Class
Represented by a rectangle with possibly 3 compartments
Customer
Class name
Customer
Class name
Customer
Class name
getName()
checkCreditRating()
operations
Customer
Name
Address
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Class name
attributes
ACS-3913
Name
Address
attributes
getName()
checkCreditRating()
operations
Ron McFadyen
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Class
Some classes are stereotyped:
«Singleton»
dbFacade
Later in the course we study the Singleton design
pattern.
Some methodologies have 3 stereotypes for “analysis”
classes: boundary, control, entity
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Attributes
an object contains data which are defined as part of the Class
definition
examples:
• Students have names, addresses, etc;
• Courses have titles, descriptions, prerequisite information.
Student
name
address
Rectangle
corner: Point
Level of detail present will depend on whether you are in
analysis or design, and your purposes at the time
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Attributes
To what degree is an attribute visible to other classes?
Private –
Public +
Protected #
Package ~
Student
-name
-address
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Attributes
Default values =
Derived values /
Multiplicity [ ]
Ordering
{ordered}
Uniqueness {unique}
Invoice
-date:Date = today
-/total: Currency
-payments[0..*]: Currency
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Student
-name
-address[1..3] {unique}
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Operations.
What are the responsibilities of a class? What can it do?
Visibility
Parameters
Signature
the name, parameters, and return type of the operation
Student
+getName()
+getGPA(term :Term, gpaType: String)
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6
Associations
• correspond to verbs expressing a relationship between classes
• example
a Library Member borrows a Copy of a Book
•Navigability
•A directed association show that messages will be sent in
that direction
•Multiplicities
• we indicate via multiplicities the range of allowable
cardinalities for participation in an association
• examples: 1, 1..*, 0..*, 1..3
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Associations
• Names and roles
• you can name the relationship and indicate how to read it
• you can give role names for participating objects
The name of the relationship and the
direction for reading the name
Person
1..*
employee
employer
The role of a Person in this relationship
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Works for
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Company
The role of a Company in this relationship
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Associations
•example:
A duck uses a flying behavior
Duck
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1
uses
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FlyBehavior
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Associations
• example:
An employee is supervised by an employee
reports to
supervised
*
Employee
0,1 supervisor
A reflexive association: an instance of
this association involves two Employee
objects (two objects from the same
class).
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Inner Class
It is common to use +
SwingObserverExample +
to indicate an inner class
Angel listens to
AngelListener
+
Devil listens to
DevilListener
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11
Navigability
The association below is directed. The arrow indicates the
direction in which messages are sent. Note this means that a duck
will “know” its flying behaviour. In the implementation of a duck
there is need for an attribute that is a reference to a flying
behaviour object.
1
uses
Duck
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FlyBehavior
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A
b: B
B
Navigability:
An association line with a navigability adornment indicates that an object of
one class (A) is connected uni-directionally to an object of another class (B)
An object of class A can navigate to an object of class B.
•I.e. an object of class A needs to know the B object, but not the other
way around.
•An instance of A can send a message to an instance of B, the instance
can respond, but doesn’t initiate.
An association line that has no specific navigation indicated, is considered to
be bi-directional
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Association Class
*
*
Company
Business rule: a
person contracts their
services to a
company
Person
Contract
startDate
Association Class: a modeling element that is both an association
and a class. It has attributes, operations, multiplicities, etc. It can
participate in other relationships. Note the dashed line.
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*
*
Company
Person
Contract
startDate
Many to many associations
•likely candidate for an Association Class
Limitation: each company object can be associated to a
person object only once. If we wanted to provide for a
person to be contracted to the same company more than
once, we would need to promote Contract to be a regular
class. How do we model this?
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Reflexive Association
An association involving the same class more than once.
Person
1
1
marries
Person
?
*
*
marries
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Reflexive Association
An association involving the same class more than once.
Part
*
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*
comprises
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Interfaces
An interface is special type of class that cannot be instantiated.
An application can never instantiate an interface.
An interface defines a set of public attributes and operations that
some class must use (depends on)
There is no behaviour defined, no method coded
Some other class inherits the interface and provides the
implementation (generalization, inheritance)
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Interfaces
The interface named
FlyBehavior comprises the
fly operation
<<interface>>
FlyBehavior
fly()
FlyWithWings
fly()
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FlyNoWay
fly()
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Ron McFadyen
These classes implement the
fly operation
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Abstract Classes
An abstract class is a special type of class in a class hierarchy
that cannot be instantiated. An application can never instantiate
an abstract class and so must instantiate objects at a more
specialized level in the hierarchy.
An abstract class defines a set of attributes and operations that
some class must use (depends on)
If an operation is not abstract, then its behaviour is defined in the
abstract class, i.e. there is an implementation, but this may be
overriden in a more specialized subclass.
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Abstract Classes
Duck
The abstract class has its
name in italics.
performfly()
swim()
display()
MallardDuck
display()
Fall 2009
The performFly() and
swim() operations are
defined, but display() is not
defined (it is an abstract
operation)
RubberDuck
swim()
display()
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The swim operation is
overridden in RubberDuck.
Both subclasses have
implementations of
display().
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