Introduction to Java Programming编程题9.32<检测ISBN>

/*
Enter the ISBN numbers of the book: 013601267
0136012671
*/
import java.util.Scanner;

public class CheckISBN1 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter the ISBN numbers of the book: ");
        String s = input.next();
        for (int i = 0; i < s.length(); i++) {
            if (!Character.isDigit(s.charAt(i)) || s.length() > 9) {
                System.out.println("The string must be numbers.");
                System.exit(0);
            }
        }
        s = computeTenth(s);

        System.out.println(s);
    }

    public static String computeTenth(String s) {
        StringBuilder stringBuilder = new StringBuilder(s);
        int[] isbn = new int[9];
        int Ten = 0;

        for (int i = 0; i < s.length(); i++) {
            isbn[i] = charToInt(s.charAt(i));
            Ten += isbn[i] * (i + 1);
        }
        Ten %= 11;
        if (Ten == 10)
            stringBuilder.append('X');
        else
            stringBuilder.append(Ten);

        return stringBuilder.toString();
    }

    public static int charToInt(char ch) {
        return ch - 48;
    }
}