in this code why the figures don't show on the screen just the gray screen show $($import javafx.application.Application;

import javafx.scene.Group;

import javafx.scene.PerspectiveCamera;

import javafx.scene.Scene;

import javafx.scene.paint.Color;

import javafx.scene.paint.PhongMaterial;

import javafx.scene.shape.AmbientLight;

import javafx.scene.shape.Cylinder;

import javafx.scene.shape.Sphere;

import javafx.stage.Stage;

import javafx.scene.transform.Rotate;

public class ThreeDSceneExample extends Application $\{$

@Override

public void start$($Stage stage$)\{$

$//$ Root group for all $3$D shapes

Group root $=$ new Group$()$;

$//$ Create the main central sphere

Sphere centralSphere $=$ new Sphere$(50)$;

PhongMaterial redMaterial $=$ new PhongMaterial$($Color$.$RED$)$;

centralSphere.setMaterial$($redMaterial$)$;

$//$ Create smaller spheres and cylinders for connections

createAndAddConnection$($root$,$ centralSphere, $100,0,0,$ Color.BLUE$)$; $//$ right

createAndAddConnection$($root$,$ centralSphere, $-100,0,0,$ Color.GREEN$)$; $//$ left

createAndAddConnection$($root$,$ centralSphere, $0,100,0,$ Color.BLUE$)$; $//$ top

createAndAddConnection$($root$,$ centralSphere, $0,-100,0,$ Color.GREEN$)$; $//$ bottom

createAndAddConnection$($root$,$ centralSphere, $0,0,100,$ Color.BLUE$)$; $//$ front

createAndAddConnection$($root$,$ centralSphere, $0,0,-100,$ Color.GREEN$)$; $//$ back

$//$ Add ambient light

AmbientLight light $=$ new AmbientLight$($Color$.$WHITE$)$;

root.getChildren$().$add$($light$)$;

$//$ Set up the camera

PerspectiveCamera camera $=$ new PerspectiveCamera$($true$)$;

camera.setTranslateZ$(-500)$;

Scene scene $=$ new Scene$($root$,600,600,$ true$)$;

scene.setFill$($Color$.$LIGHTGRAY$)$;

scene.setCamera$($camera$)$;

$//$ Adding rotation transformation

root.getTransforms$().$addAll$($

new Rotate$(45,$ Rotate.X$\_$AXIS$),$

new Rotate$(45,$ Rotate.Y$\_$AXIS$)$

$)$;

$//$ Set up the stage

stage.setTitle$("3$D Scene Example"$)$;

stage.setScene$($scene$)$;

stage.show$()$;

$\}$

private void createAndAddConnection$($Group root, Sphere centralSphere, double x$,$ double y$,$ double z$,$ Color color$)\{$

$//$ Create a small sphere at the end of each arm

Sphere sphere $=$ new Sphere$(20)$;

PhongMaterial material $=$ new PhongMaterial$($color$)$;

sphere.setMaterial$($material$)$;

sphere.setTranslateX$($x$)$;

sphere.setTranslateY$($y$)$;

sphere.setTranslateZ$($z$)$;

$//$ Create a cylinder to connect the central sphere to the outer sphere

Cylinder connection $=$ new Cylinder$(10,100)$;

connection.setMaterial$($new PhongMaterial$($Color$.$DARKGRAY$))$;

connection.setTranslateX$(($x $+$ centralSphere.getTranslateX$())/2)$;

connection.setTranslateY$(($y $+$ centralSphere.getTranslateY$())/2)$;

connection.setTranslateZ$(($z $+$ centralSphere.getTranslateZ$())/2)$;

if $($x $!=0)\{$

connection.setRotationAxis$($Rotate$.$Y$\_$AXIS$)$;

connection.setRotate$(90)$;

$\}$ else if $($y $!=0)\{$

connection.setRotationAxis$($Rotate$.$X$\_$AXIS$)$;

connection.setRotate$(90)$;

$\}$

root.getChildren$().$addAll$($sphere$,$ connection$)$;

$\}$

public static void main$($String$[]$ args$)\{$

launch$($args$)$;

$\}$

$\})$