public boolean validateIsbn13(String isbn) {
if (isbn == null) {
return false;
}
// remove any hyphens
isbn = isbn.replaceAll("-", "");
// must be a 13 digit ISBN
if (isbn.length() != 13) {
return false;
}
try {
int tot = 0;
for (int i = 0; i < 12; i++) {
int digit = Integer.parseInt(isbn.substring(i, i + 1));
tot += (i % 2 == 0) ? digit * 1 : digit * 3;
}
// checksum must be 0-9. If calculated as 10 then = 0
int checksum = 10 - (tot % 10);
if (checksum == 10) {
checksum = 0;
}
return checksum == Integer.parseInt(isbn.substring(12));
} catch (NumberFormatException nfe) {
// to catch invalid ISBNs that have non-numeric characters in them
return false;
}
}
