title: Find Java classes implementing an interface
body: <p>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 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. Where can these functions be found?</p>
  
  <p>Edit: I'm not looking for any IDE functions or anything, but rather something that can be executed within the Java application.</p>