(FR)
Ce code semble totalement inoffensif, mais peut causer des erreurs sous certaines circonstances.
Pouvez-vous détecter le problème ?

(EN)
This code may seem harmless, but will cause serious problems in certain circumstances.
Can you spot the problem ?

public class Quiz42 {
 
	public static void main(String[] args) {
		new Quiz42();
	}
 
	private static final int MAX_STRING_LENGTH = 6;
	private Map<Integer, String> db = new HashMap<Integer, String>();
	private int nextId = 0;
 
	public Quiz42() {
		// Introductory text
		Console console = System.console();
		if (console==null) {
			System.out.println("Don't cheat in Eclipse :)");
			System.exit(0);
		}
		console.printf(
			"FakeDB 1.0%n"+
			"'exit': exits FakeDB.%n" +
			"'db' : dumps the DB content.%n"+
			"Words are limited to %d characters.%n%n> ",MAX_STRING_LENGTH);
 
		// Read - Eval loop
		String s = null;
		while ((s = console.readLine()) != null) {
			if ("exit".equals(s)) {
				break;
			}
			if ("db".equals(s)) {
				console.printf("DB content : %s%n",db);
				continue;
			}
 
			// Check DB constraints client-side, then save the user's string.
			if (s.length() > MAX_STRING_LENGTH) {
				console.printf("String too long, please enter another one.%n");
				continue;
			}
			persistInDatabase(s.toUpperCase());
			console.printf("Saved '%s'.%n> ",s);
		}
	}
 
	private void persistInDatabase(String s) {
		// Simulate a database constraint
		if (s.length() > MAX_STRING_LENGTH) {
			throw new IllegalArgumentException("DATA TOO LARGE");
		}
		db.put(nextId++, s);
	}
 
}

I'm in the process of learning scales, modes and chords for the guitar, but these aren't easy to remember. Being a developer, I thought I could write a small program to help me understand how they are built, and where I can find the related notes on the guitar neck.
So I spent a couple of hours on it tonight (mainly to find documentation on music theory) and here it is : a small companion program that can calculate and display any chord in any mode and key.

The API is very compact and ultra-easy to understand :
(A "Scale" is basically a collection of Notes. It is used to contain notes for whole Scales, Chords, etc.)

Scale scale = Scale.of(Note.C);
System.out.println("Scale of C : " + scale);
 
Scale mode = Mode.IONIAN.of(scale);
System.out.println("Scale of C in "+Mode.IONIAN+" mode : " + mode);
 
Scale chord = Chord.major(mode);
System.out.println("Major chord : " + chord);
 
Guitar.display(chord, Guitar.STANDART_TUNING, 12); // 12 frets

And here is the result :

Scale of C : [C, C#, D, D#, E, F, F#, G, G#, A, A#, B]
Scale of C in IONIAN mode : [C, D, E, F, G, A, B]
Major chord : [C, E, G]
                        3             5             7             9                    12  
--E --||------|------|--G --|------|------|------|------|--C --|------|------|------|--E --|
------||--C --|------|------|------|--E --|------|------|--G --|------|------|------|------|
--G --||------|------|------|------|--C --|------|------|------|--E --|------|------|--G --|
------||------|--E --|------|------|--G --|------|------|------|------|--C --|------|------|
------||------|------|--C --|------|------|------|--E --|------|------|--G --|------|------|
--E --||------|------|--G --|------|------|------|------|--C --|------|------|------|--E --|

The source code is available for download just below.
This ain't rocket science but hey, I thought It might be cool to share it with you :)
Comments and suggestions welcome !