title: Center stage on parent stage
body: <p>I am creating an application in JavaFx, In which I want to do that if any child stage is getting opened then it should be opened in center of parent stage.
  I am trying to do this using <code>mystage.centerOnScreen()</code> but it'll assign the child stage to center of screen, not the center of parent stage.
  How can I assign the child stage to center of parent stage?</p>
  
  <pre><code>private void show(Stage parentStage) {
      mystage.initOwner(parentStage);
      mystage.initModality(Modality.WINDOW_MODAL);
      mystage.centerOnScreen();
      mystage.initStyle(StageStyle.UTILITY);
      mystage.show();
   }
  </code></pre>