How Android can finish off another activity in one activity

==================== Problem Description ====================
Ask: How does Android finish off another activity in one activity?
==================== Solution 1====================
1, Finishacyivity () 2, with radio monitoring 3, with activitymanager am = (activitymanager) getsystemservice (activity_service); try it.
==================== Solution 2====================
For example, B to finish off a.
Set a static variable in a instance
And then in the OnCreate,
Instance=this;
Then call A.instance.finish () in B;

Or use the activity stack to manage it, but I won't.

How Android can finish off another activity in one activity