public class HelloTextField extends Application {
    @Override public void start(Stage stage) throws Exception {
        TextField a = new TextField();
        a.setPromptText("Enter text here");

        TextField b = new TextField();
        b.textProperty().bind(a.textProperty());

        TextField c = new TextField();
        c.setPromptText("This box and the next one are bidirectionally bound");

        TextField d = new TextField();
        d.setPromptText("This box and the previous one are bidirectionally bound");
        c.textProperty().bindBidirectional(d.textProperty());

        VBox box = new VBox(5);
        box.getChildren().addAll(a, b, c, d);
        stage.setScene(new Scene(box, 500, 500));
        stage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}