How can I continue to prompt for input, if my REGEX is not matched?

Question

I'm trying to get this loop to continue. So far, when input is not matched to my REGEX, "input not valid" gets displayed but loop won't continue. What am I missing here?

Apreciate your help!

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {

public static void main(String[] args) {

    String input;
    //some variables
    Pattern pattern = Pattern.compile(REGEX);
    Scanner scn = new Scanner(System.in);


    boolean found = false;
    do {
        System.out.println("ask user for input");
        input = scn.next();
        Matcher matcher = pattern.matcher(input);
        try {
            matcher.find();
            //some Code
            found = true;
            scn.close();
        
        } catch (IllegalStateException e) {
            System.out.println("input not valid."); //stuck here
            scn.next();
            continue;
        }
    } while (!found);

            // some more Code

}
}

Answer 1

There are many problems with your code:

• IllegalStateException is not raised by the "not-match", but by the Scanner class, so why catch it?
• you are not doing anything with the result of matcher.find(), I think you want found = matcher.find()
• in case the input is not valid, you execute twice scn.next();

Moreover:

• you can simplify the initialization boolean found = false; with boolean found;
• continue; at the end of a loop is not necessary

Fixed code:

    boolean found;
    do {
        System.out.println("ask user for input");
        input = scn.next();
        found = pattern.matcher(input).find();
        if (!found) {
            System.out.println("input not valid.");
        }
    } while (!found);
    scn.close();