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What is Android?

Android is a free and open source operating system from Google running on everything from watches to eBook readers to smartphones to tablets to telivision sets.

What makes Android so special?

You can target a ton of different devices with just one platform. Google provides all the tools required for developing Android apps for free.

The Architecture of Android

Application Framework

• Views:                             Lists,Grids,Buttons
• Content Providers:           Contacts,Bookmarks
• Resource Manager:          Layout files,Graphics,Localized strings
• Notification manager:       Custom alerts in status bar
• Activity manager:             Application lifecycle,Navigation backstack

Libraries

• System C library (libc)
• Media Libraries (OpenCORE)
• SQLite
• Surface Manager
• LibWebCore
• SGL
• FreeType
• 3D Libraries

Android Runtime

• Dalvik Virtual Machine
• Core Libraries

Linux Kernel

• Memory management
• Process management
• Drivers
• Network stack
• Security

Application components

• Activities:
      Single screen with a user interface.
      All activities are independent of each other.
• Services:
      Background process to perform long-running task.
      No user interface.
• Content providers:
      Manages a shared set of application data.
      Store data in file system, SQLite database or any other persistent storage location.
      With proper permissions application can read and write data to another application.
• Broadcast receivers:
      Responds to system-wide announcements.
      Form of event handler.

Activity Lifecycle