The stated goal of this article was to give you a non-trivial extension to Eclipse's Java development environment that enhanced its productivity. In all honesty, more than once I skipped over some details for reasons of brevity. The solution itself makes some simplifying assumptions, like only allowing modifications to Java source already open in the editor. You would probably want to relax that restriction in a fuller implementation.
Nonetheless, I hope that you got a good taste of what's possible and you're convinced that it isn't all too difficult. What we've covered in this article is a portion of one of the advanced chapters in our book, The Java Developer's Guide to Eclipse. Eleven less advanced chapters cover the fundamentals of plug-in development. Like this article, most chapters include a documented working solution that reinforces what you've learned, much in the same style as what you've seen in this article (though perhaps not covered at such a breakneck pace!).