title: Check if a package (API) is loaded in Java
body: <p>I'd like to ask, 
  is there a way for a java program to see if package x is loaded?
  I've been making mods (for minecraft), and I have realised that almost all of my programs need to use the same methods. So I want to make an API. But I need to make sure that if the API isn't loaded, the program won't work.</p>