title: Is there any difference between "center_horizontal|center_vertical" and "center"
body: <p>I want to center an image in a linearLayout.</p>
  
  <p>Is there any difference between</p>
  
  <pre><code>android:gravity="center_horizontal|center_vertical"
  </code></pre>
  
  <p>and </p>
  
  <pre><code>android:gravity="center"
  </code></pre>
  
  <p>?</p>