1. Ch 17: Use Case Realizations with GRASP Patterns
(assigning responsibilities to objects to achieve user goals)
Section 17.3 makeNewSale
1st 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.

2. Ch 17: Use Case Realizations with GRASP Patterns
By “Controller”, Register is our “façade” controller.
:Register
makeNewSale()

3. 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

4. Ch 17: Use Case Realizations with GRASP Patterns
2nd 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 …

5. Ch 17: Use Case Realizations with GRASP Patterns
By “Creator”, Register creates a Sale.
:Register
makeNewSale()
create()
:Sale

6. 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

7. Ch 17: Use Case Realizations with GRASP Patterns
3rd 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…

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

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

10. Ch 17: Use Case Realizations with GRASP Patterns
Section 17.5 enterItem
1st 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.

11. 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

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

13. Ch 17: Use Case Realizations with GRASP Patterns
Page 315
public class Sale
{ …
public void makeLineItem (…, …) {
lineItems.add ( new SalesLineItem (…, …) ) ; }
The “create” message for a new sales line item
The “add” message sent to the multiobject

14. 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 itemarranges that the sales line item knows its product specification and its quantity

15. Ch 17: Use Case Realizations with GRASP Patterns
Section 17.5 enterItem
2nd 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.

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

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

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

19. Ch 17: Use Case Realizations with GRASP Patterns
Given the previous collaboration, what methods/responsibilities have been assigned to the various classes?
Register
Sale
ProductCatalog
SalesLineItem