This assignment focuses on implementing a Stack ADT in two ways—with an array and a linked list. Turn in
three files named ArrayStack.java, LinkedStack.java, and README.txt (this will contain your answers to the
questions as described below). Your Stack implementations should implement the DoubleStack.java interface.
Your LinkedStack.java should use LinkedStackNode.java. You will also need SoundBlaster.java, bot.wav,
bot.dat, and secret.wav files to test your Stack implementations. All of these files can be found on the course
This assignment involves using your Stack implementations to do sound manipulation, namely reversing a
sound clip. This process, called “backmasking”, was used by musicians including the Beatles, Jimi Hendrix, and
Ozzy Osbourne. However, it seems to have fallen out of favor in recent years. You do not need to know how
to handle music files. You will use the given SoundBlaster.java and your Stack implementations to reverse
human-readable, text-based, sound files (i.e. the files that end in .dat). Once you have used SoundBlaster.java
to produce a .dat file that contains the reversed sound clip, you can use the sox program to convert your .dat
file into a .wav file that can be played on your computer by common media players (Windows Media Player,
Winamp, VLC, etc.). We discuss how to use the sox program later in the specification.
Step 1: Eclipse
In addition to learning how to implement an ADT, one of the goals of this assignment is to give you an
opportunity to gain experience working in Eclipse. Eclipse is a very powerful environment for Java so we
encourage you to try working on your project in Eclipse (http://www.eclipse.org/). Eclipse is so powerful that it
may seem like overkill for this assignment, but as the projects get larger, having an integrated development
environment (IDE) with lots of features will come in handy, so you should consider trying it out now.
You can use Eclipse in the lab, or download it to your personal machine. The download site
(http://www.eclipse.org/downloads/) offers a number of different versions; you’ll want “Eclipse IDE for Java
Developers” (NOT the similar sounding “Eclipse IDE for Jave EE Developers”).
After finding a way to run Eclipse, check out an Eclipse tutorial to ease you into the environment (e.g.,
http://www.cs.washington.edu/education/courses/cse143/11wi/eclipse-tutorial/). There are many more off of
the course website and on the web.
We encourage you to write and run a simple “Hello World” program using Eclipse before starting on the
project. This is just a program that does nothing more than print out the string “Hello World”. Once you have
mastered “Hello World”, you might try something with multiple files, or re-doing one of your projects from
Here are some starter instructions for opening the project in Eclipse.
1. Download the file 373_12sp_hw1_soundblaster.zip from the course website to your desktop. This is
an archive of an Eclipse project to get you started.
2. Open Eclipse.
3. If this is the first time you’ve run Eclipse, it will ask you to choose a location for a workspace. The
default location is probably fine.
4. Go to File Import. Choose General Existing Projects Into Workspace. Choose “Select archive
file” and find the zip file you just downloaded. You should see the project appear with a check box next
to it. Press Finish.
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5. There should now be a SoundBlaster project in the left-hand window. There should be little red Xs on
some of the files and folders – this means that the code has errors in it. As you edit the code, Eclipse
automatically compiles the code and tells you if you’ve made any errors.
6. Find SoundBlaster.java under the src (default package) area of the project and double-click. The
file pops up. Now you can scroll down and hover on little light bulb in the left margin to see what the
errors in the code are.
7. It appears that we don’t have classes named LinkedStack or ArrayStack yet – which makes sense, as
those are the files you need to write for your assignment. Here’s where Eclipse gets really useful. Click
on the light bulb – Eclipse pops up a list of possible remedies.
8. We want to create a new Java class in a file, so choose (by double-clicking) the appropriate option. A
dialog window pops up with various options – click Finish.
9. Eclipse auto-generates the file LinkedStack.java (or ArrayStack.java, depending on which light
bulb you clicked) with stub methods for all of the methods in the DoubleStack interface.
Step 2: Implementing the Stack ADT
The assignment asks you to write two implementations of a Stack. Both implementations should implement the
DoubleStack interface. The DoubleStack interface contains the following methods:
• public void clear()
Removes/deletes all elements from the Stack.
