Android Basic Go Back Designing Your App views 8:31 The next folder is java. There are three sub-folders under it. Com.example.user.helloworld, Com.example.user.helloworld(androidTest), Com.example.user.helloworld(test). Com.example.user.helloworld: The file MainActivity.java is present in this folder. The code that we will change or write is all present in this file. Android Operating Systems & Apps Creating First App Designing Your App Views of Apps Changing the Apps Look Making an Interactive App