Java Scanner读取输入报NoSuchElementException异常排查

程序预期实现功能：接收用户输入的两个整数、一个由逗号分隔数字组成的字符串，输出字符串中可同时被这两个整数整除的元素的索引位置。代码运行时在main方法第9行nextInt()调用位置抛出java.util.NoSuchElementException异常。

Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Scanner.java:862)
    at java.util.Scanner.next(Scanner.java:1485)
    at java.util.Scanner.nextInt(Scanner.java:2117)
    at java.util.Scanner.nextInt(Scanner.java:2076)
    at Main.main(Main.java:9)

import java.util.Scanner;
class Main {
    public static void main(String args[]) {
        System.out.println("This program receives an integer vector and checks if it has any element divisible by N and M.");
        System.out.println("Note that you should only enter numbers (do not use any letter or space) otherwise the execution will be terminated.");
        Scanner sc = new Scanner(System.in);
        Scanner scString = new Scanner(System.in);
        System.out.print("Enter an integer value for N: ");
        int n = sc.nextInt();
        System.out.print("Enter an integer value for M: ");
        int m = sc.nextInt();
        //sc. nextLine();
        System.out.println("Please enter your vector elements (comma separated) below.");
        String str = scString.nextLine();
        String[] arrOfStr = str.split(",", 0);
        int i=0;
        for (String a : arrOfStr){
            int x = Integer.parseInt(a);
            if(x%n ==0 && x%m == 0){
                break;
            }
            i=i+1;
        }
        System.out.print("Element "+i+" of the entered vector is divisible by both "+n+" and "+m);
    }
}

• 直接触发异常的原因：代码同时创建了两个绑定System.in标准输入流的Scanner对象。两个独立Scanner会各自维护输入流的读取位置和缓冲区，互相不会同步读取状态，当其中一个Scanner预读取了流中内容后，另一个Scanner尝试读取时会判定流中没有可读取内容，直接抛出NoSuchElementException。
• 代码还存在两个隐藏逻辑缺陷：
  • 调用nextInt()读取整数时，只会读取数字本身，不会消费数字后面输入的换行符，如果不手动调用一次nextLine()消费残留换行，后续读取字符串的操作会直接读到空内容。
  • 原循环逻辑只会返回第一个匹配元素的索引，遇到第一个符合条件的元素就直接跳出循环；如果数组中没有任何元素符合整除条件，最终输出的索引值等于数组长度，属于无效索引，会误导用户。

修复点说明：

• 删除多余的Scanner实例，所有输入操作复用同一个Scanner对象，避免多实例抢占输入流的问题
• 读取完两个整数后，主动调用nextLine()消费残留的换行符
• 优化遍历逻辑，遍历全量数组收集所有符合条件的索引，无匹配时给出明确提示
• 增加trim()处理兼容用户输入时不小心夹带的空格

import java.util.Scanner;
class Main {
    public static void main(String args[]) {
        System.out.println("This program receives an integer vector and checks if it has any element divisible by N and M.");
        System.out.println("Note that you should only enter numbers (do not use any letter or space) otherwise the execution will be terminated.");
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter an integer value for N: ");
        int n = sc.nextInt();
        System.out.print("Enter an integer value for M: ");
        int m = sc.nextInt();
        // 消费读取整数后残留的换行符
        sc.nextLine();
        System.out.println("Please enter your vector elements (comma separated) below.");
        String str = sc.nextLine();
        String[] arrOfStr = str.split(",", 0);
        StringBuilder matchIndexes = new StringBuilder();
        for (int i = 0; i < arrOfStr.length; i++) {
            int x = Integer.parseInt(arrOfStr[i].trim());
            if(x % n == 0 && x % m == 0){
                matchIndexes.append(i).append(" ");
            }
        }
        if (matchIndexes.length() == 0) {
            System.out.printf("No element of the entered vector is divisible by both %d and %d%n", n, m);
        } else {
            System.out.printf("Index of elements divisible by both %d and %d: %s%n", 
                n, m, matchIndexes.toString().trim());
        }
        sc.close();
    }
}

内容的提问来源于stack exchange，提问作者Hash Blog