什么是java.util.NoSuchElementException？如何解决？ [英] What is java.util.NoSuchElementException and how do i fix it?

问题描述

我正在尝试对战舰游戏进行编程，并在提示用户输入其猜测坐标的时候遇到了此错误：

I was trying to program a game of battleship and i ran into this error at the point where the user was prompted to enter their guess coordinates:

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 game.User.takeTurn(User.java:121)
        at game.Game.main(Game.java:61)

这里是发生错误的User.takeTurn（）方法：

Here is the method User.takeTurn() where the error occured:

    static void takeTurn() {
           System.out.println("Yout turn!");
           System.out.println("Enter your x guess:");
           Scanner scanInput = new Scanner(System.in);
           int x;
           x = scanInput.nextInt();
           System.out.println("You entered "+ x + ", Now enter your y     coord:");
           int y;
           y = scanInput.nextInt();
           System.out.println("You entered + " + y);
           if(Board.aiBoard[x][y] == 2) {
               System.out.println("Hit! You got a hit at: " + x + "," + y);
               Board.enemyBoardDisplay[x][y] = 'h';
               Board.aiBoard[x][y] = 3;
           }
           else {
            System.out.println("Miss!");
            Board.enemyBoardDisplay[x][y] = 'x';
            Board.aiBoard[x][y] = 1;
          }

           scanInput.close();
      }

我不确定是否很重要，但我也早先使用了另一台扫描仪在课堂里。如果您需要更多代码来帮助，请告诉我。谢谢！

Im not really sure if it matters or not but i also use another scanner earlier in the class. If you need more code to help just let me know. Thanks!

编辑1：
好​​吧，即使在我执行scanInput.hasNextInt（）之后，它也不起作用。我还放入了else语句，该语句为x提供了一个值，但现在x始终具有else语句提供的值。它甚至要求输入仅默认为该值的输入。但是我不想让它成为默认值，我希望用户选择。

edit 1: Ok, even after I do scanInput.hasNextInt() its not working. I also put in an else statement that gave x a value but now x always has the value that the else statement gives. It dosent even ask for an input it just defaults to that value. But i dont want it to go to a default i want the user to pick.

编辑2：这是我在主存根中调用代码的地方

edit 2: This is where i call the code in my main stub

while (gameOn == true) {
            if (turn == 0) {
                User.takeTurn();
                Board.sunkCheck();
                if (gameOn == false)
                    break;
            }

            else if (turn == 1) {
                Computer.takeTurn();
                Board.sunkCheck();
                if (gameOn == false)
                    break;
            }

这是我在与IM尝试使用的同一班级中较早使用扫描仪的地方立即使用扫描仪：

This is where i use a scanner earlier in the same class as im trying to use the scanner now:

System.out
                .println("\n Please enter the first x value for your ship  (Note, this will be the first point, from this point the \n"
                        + " ship can either go vertically downward or horizontally to the right so please choose the topmost point or leftmost \n"
                        + "point to do this. Also, the board is 10x10 but due to java array indexing the coordinates go x 0-9 y 0-9: ");
        try {
        Scanner coord = new Scanner(System.in);
        userX = coord.nextInt();
        System.out.println("You entered: " + userX);
        System.out.println("Now enter the y coordinate for this point: ");
        userY = coord.nextInt();
        System.out.println("You entered: " + userY);
        System.out
                .println("Please choose the direction of your ship. Enter v for verticle or h for horizontal(case sensitive): ");
        dir = (char) System.in.read();
        coord.close();
        }
        catch(InputMismatchException e) {
            System.out.println("Good job doof, since you tried to troll we did all the values for you!");
            userX = 3;
            userY = 3;
            dir = 'v';
        }

推荐答案

您可能需要先检查 next 元素，然后再将 Scanner 放入 Scanner 中。 code> scanInput.hasNextInt（）。

You might want to check for next element before getting it in Scanner with scanInput.hasNextInt().

已更新：

如果您使用上述 Scanner coord = new Scanner（System.in）; ，然后调用 Scanner scanInput = new Scanner（System.in）; 而不关闭 coord 扫描器，那么您将遇到问题。

If you use the above Scanner coord = new Scanner(System.in); and then call the function with Scanner scanInput = new Scanner(System.in); without closing the coord Scanner, then you will be having issues.

扫描器将继续t o消耗数据流-可能（将）导致
意外的副作用。

Scanners will continue to consume the stream - this may (will) lead to unexpected side-effects.

您可能想关闭使用第一个之前（此处提供更多参考 ）。

You may want to close the first one before using another (here for more ref).

更新：

当您关闭 coord.close（）时，您正在关闭 System.in ，并且当您尝试重新阅读时从它，它将抛出异常。

When you close coord.close() you are closing System.in and when you try to re-read from it, it will throw the exception.

您不必每次都需要重新打开流，而只需创建一次 Scanner ，然后重新使用它。

Instead of re-opening the stream every time you need input you could create your Scanner once and just re-using it.

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