Beginner’s Projects
by Roedy Green ©1996-2009 Canadian Mind Products
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. 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 in any way you please and
to keep all the profits from your endeavor.
These projects are simple enough to be completed in an hour or two, and are aimed at rank beginners.
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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