捕获异常后继续循环

Question

I am catching an inputMismatchException in my main method and want my do-while loop to iterate again after the exception is caught. I even coded an explicit continue statement but that didn't work. How can I do so?

public class AddressBookApp {

public static void main(String[] args) {
    AddressBook abook = new AddressBook();

    System.out.println("Welcome to the Address Book Application\n");
    Scanner sc = new Scanner(System.in);

    int menuNumber = 4;
    loop:
    do {
        abook.menu();

        try{
            menuNumber = sc.nextInt();
            System.out.println();

            if (menuNumber < 1 || menuNumber > 4){
                System.out.println("Please enter a valid menu number\n");
            } else if (menuNumber == 1) {
                abook.printEntries();
            } else if (menuNumber == 2) {
                abook.addEntry();
            } else if (menuNumber == 3) {
                abook.removeEntry();
            } else {
                System.out.println("Thanks!  Goodbye.");
                sc.close();
                return;
            }


        } catch (InputMismatchException ime) {
            System.out.println("Please enter an integer");
            sc.next();

            continue loop;
        }

    } while (menuNumber != 4);
    sc.close();
  } 
}

Answer 1

You left menuNumber equal to 4, which is the termination condition of your loop. Of course your loop will end.

Answer 2

You initialized menuNumber to 4, but do not change it in case of an exception. The loop does attempt to continue, but exits because the statement menuNumber != 4 is false.

int menuNumber = 4;
loop:
do {
    abook.menu();

    try{
        menuNumber = sc.nextInt();
        System.out.println();

        if (menuNumber < 1 || menuNumber > 4){
            System.out.println("Please enter a valid menu number\n");
        } else if (menuNumber == 1) {
            abook.printEntries();
        } else if (menuNumber == 2) {
            abook.addEntry();
        } else if (menuNumber == 3) {
            abook.removeEntry();
        } else {
            System.out.println("Thanks!  Goodbye.");
            sc.close();
            return;
        }


    } catch (InputMismatchException ime) {
        System.out.println("Please enter an integer");
        sc.next();

        continue loop;
    }

} while (menuNumber != 4);

Answer 3

Try this

  } catch (InputMismatchException ime) {
    if (fatal(ime)) {
        throw ime;
    } else {
        // try again
        continue;
    }

Answer 4

The loop doesn't continue because an exception of a type OTHER than InputMistmatchException is being thrown. Change the catch to:

catch (Exception e)

or at least add that all encompassing catch condition.

A better solution is to inspect exactly what exception is being thrown and why, and then fix the problem leading to the exception. Having an all encompassing catch with a continue statement could, in theory, lead to an infinite loop because menuNumber is not incremented.