public static void save(List<User> userList) throws IOException{
		File mfile = new File("user.dat");
		if(!mfile.exists()) mfile.createNewFile();
		ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(mfile));
		for(Iterator<User> it=userList.iterator();it.hasNext();)
			oos.writeObject(it.next());
		oos.flush();
		oos.close();
	}