CSCI 114 Lab 4 Wallet

© Anthony W. Smith, 2015

CSCI 114 Programming Fundamentals II

Lab 4 Wallet

1

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

}

© Anthony W. Smith, 2015

CSCI 114 Programming Fundamentals II

Lab 4 Wallet

2

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.

© Anthony W. Smith, 2015

CSCI 114 Programming Fundamentals II

Lab 4 Wallet

3

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

© Anthony W. Smith, 2015

CSCI 114 Programming Fundamentals II

Lab 4 Wallet

4

? 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.

© Anthony W. Smith, 2015

CSCI 114 Programming Fundamentals II

Lab 4 Wallet

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]

© Anthony W. Smith, 2015

CSCI 114 Programming Fundamentals II

Lab 4 Wallet

6

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…

© Anthony W. Smith, 2015

CSCI 114 Programming Fundamentals II

Lab 4 Wallet

8

? 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

awsmith@palomar.edu

? 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:

CSCI 114 Lab 4 Anthony W. Smith

? 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

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