Symmary You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities (Define its own layout for each fragment, and move logic operation to gragment from activity, then you can define different activities for tablet or handset to reuse the same segments). You can think of a fragment as a modular section of an activity, which has its own lifecycle (the fragment's lifecycle is directly affected by the host activity's lifecycle), receives its own input events, and which you can add or remove while the activity is running. You add/replace/remove fragement in transaction, when you perform such a fragment transaction, you can also add it to a back stack that's managed by the activity (with API addToBackStack)—each back stack entry in the activity is a record of the fragment transaction that occurred. The back stack allows the user to reverse a fragment transaction (navigate backwards), by pressing the BACK button.
