[Java] Arabic to Roman Method

import java.util.Scanner;

public class arabicToRoman {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        System.out.println("Enter a number between 1 and 3999 (-1 to quit): ");

        while (!input.hasNext("-1")) {
            String a = input.next();

            try {
                Integer number = Integer.parseInt(a);

                if ((number <= 3999) && (number > 0)) {
                    System.out.println(arabicToRoman(number));

                } else if (number > 3999) {
                    System.out.println("Error: number must be between 1 and 3999");

                } else if (number == 0) {
                    System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

                } else {
                    System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

                }
            } catch (NumberFormatException e) {
                System.out.println("You did not enter a number!");
            }
        }
    }

    public static String arabicToRoman(int arabic) {
        String a = "";

        while (arabic >= 1000) {
            a += "M";
            arabic -= 1000;
        }
        while (arabic >= 900) {
            a += "CM";
            arabic -= 900;
        }
        while (arabic >= 500) {
            a += "D";
            arabic -= 500;
        }
        while (arabic >= 400) {
            a += "CD";
            arabic -= 400;
        }
        while (arabic >= 100) {
            a += "C";
            arabic -= 100;
        }
        while (arabic >= 90) {
            a += "XC";
            arabic -= 90;
        }
        while (arabic >= 50) {
            a += "L";
            arabic -= 50;
        }
        while (arabic >= 40) {
            a += "XL";
            arabic -= 40;
        }
        while (arabic >= 10) {
            a += "X";
            arabic -= 10;
        }
        while (arabic >= 9) {
            a += "IX";
            arabic -= 10;
        }
        while (arabic >= 5) {
            a += "V";
            arabic -= 5;
        }
        while (arabic >= 4) {
            a += "IV";
            arabic -= 4;
        }
        while (arabic >= 1) {
            a += "I";
            arabic -= 1;
        }
        return a;
    }
}