MC28 Lab 7: CompuDuds in Java (Fall 1996)

Due: December 13, 1996

In this lab, you'll make a few minor alterations to a Java version of the CompuDuds program from our textbook. The point is to become familiar with the mechanics of Java. The program is divided into five classes, each in its own file. The five files are To make a copy of all the files, the simplest approach would be to use the shell to copy the whole directory containing the files. If you in a shell window type
cp -r ~max/www-docs/MC28/labs/lab7/code .
(note that this command ends with a space and then a period), you will get a subdirectory called code containing all the files. Ask for help with this if you need it.

To compile and run the program, you'll need to work in a shell (terminal) window. First you'll need to change directory into the directory where you have the files, e.g.

cd code
Then you need to execute a special command that makes the Java compiler and execution system (``virtual machine'') available to you:
set path=(/usr/java/bin $path)
Now you can compile each of the files; for example, to compile, you'd use the command
You need to do the corresponding command for each of the other four files as well. The most important thing to remember is this: if you make any change to any of the files, you must recompile that particular file before you can test the program, and you must save it out of the editor before you recompile it. In other words, after making any change, you have to save, then compile, then test. When you add a new class, it should go in a file of its own, named after the class. You should then compile that new file as well.

Once you have the five original files compiled, the first thing to do is to test the program out without yet having made any changes. That way you have a baseline for comparison: if it isn't working, you aren't the one who broke it. To run the program, use the command

java CompuDuds

Now you can start making the necessary changes, and test and debug as you go along. You are to do the following:

  1. Modify the ItemList class so that it keeps a running total price as Items are added and deleted, and simply returns that in the totalPrice method, rather than adding up all the prices then. The program's outward behavior should remain unchanged.
  2. Add one or more new kinds of clothing, perhaps to suit your own tastes better.
  3. Add the ability to mark down the price of an Item by 10%, and use it to add the ability to mark down the price of all the Items in an ItemList by 10%. Finally, add a new option to the CompuDuds user interface that discounts everything that has been selected by 10%. Warning: discounting each item by 10% and discounting the total price by 10% may wind up with a total price that doesn't match the sum of the individual prices, due to roundoff.
Course web site:
Instructor: Max Hailperin <>
Lab instructor: David Wolfe <>