我得到＆＃34; java.util.NoSuchElementException：找不到行＆＃34;使用Scanner.nextLine（）时

Question

这是主要方法及其类：

import java.util.*;

public class TestWithCLI {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String command = null;
        do {
            System.out.print(">");
            try {
                command = in.nextLine();
                switch (command){
                    case "add user":
                        System.out.println("Enter the email then the password of the user you wish to add:");
                        System.out.println(DatabaseManager.addNewUser(new User(in.nextLine(), in.nextLine(), 0)));
                        break;
                    case "restore":
                        System.out.println(DatabaseManager.restore());
                        break;

                    case "exit":
                        break;

                    default:
                        System.out.println("Please enter a valid command.");
                        break;
                }
            }
            catch (Exception e){
                System.out.println("An error has been thrown.");
                System.out.println(e.getMessage());
                e.printStackTrace();
            }
            System.out.println();
        } while (!command.equals("exit"));
    }
}

这是restore（）方法，它返回一个成功的布尔值：

public static boolean restore() {
        try {
            Scanner in = new Scanner(System.in);
            System.out.print("Are you sure you want to delete the changes made to the database since the last backup? [y/n]\n>");
            if (in.nextLine().equals("y")){
                BufferedReader br = new BufferedReader(new FileReader(backup));
                BufferedWriter bw = new BufferedWriter(new FileWriter(db));
                String line = br.readLine();
                while (line != null){
                    bw.write(line);
                    bw.newLine();
                    line = br.readLine();
                }

            bw.close();
            br.close();
            in.close();
            return true;
        }
        else {
            in.close();
            return false;
        }
    }
    catch (Exception e){
        return false;
    }
}

每当我打电话给DatabaseManager.restore()时，我都会遇到无穷无尽的错误。这是它在无限循环中打印的内容：

>An error has been thrown.
No line found
java.util.NoSuchElementException: No line found
    at java.util.Scanner.nextLine(Unknown Source)
    at database.TestWithCLI.main(TestWithCLI.java:9)

我瞥见了＃34; true＆＃34;在错误向地平线滚动之前，我知道restore（）正确执行，因为确实恢复了数据库文件。 ＆＃34;添加用户＆＃34;命令也很好。