JAVA LUHN

 1 static boolean luhn(String pnr){
 2     // this only works if you are certain all input will be at least 10 characters
 3     int extraChars = pnr.length() - 10;
 4     if (extraChars < 0) {
 5       throw new IllegalArgumentException("Number length must be at least 10 characters!");
 6     }
 7     pnr = pnr.substring(extraChars, 10 + extraChars);
 8     int sum = 0;
 9     for (int i = 0; i < pnr.length(); i++){
10       char tmp = pnr.charAt(i);
11       int num = tmp - ‘0‘;
12       int product;
13       if (i % 2 != 0){
14         product = num * 1;
15       }
16       else{
17         product = num * 2;
18       }
19       if (product > 9)
20         product -= 9;
21       sum+= product;              
22     }
23     return (sum % 10 == 0);
24   }
25 
26   private static void printMessage(boolean valid) {
27     if (valid){
28       System.out.print("Valid!\r");
29     }
30     else{
31       System.out.print("Invalid!");
32     }
33   }
34 }