String USER_DIR = "Users"

public void saveUser(User user) {
	File userFile = File(USER_DIR + "\\" + cardnumber + ".txt");
	if (userFile.CanRead()) { }
	try{
		PrintWriter writer = new PrintWriter(new FileOutputStream(USER_DIR + "\\" + cardnumber + ".txt", false), "US-ASCII");
		writer.println(user.cardnumber + "-" + user.password + "-" + user.balance);
		writer.close();
	} catch (IOException e) {
	// do something
	}
}