Input validation: Re-prompt user in main menu if they enter wrong input format

[Sina Meraji]

I'm building a small auction system. this is my main menu (UI).
In each switch case, I prompt user to enter some values (item name, date, price etc.). I wanna re-prompt user to re-enter values for each prompt if the initial entry is in wrong format or simply wrong.

for example, if program asks user to enter date and user enters invalid input, i want the user to be re-prompted. I tried a couple of different things but the result I got was repeating all question from beginning (name, startDate, minBidAmount etc) if [for example] startDate was wrong.

one way that i can think of (which sounds bad) is creating one while loop for each question!!

Any tips?

do {
            System.out.println("1.New Auction");
            System.out.println("2.Edit");
            .....
            System.out.println("7.Logout");


            Scanner input = new Scanner(System.in);
            int choice = input.nextInt();
            if(choice == 7)
                break;
            else if(choice > 7){
                System.out.println("Invalid entry. Please try agains");
                System.out.println("");
                continue;
            }
            input.nextLine();
//            while(true){
                System.out.println("");
                switch(choice){
                    case 1:
                        addOrEditUI(input, newSeller, null, "add");
                        break;
                    case 2:
                        ...
                        break;
                    case 3:
                        ...
                        break;
                        .....

where

    private static void addOrEditUI(Scanner input, Seller sellerID, String itemID, String addOrEdit){
        String auctionType = "", deadline = "", startDate = "";
        double minBidAmount = -1;
        
        System.out.print("Enter item name: ");
        String itemName = input.nextLine();

        validDateUI("auction start date and time", input);

        System.out.print("Would you like to enter minimum bid amount? (optional) y/n ");
        String yn = input.nextLine();
        if(yn.equalsIgnoreCase("y") || yn.equalsIgnoreCase("n")){
            if(yn.equalsIgnoreCase("y")){
                System.out.print("Enter minimum bid amount:");
                minBidAmount = input.nextDouble();
            }
        }

and

String validDateUI(String date, Scanner input)

will prompt user to enter Date and time and verify correct format.

[Dave Tolls]

If each prompt and validation was its own method then that method can simply loop until it's got valid data:

Date getDateFromUser() {
    do {
        // prompt for date
        // read date
        // validate
        // if invalid then say so and go back round.
    } while (invalidDate);
}

[Winston Gutkowski]

Sina Meraji wrote:...will prompt user to enter Date and time and verify correct format.

Dates and times are particularly tricky, since you have 6 components (I assume), ALL of which might have something wrong with them.

One approach is to take each component separately, ie, year, then month, then day, then hour...etc, etc. Pretty simple, but maybe too laborious for your "users".

Another would be to use a SimpleDateFormat to parse the whole string, and use the messages from its Exceptions. Trouble is: I don't know how good they are.

You might also get some tips from this page.

HIH

Winston

[Sina Meraji]

Winston Gutkowski wrote:

Sina Meraji wrote:...will prompt user to enter Date and time and verify correct format.

Dates and times are particularly tricky, since you have 6 components (I assume), ALL of which might have something wrong with them.

One approach is to take each component separately, ie, year, then month, then day, then hour...etc, etc. Pretty simple, but maybe too laborious for your "users".

Another would be to use a SimpleDateFormat to parse the whole string, and use the messages from its Exceptions. Trouble is: I don't know how good they are.

You might also get some tips from this page.

HIH

Winston

I use this to validate date and type. all good except it doesn't detect an input like hour 26:00. (i'll do another topic for that )

private static String validDateUI(String date, Scanner input){
        String startDate = "";
        while(true){
            System.out.print("Enter " + date + " (DD-MM-YYYY hh:mm) : ");
            startDate = input.nextLine();
            if(!isValidDate(startDate))
                System.out.println("Please enter date and time in the right format (DD-MM-YYYY hh:mm)");
            else
                break;
        }
        return startDate;
    }

thanks

[Winston Gutkowski]

Sina Meraji wrote:I use this to validate date and type. all good except it doesn't detect an input like hour 26:00.

Well, you haven't shown us your isValidDate(String) method, so it's difficult to comment.
However, I think the idea of such a method is very good (it's called 'single responsibility').

The only thing I would say is that your validDateUI() method should return a Date, not a String.
Have a look here to find out why.

And do have a look at SimpleDateFormat:
1. It'll save you a LOT of code.
2. It can be used for validating AND formatting - in the exact style you're using.

HIH

Winston

[Sina Meraji]

Winston Gutkowski wrote:

Sina Meraji wrote:I use this to validate date and type. all good except it doesn't detect an input like hour 26:00.

Well, you haven't shown us your isValidDate(String) method, so it's difficult to comment.
However, I think the idea of such a method is very good (it's called 'single responsibility').

The only thing I would say is that your validDateUI() method should return a Date, not a String.
Have a look here to find out why.

And do have a look at SimpleDateFormat:
1. It'll save you a LOT of code.
2. It can be used for validating AND formatting - in the exact style you're using.

HIH

Winston

Thanks Winston

I read the article. Great insights
here's my isValidDate btw

public static boolean isValidDate(String date_time) {
        SimpleDateFormat myDateFormat = new SimpleDateFormat("dd-MM-yyyy HH:mm");
        try {
            myDateFormat.parse(date_time);
            return true;
        } catch (ParseException ex) {
            // You may want to print the exception here, or do something else with it
            return false;
        }
    }

[Winston Gutkowski]

Sina Meraji wrote:here's my isValidDate btw

Very nice.

One small, but rather important, point. When you use SimpleDateFormat for validation, it should be "strict", so add:
  myDateFormat.setLenient(false);
at line 3.

You might also want to think about putting that section of code into a DateValidator class that wraps (or possibly extends) a strict SimpleDateFormat.

Winston