Introducing the Android Software Development Platform
The Android platform is a collection of software that includes an operating system and a number of higher-level libraries that simplify the task of communicating with the operating system. It also includes several applications that smartphone, tablet, e-reader and iTV users have come to expect, such as a phone (obviously) dialer, e-mail client, social media client, contact manager, Google Maps, Google Search, a web browser, a calendar, basic games, and so on.
Everything in the Android development environment, as well as all of the included applications, can be programmed with a combination of Java and XML thanks to the so-called runtime that is included with the Android SDK. ...