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CRC Cards

CRC Cards. Shon Vick CMSC 445. Introductory Ideas. CRC Cards are an informal technique for exploring initial design Use of the cards is scenario based Once cards (classes) are developed more formal techniques may be more appropriate. Finding Classes.

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CRC Cards

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  1. CRC Cards Shon Vick CMSC 445

  2. Introductory Ideas • CRC Cards are an informal technique for exploring initial design • Use of the cards is scenario based • Once cards (classes) are developed more formal techniques may be more appropriate

  3. Finding Classes • Group discusses a scenario – perhaps from a Use Case • Noun phrases in requirements specification or system description -> classes • Verbs are responsibilities • Model known interfaces to outside world • User interfaces • Interfaces to other programs • Write a description of how people will use the system. This description is a source of interface objects

  4. Format of a CRC Card Class Responsibilities Collaborators

  5. Responsibilities • The knowledge an object maintains • The actions an object can perform • If responsibility can’t be assigned to any card – create a new card • Be wary of any card with a large number of responsibilities

  6. Categories of Classes • Data Managers • Principle responsibility is to maintain data • Examples: stack, collections, sets • Data Sinks or Data Sources • Generate data or accept data and process it further • Do not hold data for long • Examples: Random number generator, File IO classes

  7. More Categories of Classes • View or Observer classes • Example: GUI classes • Facilitator or Helper classes • Maintain little or no state information • Assist in execution of complex tasks

  8. General Guidelines • Consider public responsibilities, not private ones • Specify what gets done, not how it gets done • Keep responsibilities in general terms • Define responsibilities at an implementation-independent level • Keep all of a class's responsibilities at the same conceptual level

  9. References • Wirfs-Brock,Designing Object-Oriented Software, chapters 1- 5 • Mark Lorenz, Object-Oriented Software Development: A Practical Guide, 1993, Appendix I Measures and Metrics • http://www.eli.sdsu.edu/courses/fall97/cs535/notes/OODesign1/OODesign1.html

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