1. Next Gen POS Example
GRASP again

2. Same Patterns Different Example!

3. Apply Creator
SalesLineItem

4. Fig

5. Fig

6. Contraindications When creation is complex:
Using recycled instances
External property values
Then consider a helper class (Factory)

7. Information Expert Some class needs to know the grand total for a sale
Who has the information

8. Fig

9. Fig

10. Fig

11. Responsibility Sale – knows sale total
SalesLine Item – knows line item subtotal
Product Description – knows price

12. Fig. 17.17 Calculate sale total

13. Discussion Information Expert
Common guide to responsibilities
Spreading of information means spreading of responsibilities
Analogy to real world operations

14. Contraindications Example: who saves into the DB?
This is not something to spread across classes
Separation of concerns
Cohesion

15. Low coupling
Create a payment instance and associate it with a sale

16. Fig Create Payment

17. Fig. 17.19 Alternate Solution

18. Discussion Always consider this during all patterns!
Kinds of coupling in Java, C++ or C#
By attribute reference to an instance
By call
A method refers to a type (param, local, etc.)
Direct or indirect subclass
Implement an interface

19. Reduce impact of later change
Can’t reduce to zero coupling!

20. Contraindications
High coupling to stable elements is ok

21. Controller
What first element beyond the UI receives and coordinates a system operation?

22. Fig System Operations

23. Fig

24. Fig. 17.22 Controller choices

25. Fig. 17.23 Allocation of Operations

26. Discussion
Be careful of over responsibility

27. Fig. 17.24Desirable Coupling

28. Fig Less desirable!

29. Fig Bad for Cohesion

30. Fig Better

31. GRASP Patterns
Patterns for object design
Still requires judgement