java - 当用户输入的号码不存在时如何捕获 Switch 语句中的错误

Question

我正在尝试对我的程序进行错误证明，该程序基本上用作迷你计算器。但我不知道如何编写一个“Catch”语句来检测用户何时输入不存在的案例编号，在我的例子中是任何负数或> 4

        System.out.println("Hello user! Which operation would you like to use?");
        System.out.println("1) + \n2) - \n3) * \n4) /");


        Scanner operacijai = new Scanner(System.in);
        int operacija = operacijai.nextInt();


        int n=1;
        do {
        try {
            switch (operacija) {
            case 1:
                addingMethod();
                n=2;
                break;

            case 2:
                subtractingMethod();
                n=2;
                break;

            case 3:
                multiplyingMethod();
                n=2;
                break;

            case 4:
                dividingMethod();
                n=2;
                break;
                    }       
            }
            catch(Exception e) {
                System.out.print("Enter a correct number!");
            }

        } while(n==1);
        operacijai.close();

    } ```

Answer 1

为什么要抛出不必要的异常？我建议您在 switch 中放置一个 default 案例，并包含所需的错误消息。另外，将输入部分移动到循环内，以便它继续接受输入。

我还建议您使用 nextLine() 而不是 nextInt()。检查Scanner is skipping nextLine() after using next() or nextFoo()?了解更多信息。

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello user! Which operation would you like to use?");
        System.out.println("1) + \n2) - \n3) * \n4) /");
        Scanner operacijai = new Scanner(System.in);
        int operacija = 0, n = 1;
        boolean valid;
        do {
            do {
                valid = true;
                try {
                    operacija = Integer.parseInt(operacijai.nextLine());
                } catch (NumberFormatException e) {
                    System.out.println("Enter an integer only.");
                    valid = false;
                }
            } while (!valid);
            switch (operacija) {
            case 1:
                System.out.println("addingMethod()");
                n = 2;
                break;

            case 2:
                System.out.println("subtractingMethod()");
                n = 2;
                break;

            case 3:
                System.out.println("multiplyingMethod()");
                n = 2;
                break;

            case 4:
                System.out.println("dividingMethod()");
                n = 2;
                break;
            default:
                System.out.println("Invalid input");
            }
        } while (n == 1);
    }
}

示例运行:

Hello user! Which operation would you like to use?
1) + 
2) - 
3) * 
4) /
5
Invalid input

另一个示例运行:

Hello user! Which operation would you like to use?
1) + 
2) - 
3) * 
4) /
a
Enter an integer only.
5
Invalid input
2
subtractingMethod()