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2. Explain this design in less than 10 words, without diagrams or code Command cmd = createCommand(commandString); cmd.execute(); history.add(cmd); … cmd.undo(); Add {abstract} Command execute() undo() * execute() {abstract} undo() {abstract} Delete History execute() undo() add(Command) Edit execute() undo()

4. Design (a)

5. Design (a)

6. Design (a)

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8. Design (b)

9. Design (c)

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12. Design (c)

17. Book copies in a library TV drama episodes Video copies in a rental shop

18. Book copies in a library TV drama episodes Video copies in a rental shop

19.  Book copies in a library TV drama episodes Video copies in a rental shop   

20.  • Book copies in a library • TV drama episodes • Video copies in a rental shop    Recurring tasks in a schedule

21. Déjà vu: Using patterns to solve recurring problems CS2103/T, Lecture 9, Part 2, [March, 2017]

22. Déjà vu: Using patterns to solve recurring problems

23. experience Déjà vu: Usingpatterns to solve recurring problems

24. experience … is what you get when you didn’t get what you wanted.

25. experience … is valuable.

26. Learning from experience … is too costly.

27. Learning from experience Note to self: never volunteer to be the headstand guy

28. Learning from experience Patterns

30. Context:Multiple stock items of same TV model • Problem: Some data (but not all) shared among stock items of the same model. • Solution: Represent TV model andTV stock item as different classes.

31. Context:Multiple stock items of same TV model • Problem: Some data (but not all) shared among stock items of the same model. • Solution: Represent TV model andTV stock item as different classes. • Stock items • Book copies in a library • TV drama episodes • …

32. Context: Multiple stock items of same TV model • Problem: Some data (but not all) shared among stock items of the same model. • Solution: Represent TV model andTV stock item as different classes.

33. Context: Multiple occurrences of some abstraction • Problem: Some data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes.

34. Context: Multiple occurrences of some abstraction • Problem: Some data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. * <<Abstraction>> <<Occurrence>>

35. Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. * <<Abstraction>> <<Occurrence>>

36. TVModel BookTitle Lesson * * * TVStockItem BookCopy LessonDelivery * <<Abstraction>> <<Occurrence>>

37. TVModel BookTitle Lesson * * * TVStockItem BookCopy LessonDelivery * <<Abstraction>> <<Occurrence>>

38. Name: Abstraction Occurrence Pattern • Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. * <<Abstraction>> <<Occurrence>>

39. Name: Abstraction Occurrence Pattern • Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. * <<Abstraction>> <<Occurrence>> Pattern [An elegant solution to a recurring problem]

40. Name: Abstraction Occurrence Pattern • Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. * <<Abstraction>> <<Occurrence>> Pattern [An elegant solution to a recurring problem]

41. Name: Abstraction OccurrencePattern • Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. * <<Abstraction>> <<Occurrence>>

42. … for that, I used the Name: Abstraction OccurrencePattern • Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. Show off ! * * <<Abstraction>> <<Abstraction>> <<Occurrence>> <<Occurrence>>

43. Patterns = a high-level vocabulary

44. Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction.

45. Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. Anti-Pattern [A stupid solution to a recurring problem]

46. Context: Multiple occurrences of some abstraction • Problem: Same data (but not all) shared among occurrences of the same abstraction. • Solution: Represent abstraction and occurrences as different classes. Anti-Pattern [A stupid solution to a recurring problem]

47. 1. Abstraction occurrence 2. Singleton 3. Façade 4. Command 5. MVC 6.Observer

48. 1. Abstraction occurrence 2. Singleton 3. Façade 4. Command 5. MVC 6.Observer

49. 1. Abstraction occurrence 2. Singleton3. Façade 4. Command 5. MVC 6.Observer Context: one-and-only-one object, shared among others

50. 1. Abstraction occurrence 2. Singleton3. Façade 4. Command 5. MVC 6.Observer Context: one-and-only-one object, shared among others Problem: how to avoid multiple objects?