Chapter 10 Lab More Classes and Objects Solution

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 © 2016 Pearson Education, Inc., Hoboken NJ
Copyright © 2016 Pearson Education, Inc., Hoboken NJ
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 15 cents.
4. 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. 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 2.5%.
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. 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.
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6. 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. Write a method that overrides the getAccountNumber method in the
superclass.
8. 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:
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 = $499.85
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 monthly interest has been posted, balance = $901.88
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
Account Number 100003-10 belonging to Isaac Newton
Code Listing 10.1 (AccountDriver.java)
/**
This program demonstrates the BankAccount and
derived classes.
*/
Copyright © 2016 Pearson Education, Inc., Hoboken NJ
public class AccountDriver
{
public static void main(String[] args)
{
double put_in = 500;
double take_out = 1000;
String money;
String money_in;
String money_out;
boolean completed;
// Test the CheckingAccount class.
CheckingAccount myCheckingAccount =
new CheckingAccount("Benjamin Franklin", 1000);
System.out.println("Account Number " +
myCheckingAccount.
getAccountNumber() +
" belonging to " +
myCheckingAccount.getOwner());
money = String.format("%.2f",
myCheckingAccount.
getBalance());
System.out.println("Initial balance = $" + money);
myCheckingAccount.deposit(put_in);
money_in = String.format("%.2f", put_in);
money = String.format("%.2f",
myCheckingAccount.
getBalance());
System.out.println("After deposit of $" +
money_in + ", balance = $" +
money);
completed = myCheckingAccount.withdraw(take_out);
money_out = String.format("%.2f", take_out);
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money = String.format("%.2f",
myCheckingAccount.
getBalance());
if (completed)
{
System.out.println("After withdrawal of $" +
money_out + ", balance = $" +
money);
}
else
{
System.out.println("Insuffient funds to " +
"withdraw $" + money_out +
", balance = $" + money);
}
System.out.println();
// Test the SavingsAccount class.
SavingsAccount yourAccount =
new SavingsAccount("William Shakespeare", 400);
System.out.println("Account Number " +
yourAccount.getAccountNumber() +
" belonging to " +
yourAccount.getOwner());
money = String.format("%.2f",
yourAccount.getBalance());
System.out.println("Initial balance = $" + money);
yourAccount.deposit(put_in);
money_in = String.format("%.2f", put_in);
money = String.format("%.2f",
yourAccount.getBalance());
System.out.println("After deposit of $" +
money_in + ", balance = $" +
money);
completed = yourAccount.withdraw(take_out);
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money_out = String.format("%.2f", take_out);
money = String.format("%.2f",
yourAccount.getBalance());
if (completed)
{
System.out.println("After withdrawal of $" +
money_out + ", balance = $" +
money);
}
else
{
System.out.println("Insuffient funds " +
"to withdraw $" + money_out +
", balance = $" + money);
}
yourAccount.postInterest();
money = String.format("%.2f",
yourAccount.getBalance());
System.out.println("After monthly interest " +
"has been posted, " +
"balance = $" + money);
System.out.println();
// Test the copy constructor of the
// SavingsAccount class.
SavingsAccount secondAccount =
new SavingsAccount(yourAccount, 5);
System.out.println("Account Number " +
secondAccount.
getAccountNumber() +
" belonging to " +
secondAccount.getOwner());
money = String.format("%.2f",
secondAccount.getBalance());
System.out.println("Initial balance = $" + money);
secondAccount.deposit(put_in);
Copyright © 2016 Pearson Education, Inc., Hoboken NJ
money_in = String.format("%.2f", put_in);
money = String.format("%.2f",
secondAccount.getBalance());
System.out.println("After deposit of $" + money_in +
", balance = $" + money);
secondAccount.withdraw(take_out);
money_out = String.format("%.2f", take_out);
money = String.format("%.2f",
secondAccount.getBalance());
if (completed)
{
System.out.println("After withdrawal of $" +
money_out + ", balance = $" +
money);
}
else
{
System.out.println("Insuffient funds " +
"to withdraw $" + money_out +
", balance = $" + money);
}
System.out.println();
// Test to make sure new accounts are
// numbered correctly.
CheckingAccount yourCheckingAccount =
new CheckingAccount("Issac Newton", 5000);
System.out.println("Account Number " +
yourCheckingAccount.
getAccountNumber() +
" belonging to " +
yourCheckingAccount.getOwner());
}
}
Copyright © 2016 Pearson Education, Inc., Hoboken NJ
Code Listing 10.2 (BankAccount.java)
/**
The BankAccount class is an abstract class that holds
general data about a bank account. Classes representing
specific types of bank accounts should inherit from
this class.
*/
public abstract class BankAccount
{
// Class variable so that each account
// has a unique number
protected static int numberOfAccounts = 100001;
// Current balance in the account
private double balance;
// Name on the account
private String owner;
// Number bank uses to identify account
private String accountNumber;
/**
Default constructor
*/
public BankAccount()
{
balance = 0;
accountNumber = numberOfAccounts + "";
numberOfAccounts++;
}
Copyright © 2016 Pearson Education, Inc., Hoboken NJ
/**
Standard constructor
@param name The owner of the account.
@param amount The beginning balance.
*/
public BankAccount(String name, double amount)
{
owner = name;
balance = amount;
accountNumber = numberOfAccounts + "";
numberOfAccounts++;
}
/**
Copy constructor creates another account
for the same owner.
@param oldAccount The account with information
to copy.
@param amount The beginning balance of the
new account.
*/
public BankAccount(BankAccount oldAccount,
double amount)
{
owner = oldAccount.owner;
balance = amount;
accountNumber = oldAccount.accountNumber;
}
/**
Allows you to add money to the account.
@param amount The amount to deposit in the account.
*/
public void deposit(double amount)
{
balance = balance + amount;
}
Copyright © 2016 Pearson Education, Inc., Hoboken NJ
/**
Allows you to remove money from the account if
enough money is available, returns true if the
transaction was completed, returns false if
there was not enough money.
@param amount The amount to withdraw from
the account.
@return True if there was sufficient funds to
complete the transaction, false otherwise.
*/
public boolean withdraw(double amount)
{
boolean completed = true;
if (amount <= balance)
{
balance = balance - amount;
}
else
{
completed = false;
}
return completed;
}
/**
Accessor method to balance
@return The balance of the account.
*/
public double getBalance()
{
return balance;
}
/**
accessor method to owner
@return The owner of the account.
*/
public String getOwner()
{
return owner;
}
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/**
Accessor method to account number
@return The account number.
*/
public String getAccountNumber()
{
return accountNumber;
}
/**
Mutator method to change the balance
@param newBalance The new balance for the account.
*/
public void setBalance(double newBalance)
{
balance = newBalance;
}
/**
Mutator method to change the account number
@param newAccountNumber The new account number.
*/
public void setAccountNumber(String newAccountNumber)
{
accountNumber = newAccountNumber;
}
}
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