What is Android

What is Android

Android is an open source operating system, created by Google specifically for use on mobile devices (cell phones and tablets)

Linux based (2.6 kernel)

Can be programmed in C/C++ but most app development is done in Java (Java access to C Libraries via JNI (Java Native Interface))

Supports Bluetooth, Wi-Fi, and 3G and 4G networking

Android has a large number of applications available for download in Google play store. Around 1 million apps are published and over 50 billion downloads.

 According to survey conducted in April-May 2013 found that Android is the most popular platform for developers .It is used by almost 71% of the mobile developer’s population.

Google Proudly announced that 1 billion activated devices now use the Android OS worldwide.

Android was founded by  Andy Rubin(co-founder of Danger),

Rich Minner(co-founder of wild-fire communications)and

Chris White(headed design and interface development  at WebTV).

Android Application Life Cycle

The Android application life cycle is unique in that the system controls much of the life cycle of the application. All Android applications, or Activities, are run within their own process. All of the running  processes are watched by Android and, depending on how the activity is running (this is, a foreground activity, background activity, and so forth),Android may choose to end the activity to reclaim needed resources.
An activity represents a single screen with a user interface just like window or frame of Java.Android activity is the subclass of ContextThemeWrapper class.
If you have worked with C, C++ or Java programming language then you must have seen that your program starts from main() function. Very similar way, Android system initiates its program with in an Activity starting with a call ononCreate() callback method. There is a sequence of callback methods that start up an activity and a sequence of callback methods that tear down an activity as shown in the below Activity life cycle diagram:

Some of the specific methods and description

onCreate()      This is the first callback and called when the activity is first created.

onStart()         This callback is called when the activity becomes visible to the user.

onResume()     This is called when the user starts interacting with the application.

onPause()        The paused activity does not receive user input and cannot execute any code and                                   called when the current activity is being paused and the previous activity is being                                 resumed.

onStop()          This callback is called when the activity is no longer visible.

onDestroy()     This callback is called before the activity is destroyed by the system.

onRestart()       This callback is called when the activity restarts after stopping it.