What do the Manager classes in Application Framework and libraries do?

Question

I am trying to understand the Android Stack given below:

I understand what Application layer is. It is a collection of Android Applications installed on the device.

Linux Kernel as I understand is also the part of the Android OS.

My question is regarding the Libraries and Applications Framework. Are libraries as shown above in screenshot the part of the OS or SDK (Software development kit)? If both? how?

Same question of the Applications Framework. Is it part of developer's SDK or something specifically for Android OS? As I haven't typically seen the use of such classes like ActivityManager, WindowManager, and NotificationManager. So that means they are used by the system itself or the user according to the screenshot?

Answer 1

The diagram you posted is a diagram of software on Android devices. It does not represent in any way the Android SDK available for developing Android applications.

The libraries listed in the Libraries layer are in the Android operating system itself. Similarly, the items listed in the Applications Framework layer are provided by the operating system.

The Android SDK exposes interfaces to developers for interacting with elements of the operating system. For example, while the OS itself has a notification manager that is responsible for displaying (and otherwise managing) notifications, the SDK exposes a NotificationManager class that developers can use to interact with the notification system. Not every OS component has an SDK counterpart, and vice-versa.

Also keep in mind that nothing in that diagram is necessarily guaranteed to exist on all devices. Manufacturers may fork Android and remove certain components, or newer versions of Android may render that diagram obsolete. It exists solely as an illustration of the overall architecture of Android.