1. Chapter 9: Relationships Chapter 10: Inheritance and Polymorphism [Arlow and Neustadt, 2005] CS 426 Senior Projects in Computer Science University of Nevada, Reno Department of Computer Science & Engineering

2. 2  Relationships Links Associations Dependencies  Inheritance and Polymorphism Generalization Class inheritance Polymorphism Advanced generalization

3. 3 Relationships = semantic connections between modeling elements Links = connections between objects Associations = connections between classes Links are instances of associations

4. 4  A link is a connection between objects that communicate via messages  Links can be: Unidirectional, if only one object (the source) contains a reference to the other (the target). Bidirectional, if both objects have a reference to the other  Object diagrams show objects and their relationships at some point in time. Thus, links are dynamic connections between objects

5. 5  Example of object diagram, that shows objects, links, and roles. It also illustrates the oblique style of drawing paths in UML diagrams.

6. 6 Example of unidirectional link The orthogonal style of drawing paths in UML diagrams

7. 7  Associations are relationships between classes  Links depend on associations, and instantiate them

8. 8  The syntax for an association includes:  Association name  Role names  Multiplicity  Navigability

9. 9  Multiplicity constrains the number of objects of a class that can be involved in a given relationship at any point in time

10. 10  There is no default value for multiplicity in UML. If not specified, multiplicity is undecided

11. 11  Multiplicity constraints encode business rules of the model  It is important to “read the model as written”

12. 12 Example of association hierarchy Example of association network

13. 13  Navigability can be read “messages can only be sent in the direction of the arrow”  Relationships without arrows are bidirectional  Unidirectional associations reduce coupling between classes

14. 14  One-to-one and one-to-many associations can be modeled using attributes

15. 15 Many-to-many associations can lead to association classes Corresponding association class

16. 16  However, many-to-many associations can also be modeled using regular classes

17. 17  “A dependency is a relationship between two elements where a change to one element (the supplier) may affect or supply information needed by the other element (the client)” [Rumbaugh et al., The UML Reference Manual]  Three types of dependency

18. 18  Examples of different types of dependencies

19. 19  The > dependencies are the most common type of dependency. They state that the client makes use of the supplier in some way. Java code for the above example

20. 20  Abstraction dependencies are dependencies between model elements that are at different level of abstraction: >, >, > and >

21. 21  Permission dependencies indicate the capability of one model element to access another model element.  Examples of permission dependencies: > > (formerly >)

22. 22  Generalization applies to all classifiers and to some other elements such as associations, states, and events

23. 23  Example of class hierarchy

24. 24  Example of overriding

25. 25  Example of abstract classes and operations

26. 26  In generalization hierarchies it is important to maintain a uniform level of abstraction at each level  Incorrect example

27. 27  Polymorphism means “many forms”. A polymorphic operation has several different implementations

28. 28  Example of polymorphism “in action”

29. 29  Object diagram with polymorphism

30. 30  Another example of polymorphism

31. 31  An example of generalization set

32. 32  Constraints on generalization sets