Annotation processor Filer expects a fully qualified path name and not a file system path.
The fully qualified name should return the package, if there is one, and the simple name.
Include a space after a return if an expression is used.
Fix a couple open/close bracket sections.
Ensure the if statement gets written if there is also an else statement.
A nested type should create a NestedJType from a ReferenceJType rather than a new ReferenceJType.
Parameters cannot be public