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

9. Fig. 17.4 apply Creator

10. Fig. 17.5 Apply Creator

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

12. Fig. 17.6

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

14. Fig. 17.7

15. 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

16. Fig. 17.8 SSD

17. Fig. 17.9

18. Fig. 17.10

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

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

21. Fig. 17.11

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