What are the differences between activity and fragment?

Question

As per my research, there is a significant difference in the concept of backstack and how they exist:

Activity

• When an activity is placed to the backstack of activities the user can navigate back to the previous activity by just pressing the back button.

• Activity can exist independently.

Fragment

• When an fragment is placed to the activity we have to request the instance to be saved by calling addToBackstack() during the fragment transaction.

• Fragment has to live inside the activity

Are there any additional differences?

Answer 1

Those are two completely different things:

An Activity is an application component that provides a screen, with which users can interact in order to do something. More details: http://developer.android.com/guide/components/activities.html

Whereas a Fragment represents a behavior or a portion of user interface in an Activity. http://developer.android.com/guide/components/fragments.html