Java中线程“main”java.util.NoSuchElementException中的异常

Question

this error seems to be a very common issue. I've looked up on other Stack Overflow posts that ask about this and tried to implement their solutions, but I'm still getting the same error. The complete error is:

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 src.file.main(file.java:29)

I'm sure there's something really simple I'm missing, but I can't quite find it as when I read through my code, the logic seems good. This is my file:

public class file {
    
    public static void main(String[] args) throws IOException {

        int choice = 0;

        while(choice != 3) {

            System.out.println("1. enter info \n2. print info \n3.exit");

            Scanner myVal = new Scanner(System.in);

            System.out.println("Enter a choice: ");
            choice = myVal.nextInt(); //Line 29

            if(choice == 1) {
                enterInfo();
            }
            else if(choice == 2) {
                print();
            }
            else if(choice == 3) {
                System.exit(0);
            }
        }
    }

    static ArrayList<newType> studInfo = new ArrayList<src.newType>();

    static void enterInfo() {

        Scanner keyboard = new Scanner(System.in);

            System.out.println("Enter the information (Program year average lastname): ");
            String info = keyboard.nextLine().trim();
            if(info.isEmpty()) {
                System.out.println("Error, no input was made.");
                keyboard.close();
                return;
            }
            String[] tokens = info.split(" ");
            int size = tokens.length;
            String prgm = tokens[0];
            int yr = Integer.parseInt(tokens[1]);

            String lastname = tokens[3];
            Double avg = Double.parseDouble(tokens[2]);
            newType inf = new newType(prgm, yr, avg, lastname);
            studInfo.add(inf);
            System.out.println("Information added.");
            keyboard.close();
        return;
    }

Example input: math 5 76 Smith, this information is added to the arraylist of type newType where it can be printed, or another profile can be added.

The program compiles without errors or warnings, and I can successfully run the program. When I choose option 1, I enter all the information, in the correct format, to which I get the information added message, signaling it was a successful process. After this message, the exception appears. This leads me to believe the error doesn't actually lie within my enterInfo function, as I first thought, but rather when it reaches line 29 for the second time. I don't know how to fix this error, could anyone help? Thanks in advance!

Answer 1

Apart from the mistakes done in using Scanner, the standards followed in java is also missing.

1. Classname should start with caps (file should be as File, same with newType as well. It should be NewType)
2. If you are naming any class then it should be a noun and so should be named as per the goal to be achieved in the program such as AddingNumbers, ReverseNumbers.

Pls refer here why we shouldn't use multiple scanner in a program : Why does closing a scanner seem to break new scanners?

I have made few changes in your code.Hope this works !!!

// modified code

    public class File {
        
        static Scanner myVal = new Scanner(System.in);   // Use this scanner throughout the program
        static ArrayList<newType> studInfo = new ArrayList<src.newType>();
    
        public static void main(String[] args) throws IOException {
    
            int choice = 0;
    
            while (choice != 3) {
    
                System.out.println("1. enter info \n2. print info \n3.exit");
    
                System.out.println("Enter a choice: ");
                choice = myVal.nextInt(); // Line 29
    
                if (choice == 1) {
                    enterInfo();
                } else if (choice == 2) {
                    // print();
                } else if (choice == 3) {
                    System.exit(0);
                }
                
            }
            myVal.close();    // Can be closed once the need is over.
        }           
    
        static void enterInfo() {
    
    //      Scanner keyboard = new Scanner(System.in);    No need of multiple scanners.
    
            System.out.println("Enter the information (Program year average lastname): ");
            String info = myVal.nextLine().trim();
            if (info.isEmpty()) {
                System.out.println("Error, no input was made.");
    //          keyboard.close();
                return;
            }
            String[] tokens = info.split(" ");
            int size = tokens.length;
            String prgm = tokens[0];
            int yr = Integer.parseInt(tokens[1]);
    
            String lastname = tokens[3];
            Double avg = Double.parseDouble(tokens[2]);
             newType inf = new newType(prgm, yr, avg, lastname);
             studInfo.add(inf);
            System.out.println("Information added.");
    //      keyboard.close();
            return;
        }
    }