Fall 2009ACS-3913 Ron McFadyen1 Class Represented by a rectangle with possibly 3 compartments Customer Name Address Customer Name Address getName() checkCreditRating()

Fall 2009 ACS-3913 Ron McFadyen 1

Class

Represented by a rectangle with possibly 3 compartments

Customer

Customer

NameAddress

Customer

NameAddress

getName()checkCreditRating()

Customer

getName()checkCreditRating()

Class name

attributes

operations

operations

attributes

Class nameClass name

Class name


Class

«Singleton»dbFacade

Some classes are stereotyped:

Later in the course we study the Singleton design pattern.

Some methodologies have 3 stereotypes for “analysis” classes: boundary, control, entity


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.

Rectangle

corner: Point

Student

nameaddress

Level of detail present will depend on whether you are in analysis or design, and your purposes at the time


Attributes

To what degree is an attribute visible to other classes?Private –Public +Protected #Package ~

Student

-name-address


Attributes

Default values =Derived values /Multiplicity [ ]Ordering {ordered}Uniqueness {unique}

Invoice

-date:Date = today-/total: Currency-payments[0..*]: Currency

Student

-name-address[1..3] {unique}


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)


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


Associations

• Names and roles

• you can name the relationship and indicate how to read it• you can give role names for participating objects

Person CompanyWorks for1..* 1

employer employee

The role of a Person in this relationship The role of a Company in this relationship

The name of the relationship and thedirection for reading the name


Associations

•example: A duck uses a flying behavior

Duck FlyBehavior1uses


Associations

• example: An employee is supervised by an employee

*

0,1Employee

reports to

supervised

supervisor

A reflexive association: an instance of this association involves two Employee objects (two objects from the same class).


Inner Class

SwingObserverExample AngelListener Angel listens to

DevilListener Devil listens to

+

+

+It is common to use to indicate an inner class


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.

Duck FlyBehavior 1uses


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

In an OO language,

an A will have an

attribute that

references a B instance

A

b: B

B


Association Class

Business rule: a person contracts their services to a company

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.

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?

Company Person

Contract

startDate

* *


Reflexive Association

An association involving the same class more than once.

marries

Person1

1

marries

Person*

*

?


Reflexive Association

An association involving the same class more than once.

comprises

Part*

*


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)


Interfaces

<<interface>>FlyBehavior

FlyNoWay

fly()

These classes implement the fly operation

FlyWithWings

fly() fly()

The interface named FlyBehavior comprises the fly operation


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.


Abstract Classes

Duck

RubberDuck

performfly()swim()display()

The swim operation is overridden in RubberDuck.

Both subclasses have implementations of display().

MallardDuck

display() swim()display()

The abstract class has its name in italics.

The performFly() and swim() operations are defined, but display() is not defined (it is an abstract operation)

Fall 2009ACS-3913 Ron McFadyen1 Class Represented by a rectangle with possibly 3 compartments Customer Name Address Customer Name Address getName() checkCreditRating()

Documents