title: What are the differences between activity and fragment?
body: <p>As per my research, there is a significant difference in the concept of backstack and how they exist:</p>
  
  <h3>Activity</h3>
  
  <ul>
  <li><p>When an <code>activity</code> is placed to the <code>backstack</code> of <code>activities</code> the user
  can navigate back to the previous activity by just pressing the <code>back</code>
  button.</p></li>
  <li><p><code>Activity</code> can exist independently.</p></li>
  </ul>
  
  <h3>Fragment</h3>
  
  <ul>
  <li><p>When an <code>fragment</code> is placed to the activity we have to request the
  instance to be saved by calling <code>addToBackstack()</code> during the <code>fragment</code>
  <code>transaction</code>.</p></li>
  <li><p><code>Fragment</code> has to live inside the <code>activity</code></p></li>
  </ul>
  
  <p>Are there any additional differences?</p>