1. Class Diagram
M. Seidl, et al., Introduction to Object-Oriented Modeling, Springer, Chaper 4. Soft copy (pdf) downloadable freely through UTEP library.

2. Motivation
Battleship app consists of 2,903 lines of Android Java source code in three different packages.
12 UI classes
10 model classes (including computer strategies)
Q: How to express or learn its design?
Why?
Read the code …

3. <<activty>>
Expressing Designs
Draw pictures/diagrams.
“A diagram is worth three thousands lines of code.”
E.g., UI related classes
AbstractBoardView
FleetBoardView
BoardView
TouchBoardView
<<activty>>
MainActivity
FleetActivity
PlayActivity
ShipView

4. Class Diagram Models data, entities and static structures
Most important and most widely-used diagram among 12+ UML diagrams
Central model due to stability (of data), say, compared to functionalities such as use cases.
Describes the structure of a system by showing the system's classes, their attributes/operations, and the relationships among the classes

5. Example: IBM PC Architecture
0..2
0..2
interface
IdeDevice
Motherboard
IdeBus
interface ScsiDevice
CdRom
{abstract}
HpCdWriter
LaserController

6. Types of Relationships
Construct
Notation
Association
Aggregation
Composition
Generalization
Realization
Dependency

7. Association General binary relationships between classes
Commonly represented as direct or indirect references between classes
Student
Course

8. Association Details Can express the following optional information
Association name (e.g., enroll)
Navigability (e.g., ->)
Multiplicity (e.g., 10..*)
Role names (e.g., course) 1 2
enroll
Student
Course
10..*
course 3 4

9. Association Name
May have an optional label consisting of a name and a direction drawn as a solid arrowhead with no tail.
The direction arrow indicates the direction of association with respect to the name, i.e., the direction in which the name should be read.
Use a verb or verb phrase.
advise
Faculty
Student

10. Navigability
An arrow may be attached to the end of path to indicate that navigation is supported in that direction.
advise
Faculty X
Student

11. Multiplicity
Optional multiplicity specification defining the number of objects that can participate in an instantiated relation
On one or both association ends
The multiplicity specifies an integer interval, e.g.,
l..u closed (inclusive) range of integers
i singleton range
0..* entire nonnegative integer, i.e., 0, 1, 2, …
advise 1
0..*
Faculty
Student

12. Role Names Optional role name on one or both association ends
Use a noun or noun phrase describing the semantics of the role.
advise 1
0..*
Faculty
Student
advisor
advisees

13. Exercise Write skeletal Java code conforming to the following model.
10..*
enroll
0..*
Student
Course
1..3
0..*
is-taught
instructor 1
is-advised 1
Faculty
advisor

14. Aggregation
Special form of association representing has-a or part-whole relationship.
Distinguishes the whole (aggregate class) from its parts (component class).
No relationship in the lifetime of the aggregate and the components (can exist separately).
Aggregate
Component

15. Composition Stronger form of aggregation
Implies exclusive ownership of the component class by the aggregate class
The lifetime of the components is entirely included in the lifetime of the aggregate (a component can not exist without its aggregate).
Composition
Component

16. Example University 1..* 1..* 0..* College Department Student chair-of
member-of 1
1..*
Faculty

17. Generalization And Realization
An extension relation is called specialization and generalization.
An implementation relation is called realization.
Superclass
Superinterface
Interface
Subclass
Subinterface
Class
extension of
classes
extension of
interfaces
implementation
of interfaces

18. Example Student {abstract} Graduate {abstract} Nondegree Undergraduate
Master
PhD

19. Dependency
Relationship between the entities such that the proper operation of one entity depends on the presence of the other entity, and changes in one entity would affect the other entity.
The common form of dependency is the use relation among classes.
<<use>>
Class1
Class2

20. Exercise: Strength (Coupling)?
Association, aggregation, composition, generalization, realization, and dependency.
Weakest
Strongest

21. Class Details
The UML notation for classes is a rectangular box with as many as three compartments.
Name
attribute1 ……
attributen
operation1 …
operationn
The top compartment show the class name.
The middle compartment contains the
declarations of the attributes (fields) of the class.
The bottom compartment contains the
declarations of the operations (methods) of the class.

22. Example Attribute type Name of the class Attribute name
Student
- name: String = “John” {readOnly}
- courses: Course [*]
+ register (c: Course)
+ isRegistered (c: Course) : Boolean
Other Properties
Visibility:
+, -, #, ~
Default value
Multiplicity
Operation
name
Return value
Parameters 22 22

23. Inline vs. Diagram Notation
Two ways to express associations
Use either one, but not both. 1
Course
Instructor
Course
-instructor: Instructor
-students: Student[10..*]
-instructor
10..*
-students
Student

24. Guidelines Identify important data, entities, and domain concepts
List all nouns or noun phrases
Determine candidate classes
Define relationships among classes
Association/aggregation: has-knowledge-of, is-part- of
Generalization/realization: is-a relation
Define responsibilities of classes (operations)
Define internal structures of classes (attributes)
Refine, refine, refine …

25. Exercise
Form a pair.
Model the Battleship game by drawing a class diagram; focus on the business logic (or functional core), not UI.
Assume (see handout: Battleship use cases)
A board consists of n*n places (or squares), where n >= 10.
A player’s feet consists of 5 ships: aircraft carrier (of size 5), battleship (4), frigate (3), submarine (3), and minesweeper (2).
There are two players: a human player and a computer player.

26. Layered Architecture MainActivity, Presentation
PlayActivity, BoardView, …
Presentation
Business logic
Communication/Storage
WifiNetAdapter, BluetoothNetAdapter, …

27. Sample Solution has_fleet_of Ship isSunk is_placed_on 5 0..1
s: ship size
0, s
Game
isOver
activePlayer
makeShot
changeTurn
place_ships
Board
placeShip
getShip
n*n
Place
isHit
hit 2 1
Player 1
pick_place_of
ComputerPlayer
placeShips 1
Strategy
pickPlace