import static ch.codeblock.qrinvoice.util.QRReferenceUtils.*;
// ...
System.out.println(QRReferenceUtils.modulo10Recursive("12345"));
// prints the checksum of 12345 "7"
The QRReferenceUtils contains the modulo10 calculation, which is used to calculate the checksum of a digit string.
import static ch.codeblock.qrinvoice.util.QRReferenceUtils.*;
// ...
System.out.println(QRReferenceUtils.modulo10Recursive("12345"));
// prints the checksum of 12345 "7"