What is Activity.finish() method doing exactly?

When calling finish() on an activity, the method onDestroy() is executed. This method can do things like:

1. Dismiss any dialogs the activity was managing.
2. Close any cursors the activity was managing.
3. Close any open search dialog

Also, onDestroy() isn't a destructor. It doesn't actually destroy the object. It's just a method that's called based on a certain state. So your instance is still alive and very well* after the superclass's onDestroy() runs and returns.Android keeps processes around in case the user wants to restart the app, this makes the startup phase faster. The process will not be doing anything and if memory needs to be reclaimed, the process will be killed

My 2 cents on @K_Anas answer. I performed a simple test on finish() method. Listed important callback methods in activity life cycle

1. Calling finish() in onCreate(): onCreate() -> onDestroy()
2. Calling finish() in onStart() : onCreate() -> onStart() -> onStop() -> onDestroy()
3. Calling finish() in onResume(): onCreate() -> onStart() -> onResume() -> onPause() -> onStop() -> onDestroy()

What I mean to say is that counterparts of the methods along with any methods in between are called when finish() is executed.

eg:

 onCreate() counter part is onDestroy()
 onStart() counter part is onStop()
 onPause() counter part is onResume()

Also notice if you call finish() after an intent you can't go back to the previous activity with the "back" button

startActivity(intent);
finish();

onDestroy() is meant for final cleanup - freeing up resources that you can on your own,closing open connections,readers,writers,etc. If you don't override it, the system does what it has to.

on the other hand, finish() just lets the system know that the programmer wants the current Activity to be finished. And hence, it calls up onDestroy() after that.

Something to note:

it isn't necessary that only a call to finish() triggers a call to onDestroy(). No. As we know, the android system is free to kill activities if it feels that there are resources needed by the current Activity that are needed to be freed.

Finish() method will destroy the current activity. You can use this method in cases when you dont want this activity to load again and again when the user presses back button. Basically it clears the activity from the.current stack.