UML Class Diagram

A class diagram shows 1.Classes 2.The relationships between them

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

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

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

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

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

Association  Specify that classes know each other  Can be named (typically verbs) CourseProfessor teaches

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 CourseProfessor 10..* teaches

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

Association  Associations can be reflexive  In this case role names are required Professor mentor mentee

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 o To prohibit access use TextBookCourse

Association Class A class that represents the association CourseStudent 0..* Enrolment grade: integer

Aggregation  One class contains an aggregate of objects from the other class  But aggregated objects are still independent  Implies container attribute ProfessorDepartment

Composition  A stronger form of aggregation  One class contains objects from the other class  These objects have no existence without the containing object CourseProgram 1

AggregationComposition Relationshiphas-awhole-parts Container typereferencesobjects Lifecycleelements are independent elements are created with container and die with container Elementscan be in multiple aggregations can be in only one composition

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

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

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

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