Transcript A Student Guide to Object- Oriented Development Chapter 6 Identifying Functionality 1

A Student Guide to ObjectOriented Development
Chapter 6 Identifying Functionality
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Responsibilities

Overall system functionality divided up
between classes

Each class has certain responsibilities
to provide a service to a user (e.g.maintain
a customer record) or to another class
(e.g. to supply data)
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CRC cards
Responsibilities are allocated to the
most appropriate class
 Sometimes a class needs to
collaborate with another class to
fulfil its responsibilities

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CRC card for the Customer class
Customer
Responsibility
Collaborator
Provide customer
information
Keep track of hire
transactions
Hire
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Identifying responsibilities from scenarios
 Stephanie arrives at the shop at 9.00am one Saturday and chooses a
mountain bike
 Annie sees that its number is 468
 Annie enters this number into the system
 The system confirms that this is a woman’s mountain bike and displays
the daily rate (£2) and the deposit (£60) (:Bike)
 Stephanie says she wants to hire the bike for a week
 Annie enters this and the system displays the total cost £14 + £60 =
£74 (:Bike)
 Stephanie agrees this
 Annie enters Stephanie’s name, address and telephone number into
the system (:Customer)
 Stephanie pays the £74
 Annie records this on the system and the system prints out a receipt
(:Payment collaborating with :Customer)
 Stephanie agrees to bring the bike back by 5.00pm on the following
Saturday
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Collaboration of objects
A collaboration is the group of objects that interact
to execute a use case
: Customer
: Hire
: Payment
: Bike
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.Sample Collaboration Diagram
.
2: validate id
1: enter id 3: enter current semester
registration form
4: create new schedule
5: display
John : Student
available classes
schedule form
6: get courses
Sample Sequence Diagram
registration
form
John :
Student
schedule
form
1: enter id
2: validate id
3: enter current semester
4: create new schedule
5: display
6: get courses
available
courses
CRC card for the Hire class
Hire
Responsibility
Collaborator
Provide details of a hire
transaction
Deal with the processing of a
bike return i.e. know if it is
late; calculate and store
lateness penalty. Store any
damage penalty
Bike
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CRC card for the Bike class
Bike
Responsibility
Collaborator
Provide bike information
Calculate the hire cost for a
specified number of days
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CRC card for the Payment class
Payment
Responsibility
Collaborator
Keep a record of all
customer payments
Calculate and store amount
of deposit returned
Issue receipt
Customer
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Deriving operations from responsibilities
We need to specify responsibilities in
terms of individual operations and
attributes.
 Ensure that each class has data and
operations to fulfil responsibility
 Walk through use case description

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Use case description: Issue bike
Use case :
Actors:
Goal:
Issue bike
Receptionist
To hire out a bike
Overview:
When a customer comes into the shop they choose a bike to hire. The receptionist looks up the
bike on the system and tells the customer how much it will cost to hire the bike for a specified
period. The customer pays, is issued with a receipt, then leaves with the bike.
Cross reference
R3, R4, R5, R6,R7, R8, R9, R10
Typical course of events
Actor action
1.
2.
The customer chooses a bike
The Receptionist keys in the bike number
4.
5.
7.
8.
10.
11.
Customer specifies length of hire
Receptionist keys this in
Customer agrees the price
Receptionist keys in the customer details
Customer pays the total cost
Receptionist records amount paid
System response
3. Displays the bike details including the daily
hire rate and deposit
6. Displays total hire cost
9. Displays customer details
12 Prints a receipt
Alternative courses
Steps 8 and 9. The customer details are already in the system, so the Receptionist need only key
in an identifier and the system will display the customer details.
Steps 7 – 12. The customer may not be happy with the estimated price and may terminate the
transaction at this stage.
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Operations required for ‘issue bike’ use case
Bike
findBike(bike#)
getCharges(no.Days)
Bike()
Customer
recordDetails(custID, name, address, tel)
Customer()
Payment
calcTotalPayment()
issueReceipt()
Payment()
Hire
Hire(startDate, no.Days)
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Class diagram for Wheels with attributes and
operations
Hire
Customer
startDate
numberDays
dateReturned
latenessDeduction
damageDeduction
custId
name
address
tel
recordDetails( )
returnHire( )
findCustomer(name)
editCust(name,addr,tel)
Customer( )
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processReturn( )
1..* calcDaysOverDue( )
recordReturnDate( )
latenessDeduction(amt)
damageDeduction( )
Hire( )
1
0..*
1..*
Payment
date
totalAmountPaid
totalDeposit Paid
totalDepositReturned
calcTotalPayment( )
calcRemainingDeposit( )
issueReceipt( )
Payment( )
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Bike
bike#
availabl e
type
size
make
model
dail yHireRate
deposit
getCharges( )
findBi ke(bike#)
regi sterBike( )
getBike#( )
Bike( )
SpecialistBike
epoch
insurance
findSpecialBike( )
SpecialistBike( )
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Interaction Diagrams

