After an activity started, restarted (onRestart() happens before onStart()), or paused (onPause()), onResume() called. When the activity is in the state of onResume(), the activity is ready to be used by the app user.
I have studied the activity lifecycle a little bit, and here's my understanding of this topic: If you want to restart the activity (A) at the end of the execution of another, there could be a few different cases.
The other activity (B) has been paused and/or stopped or destroyed, and the activity A possibly had been paused (onPause()), in this case, activity A will call onResume()
The activity B has been paused and/or stopped or destroyed, the activity A possibly had been stopped (onStop()) due to memory thing, in this case, activity A will call onRestart() first, onStart() second, then onResume()
The activity B has been paused and/or stopped or destroyed, the activity A has been destroyed, the programmer can call onStart() manually to start the activity first, then onResume() because when an activity is in the destroyed status the activity has not started, and this happens before the activity being completely removed. If the activity is removed, the activity needs to be created again. Manually calling onStart() I think it's because if the activity not started and it is created, onStart() will be called after onCreate().
If you want to update data, make a data update function and put the function inside the onResume(). Or put a loadData function inside onResume()
It's better to understand the lifecycle with the help of the Activity lifecycle diagram.