java - How to lookup the thumb of a slider in a controller class for fxml? -

i want customize slider , found working example here on stackoverflow:

import javafx.application.application; import javafx.geometry.insets; import javafx.scene.scene; import javafx.scene.control.label; import javafx.scene.control.slider; import javafx.scene.layout.pane; import javafx.scene.layout.stackpane; import javafx.stage.stage;  public class sliderwithlabeledthumb extends application {      @override     public void start(stage primarystage) {         slider slider = new slider();         stackpane root = new stackpane(slider);         root.setpadding(new insets(20));          scene scene = new scene(root);          slider.applycss();         slider.layout();         pane thumb = (pane) slider.lookup(".thumb");         label label = new label();         label.textproperty().bind(slider.valueproperty().asstring("%.1f"));         thumb.getchildren().add(label);           primarystage.setscene(scene);         primarystage.show();      }      public static void main(string[] args) {         launch(args);     } } 

unfortunately, if thumb of slider in controller class fxml view, nullpointerexception when trying add label thumb's children… thumb can not looked up. found answer here says lookup() must called after stage.show(), here question again:
how can slider thumb in controller class manages fxml components (that not have stage.show())?
tried creating slider in code , used 1 fxml, both lookups return null when calling in controller's initialize(…) method.
is somehow possible customize slider's thumb in controller class?

edit:

the code produces exception in controller class gets automatically instantiated due entry in corresponding xml file. no matter if use slider loaded fxml annotation, having member , initialize or create new slider object. long in controller class, keep getting nullpointerexceptions line commented in code below:

public class mainviewcontroller implements initializable {      @fxml private vbox root;     private slider timeslider;      @override     public void initialize(url location, resourcebundle resources) {         timeslider = new slider();         root.getchildren.add(timeslider);         timeslider.setmax(360);         timeslider.setmin(0);         timeslider.setcursor(cursor.open_hand);         timeslider.applycss();         timeslider.layout();          pane thumb = (pane) timeslider.lookup(".thumb");         label label = new label();         label.textproperty().bind(timeslider.valueproperty().asstring("%.1f"));         // following line points thumb, null then… (debugger proof)         thumb.getchildren().add(label);     } } 

in main.java load fxml file:

public class main extends application {     @override     public void start(stage primarystage) {         try {             fxmlloader loader = new fxmlloader();             loader.setlocation(getclass().getresource("mainview.fxml"));             parent root = loader.load();             scene scene = new scene(root,800,600);             scene.getstylesheets().add(getclass().getresource("application.css").toexternalform());             primarystage.setscene(scene);             primarystage.show();         } catch(exception e) {             e.printstacktrace();         }     }      public static void main(string[] args) {         launch(args);     } } 

finally, fxml file:

<?xml version="1.0" encoding="utf-8"?> <?import javafx.scene.layout.vbox?> <vbox fx:id="root" maxheight="600" maxwidth="800" prefheight="600"     prefwidth="800" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1"     fx:controller="application.mainviewcontroller"> </vbox> 

wiki