title: Open an activity via intent or via instance
body: <p>I have a class REG that extends <code>Activity</code>: it has a window, buttons, actions, etc. I know how to open the activity via an <code>Intent</code>.</p>
  <p>Yet, I could also make a new instance of the class:</p>
  <pre><code>new REG(...)
  </code></pre>
  <p>When/why I should use one over the other?</p>