Device Configuration Changes and the Activity Lifecycle
Rotating the device changes the device configuration. The device configuration is a set of characteristics that describe the current state of an individual device. The characteristics that make up the configuration include screen orientation, screen density, screen size, keyboard type, dock mode, language, and more.
Typically, applications provide alternative resources to match device configurations. You saw an example of this when you added multiple arrow icons to your project for different screen densities.
When a runtime configuration change occurs, there may be resources that are a better match for the new configuration. So Android destroys the activity, looks for resources ...