It is very easy to convert java application to android application. you can convert .jar/.jad file to .apk file for smartphone uses.
You’re going to need these two files:
-In dex2jar directory, paste your classes.dex file.
-Open CMD, go to dex2jar durectory using cd, and type dex2jar YourApp.apk
-You will automatically get a .jar. Use jd gui to decompile it.