import java.util.Scanner;
import java.net.MalformedURLException;
import java.net.URL;
import java.io.IOException;

public class Main {

    // takes user input and validates
    public static URL URLPrompt() throws MalformedURLException {
        URL pageLocation = null;
        Scanner in = new Scanner(System.in);
        System.out.println("Please enter a webpage URL to find all it's links: ");
        try {
            pageLocation = new URL(in.nextLine());
        } catch (MalformedURLException exception) {
            System.out.println("Invalid URL");
            URLPrompt();
        }
        return pageLocation;
    }

    public static void main(String[] args) throws MalformedURLException, IOException {
        Scanner in = new Scanner(System.in);
        URL pageLocation = URLPrompt();
        Scanner scan = new Scanner(pageLocation.openStream());
        while (scan.hasNext()) {
            String webFile = scan.nextLine();
            // Searches for all hyperlinks in <a href=> </a> form
            if (webFile.contains("<a href=") && webFile.contains("</a>")) {
                int x = webFile.indexOf("<a href=");
                int y = webFile.indexOf("</a>");
                String link = webFile.substring(x, y + 4);
                System.out.printf("%s\n", link);

            }
        }
        scan.close();
        in.close();

    }
}

So this program is supposed to take a user inputted url link and print out all of the hyperlinks in html form, "a href" to the closing "a" tag. This code does just that if the url is valid initially. However, if an invalid url is input the system catches it and the Urlprompt method calls itself, when the method calls itself after an invalid input and then a valid URL is input during recursion I get a nullpointer exception on line 24... How can I get the URLPrompt method to accurately fill the variable pageLocation during recursion?