UML Class Associations Sipping from the Fire Hose

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UML Class AssociationsSipping from the Fire Hose

• November 16, 2007

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Exercise From Last Time Possible Solution
Recipe
Cookbook
- name - ingredients - instructions -
nutritionInformation
- categories - recipes - name
setName(name String) add(ingredient
Ingredient) remove (ingredient
Ingredient) display() print()
setName(name String) add(recipe Recipe,
category String) remove(recipe Recipe,
category String) display() print()
Ingredient
- name - amount - nutritionInformation
setName(name String) setAmount(amount
float) setUnit(unit String)
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Session Goals

• At the end of this session, you will be able to
  define and apply the following class
  relationships
• Dependency
• Association
• Shared Aggregation
• Composite Aggregation
• Generalization/Specialization

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Relationships

• Classes can relate to other classes in several
  ways
• UML relationship types in increasing strength
• Dependency
• Association
• Aggregation
• Composition
• Generalization

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Dependency

• The weakest relationship
• Represented by a dashed arrow
• Only implies a change the target may affect the
  source
• Further investigation is required

Position
BilliardBall
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Source Code Example
The dependency may be relatively weak. Here the
dependency is only in the fact that setPosition()
uses the type for a parameter.
public class BilliardBall private int
color private int number private int
xPixel private int yPixel public void
setPosition (Position p) public void hitBy
(BilliardBall b) public void draw()
public class Position private double x
private double y private double z public
void moveTo (double x, double y, double z)
public void tranform (Matrix matrix)
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Source Code Example
The dependency may be relatively strong. Here the
dependency exists because the class has an
attribute of the type.
public class BilliardBall private int
color private int number private
Position position public void setPosition
(Position p) public void hitBy
(BilliardBall b) public void draw()
public class Position private double x
private double y private double z public
void moveTo (double x, double y, double z)
public void tranform (Matrix matrix)
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Dependencies and Other Relationships

• Dependencies can exist in many forms
• In fact, all other relationships are a form of
  dependency
• UML provides other notations to assert common
  forms
• Advanced - For those UML does not supply,
  stereotypes can be used

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Association

• Directed relationship
• Represented by a regular line with an arrow
• May be bi-directional
• Represented by a line (no arrow heads)
• Implies that an instance of the source is aware
  of an instance of the target

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Association
Unidirectional Association
Road
Car
Bidirectional Association
University
Professor
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Associations and Class Structure

• There are different ways to code the association
  relationship
• IST 240 Method!
• Associations require an attribute
• Associations will have set operations
• May be set like (e.g., add() in the case of
  multiplicity)
• May be encapsulated in the constructor
• Associations may have get operations
• These access state data
• May be get like (e.g., find())

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Source Code Example - Unidirectional
Notice that Car has an attribute of type Road but
Road does not reference Car.
public class Car private Road currentRoad
private int speedInMPH public void
setCurrentRoad(Road r) public Road
getCurrentRoad() public void
setSpeedInMPH (int newSpeedInMPH) public
void setSpeedInKPH (int newSpeedInMPH)
public int getSpeedInMPH() public int
getSpeedInKPH()
public class Road private String name
private int speedLimitInMPH public void
setName(String name) public void
setLimitInMPH (int limitInMPH) public void
setLimitInKPH (int limitInKPH) pubic
String getName() public int
getLimitInMPH() public int
getLimitInKPH()
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Source Code Example - Bidirectional
Here Professor has an attribute of type
University. University has an array of type
Professor.
class Professor private String name
private CV cv private University
currentEmployer public void setUniversity
(University u) public void displayCV()

class University private Professor
professors100 private int
currentNumberOfProfessors public void
hireProfessor (Professor p) public void
fireProfessor (Professor p)
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Roles Names and Multiplicity

• Associations may also have role names
• An instance of the source refers to an instance
  of the target via the role name
• Associations may also indicate multiplicity
• Multiplicity describes the number (or range) of
  instances of a class that can take part in the
  association
• Multiplicity can be placed at either the source
  or target in association

Multiplicity Options 0 lt n lt m
n exactly n n .. at least n Unspecified
.. m at most m n .. m between n and m
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Associations
Unidirectional Association
0..1

Road
Car
currentRoad
Bidirectional Association

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University
Person
employer
employee
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Associations
An instance of road cannot be aware of an
instance of car, hence there is no role name.
Unidirectional Association
0..1

Road
Car
currentRoad
Bidirectional Association

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University
Person
employer
employee
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For Car Is there a difference?
0..1

Road
Car
currentRoad
Car
Road
currentRoad Road
setRoad(road Road)
getRoad() Road
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For Car Is there a difference?
0..1

Road
Car
currentRoad
Car
Road
currentRoad Road
setRoad(road Road)
getRoad() Road
No. Both diagrams indicate that class Car has an
attribute, currentRoad, of type Road and at any
point in time currentRoad may or may not
reference a Road object
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For Car Is there a difference?
1

Road
Car
currentRoad
Car
Road
currentRoad Road
setRoad(road Road)
getRoad() Road
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For Car Is there a difference?
1

Road
Car
currentRoad
Car
Road
currentRoad Road
setRoad(road Road)
getRoad() Road
Structurally, no. Formally, the multiplicity of
1 indicates that currentRoad must reference an
instance of Road at all times.
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Aggregation

• Aggregation captures a part of relationship
• Represented as a line between two classes with a
  diamond at the source (the larger object)
• There are two flavors
• Shared aggregation
• A hollow diamond
• Composite Aggregation
• A filled in diamond