• public boolean isEmpty()
Returns true when the Stack contains no elements, or false otherwise.
• public double peek()
Returns the double value that is on top of the Stack without deleting it from the Stack. Your peek
method should not alter the state of the Stack. If this method is called on an empty Stack, an
EmptyStackException should be thrown.
• public double pop()
Deletes the double value that is on top of the Stack and returns it. If this method is called on an empty
Stack, an EmptyStackException should be thrown.
• public void push(double value)
Inserts a double at the top of the Stack.
• public String toString()
Returns a String representation of the Stack. The String should begin with a [, end with a ], and
each element should be separated by a comma and a single space. The elements should appear in
reverse order from which they were pushed onto the Stack. For example, if we have a DoubleStack
called stack, and the following method calls were made: stack.push(1.12121212),
stack.push(2.34343434), and stack.push(3.56565656), a subsequent call to toString should
return “[3.565657, 2.343434, 1.121212]”. In other words, the values in the String start at the
top of the Stack and end at the bottom of the Stack. If the Stack is empty, “” should be returned.
Your toString should not alter the state of the Stack in any manner.
Additionally, the values in the String should be rounded to six digits past the decimal. To do this,
use Math.round as described below. You may NOT use Arrays.toString to write this method.
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To get your toString to contain the double values stored in the Stack rounded to six digits past the decimal, use
Math.round as follows:
double d1 = 3.141592121;
d1 = Math.round(d1 * 1000000.0) / 1000000.0;
double d2 = 1.6666667;
d2 = Math.round(d2 * 1000000.0) / 1000000.0;
double d3 = 1.0;
d3 = Math.round(d3 * 1000000.0) / 1000000.0;
System.out.print(“d1 = ” + d1 + “; d2 = ” + d2 + “; d3 = ” + d3);
The preceding code produces the following output: d1 = 3.141592; d2 = 1.666667; d3 = 1.0
For the array-based implementation of the DoubleStack interface, your array implementation should start with a
small array (say, 10 elements) and resize to use an array twice as large whenever the array becomes full,
copying over the elements in the smaller array. You should do this by using the Arrays.copyOf method found in
For the linked list-based implementation of the DoubleStack interface, you should use the instructor provided
LinkedStackNode.java class to store the nodes in your LinkedStackNode.java.
The only Java classes that you may use to complete the implementations of your Stacks are
java.util.EmptyStackException and java.util.Arrays. The only method that you can use in
java.util.Arrays is the copyOf method to grow your ArrayStack when it becomes full. You may use
the length field of an array.
Step 3: Testing Your Stacks
You can test your Stack implementations by running the SoundBlaster.java program. SoundBlaster.java
reads in a .dat sound file that is specified at the console, puts the sound values on a stack, pops them off in
reverse order, and puts these reversed values in a the second .dat sound file that is specified on the console.
Additionally, the user must tell SoundBlaster.java whether they want to use the ArrayStack implementation
or the LinkedStack implementation by entering the letter a or l, respectively.
Below is an example log of execution from the program; user input is in bold.
Welcome to SoundBlaster!!
Input file (.dat) to reverse: bot.dat
Output file (.dat) to write backmask to: out.dat
ArrayStack or LinkedStack (enter ‘a’ or ‘l’)? a
223411 samples in file
Note: In order for SoundBlaster.java to find your input file, your input file must be directly under your
project directory. For example, my project is named 373_12sp_hw1_soundblaster and so there is a
373_12sp_hw1_soundblaster folder in my Eclipse workspace directory. The log of execution above works
because bot.dat can be found directly under the 373_12sp_hw1_soundblaster folder.
Once you have run SoundBlaster.java, you can convert your output file (e.g., out.dat in the above
execution) to a .wav file to play your reversed sound clip. See the Sox section of the specification below for
more information about how to convert between a .dat file and a .wav file.
SoundBlaster.java is not a great testing program; it does not call all of the methods in your Stacks or may not
call them in a very exhaustive way that tests all cases and combinations. Therefore we highly suggest creating
another small client program of your own to help test other aspects of your Stack implementations behavior.
