GenerateCustomerIdentifier

import java.util.Arrays;

public class GenerateCustomerIdentifier {

    public static void main(String[] args) {

        GenerateCustomerId(); /* Generate a new customer number */
        IsValid("KD8743311734", true); /* Check if a given customerId is valid and output this */

    }

    static String customerId;
    static String validationId;
    static int checksum;

    static void GenerateCustomerId() { /* Generate a new customerId */

        do{
            checksum = 0;

            customerId = "KD";
            for (int i = 2; i <= 9; i++) { /* Generate 8 random integers */
                int decimal = Integer.parseInt(GenerateRandomInt().charAt(0)+"");
                customerId += decimal;
                checksum += decimal;
            }
            customerId += checksum;

        }while(IsValid(customerId, false) == false); /* Check if the customerId is valid and don't output this. */

        System.out.printf("Here is your new customer ID: %s\n", customerId);

    }

    static String GenerateRandomInt() { /* Generate a random integer between 1 and 9 and return it as string */
        return (byte)((Math.random() * 9) + 1)+"";
    }

    static boolean IsValid(String customerId, boolean output) { /* Return a proof that an existing customerId is valid */

        String[] customerIdArray = customerId.split("");
        boolean result;

        checksum = 0;

        validationId = "KD";
        for (int i = 2; i <= 9; i++) { /* transfer the data in a new array to re-calculate the checksum */
            validationId += customerIdArray[i];
            checksum += Integer.parseInt(customerIdArray[i].charAt(0)+"");
        }
        validationId += checksum;

        if (customerId.equals(validationId)) { /* Compare the given customerId with the new generated checksum */
            result = true;
        } else {
            result = false;
        }

        if (output) {
            System.out.printf("Is %s valid? %s\n", customerId, result);
        }

        return result;
    }
}