NoSuchElementException - 完全无法修复

问：

我正忙于开发一个相对简单的程序。

该程序涉及使用主菜单，该菜单由名为“mainMenu（）”的方法创建和显示;其代码包含在我的“Main”类中（本身包含 main（） 方法）。此方法通过扫描程序接受输入，并根据用户输入的选项调用相应的方法。

其中一个选项是“quit”（选项 q），如果扫描程序选择 Q 作为用户输入，mainMenu（） 方法就会调用一个名为“quitProgram（）”的相应方法。

quitProgram（） 方法还使用一个 scanner 对象（尽管与 mainMenu（） 方法使用的对象不同）。这样做是因为，通过提示，询问用户：“你想退出这个程序吗？是/否？“，该问题的输入被扫描仪捕获。

希望您正在关注所有这些......

关于quitProgram（）方法，我遇到了问题。具体来说，如果输入了“n”或“no”，则会引发 NonSuchElementException。如果输入“yes”或“y”，则代码将完美执行。

输入“no”或“n”应该（如果我可以修复这个错误），再次调用mainMenu（）方法并将用户带回主菜单，除非它没有。如前所述，它会引发 NoSuchElementException。

我希望通过向您展示这两种方法的代码，您可以告诉我如何解决问题。

mainMenu（） 方法：

     public static void mainMenu() {
         
         Scanner sc = new Scanner(System.in);   // Create a Scanner object. 
         
         boolean userInputCorrect = false;      // initialise boolean flag.
         
         String choice;                         // initialise String for holding user input.                    
         
        // start do ... while loop
        do {
            
                    // ask user to input their choice of option:
                    System.out.println("*********************************************************************************************************" + "\r"
                    + "PROGRAMMING ASSIGNMENT:" + "\r"
                    + "----------------------" + "\r\n" + "\r\n"
                    + "STUDENT ID: 2136272" + "\r"
                    + "NAME: William van Zwanenberg" + "\r"
                    + "MODULE NAME: LAAM39 - Introduction to Programming" + "\r"
                    + "MODULE TUTOR: Dr. Livio Robaldo" + "\r\n" + "\r\n"
                    + "DESCRIPTION:" + "\r\n"
                    + "------------" + "\r\n"
                    + "Program to manage a desk and the items on it as per assignment for LAAM39 - Intro to Programming Module." + "\r\n"  + "\r\n" 
                    + "ASSIGNMENT TITLE:"  + "\r\n"
                    + "-----------------" + "\r\n"
                    + "Implement a Java class \"Desk\" with suitable attributes and methods to put and remove items on the desk " + "\r"
                    + "and, optionally, other methods to move the desk, buy&sell the desk, etc. Items are instances of another " + "\r"
                    + "Java class \"Item\". By using inheritance among classes, you can then optionally distinguish different " + "\r"
                    + "kinds of items (notebooks, pens, pencils, etc.)" + "\r\n" + "\r\n" 
                    + "**********************************************************************************************************"  + "\r\n" + "\r\n" 
                    + "Please enter the corresponding number for the specific action you'd like the program to perfom." + "\r\n" + "\r\n"
                    + "YOUR CHOICE OF OPTIONS ARE:" + "\r\n" + "\r\n"
                    + "(1) Create a new desk object;" + "\r\n"
                    + "(2) Change the properties of an existing desk object;" + "\r\n"
                    + "(3) Add a new stationery item to the desk;" + "\r\n"
                    + "(4) Remove an existing stationery item from the desk;" + "\r\n"
                    + "(5) Change the properties of an existing stationery item;" + "\r\n"
                    + "(6) Move the desk" + "\r\n"
                    + "(7) Sell the desk and assign it a new owner." + "\r\n" + "\r\n"
                    + "To quit the program, type \"q\"." + "\r\n");
                 
                 choice = sc.nextLine();
             
                 // now instigate switch
                 switch (choice.toLowerCase()) {
                        case "1":
                        case "2":
                        case "3":
                        case "4":
                        case "5":
                        case "6":
                        case "7":
                        case "q":
                        case "quit":
                        case "Quit":
                        case "QUIT":
                    
