The best practice is to use “contract-first”, and here is the link that explains this much better with examples –>  contract-first versus contract-last web services In a nutshell, the contract-last is more fragile than the “contract-first”.You will have to decide what is most appropriate based on your requirements, tool sets you use, etc.

Note: More Java Web Services interview questions and answers including WSDL, SOAP, UDDI, JAXR, SAAJ, etc are covered in Java/J2EE Job Interview Companion with diagrams.