Design By Contract If we use DbC, then the expectations and assumptions are expressed as Require and Ensurements! Hence, the method register could look like

46 Design By Contract If we use DbC, then the expectations and assumptions are expressed as Require and Ensurements! Hence, the method register could look like

47 Let s apply Design By Contract

48 Let s apply Design By Contract

49 Let s apply Design By Contract

50 Let s apply Design By Contract

51 Let s apply Design By Contract

52 Wow, Hold Your Horses

53 Wow, Hold Your Horses

54 Wow, Hold Your Horses

55 Wow, Hold Your Horses

56 Let s Take a Look At... Law of Demeter

57 Law of Demeter The Law of Demeter was proposed at Northeastern University back in 1987! The fundamental idea may be expressed as Each unit should only talk to its friends; don't talk to strangers.! -

58 Law of Demeter Hence, one should never reach through an object for another object s functionality! Damian Guy tweeted back in 2009! Every time a mock returns a mock, a fairy dies! Oct 19 Dan Bergh Johnsson has written an excellent post on his blog Dear Junior - Letters to a junior programmer on how this affect testability ( Demeter Saves Mocking Fairies 16 nov 2009)

59 Let s Apply Law of Demeter

60 Let s Apply Law of Demeter

61 Let s Apply Law of Demeter

62 Let s Apply Law of Demeter

63 Let s Apply Law of Demeter

64 Let s Apply Law of Demeter

65 Let s Take a Look At... Tell, Don t Ask

66 Tell, Don t Ask Martin Fowler summarizes the Tell, Don t Ask principle in the following way! Tell-Don't-Ask is a principle that helps people remember that object-orientation is about bundling data with the functions that operate on that data. It reminds us that rather than asking an object for data and acting on that data, we should instead tell an object what to do. This encourages to move behavior into an object to go with the data.! -

67 Let s Apply Tell, Don t Ask

68 Let s Apply Tell, Don t Ask

69 Let s Apply Tell, Don t Ask

70 Let s Apply Tell, Don t Ask

71 Let s Apply Tell, Don t Ask

72 Let s Apply Tell, Don t Ask

73 Requirements Möte Ett möte har en titel, start- och sluttid, en sammankallande och minst en inbjuden deltagare. Ett mötesrum får inte ha multipla möten under samma tidsperiod. När ett rum bokats skall samtliga inbjudna deltagare notifieras.

74 Let s Refactor...

75 Let s Refactor...

76 Let s Refactor...

77 Så vad har vi lärt oss?

78 Så vad har vi lärt oss? Strongly Typed Objects

79 Så vad har vi lärt oss? Dependency Injection Strongly Typed Objects

80 Så vad har vi lärt oss? Dependency Injection Design by Contract Strongly Typed Objects

81 Så vad har vi lärt oss? Dependency Injection Design by Contract Strongly Typed Objects Law of Demeter

82 Så vad har vi lärt oss? Dependency Injection Design by Contract Strongly Typed Objects Tell, Don t Ask Law of Demeter

83 Is this a Silver Bullit? Detta till trots så kan oväntade beteenden förekomma!! Vanliga problem

84 Is this a Silver Bullit? Detta till trots så kan oväntade beteenden förekomma!! Vanliga problem Strongly Typed Objects Många typer Konstiga typhierarkier kan uppstå

85 Is this a Silver Bullit? Detta till trots så kan oväntade beteenden förekomma!! Vanliga problem Dependency Injection Felaktiga beroenden Onödiga tillstånd Shared mutable state

86 Is this a Silver Bullit? Detta till trots så kan oväntade beteenden förekomma!! Vanliga problem Design by Contract Avsaknad av kontrakt Svaga kontrakt Felaktiga kontrakt

87 Is this a Silver Bullit? Detta till trots så kan oväntade beteenden förekomma!! Vanliga problem Law of Demeter Duplicerade API:er

88 Is this a Silver Bullit? Detta till trots så kan oväntade beteenden förekomma!! Vanliga problem Tell, Don t Ask Kan upplevas som svårt

89 Is this a Silver Bullit? Detta till trots så kan oväntade beteenden förekomma!! Vanliga problem Generellt Felaktig exekveringsordning

90 Resultat

91 Resultat

92 Q & A

93 Tack!