UML Class Diagram

1. UML Class Diagram

2. A class diagram shows • Classes • The relationships between them

3. Classes • Class name • Class attributes (state) • Class methods (operations) • Visibility • + means public • # means protected • − means private • ~ means package Course name: String number: Integer addStudent()

4. Class Details • Abstract class: name in italics • Member properties: • static • abstract • CONSTANT • Specify type of attributes • Specify signature and return value of methods • addStudent( s : Student ) : void

5. Inheritance Shape -color: Color +setColor(c: Color): void +getArea(): double Think “tree” not “arrow” Circle -radius: double override +setRadius(r: double): void +getRadius(): double +getArea(): double

6. Interfaces «interface» Drawable +draw(): void Note dashed line Circle -radius: double implement +setRadius(r: double): void +getRadius(): double +draw(): void

7. Associations • When one class knows about another class and may call methods of that class’s objects • General association • Aggregation • Composition • dependency

8. Association • Specify that classes know each other • Can be named (typically verbs) Professor Course teaches

9. Multiplicity • Specify the numerical relationship • 1 – exactly one • 0..1 – zero or one • 0..* (or just *) – any number or none • 1..*– one or more • 3..8 – three to eight Professor Course teaches 1 0..*

10. Association • Classes can have role names (nouns) • Typically represent attribute name in other class Professor Course teacher Class Professor { myCourse: Course; … } Class Course { teacher: Professor; … }

11. Association • Associations can be reflexive • In this case role names are required Professor mentor 1 mentee 0..2

12. Navigability • The course knows the textbook(s) used • The textbook does not know course(s) which use it • Alternative interpretation: navigability from textbook to course is unspecified • To prohibit access use Course TextBook

13. Association Class • A class that represents the association Student Course 0..* 0..* Enrolment grade: integer

14. Aggregation • One class contains an aggregate of objects from the other class • But aggregated objects are still independent • Implies container attribute Department Professor

15. Composition • A stronger form of aggregation • One class contains objects from the other class • These objects have no existence without the containing object Program Course 1

17. Dependency • One class uses another • Local in method • Argument to method • Creation of objects (e.g. factory) • But it is not an attribute (field) • Usually many; show only important ones B A C «creates» method(arg : B)

18. Derived Attributes • An attribute whose value is derived from other attributes • Does not have a setter Course name: String /enrolment: Integer addStudent() Student

19. Constraints and Notes • Provide additional information Course capacity: integer /enrolment: integer {enrolment  capacity} addStudent() Student Only nice ones

20. Object Diagrams • Similar to class diagrams • Show object instances rather than classes • Reflect relationships at runtime • No reflexive associations • ListNode class: next is reflexive • ListNode object: next is reference to another object UML Class Diagrams