Provided source code:

You will need the following files: DStack.java and Reverse.java

The purpose of this project is to implement a Stack ADT in the two most common ways, an array and a linked list. You will implement stacks for Java double numbers.

Below, see how your Stack implementations can be used to do sound manipulation with .dat files and the provided Reverse.java, namely reversing a sound clip. This process, called "backmasking," was used by musicians including the Beatles, Jimi Hendrix, and Ozzy Ozbourne, although it seems to have fallen out of favor in recent years. Here (Links to an external site.) is a history of this (sometimes controversial!) practice. "But wait," you say, "CS 145 never taught me how to work with music..." Don't worry! All the music-handling parts have been done for you.

The Program

You will write two implementations of the Stack Data Structure that implement the DStack interface. The DStack interface defines a set of methods for your Stack implementations to implement to store Java doubles. See below for a description of this interface and familiarize yourself with the file. You will also need to test your implementations to verify that they work. One way you can start to test them is through the sound manipulation described throughout the writeup. We have provided a class Reverse whose main method reads in a .dat sound file, pushes all the sound values on a stack, then pops them all off and writes them into a new .dat sound file. You can familiarize yourself with the code, but the usage instructions are also described below.

Implementing the Stack ADT

You need to provide two stack implementations, one using an array and one using a linked list. They should be called ArrayStack and ListStack, respectively. They should implement the DStack interface given to you. Once you provide these implementations, Reverse should work and create backward sound files. It should take no more than a page or two of code to provide the implementations. 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. While there are convenient Java library methods for copying arrays, for this assignment, use your own loop to copy array elements manually (so you can "see" the work involved in copying).

Both ArrayStack and ListStack should throw an EmptyStackException if pop() or peek() is called when the stack is empty. To use EmptyStackException, add the following line to your file:

import java.util.EmptyStackException;

The only Java class that you should use to complete the implementations of your stacks is java.util.EmptyStackException. You should also use the length field of an array.

Running Reverse

Here (Links to an external site.) is a historical, useful reference for using the command line.

The Reverse program takes 3 arguments (also known as "command-line arguments"). The first is the word array or list and specifies which implementation to use. The next two are the input and output .dat file names (you need to include the .dat extension). Running the program will depend on your system; from a command line it will look something like:

java Reverse list in.dat out.dat 

In an IDE there is usually a dialog box for setting program parameters which contains a field for the program arguments. (For example, in jGRASP select Build->Run Arguments and a bar will appear at the top of the screen that allows you to type in the arguments.)

To test your program, you will need a .dat file, which you can create from a .wav file as explained in the Digital Sound section. It is also useful to create short .dat files by hand to aid testing.

Testing Your Stack Implementations

You should be using your knowledge of the Stack ADT and writing your own client code to test your implementations.

We have also provided you a client program, Reverse.java, that uses the stack implementations you will write. Getting Reverse.java to run and correctly reverse a sound file is fun and indicates that your stack implementations will compile and run. It does not, however, imply that your stack implementations have been thoroughly tested. Reverse.java just uses your stacks in one particular way: pushing a bunch of elements onto the stack and then popping them all off. There are other ways that someone use your stack implementations and other cases that are not tested by just being able to successfully listen to sound files in reverse.

We will be testing your stack implementations more generally and you should too! We highly suggest creating another small client program of your own to help test other aspects of your code. You also might consider creating some short (e.g., 10 line) .dat files by hand to aid testing. (See the ".dat File Format" section of the write-up below for more information).

Write-Up Questions

Turn in a file README.txt containing answers to the following questions.

How did you test that your stack implementations were correct?

Your array stacks start with a small array and double in size if they become full. For an input file with 1 million lines, where each line will be pushed on the stack, how many times would this resizing occur? What about with 1 billion lines or 1 trillion lines (assuming the computer had enough memory)? Explain your answer.

Suppose that, instead of a DStack interface, you were given a fully-functional FIFO Queue class. 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. Assume your Queue class provides the operations enqueue, dequeue, isEmpty, and size.

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?

What did you enjoy about this assignment? What did you not enjoy? What could you have done better?

What else, if anything, would you would like to include related to this homework?

