Beginner’s Projects
by Roedy Green ©1996-2008 Canadian Mind Products
This essay is about a suggested
student project in
Java programming. This essay gives a rough overview of how it might work. It
does not describe an actual complete program. I have
no source, object,
specifications, file layouts or anything else useful to implementing this
project. Everything I have to say to help you with this project is written below.
I am
not prepared to help you implement it; I have too many other
projects of my own.
I do contract work for a living, which could include writing a program such as
this. However, 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 any way you please.
Goldilocks
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.
Fortune Teller
A simple GUI 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 selling price.
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.
Phone Directory
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 serialisation.
Your gui lets you find objects in various ways, create, delete and update them.
In Words
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.
Roman Numerals
Write a program to convert a long to Roman
numerals. Write another to convert it back. See the InWords
Applet for inspiration.
Tunings
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 catching attention.
Predator Prey
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 )
and finally:
public static Species[] speciesByWeight()
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.
Implement speciesByWeight using a Collections.
sort rather than a TreeSet.
Make sure you include all species, without duplicates.
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.
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