Give an error message and restart loop if user input is not the correct datatype in java while continue if it is?

Question

Hey this is a small part of my program that I'm having big issues with. I want the program to give the user an error message and start the loop from the beginning if the input is not an integer, while I want it to continue into the switch/case if it is an integer. This is what I got so far, but it is not working since I get the inputmismatchexception if its incorrect and it doesn't continue in to the switch/case if it is correct?

public static void main(String[] args) {
    ArrayList<Dog> doglist = new ArrayList<Dog>();
    Scanner myscan = new Scanner(System.in);
    boolean running = true;

    while (running) {
        System.out.println("\n************************************");
        System.out.println("\nWelcome to the kennel club!");
        System.out.println("\n************************************");
        System.out.println("\n[1] Register new dog");
        System.out.println("[2] Print out list");
        System.out.println("[3] Increase age");
        System.out.println("[4] Remove dog");
        System.out.println("[5] Quit program");
        System.out.println("\n************************************");
        System.out.println("\nChoose: ");

        int option = 0;
        boolean inputOk = false;
        do {
            try {
                option = myscan.nextInt();
                inputOk = true;
            } catch (InputMismatchException e) {
                System.out.println("Option must be a number");
                myscan.nextLine(); // to consume the \n that remains at the end of the line after using nextInt();
            }
        }
        while (!inputOk);

        switch (option) {
            case 1:
                System.out.println("Write name:");
                String name = myscan.next();
                System.out.println("Write race:");
                String race = myscan.next();
                System.out.println("Age:");
                int age = myscan.nextInt();
                System.out.println("Weight:");
                double weight = myscan.nextDouble();

                Dog dog = new Dog(name, race, age, weight);

                doglist.add(dog);

                break;

            case 2:

                System.out.println("Minimum length of tail:");
                double userInput1 = myscan.nextDouble();

                for (Dog d : doglist) {
                    if (d.getTailLength() >= userInput1) {
                        System.out.println(d.toString());
                    }
                }

                break;

            case 3:

                System.out.println("Name of dog:");
                String userInput2 = myscan.next();
                int flag = 0;
                for (Dog d : doglist) {
                    if (d.getName().equals(userInput2)) {
                        d.increaseAge();
                        d.increasetailLength();
                        flag = 1;
                        break;
                    }
                }

                if (flag == 0) {
                    System.out.println("Error, can't find dog with name:" + userInput2);
                }

                break;

            case 4:

                System.out.println("Name of dog:");
                String userInput3 = myscan.next();

                Dog dogToRemove = null;

                for (Dog d : doglist) {
                    if (d.getName().equals(userInput3)) {
                        dogToRemove = d;
                        System.out.println("Dog is removed");
                    }
                }

                if (dogToRemove == null) {
                    System.out.println("Error, can't find dog with name: " + userInput3);
                } else {
                    doglist.remove(dogToRemove);
                }

                break;

            case 5:

                running = false;//Avslutar loopen och därmed programmet
                System.out.println("Program finshed");
                break;

            default:

                System.out.println("Error, choose between [1] [2] [3] [4] [5]");//Felmeddelande om valet är någon annan siffra än de som menyn innehåller
                break;
        }
    }
}

Answer 1

Instead of grabbing and expecting an integer when you aren't guaranteed one, simply grab whatever the next line is and determine if the value entered is an integer with a regular expression like this

      while(running)
      {
          inputFromUser = myscan.nextLine();
          int option = -1; //some default invalid value
          boolean doSwitch = false;

          if(inputFromUser.matches("\\d+"))
          {
              option = Integer.parseInt(inputFromUser);
              doSwitch = true;
          }
          else{
              System.out.println("Incorrect input was received - " + inputFromUser);
          }

          if(doSwitch)
          {
              //switch logic
          }
      }

Answer 2

You can add a do-while to read the option catching the InputMismatchException:

int option = 0;
boolean inputOk = false;
do{
    try {
        option = myscan.nextInt();
        inputOk = true;
    } catch (InputMismatchException  e) {
        System.out.println("Error, this is not an integer.");
        myscan.nextLine(); // to consume the \n that remains at the end of the line after using nextInt();
    }
}while (!inputOk);

This way it will loop until you get a valid number.

EDIT

If you want to print the menu again then you can do this: in your original code, change the break statement with a continue statement and also include a call to the nextLine method to consume the remaining \n:

int option = 0; // don't read the value directly before validating that is actually an integer value or you will get the InputMismatchException

if (!myscan.hasNextInt()) {
    System.out.println("Error, this is not an integer:");
    myscan.nextLine(); // consume the \n
    continue; // loop again
} else {
    option = myscan.nextInt();
}