Here is a simple video tutorial showing how you can easily extract or obtain the entire source code from a fully compiled Android APK file of application.
Just follow all the instructions and you will surely end up with the source code.
Here are the links to the required files:
dex2jar ——- http://bit.ly/1DI1yQv
Java Decompiler —— http://bit.ly/1DxB1Ei
framework-res.apk ——- http://bit.ly/1z9XNXz
apktool & apktool install window —— http://bit.ly/1doYLW5