Question

我正在上课的项目，我们的任务是设计一个包含5个选项的菜单的计算器程序。如果用户输入的输入不在1到5之间，则在尝试捕获代码时遇到了一个问题。当前，如果用户输入的数字在6到9之间。则将在第一次捕获该异常，并显示错误将显示一条消息，提示您输入1到5之间的一个选项，并出现一条要重新输入的消息。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，并且会显示主菜单。我还试图捕获输入字符串而不是在1和5之间进行选择的时间，并显示不同的错误消息，提示用户输入了无效的输入，然后要求用户重新输入，但是输入字符串时作为选择，我得到了输入不匹配异常错误，但是当选择了操作之后，如果输入的是字符串而不是浮点数，则会显示正确的错误消息。

我是Java的初学者，并且乐于接受所有建议，但是如果可能的话，我希望我的代码保持与当前编写方式相似的方式。

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

您只需要将欢迎消息移至do-while之外，将您的初始scan.nextInt()调用移至try块内，然后将scan.nextInt()调用移至if语句中：

// 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;
        }
        ...

如何解决switch case语句中的异常处理问题？

1 个答案: