1. Oct 200391.3913 Ron McFadyen1 Ch 17: Use Case Realizations with GRASP Patterns P. 248: “The assignment of responsibilities and design of collaborations are very important and creative steps during design” “there is no ‘magic’ or unjustifiable decisions in object design” “A use-case realization describes how a particular use case is realized within the design model, in terms of collaborating objects” Section 17.4 makeNewSale Section 17.5 enterItem Section 17.6 endSale Section 17.7 makePayment Section 17.8 startUp You should review these sections

2. Oct 200391.3913 Ron McFadyen2 Ch 17: Use Case Realizations with GRASP Patterns Section 17.4 makeNewSale 1 st concern: who/what is going to be responsible for handling the system operation makeNewSale? Decision: Using the Controller Pattern … since there aren’t very many system operations and since Register (in our domain) represents the overall system, we choose Register as a “façade” controller.

3. Oct 200391.3913 Ron McFadyen3 Ch 17: Use Case Realizations with GRASP Patterns By “Controller”, Register is our “façade” controller. makeNewSale() :Register

4. Oct 200391.3913 Ron McFadyen4 Ch 17: Use Case Realizations with GRASP Patterns Page 314 public class Register {… public makeNewSale() { … } We have just decided that Register must have a method makeNewSale Here, we are looking ahead to some code written to support the design

5. Oct 200391.3913 Ron McFadyen5 Ch 17: Use Case Realizations with GRASP Patterns 2 nd concern: who/what is going to be responsible for creating a Sale? Should Register delegate the responsibility or …? Since Register (in the domain) actually records a Sale then, by “Creator”, we decide that Register will do this. Register has the data and it needs to keep track of a Sale, so …

6. Oct 200391.3913 Ron McFadyen6 Ch 17: Use Case Realizations with GRASP Patterns By “Creator”, Register creates a Sale. makeNewSale() :Register create() :Sale

7. Oct 200391.3913 Ron McFadyen7 Ch 17: Use Case Realizations with GRASP Patterns Page 314 public class Register {… Private Sale sale; … public makeNewSale() { sale = new Sale(); } The method makeNewSale creates the sale object Here, we are looking ahead to some code written to support the design

8. Oct 200391.3913 Ron McFadyen8 Ch 17: Use Case Realizations with GRASP Patterns 3 rd concern: Sale needs to know of its SalesLineItems. A container for these is required. Who/What should create this? Since Sale will contain the lines, by “Creator”, we decide that Sale will do this…

9. Oct 200391.3913 Ron McFadyen9 Ch 17: Use Case Realizations with GRASP Patterns By “Creator”, Register creates a Sale. makeNewSale() :Register create() :Sale create() : :SalesLineItem

10. Oct 200391.3913 Ron McFadyen10 Ch 17: Use Case Realizations with GRASP Patterns Page 315 public class Sale {private List lineItems = new ArrayList(); private Date date = new Date(); private boolean isComplete = false; private Payment payment; … The constructor for Sale creates the container for the line items. Sale contains a list of line items

11. Oct 200391.3913 Ron McFadyen11 Ch 17: Use Case Realizations with GRASP Patterns Section 17.5 enterItem 1 st concern: who/what is going to be responsible for handling the system operation enterItem? We continue using the Controller Pattern … Register is responsible for handling enterItem.

12. Oct 200391.3913 Ron McFadyen12 Ch 17: Use Case Realizations with GRASP Patterns Contract for enteritem specifies Preconditions: A Sale is underway Postconditions: salesLineItem is created It is associated with the current Sale Its quantity is set It is associated with a ProductSpecification By Creator, Sale can do this Sale stores the new sales line item in its collection The product specification will need to be found

13. Oct 200391.3913 Ron McFadyen13 Ch 17: Use Case Realizations with GRASP Patterns enterItem() :Register:Sale : :SalesLineItem 2:makeLineItem() 2.1:create() 2.2:add() Message 2 … see later slide

14. Oct 200391.3913 Ron McFadyen14 Ch 17: Use Case Realizations with GRASP Patterns Page 315 public class Sale {… public void makeLineItem (…, …) { lineItems.add ( new SalesLineItem (…, …) ) ; } The “add” message sent to the multiobject is handled within Sale. Sale has a list of line items The “create” message for a new sales line item

15. Oct 200391.3913 Ron McFadyen15 Ch 17: Use Case Realizations with GRASP Patterns Page 316 public class SalesLineItem {private int quantity; private ProductSpecification productSpec; public void SalesLineItem (…spec, …quantity) { this.productSpec = spec ; this.quantity = quantity } The constructor for a sales line item arranges that the sales line item knows its product specification and its quantity

16. Oct 200391.3913 Ron McFadyen16 Ch 17: Use Case Realizations with GRASP Patterns Section 17.5 enterItem 2 nd concern: who/what is going to be responsible for finding a match for a product specification? For doing a lookup? Who has knowledge of product specifications? Who is capable of doing a lookup? Expert suggests the product catalogue is the best candidate. The product catalogue contains the product specifications … the product catalogue has the information, it is the expert.

17. Oct 200391.3913 Ron McFadyen17 Ch 17: Use Case Realizations with GRASP Patterns enterItem() :Register : :ProductSpecification :ProductCatalog 1:getSpecification() 1.1:find()

18. Oct 200391.3913 Ron McFadyen18 Ch 17: Use Case Realizations with GRASP Patterns Page 316 public class ProductCatalog { private Map productSpecifications = new HashMap(); … public ProductSpecification getSpecification (ItemID id) { Return( …. productSpecifications.get ( id ); } Collection of product specifications Method to find a specific item Handles the “find” message

19. Oct 200391.3913 Ron McFadyen19 Ch 17: Use Case Realizations with GRASP Patterns enterItem() :Register:Sale : :ProductSpecification :ProductCatalog : :SalesLineItem 1:getSpecification() 1.1:find() 2:makeLineItem() 2.1:create() 2.2:add()

20. Oct 200391.3913 Ron McFadyen20 Ch 17: Use Case Realizations with GRASP Patterns Given the previous collaboration, what methods/responsibilities have been assigned to the various classes? RegisterSale ProductCatalog SalesLineItem