Problems with java validation for user input

Question

I know there have been lots of questions on input validations for Java, but no matter what I read, I just can't seem to get this to work. I would like a user to input birth date as (MM DD YYYY). I wanted to validate that

1. the user input digits only
2. they did the correct number of digits and
3. the digits fell within the correct range.

My first attempt I had int variables, but I couldn't seem to combine a hasNextInt() with the digit length and range. I then saw a post saying to do String variable and then use Integer.parseInt() . I thought this would work well if I used (!month.matches("0[1-9]") || !month.matches("1[0-2]") because it seemed to satisfy all of my validation wishes. I tried this in a while statement, but it fell into an indefinite loop. I then tried to change that code into an if...else statement and surround it with a while(false) statement. However, it now throws an error instead of going to my statement that says fix your mistake. Here is what my code looks like for the moment:

import java.util.Scanner; //use class Scanner for user input

public class BD {
    private static Scanner input = new Scanner(System.in); //Create scanner

    public static void main(String[] args){
        //variables
        String month;
        int birthMonth;
        String day;
        int birthDay;
        String year;
        int birthYear;
        boolean correct = false;

        //prompt for info
        System.out.print("Please enter your date of birth as 2 digit "+
            "month, 2 digit day, & 4 digit year with spaces in-between"+
            " (MM DD YYYY): ");
        month = input.next();
        //System.out.printf("%s%n", month);  //test value is as expected
        day = input.next();
        year = input.next();

        //validate month value
        while (correct = false){
            if(!month.matches("0[1-9]") || !month.matches("1[0-2]")){
                System.out.println("Please enter birth month as "+
                    "a 2 digit number: ");
                month = input.next();
                //System.out.printf("%s%n", month);
            }
            else {
                correct = true;
            }
        }

        //turn strings into integers
        birthMonth = Integer.parseInt(month);
        birthDay = Integer.parseInt(day);
        birthYear = Integer.parseInt(year);

        //check values are correct
        System.out.printf("%d%d%d", birthMonth, birthDay, birthYear);
    }
}

Any help would be greatly appreciated. I would also like to try to do this validation without any try/catch blocks as those seem too bulky. Thanks!

Answer 1

If you want to use regex,you can try this

    while(!(Pattern.matches("(0)[1-9]{1}|(1)[0-2]",month)))
    {
           System.out.println("Enter again \n");
           month=input.next();
    }

For this code to work you need to include regex package, by using this at the beginning of your program

  import java.util.regex.*;

Our regex is in two parts " (0)[1-9]{1} " , this will first make sure that the string contains "0" and then any digit between 1-9. And " {1} " will make sure that it occurs only once.

Similarly write the code for day and year,if required.

Answer 2

Use DateTimeFormatter something like this:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM dd yyyy");

try {
    LocalDate date = LocalDate.parse(input, formatter);
} catch (DateTimeParseException e) {
    // Thrown if text could not be parsed in the specified format
}