ProgressBar in Javafx does not update in onAction block

Long form of tomsomtom’s precise answer:

If you use the JavaFX Thread to do this kind of long term work, you stop the UI from updating etc. So you have to run your worker in a sparate thread. If you run in a separate Thread, all GUI operatione like progress.setProgress() have to be passed back to the JavaFX Thread using runLater() as JavaFX is not multithreaded.

Try this in your Action:

    submit.setOnAction( new EventHandler<ActionEvent>() {
        @Override
        public void handle( ActionEvent event ) {
            double size = 10.0;
            new Thread(){
                public void run() {
                    for (double i = 0.0; i < size; i++){
                        final double step = i;
                        Platform.runLater(() -> progress.setProgress( step / size ));
                        System.out.printf("Complete: %02.2f%n", i * 10);

                        try {
                            Thread.sleep(1000); 
                        } catch(InterruptedException ex) {
                            Thread.currentThread().interrupt();
                        }
                    }
                }
            }.start();
        }

    } );