This essay does not describe an existing computer program, just one that should exist. This essay is about a suggested student project in
Java programming. This essay gives a rough overview of how it might work. I have no source, object, specifications, file layouts or anything
else useful to implementing this project.
This project outline is not like the artificial, tidy little problems you are spoon-fed in school, when all the facts you need are included, nothing extraneous is mentioned, the answer is
fully specified, along with hints to nudge you toward a single expected canonical solution. This project is much more like the real world of messy problems where it is up to you to fully the
define the end point, or a series of ever more difficult versions of this project, and research the information yourself to solve them.
Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; or give you any additional materials. I have too many
other projects of my own.
Though I am a programmer, I don’t do people’s homework for them. That just robs them of an education.
You have my full permission to implement this project in any way you please and to keep all the profits from your endeavour.
Please do not email me about this project without reading the disclaimer above.
These projects are simple enough to be completed in an hour or two, and are aimed at rank beginners.
You enter the temperature of some porridge on the console. The program prints out too hot, too cold or just right on
the console. See the file I/O Amanuensis for how to read and write
the console. See the Conversion Amanuensis for how to convert
Strings to ints.
This is a deceptively simple program that ensures you understand many basics.
Sieve of Eratosthenes
This is a way of finding prime numbers by crossing every second number off a list, then every 3rd, then every 5th.
You can do it most efficiently with a BitSet, or you might use an array of booleans. See prime numbers.
A simple GUI (Graphic User Interface) with a button. When you press it, the program displays one of a number of preselected
fortunes. See random numbers.
Sales Tax Calculator
A simple GUI. You enter an amount, and hit a button, and it display the tax and total price.
Then do a reverse tax calculator for a retailer to use. You enter the desired final price, and it calculates the
Simple Time and Billing Calculator
You enter data, perhaps using a CSV file of start time, stop time.
You compute the total hours worked and multiply it by the hourly rate. Once you get that, going add features like
accumulating hours by billing category. Provide a daily breakdown by billing category. Then allow breakdowns by
customer. Don’t forget to deal with the problem of people working over midnight. If you want get really fancy,
deal with daylight savings.
Do a phone directory, email list, password list, etc. Each entry is an object in a Collection that you read/write as a whole at start up and shutdown using serialization. Your gui lets you find objects in various ways, create, delete and
See the InWords Applet. It converts numbers to their equivalent
words, e.g. 123 become one hundred twenty-three in 26 different languages. Add some more languages.
Write a program to convert a long to Roman
numerals. Write another to convert it back. See the InWords
Applet for inspiration.
Look at the sound entry for how you can mathematically define sound
files. Western music is based on a 12 tone scale. Each note of the octave is the 12th root of 2 higher. Major and
minor scales pick a set of 8 of the 12 tones.
In theory you could create scales based on any other number, particularly ones with lots of divisors, e. g. 8 or
16 or 24. I would be curious to hear some scales, even ones of a prime number like 13. I would also be curious to see
what appegios, chords etc. are possible. It would be interesting to see if it is possible to transpose the music of
say Bach into a new scale and see what it sounds like.
If it turns out any of these sounds are in the least pleasant, you should be able to sell them to advertisers for
This exercise teaches basic Collections and generics. Pick an ecosystem. Create a set of Species objects that contain
some facts about each species such as name and average adult weight in k.g. Now accept facts about predator and prey
relationship encoded with a method:
public static void eats( String
predator, String prey );
There should be a method:
public static Species whoEats( String prey )
and there should be a method:
public static Species whoIsEatenBy( String predator )
Implement the predator->prey and prey->predator lookups with one-to-many mappings using a HashMap keyed by species name whose value is an ArrayList of Species that you maintain in sorted order by species name. When you insert, use Collections. binarySearch to find the new insertion point.
public static Species speciesByWeight()
Implement speciesByWeight using a Collections. sort rather than a TreeSet. Make sure you include all species, without
For bonus points, implement:
public staticSpecies whoIsIndirectlyEatenBy( String predator )
Watch out for endless recursion.
Note that I have not told you all the pieces you will need to create to solve the puzzle. I am not totally spoon
feeding you in this exercise.