Validate ISBN 10

The problem

An ISBN-10 (International Standard Book Number) consists of 10 digits: d1d2d3d4d5d6d7d8d9d10. The last digit, d10, is a checksum, which is calculated from the other nine digits using the following formula: (d1 *1+d2 *2+d3 *3+d4 *4+d5 *5+ d6 *6+d7 *7+d8 *8+d9 *9)%11

If the checksum is 10, the last digit is denoted as X according to the ISBN-10 convention. Write a program that prompts the user to enter the first 9 digits and displays the 10-digit ISBN (including leading zeros). Your program should read the input as an integer. Here are sample output:

Enter the first 9 digits of an ISBN as integer: 013601267
The ISBN-10 number is 0136012671

Enter the first 9 digits of an ISBN as integer: 013031997
The ISBN-10 number is 013031997X

Breaking it down

Reading input from the user and splitting a string on chars we will have the ISBN number to perform our calculation. Since we need to multiply the index of the array by the position, using IntStream.range is a way to handle it in java 8. Next calling mapToInt will transforms the string of streams to an IntStream. Finally calling sum, a java 8 reduction operation will sum the first 9 values together. Using total and performing a mod (modular) will find the 10th element or checkSum. Finally combining it together to output the final format for the ISBN. Don't forget not validating the input could cause an Exception.

public static void main(String[] strings) {

    Scanner input = new Scanner(System.in);
    System.out.print("Enter the first 9 digits of an ISBN as integer: ");
    String nineDigitISBN = input.next();
    input.close();

    String[] elements = nineDigitISBN.split("");

    int total = IntStream.range(1, 10)
            .mapToObj(i -> Integer.valueOf(elements[i - 1]) * i)
            .mapToInt(Integer::intValue).sum();

    int checkSum = total % 11;

    System.out.println("The ISBN-10 number is " + nineDigitISBN
            + (checkSum == 10 ? "X" : checkSum));

}

Output

Enter the first 9 digits of an ISBN as integer: 013031997
The ISBN-10 number is 013031997X