Code under the while loop runs twice when an exception has occurred-CodePudding

I have a while (true) loop that has a try and catch block inside In it. But when InputMismatchException occurred, the while code runs twice without any user input. Without try and catch while part is running correctly. I can't understand what is the problem here.

while (true)  {

        try {
            System.out.println("Enter the option here: ");
            option = scanner.next();

            if (option.equalsIgnoreCase("V")){
                viewCabins(cruiseShip);

            } else if (option.equalsIgnoreCase("A")){

                System.out.println("Enter the cabin number (0 - 11)");
                cabinNum = scanner.nextInt();
                System.out.println("Enter name of the passenger: ");
                customerName = scanner.next();
                addCustomer(cruiseShip, customerName, cabinNum);
                System.out.println("Wrong Cabin number");

            } else if (option.equalsIgnoreCase("Q")){
                System.out.println("Thank you!");
                break;

            } else if (option.equalsIgnoreCase("E")){
                emptyCabins(cruiseShip);

            } else if (option.equalsIgnoreCase("D")){
                System.out.println("Enter the room number (0 - 11)");
                cabinNum = scanner.nextInt();
                System.out.println("Enter name of the customer");
                customerName = scanner.next();
                System.out.println("Do you really want to delete this customer? ");
                deleteOption = scanner.next();
                if (deleteOption.equals("yes")){
                    deleteCustomer(cruiseShip, customerName, cabinNum);
                }

            } else if (option.equalsIgnoreCase("F")){
                System.out.println("Enter name of the customer: ");
                customerName = scanner.next();
                findCabin(cruiseShip, customerName);

            } else if (option.equalsIgnoreCase("S")){
                loadToFile(cruiseShip);
                System.out.println("Program data saved successfully");

            } else if (option.equalsIgnoreCase("L")){
                loadFromFile(cruiseShip);
                System.out.println("Program data loaded successfully");

            } else if (option.equalsIgnoreCase("O")){
                System.out.println("Passengers alphabetically by name: ");
                customerSort(cruiseShip);

            }

        }catch (InputMismatchException e){
            System.out.println("Wrong Input! Please try again.");
        }


    }

Here is the output:

Enter the option here: 
a
Enter the cabin number (0 - 11):
the
Wrong Input! Please try again.
Enter the option here: 
Enter the option here:

CodePudding user response：

When the Scanner throws an exception or simply doesn't read a token the typed input will remain inside of the Scanners buffer . So, when you entered "the" when the Scanner expects an int via nextInt(), the InputMismatchException is thrown and handled in your catch clause. "the" however is not consumed when this happens and therefore still remains in the Scanners buffer.

On the next loop iteration, the call to Scanner#next() consumes this token. However the read token doesn't fit any of your if-criteria, so nothing happens and the loop repeats again.

To fix this, clear the Scanners buffer in your catch clause via next() / nextLine().

CodePudding user response：

Try This:

while(true){
  //your variables use Inside the while
  String option,customerName,deleteOption;
  Scanner scanner=new Scanner(System.in);
  int cabinNum;
  try{
   //do samething
  }
      catch(Exception e){//do samething}
   }