Android tutorial study

Note my study from http://www.vogella.com/tutorials/Android/article.html#firstandroidapp
This is a good start for Android application develop, below is the note after I read vogella.com. Let me know if any legal problem fro this post.

Four Android Software Component:

1. Activity

2. Services

3. Broadcast Receivers

4. Content Providers

Context:

Instances of the class android.content.Context provide the connection to the Android system which executes the application.

Layout Manager:

The android.view.ViewGroup class which extends the android.view.View class which is the base class for views