P4L3 Object Design

5. Collaboration-Based Design e Also caled role-based design Alternative to strict OOD e User stories Collaboration and role identification » Documentation via sequence or collaboration diagrams e Role abstraction e Synthesis of classes from roles Ob Ject Design Elements of Analysis Model: 1. Methods 2. New classes 3. Generalization 4. Associations 5. Dependencies 6. Implementing control #. Abstract classes, interfaces, types

Generalization Example e Use sort method o Addressbook class e Organizing monthly \ expense ledger Generalization Advice e Can use subclassing features of OO language in OOD e Add features in subclasses rather than overriding e Make sure that the child \ method obeys two rules H you were implementing generaization between squares and rectangles, would you make Square 3 subclass of Rectangle in which both sides are equal? Or woud you make Rectangle 3 subclass of Square with an additional attribute? Square 3 subclass of Rectangle (both sides equal) (with an additional attribute) O O Rectangle 3 subclass of Square X Either or; it depends

Associations As Objects » A problem arises when you want to loop through all of the links in 8 two-way association e Can be cumbersome and costly Tables For Associations FooObject6 BarObject? FooObject2 BarObject3 Use a collection class FooObject10 BarObject6 (hash table, set, array) : : to hold al pairs of FooObject6 BarObjectl associated objects FooObject6 BarObject3 FooObject? BarObject6 FooObject3 BarObject2 FooObject? BarObject1 Consider the problem of implementing the Takes association between Students and Courses. For each of the folowing 4 options, match it with its major disadvantage. B [ n each Stucent, creste 8 reference that refers A. extra step involved in each query to the Course that student is taking D | I each Couse, creste 8 Vector of references B. 8 student can only take one course to Students A'| Creste 3 Takes association class that contains C. referential integrity maintenance an attribute for Student and Course C | Use symmetric Vectors in Student and Course D. hgsd '(Ot find the Courses taken by ents