Design patterns. François Schwarzentruber ENS Cachan Antenne de Bretagne

Transcription

1 Design patterns François Schwarzentruber ENS Cachan Antenne de Bretagne

2 Recall of the object designs One class = one responsibility Better extend than modify Liskov substitution principles One interface per client Dependency inversion principle

3 Problem: a system is big...

4 Solution concepts are local.

5 Example Problem We need those actions to be extended and undone. Solution We apply locally a suitable micro-architecture.

6 Solution: Design pattern + sequence diagram

7 Design pattern is about... Functional properties: Non functional property Correction of an algorithm Easy to understand Complexity in time/space Easy to maintain... Easy to test

8 Wisdom: do not reinvent the wheel Integers UML Editor Matrices Pong algorithm suite Rubik's cube... Drawing software Same concepts Same solutions Group theory Design patterns (Évariste Galois) «Façade» Subgroup «Visitor» Order of an element

9 Wisdom: some vocabulary! As the extension is Galois... The crème anglaise is perfect with with this cake. Let us apply the Visitor pattern.

10 The idea of design patterns comes from architecture Christopher Alexander : anthropologist and architect Idea of reusable concepts

11 Design patterns 1995 : Gamma, Helm, Johnson et Vlissides. Design Patterns Elements of Reusable ObjectOriented Software

12 Outline: a trip in the design pattern countryside! Creational patterns Structural patterns Behavioural patterns

13 Creational patterns Abstract factory Prototype

14 YOU want to design a software for learning algorithmic

15 Need: to adapt the software to different environments Windows Linux MacOS Android

16 Need: to design the software for different kinds of user Kids High-school students

17 The hell: you have created objects at any part of your software! new new new new new

18 Non maintainable solution b = new brickcleanall() ; if(forkids) { b = new brickcleanallforkids() ; } else { b = new brickcleanallforhighschoolstudents() ; }

19 Non maintainable solution b = new brickcleanall() ; It violates 1) the open closed principle (better extend than modify) if(forkids) { b = new brickcleanallforkids() ; } else { b = new brickcleanallforhighschoolstudents() ; }

20 Non maintainable solution b = new brickcleanall() ; It violates 1) the open closed principle (better extend than modify) 2) The dependency inversion principle (do not depend on concretions) if(forkids) { b = new brickcleanallforkids() ; } else { b = new brickcleanallforhighschoolstudents() ; }

21 Abstract factory We need to adapt our software to two different kinds of users. We apply the abstract factory pattern. How to do this?

22 Solution: to isolate the object creation in factories please... create a CleanAll brick.

23 Solution: to isolate the object creation in factories please... create a CleanAll brick. clean all for Kids

24 Solution: to isolate the object creation in factories please... create a CleanAll brick. clean all for high-school students

25 Abstract Factory pattern b = new BrickCleanAll() ; AbstractFactory factory = new FactoryForKids() factory.getnewbrickcleanall()

26 Abstract Factory pattern

27 Patron de conception : fabrique abstraite

28 Sequence diagram for the Abstract Factory pattern Source : cours de Noël Plouzeau

29 Conclusion on the abstract factory Good points depends on abstraction platforms are isolated (less coupling) Bad points Factory is difficult to maintain ~ but in fact it would worse with the abstract factory pattern!

30 Build objects from a model: prototype pattern Source : logiciel Dia

31 Needs Copy objects Being able to add elements to the palette

32 DO NOT DO THAT: one creation per button! new House(Color.RED, Color.WHITE, 16, 32, 16) new Tree(Color.GREEN, Color.BROWN, 8, 32, 8)

33 TO DO! Each button contains a prototype to clone.

34 Prototype pattern Source : wikipedia

35 Conclusion on the Prototype pattern + Buttons depend on abstraction + Only one class for buttons - Clone to implement

36 Structural pattern To adapt an object to a given interface (~ adaptor) To propose a simplified interface (~ façade) Divide responsibilities (~ bridge) Recursive structures (~ composite) Add many features (~ decoration)

37 Need I have implemented rectangles, ellipses in my software... But I also want to use graphics for statistics... GraphicalObject getbounds() : Rect Column 1 Column 2 Column Rectangle Ellipse 2 0 Row 1 Row 2 Row 3 Row 4 LibreOfficeGraphics width height LibreOffice proposes such graphics... But the interface is different...

38 Solution I have implemented rectangles, ellipses in my software... But I also want to use graphics for statistics... GraphicalObject getbounds() : Rect Column 1 Column 2 Column Rectangle Ellipse 2 0 Row 1 Row 2 Row 3 Row 4 StatGraphics LibreOfficeGraphics width height

39 Adaptor source : Wikipedia

40 Other story: new need! (+ (* 2 3) 5) Scheme evaluator 11

41 What I have... I may use the library kawa (a JAVA library for parse/compile/interpret Scheme code and handle Scheme environments)

42 Solution: Façade design pattern

43 Solution: Façade design pattern Source : Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition by Mark Grand

44 Difference between Façade and adaptor Façade We need and create an interface Adaptor We need to adapt an object to a given interface.

