There were a couple of threads on OTN where people asked whether they can have a generic default structure for a java file when JDeveloper creates it. Usually this is in order to add some header/footer type of structure/comment to the start and end of the file, for example to include file info and copy right.
Right now JDeveloper doesn't have a file template concept (it's on our to-do list for a future version), but a quick way to achieve a similar result is to create a code template that can be used with the surround with option in the code editor to enclose your file with the code you want.
This is leveraging the new capabilities of the code template mechanism in JDeveloper 11g.
Here is a short demo showing how to do this: