java - 扫描仪 : Exception in thread "main" java. util.NoSuchElementException

Question

我正在尝试创建一个实用程序类，以使用java.util.Scanner从标准控制台获取输入

package dbasics;

import java.util.*;


public class Utils {

    public static int getNumericInput() {
        System.out.println("Enter a integer ");
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        scanner.close();
        return n;
    }

    public static int[] getNumericArrayInput(int n) {
        //System.out.println("Enter "+n+"  integers seperated by a whitespace ");
         int[] numbers = new int[n];
         Scanner scanner = new Scanner(System.in);
         for (int i = 0; i < n; i++) {
                 numbers[i] =scanner.nextInt();
             }

         scanner.close();
         return numbers;
    }

}

在另一个类中调用静态方法时，方法getNumericInput()工作正常，但是以下方法getNumericArrayInput(int n)会导致一个异常(exception)。

package dbasics;

public class Demo {

    public static void main(String[] args) {

        int n = Utils.getNumericInput();
        System.out.println("Number "+n);
        int arr[] = Utils.getNumericArrayInput(n);
        for(int i : arr) {
            System.out.println(i);
        }
    }

}

运行此命令会导致以下异常

Enter a integer 
5
Number 5
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 dbasics.Utils.getNumericArrayInput(Utils.java:21)
    at dbasics.Demo.main(Demo.java:9)

我注意到的有趣的事情是，如果我注释掉第一个输入过程，数组输入就可以正常工作

Answer 1

您正在关闭导致异常的函数中的扫描仪:试试这个:

import java.util.*;


class Utils {

    public static int getNumericInput() {
        System.out.println("Enter a integer ");
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        return n;
    }

    public static int[] getNumericArrayInput(int n) {
         int[] numbers = new int[n];
         Scanner scanner = new Scanner(System.in);
         for (int i = 0; i < n; i++) {
                 numbers[i] =scanner.nextInt();
             }

         scanner.close();
         return numbers;
    }

}
public class cn {

    public static void main(String[] args) {

        int n = Utils.getNumericInput();
        System.out.println("Number "+n);
        try{
        int arr[] = Utils.getNumericArrayInput(n);

        for(int i : arr) {
            System.out.println(i);
        }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        }
    }

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