如何修复switchcase语句中的异常处理问题

Question

我正在为班级做项目，我们的任务是设计一个计算器程序，该程序的菜单包含5个选项。如果用户输入了一个不在1和5之间的选项，当我试图编写代码以捕获时，我会遇到一个问题。当前，如果用户输入一个介于6到9之间的数字。异常将在第一次被捕获，并显示一条错误消息，说明输入1和5之间的选项，并显示重新输入的消息。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。我还试图捕捉何时输入字符串作为输入而不是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，当输入字符串作为选择时，我会收到输入不匹配异常错误，但当选择操作后输入字符串而不是浮点值时，则显示正确的错误消息。

我是Java的初学者，对所有的建议都持开放态度，但如果可能的话，我希望我的代码与当前的编写方式保持一定的相似性。

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 Calculatornn (1) Additionn "
+ "(2) Subtractionn (3) Multiplicationn (4) Divisionn (5) Exitnn");
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出do-white，将初始scan.nextInt()调用移入try块，并将scan.nextInt()调用移出if语句：

// Moved welcome message outside of do-while
System.out.printf("Welcome to Paul's Handy Calculatornn (1) Additionn "
+ "(2) Subtractionn (3) Multiplicationn (4) Divisionn (5) Exitnn");
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;
}
...