It is not uncommon that you find an amazing Android app on Google Play store and wish to know how the app is designed and developed.
You need then reverse engineer the Android app (from an APK file) and convert it to a project that you can understand and edit.
I found below three tools especially useful for such purposes.
The 1st one is APKTool. You can use it to “decode” the Android resources easily.
apktool d your.apk
After running this command line tool, you get a folder where the apk file is unpacked, and you can then find the resource files that you are most comfortable with:
./d2j-dex2jar.sh /Folder/A/B/your.apk // mac
C:\SomeFolder\d2j-dex2jar.bat Your.apk // windows
Using dex2jar, you can convert android .dex file into .class file:
Once you have the jar file, you can use JD-GUI to convert the .class file to .java source code: