title: Error:(64, 72) error: non-static method getString(int)
body: <p>What's wrong? 
  I am trying to extract a string used in strings.xml 
  but I get error:</p>
  
  <pre><code>Error:(64, 72) error: non-static method getString(int) cannot be referenced from a static context
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>private static String file_url  = "http://xxxx.yy/" + getString(R.string.next_update_id);
  </code></pre>