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Chapter 17

Chapter 17. Designing with Responsibilities. Fig. 17.1. OOD. Requirements Domain model Then: Define classes Add methods to classes Define messaging Simple! RIGHT? - NOT. RDD. Responsibility - contract or obligation of a class Doing- Doing something itself

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Chapter 17

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  1. Chapter 17 Designing with Responsibilities

  2. Fig. 17.1

  3. OOD • Requirements • Domain model • Then: • Define classes • Add methods to classes • Define messaging • Simple! RIGHT? - NOT

  4. RDD • Responsibility - contract or obligation of a class • Doing- • Doing something itself • Initiate an action in another object • Control or coordinate • Knowing- • Private data • Related objects • Things it can calculate

  5. Fig. 17.2

  6. GRASP • 9 patterns, first 5 in this chapter: • Creator • Information expert • Low coupling • Controller • High cohesion

  7. Creator • Problem: Who creates A? • Solution: Assign creation to B • IF: • B contains (compositely aggregates) A • B records A • B closely uses A • B has initializing data for A

  8. Fig. 17.4 apply Creator

  9. Fig. 17.5 Apply Creator

  10. Information Expert • Problem: Assign a responsibility to an object? • Solution: Choose the class that has the information to fulfill the responsibility

  11. Fig. 17.6

  12. Low Coupling • Problem: Reduce impact of change • Solution: Keep coupling low!

  13. Fig. 17.7

  14. Controller • Problem: What object beyond UI controls a system operation • Solution: Assign responibility to object • If • Overall “system”, “root object”, device that the software runs in, major subsystem • Represents a use case scenario within which the operation occurs

  15. Fig. 17.8 SSD

  16. Fig. 17.9

  17. Fig. 17.10

  18. Next Steps • Applied controller pattern • Now what goes beyond the :MonoployGame class?

  19. High cohesion • Problem: Keep objects focused, understandable, manageable (side effect support low coupling) • Solution: assign responsibilities to improve cohesion

  20. Fig. 17.11

  21. GRASP • General Responsibility Assignment Software Patterns • We just did 5 of 9 • There rest are in Chapter 25 • Polymorphism, Pure Fabrication, Indirection, Protected Variations

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