Android R.Java File

The id for the created component is automatically generated in the R.java whenever a component is created in the android activity_main.xml file. The life cycle methods for an activity such as onCreate, onStop, OnResume, etc is provided by the Activity java class.

The android R.java file contains many static nested classes such as menu, id, layout, attr, drawable, string, etc. 

  1. Theme customizations available in newer API levels can go in 
  2.             res/values-vXX/styles.xml, while customizations related to 
  3.             backward-compatibility can go here