How to avoid reverse engineering of an APK file?

Question

I am developing a payment processing app for Android, and I want to prevent a hacker from accessing any resources, assets or source code from the APK file.<

Answer 1

 1. How can I completely avoid reverse engineering of an Android APK? Is this possible?

This isn't possible

 2. How can I protect all the app's resources, assets and source code so that hackers can't hack the APK file in any way?

When somebody change a .apk extension to .zip, then after unzipping, someone can easily get all resources (except Manifest.xml), but with APKtool one can get the real content of the manifest file too. Again, a no.

 3. Is there a way to make hacking more tough or even impossible? What more can I do to protect the source code in my APK file?

Again, no, but you can prevent upto some level, that is,

• Download a resource from the Web and do some encryption process
• Use a pre-compiled native library (C, C++, JNI, NDK)
• Always perform some hashing (MD5/SHA keys or any other logic)

Even with Smali, people can play with your code. All in all, it's not POSSIBLE.