How does the system save the state of an Activity when the device configuration changes?

When the device configuration changes (for example, screen rotation), Android destroys the current Activity and recreates it. To preserve state, the system uses lifecycle methods:

• In the onSaveInstanceState(Bundle outState) method, data can be saved into the Bundle object.
• When recreating the Activity, the saved data can be restored in the onCreate(Bundle savedInstanceState) or onRestoreInstanceState(Bundle savedInstanceState) methods.

Thus, UI state and other necessary data are automatically saved and restored by the system if the developer implements these methods.