SIN validate

import java.util.Scanner;
/*
 * Checks if entered SINs are valid.
 *
 * Based off MonkeyShrapnel's code
 *
 * SINs verified using Luhn algorithm:
 * https://en.wikipedia.org/wiki/Social_Insurance_Number#Validation
 *
 */
public class sinValidator
{
    final static int[] mult = {1,2,1,2,1,2,1,2,1}; //constant array for multiplying

    public static void main(String[] args) {
        String[] sin = new String[100]; //array of strings for storing SINs
        Scanner kb = new Scanner(System.in); //scanner
        int numSins = 0; //initialize number of SINs input to 0

        System.out.println("Please enter SINs"
        +", enter stop after last one"); //prompt

        String aSin = kb.next(); //read first SIN
    while(!aSin.equals("stop")) { //loop until "stop"
        sin[numSins++] = aSin; //set item in array to number input, increment numSins
        aSin = kb.next(); //read input from user
        }

        for (int i = 0; i < numSins; i++) { //loop through once for every SIN entered
            int sum = 0; //sum, initialized to 0
            int[] d = new int[9]; //initialize array of 9 integers

            System.out.print(sin[i] + " - "); //print out current SIN in list

        sin[i] = sin[i].replace("-", ""); //remove all hyphens

    if(sin[i].length() == 9){ //only check if current string is 9 characters long

                char[] cSin = sin[i].toCharArray(); //create array of characters from string

        for(int j = 0; j < 9; j++)
            d[j] = Character.getNumericValue(cSin[j]); //set all values in d[] to numerical values of cSin

                //math
        for (int j=0; j<9; j++) {
            int prod = d[j] * mult[j];
            if (prod > 9)
            prod = (prod/10)+(prod%10);
            sum += prod;
        }

        //print whether the string is a valid SIN or not
        if (sum % 10 == 0)
            System.out.println("Valid");
        else
            System.out.println("Invalid");
            }
            else
                System.out.println("Invalid"); //string wasn't 9 chars long, invalid
        }
    }
}