The API doc for TextBox has a couple issues.
http://java.sun.com/javafx/1/docs/api/javafx.scene.control/javafx.scene.control.TextBox.html
1. The code probably needs some height and width for its Stage. As is, it produces a frame with no height and user must resize to see anything. Something like
Stage {
    width: 36
    height: 64
 ...
will do.

2. The overview says,
"the code
<...code ..>
produces"
  and here it shows and empty box.


The images needs to be update to the usual Hello World window.