Fragment android beginner question

Question

this is a code i found in a book.the code is trying to communicate between fragments with the help of the mainActivity.

"this.listener = (WorkoutListListener) activity;"

1)why in the onAttach method we have to cast the interface to the activity?
2)why is it equals to this.listener(instance of
WorkoutListListener)

https://code.sololearn.com/cLhdwaVOm9vf/?ref=app

Answer 1

actually here it is used for getting the context of this class and used for initialization purpose so that it does not give null pointer exception