Android studio offers you to analyse any apk file.
1 - From build menu choose analyse apk option and select apk file. 2 - This will result in you the classes.dex file and other files. 3 - Click on classes.dex which will give you the list of folders, packages, libraries and files. 4 - From and android studio settings install a plugin called "Dex to Jar" 5 - click on any activity file of your extracted project and choose dex to jar from the build menu.
This will result in you the actual code of your java file.
Cheers.