Turn-in: You should turn in the following files, named as follows:

ArrayStack.java

ListStack.java

ListStackNode.java, the linked-list node for use with your ListStack class. However, you are also free to use an inner class (Links to an external site.) inside ListStack in which case you will not have a separate file.

README.txt, containing answers to the Write-Up Questions.

Do not turn in DStack.java or Reverse.java. You must not change these files. Your stack implementations must work with the code as provided to you.

You may discuss the assignment with others in the class, but your solution must be entirely your own work.

How Digital Sound Works

We will view sound as a continuous function of time from the positive real numbers (time) to the interval [-1.0, 1.0] (amplitude). Since a computer can't "hold" a function defined on the reals, we have to approximate the function. We do this by measuring (or "sampling ") the sound several thousand times per second.

This process is called "Analog to Digital Conversion", or ADC. The number of times per second the sound is sampled is called the sample rate and is measured in Hertz. For example, CDs are recorded at 44100 samples per second, or 44.1kHz. But you don't need to understand ADC for CSE240.

Sox

The only sound file format you need to know about is the .dat format described below. You don't even have to know very much about that either, as we are giving you the code that reads and writes that format. In order to play sounds you produce, you need a way to convert between the .dat format and a format that common media players (Windows Media Player, winamp, RealPlayer, etc.) understand, such as .wav. We will describe one way to do it below; however, you are free to use another converter.

sox is a command-line utility whose name stands for "SOund eXchange". It lets you 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.

Versions of sox are available for Windows, Mac, and Linux. You can download the one you need from here (Links to an external site.) by clicking on the folder for the most recent version (or, really, any version) and then downloading the correct file for your operating system.

The Windows version is also a command-line program and works in the same way as the UNIX version described below. See here (Links to an external site.) for some pointers on using it.

The general strategy for using sox is as follows.

Take a .wav sound file of your choosing (e.g., secret.wav). This sound shouldn't be longer than a few seconds, or your program will run out of memory.

Convert it to a .dat file: ./sox secret.wav secret.dat

To manipulate it with the program you will write: java Reverse list secret.dat secret-revealed.dat

Convert it back to a .wav file: ./sox secret-revealed.dat secret-revealed.wav

Listen to it with your favorite sound player.

That's all there is to it!

The .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. This 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.

 ; Sample Rate 44100 0 0 2.2675737e-05 0 4.5351474e-05 0 6.8027211e-05 0 9.0702948e-05 0 0.00011337868 0 0.00013605442 0 0.00015873016 0 0.00018140590 0 0.00020408163 0 

Here is the same file, a little deeper on:

 0.22693878 -0.0062561035 0.22696145 -0.0043945312 0.22698413 -0.0068664551 0.22700680 -0.0115661620 0.22702948 -0.0145568850 0.22705215 -0.0145416260 0.22707483 -0.0121917720 0.22709751 -0.0123901370 0.22712018 -0.0145416260 0.22714286 -0.0144958500 0.22716553 -0.0147705080 0.22718821 -0.0157012940 0.22721088 -0.0129547120 0.22723356 -0.0127105710 0.22725624 -0.0181579590 0.22727891 -0.0191497800 0.22730159 -0.0145721440 0.22732426 -0.0122375490 0.22734694 -0.0124359130 0.22736961 -0.0108184810 

Note that you shouldn't have to deal much with the .dat file yourself, as the provided Reverse.java does all the work for you. All you have to do is implement the stacks. We are explaining the format because it will be helpful for writing short files by hand for testing purposes.

For this assignment you need to implement an interface, DStack, in two ways. The DStack interface defines a simple stack:

public interface DStack { public boolean isEmpty(); public void push(double d); public double pop(); public double peek(); } 

An actual interface includes comments, including a description of how pop() and peek() should behave if they are called when the stack is empty. To implement this interface, write a class as follows:

public class ArrayStack implements DStack { public ArrayStack() { // Your constructor code } public boolean isEmpty() { // Your isEmpty() code } public void push(double d) { // Your push() code } // continue with the rest of the methods, // along with any fields, etc. } 

The ListStack class should be defined similarly. You should include appropriate comments as needed. In particular, each file should begin with a comment that describes the class in the file, and includes your name and other identifying information.

Acknowledgments

This assignment has been taken and adapted from UW's CSE 373 Data Structures and Algorithms course.