Modify Newly Created Android ProjectsWhen you create an Android project (e.g., via android create project) you supply the fully qualified class name of the main activity for the application (e.g., com.commonsware.android.SomeDemo. You will then find that your projectís src/ tree already has the namespace directory tree in place, plus a stub Activity subclass representing your main activity (e.g src/com/commonsware/android/SomeDemo.java). You are welcome to modify this file and add others to the src/ tree as needed to implement your application.
The first time you compile the project (e.g., via ant), out in the main activityís namespace directory, the Android build chain will create R.java. This contains a number of constants tied to the various resources you placed in the res/ directory tree. Throughout this book, you will see that many of the examples reference things in R.java (e.g., referring to a layoutís identifier via R.layout.main). Developer should not modify R.java yourself, but instead let the Android tools handle this for you