Explain the functionality of the code below.

ActivityResultLauncher testActivity $=$ registerForActivityResult$($

new ActivityResultContracts.StartActivityForResult$(),$

new ActivityResultCallback$()\{$

@Override

public void onActivityResult$($ActivityResult result$)\{$

if $($result$.$getResultCode$()==$ Activity.RESULT$\_$OK$)\{$

Intent i $=$ result.getData$()$;

String str $=$ i$.$getStringExtra$("$user$\_$name"$)$;

Log.d$("$MainActivity$",$ str$)$;

$\}$

$\}$

$\}$

$)$;