Describe messaging between objects to
achieve use case goal

Revisit sequence of events in each
scenario

View in terms of messages spawned by
each event.

Two types of interaction diagram:
sequence and collaboration
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Sequence diagrams
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
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Stephanie arrives at the shop at 9.00am one Saturday and chooses a mountain bike
Annie sees that its number is 468
Annie enters this number into the system
The system confirms that this is a woman’s mountain bike and displays the daily rate
(£2) and the deposit (£60)
Stephanie says she wants to hire the bike for a week
Annie enters this and the system displays the total cost £14 + £60 = £74
Stephanie agrees this
Annie enters Stephanie’s name, address and telephone number into the system
Stephanie pays the £74
Annie records this on the system and the system prints out a receipt
Stephanie agrees to bring the bike back by 5.00pm on the following Saturday
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Sequence diagrams
: Receptionist
: Bike
: Customer
: Hire
: Payment
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Sequence diagrams
return arrow
activation
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Sequence diagrams
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Sequence diagrams - without returns
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Sequence Diagrams

Sequence diagrams present the flow of
messages between instances in time.
 One can immediately see in what order
messages are sent because time is an explicit,
vertical dimension on the sequence diagram

each instance is represented as a vertical
line
Collaboration Diagrams

Collaboration diagrams show how
objects work with each other by
sending messages and exchanging
data.
 Sequence diagrams and collaboration
diagrams are two different views of object
interactions
Collaboration Diagrams
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Data dictionary - operations
findBike(bike#)
This operation finds the Bike object whose
number corresponds to the bike number
input (bike#) and returns details about the
bike (bike# + available + type + make +
model + size + dailyHireRate + deposit)
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Another example - calcDaysOverdue()
calcDaysOverdue()
This operation uses today's date from the
system clock and the attributes startDate
and numberDays to calculate whether the
bike has been returned late and if so by
how many days. It calculates the overdue
amount (Bike.dailyHireRate multipled by
the number of days late) and records it by
executing SetLatenessDeduction(amt).
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specification by contract - describes operations in terms of the
services they deliver
the signature of the operation
(its name, any arguments, and
the type of values it returns)
calcDaysOverdue ( )
the purpose of the operation
this operation works out whether a bike has been returned
late and if so by how many days
what the client object must
provide in order to obtain the
required service
the bike must have been returned by the customer, the hire
details must have been found,
a description of the internal
logic of the operation
the number of days’ hired is added to the start date and
then compared with today’s date to calculate if the bike is
late and by how many days. The daily hire rate is multiplied
by the number of days late to give the charge for late return,
this is performed by the Bike.getCharges operation
any other operations that are
called by this operation
this operation calls Bike.getCharges(noDaysLate)
any attributes of objects
whose values are changed by
the operation
this operation sets the Hire attributes dateReturned and
latenessDeduction
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