Why are UI nodes manipulate operations blocked by the code after them?

Question

public void start(Stage stage) throws Exception {
     BorderPane root = new BorderPane();
     final Pane pane = new Pane();
     Button button = new Button("Click Me");
     button.setOnAction(new EventHandler<ActionEvent>() {               
          @Override
          public void handle(ActionEvent arg0) {
               Rectangle rectangle = new Rectangle(300, 100);
               rectangle.setFill(new Color(Math.random(), Math.random(), Math.random(), 1));
               pane.getChildren().clear();
               pane.getChildren().add(rectangle);
               try {
                    Thread.sleep(3000);
                    } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
     root.setCenter(pane);
     root.setBottom(button);
     Scene scene = new Scene(root, 500, 400);
     stage.setScene(scene);
     stage.show();          
The rectangle will be added to the pane after the thread wake up. I am new to JavaFX, who can help me? Thanks.
Edited by: 981471 on Jan 12, 2013 5:29 AM
Edited by: 981471 on Jan 12, 2013 5:30 AM
Edited by: 981471 on Jan 12, 2013 5:30 AM
Edited by: 981471 on Jan 12, 2013 5:31 AM

Answer 1

This seems normal to mee, because you've added Thread.sleep(3000);
This will make your current Tread inactive for 3sec. (so no UI rendering)
Look at this tutorial for Concurrency: http://docs.oracle.com/javafx/2/threads/jfxpub-threads.htm
Edited by: 981077 on 15-jan-2013 7:16