线程java.util.NoSuchElementException中的Java异常

Question

I have a java app source code, and it gets an error same as app that I write code here. both of them get this: " Exception in thread "main" java.util.NoSuchElementException " if I fix this, then I can fix the problem in my primary java app.

When I run this java app, it run once, and when back to do-while loop, it gets error. " Exception in thread "main" java.util.NoSuchElementException "

Code:

public static void main (String args[]) {
    int c=-1;
    Scanner input=new Scanner(System.in);
    do{
        System.out.println("1- Sum");
        System.out.println("2- Sub");
        System.out.print("Enter your selection : > ");
        c=input.nextInt();
        res(c);
    }while(c!=0);
    input.close();
}

public static void res(int c) {
    switch (c) {
    case 1:
        System.out.println("++++++++++");
        sum();
        break;
    case 2:
        System.out.println("----------");
        sub();
        break;

    default:
        break;
    }
}
public static void sum() {
    float a,b,c;
    Scanner in=new Scanner(System.in);
    System.out.println("enter two number :");
    System.out.print("first number : ");
    a=in.nextInt();
    System.out.print("second number : ");
    b=in.nextInt();
    c=a+b;
    System.out.println(a+" + "+b+" = "+c+"   END.");
    in.close();
}
public static void sub() {
    float a,b,c;
    Scanner in=new Scanner(System.in);
    System.out.println("enter two number :");
    System.out.print("first number : ");
    a=in.nextInt();
    System.out.print("second number : ");
    b=in.nextInt();
    c=a-b;
    System.out.println(a+" - "+b+" = "+c+"   END.");
    in.close();
}

Does anyone can help me to fix this?

Answer 1

You are closing the Scanner at the end of sum() and sub() , which you should not be doing. Remove those two statements and the problem should be fixed.

What is happening is that the Scanner#close() method closes the underlying input stream as well, so the next time through the main loop System.in has been closed, causing the exception.

Answer 2

I think that you should open your Scanner once for all

• use it as a private static field,
• initialize it in the start of the main,
• close it at the end,
• call it normaly.

Good luck