CSCI 114 Programming Fundamentals II | Lab 4 Wallet | Solution

CSCI 114 Programming Fundamentals II
Lab 4 Wallet

Purpose
Purpose of this lab is for you to develop a program where many objects are created from a class. Primitives and objects are passed as parameters to class methods.

Problem specification

Your new Wallet class implements a wallet that contains banknotes. A banknote is represented as an int for simplicity, 1 for a $1 bill, 5 for a $5 bill, and so on. You are required to use just a simple array of int to hold the banknotes. You may NOT use an array list.
Here are some example wallets printed out:
Wallet[5, 50, 10, 5]
Wallet[]
Wallet[1, 5, 10, 50, 5]
Here's the outline of the Wallet class. You will implement each method as described
below.
public class Wallet
{
// max possible # of banknotes in a wallet
private static final int MAX = 10;
private int contents[];
private int count; // number of banknotes stored in contents[]
public Wallet()
{
// your code goes here
}
public Wallet(int a[])
{
// your code goes here
}
public void add(int banknote)
{
// your code goes here
}
public boolean remove(int banknote)
{
// your code goes here
}

public String toString()
{
// your code goes here
}
public void reverse()
{
// your code goes here
}
public void sort()
{
// your code goes here
}
public void transfer(Wallet donor)
{
// your code goes here
}
public boolean sameBanknotesSameOrder(Wallet other)
{
// your code goes here
}
//EXTRA CREDIT methods follow...
public Wallet removeBanknotePairs(Wallet w)
{
// your code goes here
}
}
Instance variables
Use exactly and only these instance variables: Wallet uses the contents[] array to store ints representing banknotes. count holds the number of banknotes in contents[], so must be updated every time a banknote is added or removed. count is 0 when a wallet is empty. MAX is the maximum number of banknotes a wallet can hold, so count is MAX – 1 when a wallet is full. count will always be the index where the next banknote is to be added. Banknotes in a wallet are maintained in the order of arrival. A new banknote is simply added to the end of contents[] and count is incremented by

1.When a banknote is removed from a wallet, the value is removed from contents[] and
count is decremented by 1. Importantly, all banknotes above the removed value must be
moved ‘down’ so that no ‘holes’ open in the array. For example, if wallet w is
Wallet[1, 5, 10, 50, 5]:
- then after w.remove(5), w will be Wallet[1, 10, 50, 5]:
Methods
You will complete the method bodies as follows:
public Wallet()
initialize the wallet to empty
 allocate memory for the contents[] array
1 5 10 50 5
index: 0 1 2 3 4 5 6 7 8 9
count
5
contents[]
Wallet object w
1 10 50 5
index: 0 1 2 3 4 5 6 7 8 9
count
4
contents[]
Wallet object w

 initialize count
public Wallet(int a[])
initialize the wallet using the array of int named a[]
an overloaded constructor
 allocate memory for the contents[] array
 initialize contents[] from a[]
 initialize count
public void add(int banknote)
add banknote to the wallet
 banknote is the banknote to add e.g. 50, 5, etc
 add banknote to the end of contents[] and update count
public boolean remove(int banknote) remove first occurrence of banknote from the wallet. Return true if banknote was removed, false otherwise
 (this banknote may not be in the wallet)
 if banknote is removed, must update contents[] so that no holes appear, and count public String toString()
return a textual representation of the wallet, in the standard format. For example:
Wallet[5, 50, 10, 5]
 use a StringBuffer to build the returned value
 convert the StringBuffer to a String and return the String
public void reverse()
reverse the order of banknotes in a wallet e.g.
Wallet[1, 5, 10, 50, 5] when reversed becomes Wallet[5, 50, 10, 5, 1]
(IMPORTANT NOTE: do not create a new Wallet object!)

 suggested algorithm:
start an index pointing at the first banknote in contents[] start another index pointing at the last of the banknotes in contents[] while these indexes do not meet or cross over swap values at the indexes (use a temp variable to do this) move two indexes towards one another
public void sort()
sort the banknotes in a wallet into ascending order e.g.

