java - JavaFX Application returning NullPointerException when other Scene is called (just sometimes) -

my application has login scene , main view scene, happening when login , mainview called exception:

java.lang.nullpointerexception     @ javafx.scene.scene.focusinitial(scene.java:1879)     @ javafx.scene.scene.access$3600(scene.java:170)     @ javafx.scene.scene$scenepulselistener.focuscleanup(scene.java:2181)     @ javafx.scene.scene$scenepulselistener.pulse(scene.java:2221)     @ com.sun.javafx.tk.toolkit.firepulse(toolkit.java:363)     @ com.sun.javafx.tk.quantum.quantumtoolkit.pulse(quantumtoolkit.java:460)     @ com.sun.javafx.tk.quantum.quantumtoolkit$9.run(quantumtoolkit.java:329)     @ com.sun.glass.ui.win.winapplication._runloop(native method)     @ com.sun.glass.ui.win.winapplication.access$100(winapplication.java:29)     @ com.sun.glass.ui.win.winapplication$3$1.run(winapplication.java:73)     @ java.lang.thread.run(thread.java:722) 

the curious doesn't happening always, just sometimes.

my class:

public class targetappdesktop extends application {      @override     public void start(stage primarystage) throws ioexception {          scene scene = new scene(new anchorpane());          loginmanager loginmanager = new loginmanager(scene);         loginmanager.showloginscreen();         primarystage.setresizable(false);         primarystage.setscene(scene);         primarystage.show();          primarystage.setoncloserequest(new eventhandler<windowevent>() {             @override             public void handle(windowevent t) {                 mainviewcontroller.deletetempfiles();                 platform.exit();                 system.exit(0);             }         });      }      public static void main(string[] args) {         launch(args);     } } 

my login manager class

public class loginmanager {      private scene scene;      loginmanager(scene scene) {         this.scene = scene;     }      public void logout() {         showloginscreen();     }      void showloginscreen() {         try {             fxmlloader loader = new fxmlloader(                     getclass().getresource("login.fxml"));             //         scene.getstylesheets().add(this.getclass().getresource("login.css").toexternalform());              scene.setroot((parent) loader.load());             logincontroller controller =                     loader.<logincontroller>getcontroller();             controller.initmanager(this);         } catch (ioexception ex) {             logger.getlogger(loginmanager.class.getname()).log(level.severe, null, ex);         }     }      void showmainviewscreen(login logintargetapp, login logingateway, gateway gateway, file file, arraylist<integer> anolist) {              try {                  fxmlloader loader = new fxmlloader(getclass().getresource("mainview.fxml"));                  scene.setroot((parent) loader.load());                  mainviewcontroller controller = loader.<mainviewcontroller>getcontroller();                  controller.initsessionid(this, scene, logintargetapp, logingateway, gateway, file, anolist);              } catch (exception ex) {                 logger.getlogger(loginmanager.class.getname()).log(level.severe, null, ex);             }      }      void autheticated(login logintargetapp, login logingateway, gateway gateway, file file, arraylist<integer> anolist) {         showmainviewscreen(logintargetapp, logingateway, gateway, file, anolist);     } } 

this problem ocurring because trying change scene in thread, must changed in javafx main thread, simple platform.runlater solved problem.

more detail can find here. (jira link)