The Android Platform comes with everything you need in a single package: the OS, device drivers, core libraries, the JNI, the optimized Dalvik VM, and the Java development environment. Developers can be assured that when they develop new applications, all key libraries will be available on the device.
The concept of a view in J2EE and Swing carries over to Android. Views are UI elements that form the basic building blocks of a user interface. Views are hierarchical and they know how to draw themselves.
An activity is a user interface concept. An activity usually represents a single screen in your application. It generally contains one or more views, but it doesn’t have to. Moreover, other concepts in Android could better represent a viewless activity (as you’ll see in the “Service” section shortly).
An intent generically defines an “intention” to do some work. Intents encapsulate several concepts, so the best approach to understanding them is to see examples of their use. You can use intents to perform the following tasks, for instance:
is similar to the web.xml file in the J2EE world, defines the contents and behavior of your application. For example, it lists your app’s activities and services, along with the permissions the application needs to run.