Chapter 18

1. Chapter 18 Object Design Examples with GRASP CS6359 Fall 2011 John Cole

2. Use Case Realization • Describes how a particular use case is realized within the design model in terms of collaborating objects CS6359 Fall 2011 John Cole

3. Command-Query Separation • A method that changes the value of a variable (or the state of the object) should not also return (query) its value. • A method that returns the value of a variable should not also change it. CS6359 Fall 2011 John Cole

4. Connect UI to Domain • An initializer object creates both the UI and the domain objects and passes the domain object to the UI • The UI object retrieves the domain object from a well-known source such as a factory object that creates domain objects CS6359 Fall 2011 John Cole

5. Basic Patterns • Creator • Information Expert • Controller • Low Coupling • High Cohesion CS6359 Fall 2011 John Cole

6. Realization • Look at the objects suggested by the use case • Determine who should create them • Decide how they should interact • Determine which patterns are being used. CS6359 Fall 2011 John Cole

7. Example: Sell Something • Register could create the Sale object • Sale object creates SalesLineItem objects in list • SalesLineItem interacts with Product to get pricing and description CS6359 Fall 2011 John Cole

8. Design makeNewSale • Register creates Sale instance s and stores the reference • Attributes of s are initialized CS6359 Fall 2011 John Cole

9. Controller Class Design • Represents the overall system or “root object” • “Store” in the POS system is a root object because other objects exist within it • POSSystem is also a root object • Register could also be a root object CS6359 Fall 2012 John Cole

10. Creating a New Sale • Register creates a Sale object • Sale object, as part of its initialization, creates an empty list of SalesLineItems • Register is, therefore, the Controller CS6359 Fall 2011 John Cole