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Shared Aggregation

• Shared Aggregation, for all intents in purposes,
  is association
• The association has a slightly stronger feel
• Part of versus Knows of relationship
• Shared Aggregation is often called aggregation
• Aggregation can have role names and multiplicities

0..1
1
Car
Driver
currentDriver
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Shared Aggregation and Class Structure

• There are different ways to code the shared
  aggregation relationship
• IST 240 Method!
• Aggregations require an attribute
• Aggregations may/may not have set operations
  for the attribute
• Aggregations may/may not have get operations
  for the attribute

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Source Code Example
public class Car private Road
currentRoad private int speedInMPH
private Driver currentDriver public void
setCurrentRoad(Road r) public Road
getCurrentRoad() public void
setDriver(Road r) public Road getDriver()
public void setSpeedInMPH (int
newSpeedInMPH) public void setSpeedInKPH
(int newSpeedInMPH) public int
getSpeedInMPH() public int
getSpeedInKPH()
Shared aggregation behaves like association. The
relationship gives rise to an attribute.
public class Driver private String name
private boolean isDriving public void
drive() public void stopDriving()
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Shared Aggregation

• Aggregation relationships can be bi-directional
• This is in the sense of awareness
• In the class diagram below
• Car is aware of at most one Driver
• Driver is aware of at most one Car

0..1
0..1
Car
Driver
currentDriver
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Source Code Example
public class Car private Road
currentRoad private int speedInMPH
private Driver currentDriver public void
setCurrentRoad(Road r) public Road
getCurrentRoad() public void
setDriver(Road r) public Driver getDriver()
public void setSpeedInMPH (int
newSpeedInMPH) public void setSpeedInKPH
(int newSpeedInMPH) public int
getSpeedInMPH() public int
getSpeedInKPH()
Bidirectional shared aggregation gives rise to
atttributes in both classes.
public class Driver private String name
private boolean isDriving private Car
currentCarl public void drive() public
void stopDriving() public void setCar(Car
car) public Car getCar()
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Composite Aggregation

• Composite Aggregation is stronger than Shared
  Aggregation
• Generally the composer exists longer than the
  composee
• This is not the case for Shared Aggregation
• Composite Aggregation is often called
  composition
• Compositions can have role names and
  multiplicities

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Car
Wheel
myWheels
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Composition and Class Structure

• There are different ways to code the composition
  relationship
• Must always ensure the target instance lives no
  longer than the source
• IST 240 Method
• Compositions require an attribute
• Compositions do not have set operations for the
  attribute
• Why?
• Compositions may have get operations for the
  attribute
• Need to do this carefully!

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Source Code Example
public class Car private Road
currentRoad private int speedInMPH
private Driver currentDriver private Wheel
wheels public Car() wheels new
Wheel4 for (int w0 wltwheels.length
w) wheelsw new Wheel()
public void setCurrentRoad(Road r)
public Road getCurrentRoad()
public void setDriver(Road r) public
Driver getDriver() public void
setSpeedInMPH (int newSpeedInMPH) public
void setSpeedInKPH (int newSpeedInMPH)
public int getSpeedInMPH() public int
getSpeedInKPH()

• Note that myWheels represents a reference to an
  array object.
• When an instance of Car is deleted, the myWheels
  array should also deleted.

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Putting It Together
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0..1
Wheel
Road
Car
0..1
Driver
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Remember the IST 240 Method

• Associations
• Source class will have an attribute, set
  operation and perhaps a get operation
• Composition
• Source class will have an attribute, no set
  operation and perhaps a get operation

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Composition vs. Aggregation

• Composers cannot share instances of their
  composees
• Aggregators can share

0..1
Car
Owner
currentOwner
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Car
Wheel
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Example

• Lets assume that a shirt has a collar, a single
  pocket, and two sleeves
• There are 12 buttons on the shirt
• 7 down the front,
• 2 for the collar
• 1 for each cuff
• 1 for the pocket

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Example

• Whats wrong with this diagram?

Shirt
12
2
1
1
2
Collar
Sleeve
Pocket
Button
1
1
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Example

• What can be said about this diagram?

Shirt
9
2
1
1
2
Collar
Sleeve
Pocket
Button
1
1
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IST 240 Method! Dont Use Shared Aggregation

• Shared aggregation can be modeled using an
  association
• Since it leads to confusion, it is typically not
  used in modeling
• We discuss it because it is important to
  understand as it does appear

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Subclassing

• Classes can be subclassed
• The representation is an arrow with an open,
  triangular head at the superclass
• This is the mechanism in UML which supports
  inheritance
• Often referred to as generalization or
  specialization

Vehicle
LandVehicle
AquaticVehicle
Sub
Boat
Tank
Auto
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Source Code Example
Vehicle
public class Vehicle . . . public
class AquaticVehicle extends Vehicle . .
. public class Sub extends AquaticVehicle
. . .
AquaticVehicle
Sub
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Specialization

• When specializing a class
• All public and protected attributes are visible
  by the subclass
• All public and protected operations can be
  overridden
• Using the leaf tag, operations can be indicated
  that they are not to be overridden

BillardBall
init(in atPosition Position) void
leaf hitBy (in ball BillardBall)
void currentPosition() Position
leaf
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Source Code Example
BillardBall
init(in atPosition Position) void
leaf hitBy (in ball BillardBall)
void currentPosition() Position
leaf
public class BilliardBall private int
color private int number private Position
p public final void init(Position p)
public void hitBy(BilliardBall b) public
final Position getCurrentPosition()
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Example Alarm Clock
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Example Digital Alarm Clock