Difference Between Activity and Fragment Activity

A FragmentActivity is a subclass of Activity that was built for the Android Support Package.

The FragmentActivity class adds a couple new methods to ensure compatibility with older versions of Android, but other than that, there really isn't much of a difference between the two. Just make sure you change all calls to getLoaderManager() and getFragmentManager() to getSupportLoaderManager() and getSupportFragmentManager() respectively.

1. Fragment is a part of an activity, which contributes its own UI to that activity. Fragment can be thought like a sub activity. Where as the complete screen with which user interacts is called as activity. An activity can contain multiple fragments.Fragments are mostly a sub part of an activity.
2. An activity may contain 0 or multiple number of fragments based on the screen size. A fragment can be reused in multiple activities, so it acts like a reusable component in activities.
3. A fragment can't exist independently. It should be always part of an activity. Where as activity can exist with out any fragment in it.