title: How to use an ExecutorCompletionService
body: <p>I would like to use the constructor on the <code>ExecutorCompletionService</code> which takes a pre-defined <code>BlockingQueue</code>.</p>
  
  <p>Can anyone provide a code snippet to show how this is done.  It seems only to take a a <code>BlockingQueue</code> with <code>Future</code>s.  How does this match with the fact that submit must be done with <code>Callable</code>s.</p>
  
  <p>I'm getting a little confused here - please help...</p>