扫描仪错误：未找到任何行

Question

我收到以下错误

Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Unknown Source)
at task1.ControlApplication2.uQueue(ControlApplication2.java:59)
at task1.ControlApplication2.main(ControlApplication2.java:20)

错误出现在较大的程序中，在第一次使用扫描程序后，调用一个方法并返回循环重新运行。只有在事先几乎立即返回一个方法之后才会发生这种情况。

public static void operations(PriorityQueueADT<String> pQueue) {
    Scanner userInput2 = new Scanner(System.in);
    boolean exit = false;
    do {
        try {
            System.out.println("Which operation would you like to perform?");
            System.out.println("1) - Enqueue");
            System.out.println("2) - Dequeue");
            System.out.println("3) - Get the item of the higest priority");
            System.out.println("4) - Check Queue Size");
            System.out.println("5) - Check if empty");
            System.out.println("6) - Exit to Menu");
            String A = userInput2.nextLine();
            int option = Integer.parseInt(A);//Line 59
            switch (option) {
                case 1: inputChoice(pQueue);
                        break;
                case 2: System.out.println("The item removed is: "+pQueue.dequeue());
                        break;
                case 3: System.out.println("The highest priority item is: "+pQueue.getHighest());
                        break;
                case 4: System.out.println("The queue size is: "+pQueue.size());
                        break;
                case 5: System.out.println("The queue is: "+((pQueue.isEmpty())? "Empty" : "Not Empty"));
                        break;
                case 6: exit = true;
                        break;
                default: System.out.println("You made an invalid choice, please try again.");
            }
        }
        catch (EmptyQueueException e) {
            System.out.println("The queue is empty");
        }
    } while (exit != true);
    userInput2.close();
    return;

}


public static void inputChoice(PriorityQueueADT<String> pQueue) {
    Scanner userInput3 = new Scanner(System.in);
    System.out.print("Would you like to enter the details from a file (Y/N)");
    String f = userInput3.nextLine();
    boolean file = (((f.equals("Y")) || (f.equals("y"))) ? true : false);
    if (file) {
        if (fileInput(pQueue)) {}
        else {
            System.out.println("Reading from the file failed. Please enter the data manually");
            manInput(pQueue);
        }
    } else manInput(pQueue);
    userInput3.close();
}

public static boolean fileInput(PriorityQueueADT<String> pQueue) {
    Scanner n = new Scanner(System.in);
    boolean exit = false;
    do {
        System.out.print("Please enter the name of the file to be read from: ");
        String name = n.nextLine();
        try {
            File file = new File(name);
            Scanner fr = new Scanner(file);
            while (fr.hasNextLine()){
                String line = fr.nextLine();
                String[] element = line.split(" ");
                if (element.length != 2) throw new InputMismatchException();
                pQueue.enqueue(element[0], Integer.parseInt(element[1]));
            }
            fr.close();
            exit = true;
        }
        catch (FileNotFoundException e) {
            System.out.println("The file could not be found"+name);
            System.out.println("Please enter a new file name");
        }
        catch (InputMismatchException f)    {
            System.out.println("The file is incomplete or corrupted");
            n.close();
            return false;
        }
    } while (exit !=true);
    n.close();
    return true;
}   

public static void manInput(PriorityQueueADT<String> pQueue) {
    Scanner userInput4 = new Scanner(System.in);
    boolean exit = false;
    do {
        System.out.print("Would you like to add an item? (y/n)");
        if (userInput4.nextLine().equals("y") || userInput4.nextLine().equals("Y")) {
            System.out.print("Please enter the item");
            String item = userInput4.nextLine();
            System.out.print("Please enter the priority");
            int priority = Integer.parseInt(userInput4.nextLine());
            pQueue.enqueue(item, priority);
        } else exit = true;
    } while (exit == false);
    userInput4.close();

}

执行输入选择后，它是后续的子方法，循环返回到开头，userInput2.nextLine()出现错误，我仍然无法解释。当我选择从操作方法返回main方法时，会出现相同的错误。

`Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Unknown Source)
at task1.ControlApplication2.main(ControlApplication2.java:18)`



`public static void main(String[] args) {
    Scanner userInput1 = new Scanner(System.in);
    boolean exit = false;
    do {
        System.out.println("Please select the implementation of" +
            "the Priority Queue which you would like to use");
        System.out.println("1) - Unsorted Priority Queue");
        System.out.println("2) - Sorted Priority Queue");
        System.out.println("3) - Sorted Queue of Queues");
        System.out.println("4) - Quit");
        int option = Integer.parseInt(userInput1.nextLine());//Line 18
        switch (option) {
            case 1: uQueue();
                    break;
            case 2: sQueue();
                    break;
            case 3: qQueue();
                    break;
            case 4: exit = true;
                    break;
            default: System.out.println("You made an invalid choice, please try again.");
        }
        } while (exit != true);`

在我尝试输入之前它会这样做。