Java Program to find check digit of an IMEI Number

/**
* The class IMEI_CheckDig inputs the first 14 digits of an IMEI number
* and finds the last check digit of the IMEI code
* @author : www.guideforschool.com
* @Program Type : BlueJ Program - Java
*/

import java.util.Scanner;
class IMEI_CheckDig
{
    int sumDig(int n) // Function for finding and returning sum of digits of a number
    {
        int a = 0;
        while(n>0)
        {
            a = a + n%10;
            n = n/10;
        }
        return a;
    }
    
    public static void main(String args[])
    {
        IMEI_CheckDig ob = new IMEI_CheckDig();
        Scanner sc = new Scanner(System.in);
        
        System.out.print("Enter first 14 digits of IMEI code : ");
        long n = sc.nextLong(); // 14 digits cannot be stored in 'int' data type
        
        String s = Long.toString(n); // Converting the number into String for finding length
        int l = s.length();
        
        if(l!=14) // If length is not 14 then IMEI is Invalid
            System.out.println("Output : Invalid Input");
        else
        {
            int d = 0, sum = 0;
            for(int i=14; i>=1; i--)
            {
                d = (int)(n%10);
                
                if(i%2 == 0)
                {
                    d = 2*d; // Doubling every alternate digit
                }

                sum = sum + ob.sumDig(d); // Finding sum of the digits
                
                n = n/10;
            }
            System.out.println("Sum = "+sum);

            int dig = (9*sum)%10; // Finding the check digit
            System.out.println("Output : The check digit = "+dig);
            
        }
    }
}