title: OQL to find instances implementing java.security.Principal
body: <p>This doesn't seem to return any result from Netbeans (which has the same heap analysis tools as VisualVM):</p>
  
  <pre><code>select x.name from java.security.Principal x
  </code></pre>
  
  <p>The query works if I put the name of a concrete class implementing Principal, but I'd need all implementations.</p>
  
  <p>Tried the same in Eclipse Memory Analyzer, same results.</p>
  
  <p>Any clue?</p>