Microsoft Word – OODP – Car Loans.docx
OODP Group Coursework – Car Loans
Imperial College London 1
OODP – Car Loans
1 UML Class Diagram
OODP Group Coursework – Car Loans
DoC MSc Computing Science 2
2 Description
The inheritance hierarchy and association classes are specifally designed for this project.
Therefore, this section will focused on the details and effects of them.
2.1 Inheritance Hierarchy
A. LegalPerson
The class called LegalPerson is designed as the superclass for the subclasses Person and
Company. These two subclasses have several same attributes and behaviors:
• Company or Person may apply to a bank for a loan to buy a car,
• Bank grants the loan to a person and a company based on certain criteria,
• Person and Company are responsible to send a letter of acceptance when he/she/it
receives the grant of a loan.
In this project, the only attribute needed in the Person class is birthday. For company, it only
needs to contain its own unique attributes, such as, turnover. These subclasses can inherit or
overwrite the same operations from the superclass.
B. Company
The inheritance relationship also exists between the classes Bank and Company. More
specifically, bank is a kind of company in the real world. Bank has the attributes turnover as
Company does. Bank can also apply for a loan from other banks. Though the information is not
specifically indicated on the problem descriptions. Summarily, Bank can inherit a few same
attributes, such as, name, address, and possibly the above-mentioned behavior.
2.2 Association Classes
A. Contract
Person works for up to three companies. Therefore, association relationship is appropriate
between these two classes and an association class called Contract is used in this project. Each
contract contains the information related the relationship between person and company, such
as start date of contract, salary. The use of class Contract can extend the functionality of this
contract relationship, to include more detailed information for further considerations.
B. Salary
A Salary class is needed to document the information related to each salary payed. The use of
Salary class can contain more detailed information related to salary, such as salary pay day,
and amount. The relationship between Salary and Contract is aggregation.
C. Loan
A Loan class is created to denote the association relationship between LegalPerson (superclass
of Company and Person) and Bank. LegalPerson applies to a bank for a loan to buy a car. The
bank grants the loan to LegalPerson based on certain criteria. In this case, borrow date, amount,
are needed in the class Loan. However, more attributes or operations can be added to this Loan
class to describe more detailed information about this “borrow” behavior for further
considerations.
To conclude, LegalPerson is the super class of Company and Person. Company, as the subclass
of LegalPerson, is also the super class of Bank. An association class Contract is used to
document the relationship between Person and Company. A Salary class is contained in
OODP Group Coursework – Car Loans
Imperial College London 3
Contract to document the salary information about each contract. An association class Loan is
created to denote the relationship between LegalPerson and Bank. Detailed design of the
association relationships and operations of each class is elaborated in implementation section.
3 Implementation
3.1 A person may be working for one or more, but for no more than three
companies.
bool Company::employ(Person),
where ‘Person’ is the employee to be employed by the company, and the function returns true
if the company employs the person successfully, otherwise returns false.The function generates
a contract between the company and the person, which records start date, salary, status (whether
the contract is expired or not) and etc. and will be stored as an attribute by both the person
using function workFor(Company) and the company. True is returned in this case. The contract
will not be generated if the person has already worked for three companies, in which case false
is returned.
3.2 A person receives a salary from each company he/she works for.
void Company::payoff(Person),
where ‘Person’ stands for the person to receive salary, and there is no return. According to the
contract between the company and the person, the function generates an instance of Salary
class which contains attributes, for example, amount, date, from (whom), to (whom) and etc.
The instance is then stored in contract object, which can be accessed by the company and the
person via contract.
3.3 The disposable income of person.
float Person::getDisposableIncome(void),
By querying all contracts the person has which records salaries, he/she is able to sum up all
salaries received. To acquire the person’s age, function Person::getAge() could be invoked.
The sum of prices of all cars owned by the person is calculated by cars stored as an attribute
inside Person object and Car::getPrice(), whereas remaining amount on existing loans by
loans stored as an attribute inside the object.
3.4 The disposable income of company.
float Company::getDisposableIncome(void),
which is an implementation of function declaration in its superclass. All employees of a
company can be acquired by the list of ‘Contract’ stored in ‘Company’, whereas remaining
amount on existing loans by loans stored inside the object.
3.5 A car may be owned by a person, a company or a bank.
virtual void LegalPerson::buy(Car),
where ‘Car’ is a car to be bought by someone, and there is no return. The function records the
car as an attribute in a list in the object LegalPerson. It can be accessed by LegalPerson via
cars collection data member.
3.6 Person or company applies to a bank for a loan
void LegalPerson::applyToBankForLoan(Bank, int, Car),
create a loan object to record the information of application and invoke the function of bank
bank.reviewLoanApplication(loan) to review the application.
OODP Group Coursework – Car Loans
DoC MSc Computing Science 4
3.7 Bank reviews the application from company or person and makes a decision
void Bank::reviewLoanApplication(Loan),
• get the objects related with grants, borrower(LegalPerson) and purpose(Car), from
passed loan object
• get the disposable income of borrower and price of car by calling corresponding
operations, getDisposableIncome() and getPrice() respectively
• compare borrower’s disposable income and car’s price multiplied by interest rate of
current bank
• if the disposable income is greater, grant the loan, add this loan object into bank’s loans
collection, and inform the result to borrower by function returning true (synchronous),
which is not used in this case or invoking borrower’s corresponding
operation(asynchronous) accepted by this design.
• if not, refuse the loan and destruct the loan object
3.8 Person or company confirms the result of application from bank and if
receiving grant, sends a confirmation letter back to bank
void LegalPerson::receiveGrantOfLoan(loan),
confirm the loan by adding this object to LegalPerson’s loans collection or database and inform
the bank of receiving the result of grant by calling its corresponding function.
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