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Thread: java.util.NoSuchElementException error

  1. #1
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    Default java.util.NoSuchElementException error

    I have this output :

    [1, 2, 3, 4, 5, 6, 7, 8]
    Enter a number : 4
    3
    Enter a number : Exception in thread "main" java.util.NoSuchElementException
            at java.base/java.util.Scanner.throwFor(Scanner.java:937)
            at java.base/java.util.Scanner.next(Scanner.java:1594)
            at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
            at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
            at NumberElementsSubArray.main(NumberElementsSubArray.java:36)

    This is a portion of my code where I think the problem comes from :

    while (true) {
                try (Scanner input = new Scanner(System.in)) {
                    System.out.print("Enter a number : ");
                    int userInput = input.nextInt();
                    if (userInput == 0)
     
                        break;
                    if (userInput != 0)
                        System.out.println(getNumberElementSubArray(userInput, numbers)); // print the number of elements
                                                                                          // of
                                                                                          // subArray
                }
            }

    Can you explain me this error? And how to fix it?
    It is weird because earlier after a lot of test case I didn't have any issue & it did run for more than 2 user input. Now this comes up right after one user input.

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: java.util.NoSuchElementException error

    One problem I see is that a new Scanner object is created each time the loop iterates. Using a try with resources closes the System.in at the end of the containing block. System.in can only be closed ONE time in a program's execution. Trying to use it a second time causes the problem.
    Move the statement that creates the new Scanner with System.in outside of the while loop.
    If you don't understand my answer, don't ignore it, ask a question.

  3. The Following User Says Thank You to Norm For This Useful Post:

    siid14 (December 24th, 2022)

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    Default Re: java.util.NoSuchElementException error

    Indeed. It worked. I put Scanner object out of the loop and put a input.close; instead of using try resource.

    --- Update ---

    so @Norm -- what is the issue when "a new Scanner object is created each time the loop iterates" ?

    (I did understand the issue about the use of try with resources)

  5. #4
    Super Moderator Norm's Avatar
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    Default Re: java.util.NoSuchElementException error

    what is the issue ...
    The issue is with closing System.in. It can only be closed one time in a program.
    I think that once it is closed, it can never be opened again in the same program.
    If you don't understand my answer, don't ignore it, ask a question.

  6. The Following User Says Thank You to Norm For This Useful Post:

    siid14 (December 24th, 2022)

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