Question

Assume that you are writing an application that will calculate the amount of interest earned for a bank account. a) Identify the potential classes in this problem domain. b) Refine the list to include only the necessary class or classes for this problem. c) Identify the responsibilities of the class or classes. d) Design the UML diagram.

Answer 1

Let’s determine possible class members for each of the above.

The bank class represents a physical bank. It has a location and a unique id. This bank also manages several accounts. **There’s an association!** What type of association is this? Is a bank entirely composed of accounts (composition)? Or are accounts ‘part of’ a bank (aggregation)? It looks like aggregation. It can’t be composition because that would mean that both classes live and die together. That’s not quite right because you can have a bank without accounts and you can have accounts without a bank. We’ll add a method called getAccounts().

The ATM class represents a physical ATM. Right off the bat, we can come up with three methods for the ATM: withdraw(), deposit(), checkBalance(). Each of these methods takes the card number as input. In terms of attributes, an ATM has a location and is managed by a specific bank.

The customer class represents a real customer. This customer has a name, address, date of birth (dob), card number, and pin. For this person to be considered a customer, they must have an account. **There’s another association!** This isn’t aggregation or composition, it’s just a bi-directional association (drawn using a blank line no arrows).

The account class represents a bank account. Common attributes of bank accounts include account number, balance, etc. You can deposit() withdraw() money from the account. In addition, banks might offer two types of accounts: a checking account and a savings account. These two can thus be considered child classes of the account class and can inherit from it too. We’ll denote this by using a solid black line with an unfilled arrow going into the account class.