This seminar covered assigning responsibilities and collaborators to classes using CRC cards and other techniques: 1. Responsibilities include a class's behaviors and knowledge, and were assigned through role-playing scenarios. Guidelines included focusing on what classes do, not how, and experimenting with different configurations. 2. Collaborators were assigned using scenarios, class hierarchies, dependencies, and identifying client/server relationships through contracts. Collaborations can be hard to identify without role-playing. 3. Additional guidelines included looking for "kind of" relationships, distinguishing "part of" from "kind of", naming key abstractions, and looking for existing frameworks that could apply to the problem.

1. Seminar 4: Wrapping upProgramming Paradigms[The Paradigms - Group 2]

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5. Assigning ResponsibilitiesResponsibilities includes the behaviors exhibited by a class or the knowledge which a class holds.KnowledgeBehaviors

6. Assigning ResponsibilitiesMain TaskUse of scenarios androle play for the discovery of responsibilities.Scenario:Withdrawing cash from ATMActor CustomerReceipt Printer ClassActor ATM

7. Assigning Responsibilities“Focus on What the classes need to do, not how they do it.” Asking how a class behaves will result deriving false semantic distinctions which disallow the use of polymorphism.

8. Assigning ResponsibilitiesLet’s get it started…Responsibility Detection Guidelines

9. Assigning ResponsibilitiesResponsibility Detection GuidelinesBrainstorm to identify a set of candidate responsibilities for the core classes. Strive for inclusion of responsibilities rather than exclusion

10. Assigning ResponsibilitiesResponsibility Detection GuidelinesThink in a more complex way will have most responsibilities listed in one of two classes.Account ClassDeposit ClassBankCardClassInsignificant to reuseInsignificant to reuseInflexible to reuseBalanceInquiry ClassWithdrawalClassInsignificant to reuseInsignificant to reuse

11. Assigning ResponsibilitiesResponsibility Detection GuidelinesReduce classes to “records”, which they simply know what information they hold.InteractsAim to have distinct role for each classes to encourage reuse!

12. Assigning ResponsibilitiesResponsibility Detection GuidelinesAbstract related classes which have common responsibilities to build hierarchies of classes.All of them execute a final transaction

13. Assigning ResponsibilitiesResponsibility Detection GuidelinesAbstract class make clear and cohesive responsibility assignment and take advantage ofuse polymorphism!

14. Assigning ResponsibilitiesResponsibility Detection GuidelinesExperiment with different configuration of classes or assignments of responsibilities.Changing the CRC cards are easier than changing the code later in the project.

16. Assigning CollaboratorsGuidelinesUsing Scenarios and Role PlayUsing Class HierarchyUsing DependenciesUsing Client, Servers and Contract Map

17. Use Scenarios and Role PlayMake a list of scenarios using the CRC core classesFill in the cards as you role play the different scenarioAssigning CollaboratorsMany practitioners uses role play and scenarios before listing the responsibilities for each classes

18. Using Class HierarchyHierarchy is a signal for collaborationLook up a hierarchy to class that is more abstract responsibilitiesLook down a hierarchy to carry out more specialize responsibilitiesLook for class that share same responsibilitiesAssigning Collaborators

19. Example19Assigning CollaboratorsTransactionsWithdrawalDepositBalanceInquiryExecuteFinancialTransaction()ExecuteFinancialTransaction()ExecuteFinancialTransaction()ExecuteFinancialTransaction()

20. Using DependenciesA class that depend on another for informationAssigning CollaboratorsWhen dealing with dependencies think of encapsulation

21. Example21Assigning CollaboratorsTransactionReceiptPrinterExecuteFinancialTransaction()printReceipt()

22. Using Client, Servers and Contract MapClient is a class that requires service from anotherServers are providers for the servicesAssigning CollaboratorsA Class can be a server and a client in a system

23. Using Client, Servers and Contract MapContracts can be used to track client server collaboration Using role play can rapidly mapped out the collaborationAssigning CollaboratorsAlternative in using client server would be identifying of message passing in the system

24. Example of ContractAssigning CollaboratorsContract 1: Access and Modify Account BalanceServer: AccountClient: withdrawal, Transfer, Deposit, InquiryDescription: Defines the manner in which account can be accessed or modified

25. Warning!!!!Collaborations can be hard to spot before role playTry to avoid class with the same responsibilities

27. GuidelinesLook for “Kind-of” relationshipDo not confuse “Part-of ” with “Kind-of”Name Key AbstractionsLook for Framework

28. Look for “Kind-of” relationshipFind classes that Share Same ResponsibilitiesShare Same BehaviorBelong Together

29. ExampleTransactionsWithdrawalDepositBalanceInquiry# completeTransaction()# completeTransaction()# completeTransaction()# completeTransaction()29

30. Do not confuse “Part-of ” with “Kind-of”Part-of DO NOT:Shared same behaviorA class maybe part of another class A and also a kind of another class B

31. Name Key AbstractionsName a key abstraction classidentify abstract classes that do not draw on colloquial ways of talking about system diagramA single class that have choices depending on situation

32. Example

33. Look for FrameworkThis take advantage of successful framework rather then inventing themUsing of analysis pattern to help looking for your own frameworks“Party” Pattern

34. 34The CRC Card Technique

35. Thank you!End of Presentation