To expand on the "use JAXB" comments above,
In Windows "%java_home%\bin\xjc" -p [your namespace] [xsd_file].xsd
e.g., "%java_home%\bin\xjc" -p com.mycompany.quickbooks.obj quickbooks.xsd
Wait a bit, and if you had a well-formed XSD file, you will get some well-formed Java classes