当我从用户那里获取输入时，为什么java向我显示异常？

当我给它一个字符串时，它给出异常，甚至不执行“sum和avg”值。如何更改代码以使其正常工作？如果我有一些错误的概念知识，请帮助我理解这个概念。多谢各位

对于

扫描仪（System.in）

，您不需要

扫描仪#hasNextInt

。此外，您不需要检查，

if（isAnInt）

。相反，您应该放置一个

try-catch

块

您不应关闭

扫描仪（System.in）

；否则，如果不重新启动JVM，就无法再次打开它

当您使用

扫描仪

处理

文件

时，上述两项都是必需的

演示：

public static void inputThenPrintSumAndAverage (){
        Scanner scanner = new Scanner(System.in);
        int count =0;
        int sum =0 ;
        long average = 0;
        boolean isAnInt = scanner.hasNextInt();
        while (true) {
            count++;
            int number = scanner.nextInt();
            if (isAnInt) {
                sum+=number;
                average = Math.round((sum/count));
            } else {
                break;
            }
            scanner.nextLine();
        }
        System.out.println("SUM = "+sum+ " AVG = "+average);
        scanner.close();
    }

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        long average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = Math.round((sum / count));
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        double average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = (double) sum / count;
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

运行示例：

public static void inputThenPrintSumAndAverage (){
        Scanner scanner = new Scanner(System.in);
        int count =0;
        int sum =0 ;
        long average = 0;
        boolean isAnInt = scanner.hasNextInt();
        while (true) {
            count++;
            int number = scanner.nextInt();
            if (isAnInt) {
                sum+=number;
                average = Math.round((sum/count));
            } else {
                break;
            }
            scanner.nextLine();
        }
        System.out.println("SUM = "+sum+ " AVG = "+average);
        scanner.close();
    }

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        long average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = Math.round((sum / count));
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        double average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = (double) sum / count;
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

注意：如果将其声明为

double

并将浮点计算存储到其中而不进行舍入，则可以获得更高的平均精度，例如

2
3
5
8
abc
SUM = 18 AVG = 4

此更改后的示例运行：

public static void inputThenPrintSumAndAverage (){
        Scanner scanner = new Scanner(System.in);
        int count =0;
        int sum =0 ;
        long average = 0;
        boolean isAnInt = scanner.hasNextInt();
        while (true) {
            count++;
            int number = scanner.nextInt();
            if (isAnInt) {
                sum+=number;
                average = Math.round((sum/count));
            } else {
                break;
            }
            scanner.nextLine();
        }
        System.out.println("SUM = "+sum+ " AVG = "+average);
        scanner.close();
    }

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        long average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = Math.round((sum / count));
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        double average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = (double) sum / count;
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

---

理解它也很有用。

您需要在while循环中测试

。hasNextInt

，而不仅仅是在它之前。你需要在把每一个都放进去之前进行测试。您还应该在获取int后立即调用

.nextLine（）

。但它仍然不起作用：（。再次显示异常。