如何使用 Java Scanner 获取整数输入？ NoSuchElementException

Question

所以我一直在寻找一段时间来了解如何使用扫描仪来获取用户的输入。发生的情况是我在第一个扫描仪之后进入了一个无限循环。我尝试将第二个扫描仪的名称更改为读取而不是读取，但这并没有改变任何内容。在我关闭以尝试解决问题之前，我将 in.nextLine() 放在第一个扫描仪实例的末尾，但这似乎不起作用。不太清楚为什么会这样。

`   private int compPlayInput(){
        int comps = -1; // Initialize 

        Scanner in = new Scanner(System.in); // Start Scanner

        //While the user input isn't between 0 and 2
        while ((comps<0) || (comps>2)){
            System.out.println("Turn: " + turnCount);
            System.out.print("How many computer controlled players will there be: ");
            //did the user input an integer?
            if (in.hasNextInt()){
                comps=in.nextInt();//change comps variable to the user's input
            }
            //The user hasn't entered an integer
            else {
                System.out.println("\n\n** ERROR: Enter an integer x that satisfies 0 <= x <= 2 **\n");
            }
        }
        in.nextLine(); //It seems like this is supposed to fix it, but it doesn't.
        in.close(); // close scanner
        return comps;
    }

    /**
     * Gets a player's guess
     * @return the player's guess (int) between 0 and 4 inclusively
     */
    private int getPlayerGuess(){
        int guess = -1; //initialize
        Scanner in = new Scanner(System.in); //start scanner

        //While the user doesn't input an int between 0 and 4
        while ((guess<0) || (guess>4)){
            System.out.println("Turn: " + turnCount);
            System.out.print("What is your guess: ");
            //If the user input an integer
            if (in.hasNextInt()){
                //make guess = to next int
                guess=in.nextInt();
            }
            else {
                System.out.println("\n\n** ERROR: Enter an integer x that satisfies 0 <= x <= 4 **\n");
            }
        }

        in.close(); // close scanner
        return guess; //return guess
    }`

这是eclipse中的输出：

    Turn: 0
How many computer controlled players will there be: 1
Turn: 1
What is your guess: 

** ERROR: Enter an integer x that satisfies 0 <= x <= 4 **

Turn: 1
What is your guess: 

** ERROR: Enter an integer x that satisfies 0 <= x <= 4 **
...

不允许用户像询问有多少计算机玩家时那样输入猜测。我不知道该如何解决这个问题。

我将 in.next() 放入 else 语句中，但似乎我遇到了错误，因为没有任何内容可供扫描仪读取。我得到的新输出是

回合：0 将有多少计算机控制的玩家：1 回合：1 你的猜测是什么：

** 错误：输入一个满足 0 的整数 x

线程“main”中的异常 java.util.NoSuchElementException at java.util.Scanner.throwFor(Unknown Source) at java.util.Scanner.next（未知来源）在 HW2TaylorZacharyGame.getPlayerGuess(HW2TaylorZacharyGame.java:114) 在 HW2TaylorZacharyGame.turn(HW2TaylorZacharyGame.java:52) 在 HW2TaylorZachary.main(HW2TaylorZachary.java:15)

Answer 1

您需要在else 中使用非int。类似的，

else {
   System.out.printf("ERROR: Enter an integer x that satisfies 0 <= x <= 2: %s "
       + "does not qualify%n", input.nextLine());

}

Answer 2

试试 in.next() 而不是 in.nextLine();并将其放在您的 else 语句中

Answer 3

我发现了我的问题。似乎扫描仪不喜欢在单个类文件中被调用两次，所以我的解决方案是简单地创建一个新的 Scanner 对象，我将在其中放置对象的私有变量。 所以是这样的：

public class HW2TaylorZacharyGame {

    private HW2TaylorZacharyPlayer player1 = new HW2TaylorZacharyPlayer();
    private HW2TaylorZacharyPlayer player2 = new HW2TaylorZacharyPlayer();
    private int winner = 0;
    private int turnCount = 0;
    Scanner in = new Scanner(System.in); // Start Scanner

非常简单的解决方案，解决了一个让我非常心痛的问题。但请注意，在接受用户的任何输入后，我也输入了in.nextLine()。对于有同样问题的其他人来说，这两件事是我认为使用 Scanner 的最佳方式。不过我也从来没有关闭过 Scanner，所以不幸的是它有点缺点。