Hi,
Currently we don't have java developer kit. Music web services are REST web services and it will be easy to call API using java.net.URLConnection(
http://java.sun.com/javase/6/docs/api/java...Connection.html ) classes. You can use HttpClient (
http://hc.apache.org/httpclient-3.x/ )for connection pooling.
For specific questions regarding BBAuth please refer
http://developer.yahoo.com/auth . We has PHP quick start package too on this page. You can download and use it.
Let us know if you have any more specific question what you need in java.
Regards
Sandy