I have a Main class with has onCreate() method. in that method i have made the MapFile class\' object.and called its readFile() and
I think your issue is not the byteArray but the findViewById. As you say that the NPE is on the first line. There are rules around this method you have two options to call it :
Either you use it to query a View you already have in the layout you called in setContentView
Or you use it on a View contained in a layout you inflated manually with a layout inflater
If you try to use it in your activity to call a View from any other layout than the one in setContentView that you have not inflated yourself, it will return null.