java - 扫描器在 nextInt 上抛出 NoSuchElementException

Question

逻辑工作正常，但是当 while 循环到达末尾并重新开始时，当它使用此行再次从键盘读取我的下一个选项时 -> option = kb.nextInt(); 。它给了我一个异常，更准确地说是下面这个:

Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at view.ClientFacade.main(ClientFacade.java:18)

下面是我的代码，为什么这个扫描仪会生成这个错误？还有其他方法可以从键盘读取吗？

public class ClientFacade {
    public static Scanner kb = new Scanner(System.in);

    public static void main(String[] args) {
        boolean exit = false;
        int option = 0;
        RegistrationController rc = new RegistrationController();

        while(exit == false){
            System.out.println("Menu:");
            System.out.println("1 - Sign up on service.");

            option = kb.nextInt(); //ERROR ON THIS LINE WHEN IT EXECUTES ON THE SECOND LOOP

            switch(option){

            case 0:{
                exit = true;
                break;
            }
            case 1:{
                rc.userSignUp();
                break;
            }
            default:{
                System.out.println("Invalid option.");
                break;
            }

            }
        }
    }
}

下面的这个方法位于另一个类文件 RegistrationController.java 中，因此它是由上面的 rc 变量实例化的。

public void userSignUp(){
        User usr = new User();
        RegistrationController rc = new RegistrationController();
        String regex = "$(\\w)+(\\,)(\\w)+(\\,)(\\d){2,3}(\\,)[F,M](\\,)(\\w)+(@)(\\w)+(.)(\\w)+((.)(\\w)+)(,)(\\w)+^";
        Scanner sc = new Scanner(System.in);
        System.out.println("Input a single line separated by COMMA,"
                + " the software will validade your entry.\n"
                + "1 - Your First Name, 2 - Your Second Name,"
                + " 3 - Your Age, 4 - Your Gender \n(F or M in UPPER CASE)"
                + " 5 - Your Email, 6 - Your Password:\n");
        String s = sc.nextLine();
        s = s.trim();
        System.out.println("trimmed"); //DEBUG
        String [] k = s.split(",");
        char[] c = k[3].toCharArray();

        if (Pattern.matches(regex, s)){
            usr.setAdmLevel(0);
            usr.setName(k[0]+" "+k[1]);
            usr.setAge(Integer.parseInt(k[2]));
            usr.setGender(c[0]);
            usr.setEmail(k[4]);
            usr.setPassword(k[5]);
            if (rc.registerUser(usr) != 0){
                System.out.println("Your are signed up! Your ID: "+usr.getId());
            }else {
                System.out.println("A problem ocurred, not registered.");
            }
        }else{
            System.out.println("Wrong input pattern, try again.");
        }
        sc.close();
    }

Answer 1

当您调用 sc.close() 时，它会关闭您的基础流，即 System.in；关闭 System.in 后，将其恢复的唯一方法是重新启动程序。

根据 close() Javadoc，

If this scanner has not yet been closed then if its underlying readable also implements the Closeable interface then the readable's close method will be invoked