扫描仪-控制台菜单应用程序上的NoSuchElementException

Question

I'm making some tests with Java to work out a menu-driven console application.

I have this code:

    public class TestClass {

    public static void main(String[] args) {

        int option = 99;

        do{
            System.out.println("1. one");
            System.out.println("2. two");
            System.out.println("3. three");
            System.out.println("0. END");

            Scanner scan = new Scanner(System.in);

            System.out.println("option : ");

            option=Integer.parseInt(scan.next());
            scan.close();
            switch (option) {
                case 0 :
                    System.exit(0);
                    break;
                case 1 :
                    caseOne();
                    break;
                case 2 :
                    caseTwo();
                    break;
                case 3 :
                    caseThree();
                    break;
                default :
                    break;

            }


        } while (option!=0);


    }

    private static void caseOne(){
        System.out.println("Case ONE");
    }

    private static void caseTwo(){
        System.out.println("Case TWO");
    }

    private static void caseThree(){
        System.out.println("Case THREE");
    }
}

When I run it it works pretty well. I choose one option and it prints out "CASE X".

The strange behaviour is when the DO loop starts over. It shows once again the menu but program immediatly terminates showing a NoSuchElementException exception. The strange thing is that it neither waits for me to enter a digit.

If a remove the

scan.close();

statement it do works fine altough compiler warns me of memory leak since scan is never closed.

It behaves very strange because on the "first pass" everything is ok even with te scan.close() but on the "second pass" it crashes even if I'm creating a new Scanner object so I think it shoul at least ask for the input.

I really get confused with this.

Any suggestions?

Answer 1

if you are closing scanner it will close wrapped input stream also so you can close scan after finishing all of your work.

scan.close();

put it after do-while loop.

Answer 2

here the better way you can achieve it

public static void main(String[] args) {

    int option = 99;

    do{
        System.out.println("1. one");
        System.out.println("2. two");
        System.out.println("3. three");
        System.out.println("0. END");

        Scanner scan = new Scanner(System.in);

        System.out.println("option : ");

        option= scan.nextInt();
        switch (option) {
            case 0 :
                System.exit(0);
                break;
            case 1 :
                caseOne();
                break;
            case 2 :
                caseTwo();
                break;
            case 3 :
                caseThree();
                break;
            default :
                scan.close();
                break;

        }


    } while (option!=0);


}