I found good piece of information about what happens when screen orientation changes.
Here is a little diagram that shows what happens with different application parts during a configuration change or during an out-of-memory event. Every Android developer should know this data, however this data is surprisingly hard to find.
| Case 1 | Case 2 | Case 3
|A configuration| An activity | A process
| change | restart | restart
—————————————- | ————- | ———— | ————
Dialog | reset | reset | reset
Activity, View, Fragment | save/restore | save/restore | save/restore
Fragment with setRetainInstance(true) | no change | save/restore | save/restore
Static variables and threads | no change | no change | reset
Case 1: A configuration change normally happens when a user flips the screen, changes language settings, attaches an external monitor, etc. More on this event you can read here: configChanges.
Case 2: An Activity restart happens when a user has set “Don’t keep activities” checkbox in Developer’s settings and another activity becomes topmost.
Case 3: A process restart happens if there is not enough memory and the application is in the background.