Consider following refactoring for the compiler:

Parser.Factory -> ParserFactory
Parser -> JavacParser

add new interface
interface Parser {
JCCompilationUnit compilationUnit();
}
with extra methods reverse-engineered from JavacParser as necessary,
so that clients of JavacParser can be clients of new Parser interface.

This all facilitates adding substitutable parsers (i.e. ANTLR),
by changing the ParserFactory.