private static void init() throws FileNotFoundException, IOException {
		File file = new File("data.gz");
		if (WRITE_MODE) {
			if (file.exists()) // Let's make it hard to overwrite the data.
				throw new RuntimeException("Please delete "
						+ file.getAbsolutePath());
			os = new ObjectOutputStream(new GZIPOutputStream(
					new FileOutputStream(file)));
		} else
			is = new ObjectInputStream(new GZIPInputStream(new FileInputStream(
					file)));
	}