Fall 2009 ACS-3913 Ron McFadyen 1

Use Case Realizations with GRASP Patterns

“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”

makeNewSale

enterItem

endSale

makePayment

startUp

read these sections

Fall 2009 ACS-3913 Ron McFadyen 2

Ch 17: Use Case Realizations with GRASP Patterns

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.

Fall 2009 ACS-3913 Ron McFadyen 3

Use Case Realizations with GRASP Patterns

By “Controller”, Register is our “façade” controller.

makeNewSale()

:Register

Fall 2009 ACS-3913 Ron McFadyen 4

Use Case Realizations with GRASP Patterns

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

Register

makeNewSale()…

Fall 2009 ACS-3913 Ron McFadyen 5

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 …

Fall 2009 ACS-3913 Ron McFadyen 6

Use Case Realizations with GRASP Patterns

By “Creator”, Register creates a Sale.

makeNewSale()

:Register

create():Sale

Fall 2009 ACS-3913 Ron McFadyen 7

Use Case Realizations with GRASP Patterns

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

Fall 2009 ACS-3913 Ron McFadyen 8

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…

Fall 2009 ACS-3913 Ron McFadyen 9

Use Case Realizations with GRASP Patterns

By “Creator”, Register creates a Sale.

makeNewSale()

:Register

create():Sale

create()lineItems: List<SalesLineItem>

Fall 2009 ACS-3913 Ron McFadyen 10

Use Case Realizations with GRASP Patterns

public class Sale

{ private List<SalesLineItem> lineItems =

new ArrayList<SalesLineItem>();

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

Fall 2009 ACS-3913 Ron McFadyen 11

Use Case Realizations with GRASP Patterns

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.

Fall 2009 ACS-3913 Ron McFadyen 12

Use Case Realizations with GRASP Patterns

Contract for enteritem specifies

Preconditions:

•A Sale is underway

Postconditions:

•salesLineItem created

•It is associated with the current Sale

•Its quantity is set

•It is associated with a ProductDescription

By Creator, Sale can do this

Sale stores the new sales line item in its collection

The product description will need to be found

Fall 2009 ACS-3913 Ron McFadyen 13

Use Case Realizations with GRASP Patterns

enterItem():Register :Sale

: SalesLineItem

2:makeLineItem()

2.1:create()

2.2:add()

Message 2 … see later slide

lineItems: List<SalesLineItem>

Fall 2009 ACS-3913 Ron McFadyen 14

Use Case Realizations with GRASP Patterns

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.

Fall 2009 ACS-3913 Ron McFadyen 15

Use Case Realizations with GRASP Patterns

enterItem():Register

:Map<ProductDescription>

:ProductCatalog

1:desc=getProductDesc(id)

1.1:desc=get(id)

Fall 2009 ACS-3913 Ron McFadyen 16

Use Case Realizations with GRASP Patterns

enterItem():Register :Sale

:ProductCatalog:SalesLineItem

1:desc=getProductDesc(id)

1.1desc=get(id)

2:makeLineItem()

2.1:create()

2.2:add()

: Map<ProductDescription>lineItems: List<SalesLineItems>

Fall 2009 ACS-3913 Ron McFadyen 17

Use Case Realizations with GRASP Patterns

Given the previous collaboration, what methods/responsibilities have been assigned to the various classes?

Register Sale

ProductCatalogSalesLineItem