private static void listClassesRec(final File dir, final List<File> files) {
		if (dir.isDirectory()) {
			for (final File subdir : dir.listFiles(new FileFilter() {
				@Override
				public boolean accept(final File file) {
					return file.isDirectory();
				}
			})) {
				listClassesRec(subdir, files);
			}
			for (final File file : dir.listFiles()) {
				if (file.isFile() && file.getAbsolutePath().endsWith(".class")) {
					files.add(file);
				}
			}
		}
	}