Some time ago, I came across a piece of code, that used some piece of standard java functionality to locate the classes that implemented a given interface. I know the the functions were hidden in some non logical place, but they could be used for other classes as the package name implied. Back then I did not need it, so I forgot about it, but now I do, and I can't seem to find the functions again. Does anyone know where to find these functions?

edit: I'm not looking for any IDE functions or anything, but rather something that can be executed within the java application.