The Layout File
The activity_main.xml is a layout file available in res/layout directory, that is referenced by your application when building its interface. You will modify this file very frequently to change the layout of your application. For your “Hello World!” application, this
The R File
The gen/com.example.helloworld/R.java file is the glue between the activity Java files likeMainActivity.java and the resources like strings.xml. It is an automatically generated file and you should not modify the content of the R.java file. Following is a sample of R.java
The Manifest File
Whatever  component  you  develop as    a  part  of  your  application,    you  must    declare    all  its  components  in a manifest file called AndroidManifest.xml which ressides at the root of the application project directory. This file works as an interface between Android
Hello World Example
Let us start actual programming with Android Framework. Before you start writing your first example usingAndroid SDK, you have to make sure that you have setup your Android development environment properly as explained in Android – Environment Setup tutorial. I