in android, it is possible to get the source file from the .apk file.
It is possible. To do this, you need a decompiler. But be careful to consider legal issues.
I use Dedexer or dex2jar . In most cases there are good results, but sometimes it is not possible to decompile all sources.
Well, as a rule, you cannot or cannot be able to, but you can try to "reverse engineer" apk (as it is called) using android-apktool:
http://ibotpeaches.imtqy.com/Apktool/
I have no experience with the program yet
just go to this tutorial
http://forum.xda-developers.com/showthread.php?t=1108798 I hope this helps you.