Puzzled by bug and bug fix

Newbie & Debugging Questions
#1

I bumped into a strange bug the other day. I found a way to fix it, but I have no idea why it works and I’m wondering if someone can explain it.

Here is the situation. I built a small set of classes to aid in my game development. One class, “SoundFactory”, has only static methods for loading and playing Clips. It also has two static fields for HashMaps. I never intended to create an instance of SoundFactory.

The first game that I wrote with the help of SoundFactory worked fine, but the next one did not. The code simply stopped executing somewhere soon after a call to a SoundFactory static method. Subsequent Game runs always stopped at the same place, until I commented out a few miscellaneous instantiations. Then the code consistently stopped at a different spot. The “stopping spots” always included an instantiation. No errors were thrown. Code just stopped executing.

So why did Game1 work and not Game2? I commented out code until I finally found the difference. Game1 had the following field declaration/assignment:

Color color = Color.BLUE;

When I added this seemingly irrelevant line as a field for Game2, the code ran fine.

Can anyone explain what I was doing wrong? I am guessing that I should abandon the whole static idea, but I am still curious about what the hang-up might be.

I code in 1.4 using Eclipse with my Mac, 10.3.

thanks,

josh

#2

You should post (parts of) your code to get proper help.

#3

Ok, here is a pared down version of Game and SoundFactory. The code hangs in the Game constructor on creating a JFrame. The same hang happened with all sorts of other classes – it doesn’t have anything to do with JFrame. If I do not call the SoundFactory loadClip method, the JFrame is created. Most puzzling is this: when I leave in the call to loadClip, but also create a reference to a static constant, everything works fine??? This only works if a actually assign the field to a static constant: just declaring it doesn’t work.

Any insights would be appreciated.

[quote]public class Game {

//Color x = Color.BLACK;

public Game() {
	File b = new File("resources/Boom.wav");
	SoundFactory.loadClip(b, 3);

	System.out.println("About to create JFrame");
	JFrame jf = new JFrame();
	//following line doesn't happen unless I uncomment Color, above
	System.out.println("Created JFrame");
}

public static void main (String [] args) {
	new Game ();
}

}
[/quote]

[quote]public class SoundFactory {

private static HashMap availableClips;

static {
	availableClips = new HashMap();
}

public static void loadClip (File soundFile, int howManyCopies) {
	try {
		for (int x = 0; x < howManyCopies; x++) {
			InputStream is = new FileInputStream(soundFile);
			loadClip (is, soundFile.getName());
			is.close();
		}
	}
	catch (Exception e) {
		e.printStackTrace();
	}
}

public static void loadClip (InputStream is, String name) {

	if (!availableClips.containsKey(name)) {
		availableClips.put(name, new LinkedList());
	}
	
	List list = (List) availableClips.get(name);

	AudioInputStream audioInputStream = null;
	
	try {
		audioInputStream = AudioSystem.getAudioInputStream(is);
	} catch (UnsupportedAudioFileException e1) {
		e1.printStackTrace();
	} catch (IOException e1) {
		e1.printStackTrace();
	}
	
	AudioFormat	format = audioInputStream.getFormat();
	DataLine.Info info = new DataLine.Info(Clip.class, format);
	Clip clip = null;
	try {
		clip = (Clip) AudioSystem.getLine(info);
		clip.open(audioInputStream);
		list.add(clip);
		
		audioInputStream.close();
	}
	catch (LineUnavailableException e) {
		e.printStackTrace();
	}
	catch (IOException e) {
		e.printStackTrace();
	}
}

}
[/quote]

#4

This really sounds like a race condition as the assignmetn has no effect on the code in question other then chnaging the timing.

Id have to look closer though to determine exactly what is racing…

#5

what is a race condition?

#6

http://java.sun.com/docs/books/tutorial/essential/threads/priority.html its been a while since I read it but I beleave it was in that section, its somewhere in the trail adleast