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

2 Class-Responsibility- Collaboration (CRC) cards useful for identifying operations not officially part of the UML views classes in terms of their responsibilities responsibilities evolve into sets of operations Identifying operations using the CRC card technique

3 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)

4 CRC cards Responsibilities are allocated to the most appropriate class Sometimes a class needs to collaborate with another class to fulfil its responsibilities

5 CRC card for the Customer class

6 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

7 Collaboration of objects A collaboration is the group of objects that interact to execute a use case

John : Student registration form schedule formavailable classes 1: enter id 2: validate id 3: enter current semester 4: create new schedule 5: display 6: get courses.Sample Collaboration Diagram.

John : Student registration form available courses schedule form 1: enter id 2: validate id 3: enter current semester 4: create new schedule 5: display 6: get courses Sample Sequence Diagram

10 CRC card for the Hire class

11 CRC card for the Bike class

12 CRC card for the Payment class

13 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 Deriving operations from responsibilities

14 Use case description: Issue bike

15 Operations required for ‘issue bike’ use case

16 Class diagram for Wheels with attributes and operations

17 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

18 Sequence diagrams

19 Sequence diagrams

20 Sequence diagrams

21 Sequence diagrams

22 Sequence diagrams - without returns

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 l 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

25 Collaboration Diagrams

26 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)

27 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).

28 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 operationthis 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