如何解决switch case语句中的异常处理问题？

Question

我正在为班级做一个项目，我们的任务是设计一个包含5个选项的计算器程序。如果用户输入的选项不在1和5之间，当我试图编码以捕获时，我面临一个问题。当前，如果用户输入6到9之间的数字。第一次捕获异常时，将显示一条错误消息，提示输入1到5之间的选项，并显示一条重新输入的消息。但是，如果用户继续输入6到9之间的数字，则不会显示错误消息，并显示主菜单。我还试图捕捉输入字符串而不是1和5之间的选择，并显示不同的错误消息，说明用户输入了无效输入，然后要求用户重新输入，然而，当输入一个字符串作为选项时，我会收到一个输入不匹配异常错误，但当选择操作后输入一个字符串而不是浮点时，则会显示正确的错误消息。

我是一名Java初学者，愿意接受所有建议，但如果可能的话，我希望我的代码与当前的编写方式有些相似。

static void promptEnterKey() {
    System.out.println("Press enter key to continue ...");
    Scanner scanner = new Scanner(System.in);
    scanner.nextLine();
}

public static void main(String[] args) {
    float Firstnum, Secondnum, Solution;
    int choice;
    Scanner scan = new Scanner(System.in);
    do {
        System.out.printf("Welcome to Paul's Handy Calculator\n\n (1) Addition\n "
                + "(2) Subtraction\n (3) Multiplication\n (4) Division\n (5) Exit\n\n");
        System.out.printf("What would you like to do? ");
        choice = scan.nextInt();
        try {
            if (choice < 1 || choice > 5) {
                System.out.printf("You have not entered a number between 1 and 5. "
                        + "Try again.\n");
                System.out.printf("Enter your choice between 1 and 5 only: \n");
                choice = scan.nextInt();
                continue;
            }
            switch (choice) {
            case 1:
                System.out.print("Please enter two floats to add, "
                        + "separated by a space: ");
                Firstnum = scan.nextFloat();
                Secondnum = scan.nextFloat();
                Solution = Firstnum + Secondnum;
                System.out.println("Result of adding " + Firstnum + " and " 
                        + Secondnum + " is " + Solution + "\n");
                promptEnterKey();
                break;
            case 2:
                System.out.println("Please enter two floats to subtract, "
                        + "separated by a space: ");
                Firstnum = scan.nextFloat();
                Secondnum = scan.nextFloat();
                Solution = Firstnum - Secondnum;
                System.out.println("Result of subtracting " + Firstnum 
                        + " and " + Secondnum + " is " + Solution + "\n");
                promptEnterKey();
                break;
            case 3:
                System.out.print("Please enter two floats to multiply, "
                        + "separated by a space: ");
                Firstnum = scan.nextFloat();
                Secondnum = scan.nextFloat();
                Solution = Firstnum * Secondnum;
                System.out.print("Result of multiplying " + Firstnum + " and " 
                        + Secondnum + " is " + Solution + "\n");
                promptEnterKey();
                break;
            case 4:
                System.out.print("Please enter two floats to divide, "
                        + "separated by a space: ");
                Firstnum = scan.nextFloat();
                Secondnum = scan.nextFloat();
                if (Secondnum == 0) {
                    System.out.println("You cannot divide by zero, "
                            + "please enter another number to divide by");
                    Secondnum = scan.nextFloat();
                }
                Solution = Firstnum / Secondnum;
                System.out.println("Result of dividing " + Firstnum + " and " 
                        + Secondnum + " is " + Solution + "\n");
                promptEnterKey();
                break;
            case 5:
                System.out.println("Thank You for using Paul's Handy Calculator");
                System.exit(0);
                break;
            default:
            }
        } catch (InputMismatchException ex) {
            System.out.println("You have entered an invalid choice. Try again.  ");
            String flush =scan.next();
        }
    } while (choice != 5);
}

Answer 1

您只需将欢迎信息移到do之外，同时移动初始的扫描。nextInt（）在try块内调用，并删除扫描。nextInt（）在if语句中调用：

// Moved welcome message outside of do-while
System.out.printf("Welcome to Paul's Handy Calculator\n\n (1) Addition\n "
        + "(2) Subtraction\n (3) Multiplication\n (4) Division\n (5) Exit\n\n");
System.out.printf("What would you like to do? ");

do {
    try {
        // Moved scan.nextInt inside of try block
        choice = scan.nextInt();
        if (choice < 1 || choice > 5) {
            System.out.printf("You have not entered a number between 1 and 5. " + "Try again.\n");
            System.out.printf("Enter your choice between 1 and 5 only: \n");          
            // Removed nextInt call
            continue;
        }
        ...