title: how to show a popover on clicking a button in java fx
body: <p>I am trying to make a popover when clicking a button in java fx, 
  what is the best way to do this, can anyone say.</p>
  
  <p>I already tried </p>
  
  <pre><code>Popup pop = new Popup
  </code></pre>
  
  <p>but this is not the one i actually need.</p>