• Written in Java language
• They are compiled to Android’s own bytecode format, Dalvik executable(DEX)
• Doesn’t have a single entry-point, such as the main method in Java
• Four components
  • Activities: visible parts of an application
  • Services: run in the background and are not interacting with the user directly, used for long running background such as mp3 playback
  • Broadcast receivers: react to global events, such as incoming calls or text messages
  • Content providers: implement domain-specific databases for, e.g. contacts
• onCreate(): gets called when the activity is launched for the first time
• Android Emulator: virtual mobile device that runs on a computer and is similar to a real device.
• Android API calls
  • Log.i(String tag, String msg):
    • Static methods which writes an info messages to the log
    • The log can be browed using the tool LogCat
  • findViewById(int id)
    • returns references to GUI objects