为什么 try/catch InputMisMatchException 即使我导入 java.util.InputMisMatchException 也不起作用？

Question

我正在尝试编写简单的计算器并实现一些异常。如果客户端尝试输入字母而不是数字，我想捕获异常 InputMisMatchException。我已经导入了 java.util.Input...但是这仍然不起作用，它结束了程序。

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

public class Calculator {
    private static Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        boolean menu = true;
        int choice;
        while (menu) {
            menuCalculator();
            System.out.println();
            System.out.println("Select operation: ");
            choice = sc.nextInt();
            sc.nextLine();
            switch (choice) {
                case 1:
                    try{
                    division();
                    } catch (InputMismatchException e){
                        System.err.println("Wrong input. Please enter valid value(s).");
                    }
                    break;
                case 5:
                    System.out.println("Shutting down calculator");
                    menu = false;
                    break;
            }
        }
    }

    public static void menuCalculator() {

        System.out.println("Press to go: \n 1. to divide \n 2. to multiplicate \n 3. to sum \n 4. to substract \n 5. to quit");
    }

    public static void division() {
        double firstNo;
        double secondNo;
        double result;

            System.out.println("Enter first number:");
            firstNo = sc.nextDouble();
            sc.nextLine();
            System.out.println("Enter second number:");
            secondNo = sc.nextDouble();
            sc.nextLine();
            result = firstNo / secondNo;
            if (secondNo == 0) {
                System.out.println("Cannot divide by 0");
            } else {
                System.out.println(firstNo + " / " + secondNo + " = " + result);
            }
    }
}

Answer 1

异常是由 nextInt 抛出的，但是您对 nextInt 的调用周围没有 try/catch，所以它没有得到抓住。移动 try/catch 块，使 nextInt 调用在其中。（您是处理来自 division 的 nextDouble 的错误，而不是来自 nextInt。）

But：您可以考虑主动调用 hasNextInt，而不是被动地处理异常。两种方法各有利弊。

以下是如何将 hasNextInt 与循环一起使用：

System.out.println("Select operation (1 - 5): ");
while (!sc.hasNextInt()) {
    sc.nextLine();
    System.out.println("Please entire a number [1 - 5]:");
}
choice = sc.nextInt();
sc.nextLine();
switch (choice) {
// ...

或者也处理范围检查，例如：

do {
    System.out.println("Select operation (1-5): ");
    choice = -1;
    if (!sc.hasNextInt()) {
        System.out.println("Please enter a number (1-5, inclusive)");
    } else {
        choice = sc.nextInt();
        if (choice < 1 || choice > 5) {
            System.out.println(choice + " isn't an option, please enter a number (1-5, inclusive");
        }
    }
    sc.nextLine();
} while (choice < 1 || choice > 5);
switch (choice) {
// ...

Answer 2

如果你想捕获异常，那么你必须包围接受扫描器输入的代码。您放错了 try-catch 块，然后它会起作用。

为什么 try/catch InputMisMatchException 即使我导入 java.util.InputMisMatchException 也不起作用？

Why try/catch InputMisMatchException doesnt work even if I import java.util.InputMisMatchException?

java

exception

inputmismatchexception