5
Wallet[5, 50, 10, 5, 1] when sorted becomes Wallet[1, 5, 5, 10, 50]
(IMPORTANT NOTE: do not create a new Wallet object!)
 suggested algorithm:
 we saw in Week 6 a sort method that works for an array of Integer objects
containing MAX elements
 take this method and modify syntax to work for contents[] and count
public void transfer(Wallet donor)
transfer the contents of one wallet (the donor wallet) to the end of another, the receiver.
(The receiver will be the Wallet object calling the method (i.e. the invoking object)).
Leave the donor wallet empty. For example:
if the receiver is Wallet[5, 10, 50, 50]
and donor is Wallet[5, 5, 10, 1, 50, 5]
then after the transfer:
receiver will be Wallet[5, 10, 50, 50, 5, 5, 10, 1, 50, 5]
and donor will be Wallet[]
 you should call the add() method as you implement this
 to set a wallet to empty, simply set its count to 0
public boolean sameBanknotesSameOrder(Wallet other)
return whether two wallets have exactly the same banknotes in exactly the same order
Extra credit
public Wallet removeBanknotePairs(Wallet w)
create a new wallet and add to it pairs of banknotes removed from two other wallets.
Return the new wallet. For example:
if w1 is Wallet[5, 1, 50, 20, 50, 5]
and w2 is Wallet[20, 10, 5, 5, 5, 50, 10]
then after the method call
Wallet w3 = w1.removeBanknotePairs(w2);
w1 will be: Wallet[1, 50]
w2 will be: Wallet[10, 5, 10]
w3 will be: Wallet[5, 5, 50, 50, 20, 20, 5, 5]

The WalletTester class
The WalletTester class tests your new Wallet class. Source code for WalletTester is given below, and can be downloaded from Blackboard, Course Documents, Week 9 folder, Example programs.
/**
* Test the Wallet class.
*
* @author Anthony W. Smith
* @version 5/31/2028
*/
public class WalletTester
{
public static void main(String args[])
{
// create a new Wallet object using an array
int a[] = {5, 50, 10, 5};
Wallet myWallet = new Wallet(a);
// show the contents of myWallet
System.out.println("myWallet contains: " +
myWallet.toString());
// reverse the order of banknotes in myWallet
myWallet.reverse();
System.out.println("\nmyWallet reversed contains: " +
myWallet.toString());
// transfer all the banknotes from myWallet to yourWallet!
Wallet yourWallet = new Wallet();
yourWallet.add(1);
yourWallet.transfer(myWallet);
System.out.println("\nnow myWallet contains: " +
myWallet.toString());
System.out.println("yourWallet contains: " +
yourWallet.toString());
// sort yourWallet
yourWallet.sort();
System.out.println("\nyourWallet sorted is: " +
yourWallet.toString());
// remove all $5 banknotes from yourWallet
while (yourWallet.remove(5))
;
System.out.println("\nyourWallet with $5s removed is: " +
yourWallet.toString());
// check whether two wallets have the same banknotes
// in the same order
int b[] = {10, 5, 10};
Wallet tom = new Wallet(b);
© Anthony W. Smith, 2015
CSCI 114 Programming Fundamentals II
Lab 4 Wallet
7
int c[] = {10, 10, 5};
Wallet dick = new Wallet(c);
int d[] = {10, 5, 10};
Wallet harry = new Wallet(d);
System.out.println(
"\ntom has same banknotes in same order as dick: " +
tom.sameBanknotesSameOrder(dick));
System.out.println(
"tom has same banknotes in same order as harry: " +
tom.sameBanknotesSameOrder(harry));
// EXTRA CREDIT – compare two wallets and remove banknote pairs
int e[] = {5, 1, 50, 20, 50, 5};
Wallet w1 = new Wallet(e);
int f[] = {20, 10, 5, 5, 5, 50, 10};
Wallet w2 = new Wallet(f);
Wallet w3 = w1.removeBanknotePairs(w2);
System.out.println("\nw1 is: " + w1.toString());
System.out.println("w2 is: " + w2.toString());
System.out.println("w3 is: " + w3.toString());
}
}
Extra credit
When you have completed all other methods, implement and test removeBanknotePairs() for 20% extra credit. You must test your method using the w1 and w2 wallets given above in the description of removeBanknotePairs().

Hints
 to start this lab, first work carefully through WalletTester line by line, writing down on a piece of paper what outputs should be produced...
 this makes sure you understand what every method does, and gives you the expected output you need to test your program
 then design, code and test each method in turn, in the order given above. You will have to comment out in WalletTester and Wallet the methods you have not yet implemented Required
 the intent of the lab is that you learn how to program by writing your own methods...

 so (other than some StringBuffer methods in your toString()) do not use API methods for processing arrays
 WalletTester in your submission may not be changed in any way
 every method must have a clear, meaningful Javadoc comment
 automatically and routinely use all the other components of simplicity and clarity, as
listed in Blackboard, Course Information, “How labs are graded”
 when you have thoroughly tested your program and are certain it is correct, save your
output into the output.txt file
Lab 4 submission
 deadline for this lab is 3 weeks, by end of Sunday 4/12
 zip your BlueJ project plus output.txt output file and email to me at
[email protected]
 you will lose points if you do not include a file named output.txt containing the
output of your program
 your email Subject line must say ‘CSCI 114 Lab 4’ followed by your full name, so
that it filters to the correct email folder for grading
 you will lose points if you format your email Subject incorrectly
 e.g. my email Subject would be:
 this is a graded lab, so a reminder that you may not copy code from other people
 reminder that late labs will be penalized 2 points per week or part of week late