Lab Assignment #9: Classes

Due by 11:59PM on Friday, April 16.

DRAFT - to be finalized by 4/9/99

Reading Assignment

Read about classes in Chapter 8 of the text.

In-Lab Work

In the lab this week, we are going to design a class hierarchy for a simple bank account structure. You will extend the same program you write for the in-lab exercise for the actual lab assignment. The basic problem has to do with bank accounts. Think of a bank account as an individual object. What are the most important data properties? What types of operations would you have on these data? In the lab, you will design a simple bank account class that can store just the basic information on that account - the account balance. Write a class BankAccountLab with the following features:

1. The class should have a data variable called balance which cannot be accessed from any other classes. (So what type of protection should you use?)
2. The class should have the following constructors:
   • A default constructor, that sets the account balance to zero.
   • A special constructor which takes in a parameter called initialbalance, and creates an account with that value as the balance.
3. The class should also have the following methods:
   • Deposit - this method should take in the amount for the deposit, and add that to the current balance.
   • PrintBalance - this method should print the current balance of the account in some useful fashion.

Save this program as BankAccountLab.java

Lab Assignment

NOTE!

To test your classes, you will need a main program to drive all your classes. I have created a main program that tests out all your methods. You should make sure your classes work with this main program. Do not change this main program. We will be using a main program like this one to test your code. If your parameters are not in proper order, make sure you order them according to how the main program expects it. The account number is treated as a string in this main program.

Download BankMain.java

For the lab, we will start with the basic lab assignment that you have created, and will make a number of changes. There are two sets of implementations that you will need to do - the first set you should be able to do by 4/13, since everything you need will be covered in the lab and lecture. The second set requires inheritence, which would be covered in class on (4/13). Of course, nothing is due until 4/16, but you should still work on the program this week, since it is significantly easier than lab 8.

The following sets of enhancements are to be made to the program:

1. First set:
   • Change the filename and classname to BankAccount
   • In addition to the account balance, you should have an accountNumber and patronName field to store the account number and the name of the person with that account number.
   • Change the constructor so that it also accepts the account number and name of client in addition to the balance
   • Change the printBalance method so that it prints the account number and name on the account in addition to the current balance.
   • Add the method Withdraw that lets someone withdraw money from the accounts, and generates an error message if the user over-withdraws from the account (i.e., a withdrawal causes the balance to fall below 0. In that case, deny the withdrawal (i.e., do not change balance, but generate an appropriate error message.)
2. Second set:
   • Create two subclasses of BankAccount - SavingsAccount and CheckingAccount. CheckingAccount should have a data variable called checks (an integer, that shows the number of checks left). This should be set to a default value of 10 by the CheckingAccount constructor.
   • Override printBalance so that it also prints something that shows what type of account it is.
   • In SavingsAccount, create a method called addInterest that takes in an interest rate, updates the account balance using a simple interest formula (balance = balance + balance * rate / 100.0).
     What change do you need to make to the BankAccount class in order to facilitate this? (Hint: balance in bankaccount was originally defined so that it cannot be accessed directly by any other class!
   • In CheckingAccount, create a method called buyChecks that takes in a number (corresponding to the number of checks being bought) and updates the remaining number of checkts.
   • In CheckingAccount, create a method called WriteCheck that takes in an amount for the check and updates the balance and the remaining number of checks. Notice that you will also need to update the balance and check for errors there, but you can do this by simply calling the corresponding method from the parent class (BankAccount). If the number of checks is exhausted, then it should display an error message and refuse the transaction.

Submitting Your Lab Assignment

For this lab, you should submit three files: BankAccount.java, SavingsAccount.java, and CheckingAccount.java

Attach these files to an e-mail sent to a201@cs.indiana.edu with lab9 as the subject.