45 New problem: to divide responsibilities Good: we are able to modify the way we emit voice (soft, hard, 8bit like...) Bad: we want also to modify the way a sound is played (strict rhythm, rubato...)

46 Solution: bridge design pattern

47 «Composite» Recursive objects: File and folders Expressions Structure of a document Commands (we will see in a few minutes) Etc.

48 «Composite» Source : wikibooks

49 To handle decorations A window may: Have / not have a border Have / not have scrollbars Have / not have a background Handle / not handle zoom Have / not have special effects Etc.

50 Multiple solutions If you can modify the interface and the window class: If you can NOT modify the interface and the window class: Use if Use a kind of bridge? Inheritance The design pattern decorator

51 With inheritance on aurait 2n classes différentes!

52 Decoration design pattern (interface of a window) With decoration design pattern: O(n) classes. Abstract decorator A simple window Concreate decorator (as window with special effects )

53 Conclusion sur le patron «Décorateur» + Meilleure maintenance que des «if» + Less classes than with inheritance + Possible to modify a decoration dynamically - Behavior not clear... new FenetreBordure(new FenetreFond(f)) ~ new FenetreFond(new FenetreBordure(f))?

54 Behaviour design patterns Dependency inversion principle Data converter Cancel feature Change the behaviour of an object

55 Need: to refresh the graphical user interface Source : interface de Windows 7

56 Need: to refresh the graphical user interface Source : OpenOffice.org Impress

57 Problem

58 Solution

59 Solution: Listener Need: to refresh the graphical user interface We may apply the pattern Listener. How to do that?

60 Listener Data The two zones (listeners) listen the data (subject).

61 Listener

62 Other application of the Listener design pattern: input/output Click! Listener

63 Autre application de «Observateur» : gestion des événements souris en JAVA The listener reacting when the button is clicked A button for instance

64 Model - view - controller utilisateur Controller View Model (data)

65 Model - view - controller Controller uses View Model subscribes

66 Another application for Listener: data converter.tex LaTEX to HTML.html

67 Another application for Listener: data converter.tex LaTEX to HTML.html.html HTML to LaTEX.tex.tex LaTEX to LibreOffice.Writer.odt

68 Another application for Listener: data converter.tex.html.tex LaTEX emitter HTML emitter LibreOffice.Writer emitter Nouveau paragraphe Nouvelle page

69 Another application for Listener: data converter New paragraph New page LaTEX generator.tex HTML generator.html LibreOffice.Writer generator.odt

70 Another application for Listener: data converter.tex LaTEX emitter w Ne raph rag pa HTML generator.html

71 Design pattern Command We want to be able to cancel. How to do that? We may apply the design pattern command.

72 Is the principle action = operation good?

73 Problem Cancel? Save macros? Too many responsibilities for the class Dessin

74 Solution: design pattern command

75 Solution: design pattern command

76 Solution: design pattern command The controller Command handler The drawing interface Ex: the command Copy

77 Solution: design pattern command

78 Memento classe des objets à sauvegarder Classe de l'objet qui gère les sauvegardes classe des objets qui représente une sauvegarde

79 Memento : saving

80 Memento : restoration

81 Operations on recursive structures DocumentElement gettableofcontents() getsizeinbytes() getnumberofsection() getnumberoffigure() checkspelling() checkgrammar()... Problem: classes become really big!

82 Solution: Visitor

83 Solution: Visitor Class Section { public void visit(visitor visitor) { visitor.visitsection(this); for(documentelement el : this) { el.visit(visitor); } } Class Paragraph { public void visit(visitor visitor) { visitor.visitparagraph(this); } } }

84 Solution: Visitor Each class has a responsibility Depends on the data Data classes must have public accessors.

85 Visitor

86 Object diagram

87 Visitor

88 Example of other applications of the Visitor pattern Music score editor: Number of notes, display the score, etc. Proof assistant: Display the proof, check the proof, etc. 3D software to display the squeleton, compute the weight, etc.

89 Implémenter plusieurs algorithmes : patron de conception «Stratégie»

90 Need of several behaviour of the hero hero.move() Source : Little Big Adventure 2

91 Need of several sorting algorithms array.sort() BubbleSort? QuickSort? HeapSort?

92 Need of several layout algorithms container.dolayout() Source :

93 Strategy

94 Example

95 Patron de conception «état»

96 Need: my software has many mode (edition, selection, preview...)

97 State pattern

98 State pattern public class Dessin { private EtatDessin monetat; public Dessin() { setetat(new EtatCrayon()); } : public void setetat(etatdessin nouveletat) { this.monetat = nouveletat; } } public void mouseup() { this.monetat.mouseup(); } class EtatPipette implements EtatDessin { : public void mouseup() { : dessin.setetat(new EtatCrayon()); } }

99 Summary We proposed concrete and local solutions to One class = one responsibility Better extend than modify Liskov substitution principles One interface per client Dependency inversion principle

100 Remark Refactoring Finding a pattern in a graph