Posted: February 26th, 2022

Lab Assignment 6 More Classes and Objects

Lab Assignment 6 More Classes and Objects

Lab Objectives:

 Be able to derive a class from an existing class

 Be able to define a class hierarchy in which methods are overridden and fields are

hidden

 Be able to use derived-class objects

 Implement a copy constructor

Introduction

In this lab, you will be creating new classes that are derived from a class called

BankAccount. A checking account is a bank account and a savings account is a bank

account as well. This sets up a relationship called inheritance, where BankAccount is

the superclass and CheckingAccount and SavingsAccount are subclasses.

This relationship allows CheckingAccount to inherit attributes from BankAccount

(like owner, balance, and accountNumber, but it can have new attributes that are

specific to a checking account, like a fee for clearing a check. It also allows

CheckingAccount to inherit methods from BankAccount, like deposit, that are

universal for all bank accounts.

You will write a withdraw method in CheckingAccount that overrides the

withdraw method in BankAccount, in order to do something slightly different than

the original withdraw method.

You will use an instance variable called accountNumber in SavingsAccount to

hide the accountNumber variable inherited from BankAccount.

The UML diagram for the inheritance relationship is as follows:

Copyright © 2022, Dallas College.

Copyright © 2022, Dallas College.

Copyright © 2022, Dallas College

Task #1 Extending the BankAccount Class

1. Copy the files AccountDriver.java (Code Listing 10.1) and BankAccount.java (Code Listing 10.2) from the Student CD or as directed by your instructor. BankAccount.java is complete and will not need to be modified.

2. Create a new class called CheckingAccount that extends BankAccount. 3. It should contain a static constant FEE that represents the cost of clearing one

check. Set it equal to 20 cents. 4. Homework help – Write a constructor that takes a name and an initial amount as parameters. It

should call the constructor for the superclass. It should initialize accountNumber to be the current value in accountNumber concatenated with –10 (All checking accounts at this bank are identified by the extension –10). There can be only one checking account for each account number. Remember since accountNumber is a private member in BankAccount, it must be changed through a mutator method.

5. Homework help – Write a new instance method, withdraw, that overrides the withdraw method in the superclass. This method should take the amount to withdraw, add to it the fee for check clearing, and call the withdraw method from the superclass. Remember that to override the method, it must have the same method heading. Notice that the withdraw method from the superclass returns true or false depending if it was able to complete the withdrawal or not. The method that overrides it must also return the same true or false that was returned from the call to the withdraw method from the superclass.

6. Compile and debug this class.

Task #2 Creating a Second Subclass

1. Create a new class called SavingsAccount that extends BankAccount. 2. It should contain an instance variable called rate that represents the annual

interest rate. Set it equal to 2.25%. 3. It should also have an instance variable called savingsNumber, initialized to 0.

In this bank, you have one account number, but can have several savings accounts with that same number. Each individual savings account is identified by the number following a dash. For example, 100001-0 is the first savings account you open, 100001-1 would be another savings account that is still part of your same account. This is so that you can keep some funds separate from the others, like a Christmas club account.

4. An instance variable called accountNumber, that will hide the accountNumber from the superclass, should also be in this class.

5. Homework help – Write a constructor that takes a name and an initial balance as parameters and calls the constructor for the superclass. It should initialize accountNumber to be the current value in the superclass accountNumber (the hidden instance variable) concatenated with a hyphen and then the savingsNumber.

Copyright © 2022, Dallas College

6. Homework help – Write a method called postInterest that has no parameters and returns no value. This method will calculate one month’s worth of interest on the balance and deposit it into the account.

7. Homework help – Write a method that overrides the getAccountNumber method in the superclass. 8. Homework help – Write a copy constructor that creates another savings account for the same person.

It should take the original savings account and an initial balance as parameters. It should call the copy constructor of the superclass, and assign the savingsNumber to be one more than the savingsNumber of the original savings account. It should assign the accountNumber to be the accountNumber of the superclass concatenated with the hyphen and the savingsNumber of the new account.

9. Compile and debug this class. 10. Use the AccountDriver class to test out your classes. If you named and created your

classes and methods correctly, it should not have any difficulties. If you have errors, do not edit the AccountDriver class. You must make your classes work with this program.

11. Running the program should give the following output: Checking Account Number 100001-10 belonging to Benjamin Franklin

Initial balance = $1000.00

After deposit of $500.00, balance = $1500.00

After withdrawal of $1000.00, balance = $499.80

Savings Account Number 100002-0 belonging to William Shakespeare

Initial balance = $400.00

After deposit of $500.00, balance = $900.00

Insufficient funds to withdraw $1000.00, balance = $900.00

After first monthly interest has been posted, balance = $901.69

After second monthly interest has been posted, balance = $903.38

Savings Account Number 100002-1 belonging to William Shakespeare

Initial balance = $5.00

After deposit of $500.00, balance = $505.00

Insufficient funds to withdraw $1000.00, balance = $505.00

Checking Account Number 100003-10 belonging to Isaac Newton

After deposit of $1000.00, balance = $6000.00

Savings Account Number 100004-0 belonging to Isaac Asimov

Initial balance = $500.00

After deposit of $500.00, balance = $1000.00

After monthly interest has been posted, balance = $1001.88

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