In general case, it can be too late to do so, the files could be lost forever, depending on what have you done after you deleted them. In programming, loosing of the previous versions of the source files is way more likely than in most other cases.
You can try to restore the file using any 3rd-party utilities. You can easily find some freeware. I don't think we can promote these products on this site.
Your
real problem is very different. Apparently, you are not using any Revision Control system (
http://en.wikipedia.org/wiki/Revision_Control_System[
^]). This is bad. Such system can be open-source, extremely light-weight, reliable, easy to use. I would say, until you start to use one on all your projects, you are not really doing software development, not owning it, leaving it to the first system malfunction or a slip of a hand. Worse, you cannot retrace your steps.
Please see this discussion:
Revision control systems, which to choose from?[
^].
—SA