Currently finding subclasses/implementors of a
given class/interface is too slow. This slows down
finding usages, more accurate code completion, etc.
Performance of getSubclasses needs to be improved by:
1) storing superclass and implemented interfaces
of a given class persistently (lazily) - this will
avoid parsing of the potential subclasses if their
superclass/interfaces information is already
available in the storage
2) improve subclasses finding alorithm (find out
using lexical analysis if a given identifier is
used in extends or implements clause before
actually parsing the file)
3) third possible improvement can be to have a
separate superclass/superinterfaces index