                        // change flag becuase user will have made a valid choice
                            userInputCorrect = true;
                    
                        // BREAK OUT OF SWITCH
                        break;
                    
                        default:
                    
                            // clear console
                            clearConsole();
                            
                            // include countdown delay. Here the for loop merely interates. Nothing more.
                            for (double i = 1; i<=1000000; i=i+ .01);  
                
                            // print out error msg:
                            System.out.println("\r\n" + "ERROR! " + "\""+ choice +"\"" + " is not a valid choice. Please try again." + "\r\n");
                    
                            
                            
            
                 } // end of switch
                 
            
         // end the do .. while loop     
         } while (!userInputCorrect);
             
                // close the Scanner class as we no longer need it. 
                sc.close();
                
                // flush the content of the buffer to the output stream
                System.out.flush();
                                     
              /*
               * If 'q', Q', 'quit', 'Quit', or 'QUIT' is inputed, then quit the program.
               * NB: For some reason (UNKNOWN) despite using the 'toLowerCase()' 
               * String method, the code does not execute
               * correctly if "Q" is entered by the user. Therefore, the
               * "||" Comparator has been used alongisde the 'equalsIgnoreCase' method in 
               * to avoid producing an error and forcing the program to quit. This is 
               * obviously a workaround.
               */
             if (choice.equalsIgnoreCase("Q") || choice.equalsIgnoreCase("QUIT")) {
                 
                 // call quit program method:
                 quitProgram();
                 
             } else {
                 
                 clearConsole();
                 
                 System.out.println("\r\n" + "You selected: " + choice);
                 
                 // now include switch to pass flow to corresponding classes/methods/ depending on the user's selection.
                 
             }
         
     } // end of mainMenu() method.

这是 quitProgram（） 方法的代码：

public static void quitProgram() {
        
        //clear console:
        clearConsole();
        
        // create a new scanner:
        Scanner scan = new Scanner(System.in);
        
        // ask user if thwy wish to quit:
        System.out.println("Do you want to quit this program? Yes/no?");
            
        // assign user input to a new String: 
        String options = scan.nextLine();
            
        // initialise boolean for use in while loop:
        boolean matchFound = false;
        
        String regex =  "yes|no|y|n";  // searches for "yes", "no", "y", and "n" - CASE INSENSITIVE.
        
        while (matchFound == false) {
            
            Pattern pt = Pattern.compile(regex , Pattern.CASE_INSENSITIVE);  
            Matcher mt = pt.matcher(options);
                                
            if (mt.find() == true) {
                    
                // match found, therefore set the boolean to true:
                matchFound = true;
                    
            } else {
                    
                // print out error msg:
                System.out.println("Invalid entry. Please try again. Do you want to quit this program? Yes/no?");
                    
                // get next entry:
                options = scan.next();
            }
            
        } // end while loop.
        
        // NOW ACT DEPENDING ON SPECIFIC CHOICE:
        
        // close the scanner:
        scan.close();
        
        // flush the content of the buffer to the output stream
        System.out.flush();
        
        if (options.equalsIgnoreCase("yes") || options.equalsIgnoreCase("y")) {
            
            // clear the Console 
             clearConsole();
             
             // print out goodbye message:
             System.out.println("GOODBYE :-) This program will now quit");
             
             // wait a short while ...
             for (double i = 1; i<=10000000; i=i+ .01);  // include countdown delay. Here, the for loop merely interates. Nothing more.
             
             // clear console again:
             clearConsole();
             
             // now definitely quit.
             System.exit(0);
            
        } else if(options.equalsIgnoreCase("no") || options.equalsIgnoreCase("n")) {
            
            // clear console:
             clearConsole();
             
            // flush the content of the buffer to the output stream
            System.out.flush();
            
             // print out take to main menu message:
             System.out.println("OK. Returning you to the main menu ...");
             
            // clear console again:
             clearConsole();
             
            // wait a short while ...
             for (double i = 1; i<=100000; i=i+ .01);  // include countdown delay. Here, the for loop merely interates. Nothing more.
            
            // return to the main menu.
            mainMenu();
            
        }
        
    } // end of quitProgram() method.