How to validate user input for this Java code?

Question

I would like to have a validation for: number input only, hour must be <=24, minutes must be <60, and the user must type the ':' sign between hh:mm.

 int total; //Total Minutes
    String time; //Input from keyboard


    final Scanner T = new Scanner(System.in);

    System.out.print("Enter the time in HH:MM :");
    time = T.next();

    //Get the value before the ':'
    int hour = Integer.parseInt(time.substring(0, time.indexOf(':')));


    //Get the value after the ':'
    int minute =Integer.parseInt (time.substring((time.indexOf(':') + 1), time.length()));


    //Formula of the calculation
    total = hour * 60 + minute;


    //Display the final value
    System.out.println( time +" is " + total + " minutes.");

Possible duplicate of Regular expression for matching HH:MM time format — Mark Sholund
– Mark Sholund, Commented Nov 1, 2015 at 19:11
You wouldn't want a time 24:53 now, do you? So why <= 24 and not <24? Also, is a single digit hour permitted? — laune
– laune, Commented Nov 1, 2015 at 19:17

laune · Accepted Answer · 2015-11-01 19:42:30Z

1

For validating, use a regular expression:

time.matches( "(?:[01][0-9]|2[0-3]):[0-5][0-9]" )

To convert, simply use

int hour = Integer.parseInt(time.substring(0, 2));
int minute = Integer.parseInt(time.substring(3));

answered Nov 1, 2015 at 19:42

laune

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Comments

Bimde · Accepted Answer · 2015-11-01 19:58:34Z

To follow your format, the user must enter a time with ':' at the 3rd character position charAt(2) and the rest of the characters (at indices 0, 1, 3 and 4) must be digits. A very quick to implement and good to learn solution is to use regex: http://www.regular-expressions.info/tutorial.html

However, I'll be showing you a simpler to understand solution using your code as a template:

Verify that the length is 5
Verify that the hours are correct
Verify that the minutes are correct
Ask the user to re-enter the value if anything is incorrect

Here's the code:

    int total; // Total Minutes
    String time; // Input from keyboard

    final Scanner T = new Scanner(System.in);

    System.out.print("Enter the time in HH:MM :");
    time = T.next();

    boolean correctFormat = false;
    int hour = 0, minute = 0;

    while (!correctFormat) {
        correctFormat = true;

        if (time.length() != 5)
            correctFormat = false;
        else {

            // Get the value before the ':'
            hour = Integer.parseInt(time.substring(0, 2));
            if (hour >= 24 || hour < 0)
                correctFormat = false;

            // Get the value after the ':'
            minute = Integer.parseInt(time.substring(3, 5));
            if (minute >= 60 || minute < 0)
                correctFormat = false;
        }
        if (!correctFormat) {
            System.out.print("Pleaase follow the format! Enter the time in HH:MM :");
            time = T.next();
        }

    }

    // Formula of the calculation
    total = hour * 60 + minute;

    // Display the final value
    System.out.println(time + " is " + total + " minutes.");

Further, if you want to make the code even more robust, you can check to see if the user actually enters numbers before and after the ':' by catching a 'NumberFormatException' that will be thrown from the Integer.parseInt() method if the parameters aren't an actual number. You can do this by editing the above code to as follows:

    int total; // Total Minutes
    String time; // Input from keyboard

    final Scanner T = new Scanner(System.in);

    System.out.print("Enter the time in HH:MM :");
    time = T.next();

    boolean correctFormat = false;
    int hour = 0, minute = 0;

    while (!correctFormat) {
        correctFormat = true;

        if (time.length() != 5)
            correctFormat = false;
        else {
            try {
                hour = Integer.parseInt(time.substring(0, 2));
                minute = Integer.parseInt(time.substring(3, 5));
            } catch (NumberFormatException e) {
                correctFormat = false;
            }
            if (correctFormat) {
                if (hour >= 24 || hour < 0)
                    correctFormat = false;

                if (minute >= 60 || minute < 0)
                    correctFormat = false;
            }
        }
        if (!correctFormat) {
            System.out.print("Pleaase follow the format! Enter the time in HH:MM :");
            time = T.next();
        }
    }

    // Formula of the calculation
    total = hour * 60 + minute;

    // Display the final value
    System.out.println(time + " is " + total + " minutes.");

This isn't really validating since your code runs into an exception due to invalid input.

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