You also might consider creating some short .dat files by hand to aid testing (see the “.dat File Format” section
below for more information).
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Step 4: Write-Up
In addition to the code that you turn in, answer the following questions in a file called README.txt.
1. How did you test your code?
2. The file secret.wav is a backwards recording of a word or short phrase from a famous movie. Use sox
and your program to reverse it, and write that as the answer to this question.
3. Let’s pretend that you were given a fully functional FIFO Queue class that provides the operations
enqueue, dequeue, isEmpty, and size. How might you implement this project (i.e., simulate a Stack)
with one or more instances of a FIFO Queue? Write pseudocode for your push and pop operations.
Refer to the link titled “Writing Pseudocode” found off of the “Homework” page for instructions on
4. In the previous question, what trade-offs did you notice between a Queue implementation of a Stack and
your original array-based implementation? Which implementation would you choose, and why?
The only sound file format you need to know about is the .dat format. You don’t even have to know very
much about that either, as we’re giving you the code that reads and writes that format (i.e.
SoundBlaster.java). In order to play the reversed sound clips produced by SoundBlaster.java and your
Stack implementations, you need a way to convert the .dat file into a format that common media players
(Windows Media Player, Winamp, VLC, etc.) understand.
sox is a UNIX command-line utility whose name stands for “SOund eXchange”. It allows you to convert
between many different sound formats including .wav, .au, etc. In particular, sox allows you to convert to and
from .dat sound files. .dat files are useful because they are human-readable, text-based sound files.
You can download sox from the sox project page at SourceForge (http://sox.sourceforge.net/). The Windows
version is also a command-line program and works in the same way as the UNIX version described below. See
the course webpage for some hints on using it.
The general strategy for using sox is as follows.
1. Take a .wav sound file of your choosing (e.g. secret.wav).
2. Convert it to a .dat file: sox secret.wav secret.dat
3. Manipulate it by running SoundBlaster.java.
4. Convert it back to a .wav file: sox secret-revealed.dat secret-revealed.wav (this assumes the
output file you saved the reversed sound clip to in step 3 is secret-revealed.dat)
5. Listen to it! (Use your favorite sound player.)
.dat File Format
The .dat file format starts with one line describing the sample rate of the sound file. This line is required. The
rest of the file is composed of two columns of numbers. The first column consists of the time (measured in
seconds) when the sample was recorded, and the second column contains the value of the sample, between -1.0
and 1.0. Below is the beginning of a sample .dat file. Notice that the numbers in the first column increase by
1/44100 each step. This is because the sample rate is 44.1kHz.
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; Sample Rate 44100
Here is the same file, a little deeper on:
Note that for this assignment, you shouldn’t have to deal much with the .dat file yourself, as the provided
SoundBlaster.java reads and outputs these files for you. All you have to do is implement the stacks. We are
explaining the format, because it will be helpful for you if you want to write a short file by hand to run, to verify
if your program works.
Style Guidelines and Grading
A large part of your grade will come from appropriately utilizing arrays and linked lists to implement your
ArrayStack.java and LinkedStack.java classes. There will be significant deductions if you use Java
collections to implement these classes. Redundancy is another major grading focus; some methods are similar
in behavior or based off of each other’s behavior. You should avoid repeated logic as much as possible. Your
class may have other methods besides those specified, but any other methods you add (except for constructors)
should be private.
You should follow good general style guidelines such as: making fields private and avoiding unnecessary
fields; appropriately using control structures like loops and if/else; properly using indentation, good variable
names and types; and not having any lines of code longer than 100 characters.
Comment your code descriptively in your own words at the top of your class, each method, and on complex
sections of your code. Comments should explain each method’s behavior, parameters, return, and exceptions.
The files provided to you use “doc comments” format used by Javadoc, but you do not have to do this. For
reference, both our ArrayStack.java and LinkedStack.java classes are around 90 lines long including
comments and blank lines.