当用户输入是一个小浮动时，扫描器抛出

Question

public static int userNumber(){

        Scanner input = new Scanner(System.in);

        int n = 0;

        while(n <= 0){
            System.out.println("Please enter a positive integer");
            n = input.nextInt();
        }

        return n;

    }

Exception in thread "main" java.util.InputMismatchException
    at java.base/java.util.Scanner.throwFor(Unknown Source)
    at java.base/java.util.Scanner.next(Unknown Source)
    at java.base/java.util.Scanner.nextInt(Unknown Source)
    at java.base/java.util.Scanner.nextInt(Unknown Source)
    at Lab5.userNumber(Lab5.java:22)
    at Lab5.main(Lab5.java:7)

我试着关闭扫描仪，但这也导致了一个错误...有人能帮我弄明白怎么回事吗？我想提示用户输入一个有效的整数，如果输入无效，则继续提示。

谢了！

Answer 1

scanner.nextInt()抛出InputMismatchException如果下一个标记与整数不匹配。

作为一个选项，在扫描输入之前，可以使用scanner.hasnextInt()方法检查输入是否是有效的整数。

示例：

try (Scanner sc = new Scanner(System.in)) {
    String msg = "Please, enter a positive Integer:";
    int n = 0;

    do {
        System.out.println(msg);
        // make the user keep entering the input until it's an Integer
        while (!sc.hasNextInt()) {
            System.out.println(msg);
            sc.next();
        }
        n = sc.nextInt();
    }
    while (n <= 0); // run until the input is a positive Integer

    return n;
}