title: what are "virtualized controls" ? (mentioned in JavaFX documentation).
body: <p>from <a href="http://docs.oracle.com/javafx/2/api/javafx/scene/control/Cell.html" rel="nofollow">http://docs.oracle.com/javafx/2/api/javafx/scene/control/Cell.html</a> :</p>
  
  <p>"The Cell API is used for <strong>virtualized</strong> controls such as ListView, TreeView, and TableView. A Cell is a Labeled Control, and is used to render a single "row" inside a ListView, TreeView or TableView."</p>
  
  <p>Why are they virtualized? </p>