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

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?

An APK file is protected with the SHA-1 algorithm. You can see some files in the META-INF folder of APK. If you extract any APK file and change any of its content and zip it again and when you run that new APK file on an Android machine, it will not work, because the SHA-1 hashes will never match.