scene - javaFX - how to use function or object of a controller from another controller -

i have seen lot of question similar mine, didn't figure out how solve problem, there code:

i have simple main:

mainclassfxgui.java

public class mainclassfxgui extends application {      @override     public void start(stage stage) throws exception {         parent root = fxmlloader.load(getclass().getresource("myprogrammainguitab.fxml"));          scene scene = new scene(root);         stage.setscene(scene);         stage.settitle("assicurazione");         stage.show();     }      /**      * @param args command line arguments      */     public static void main(string[] args) {         launch(args);     } } 

and 3 fxml files, 1 of them contains other two, tag

<fx:include source="mytab1.fxml" /> 

myprogrammainguitab.fxml

... <tabpane maxheight="1.7976931348623157e308" maxwidth="1.7976931348623157e308" prefheight="5000.0" prefwidth="5000.0" tabclosingpolicy="unavailable">           <tabs>               <tab closable="false" text="mytab1">                    <content>     <fx:include source="mytab1.fxml" />                    </content>               </tab>               <tab closable="false" text="mytab2">                    <content>     <fx:include source="mytab2.fxml" />                    </content>               </tab>           </tabs>     </tabpane> ... 

and 3 controller:

myprogrammainguitabcontroller.java

.... @fxml private label leftst; /**  * initializes controller class.  */ @override public void initialize(url url, resourcebundle rb) {     leftst.settext(""); }      public void setleftst(string st){     leftst.settext(st); } ... 

mytab1controller.java

@fxml private void handlebuttonaction(actionevent event) {     system.out.println("you clicked me!");     setleftst("can change label of myprogrammainguitabcontroller?"); } 

i tried in way:

mytab1controller.java

private myprogrammainguitabcontroller controller;  @fxml private void handlebuttonaction(actionevent event) {         system.out.println("you clicked me!");         controller.setleftst("can change label of myprogrammainguitabcontroller?"); }  @override public void initialize(url url, resourcebundle rb) {     fxmlloader fxmlloader = new     fxmlloader(getclass().getresource("myprogrammainguitab.fxml"));     try {          fxmlloader.load();                 } catch (ioexception exception) {          throw new runtimeexception(exception);     }     controller = (myprogrammainguitabcontroller)fxmlloader.getcontroller(); } 

but have null pointer exception or if move code instanzialization of object 'controller' in handlebuttonaction function, don't have error, label not change.

maybe can create static scene , static stage in mainclassfxgui.java? don't know how use them...

mainclassfxgui.java

public class mainclassfxgui extends application {     static private scene scene;     static private stage stage;      @override     public void start(stage stage) throws exception {         parent root = fxmlloader.load(getclass().getresource("myprogrammainguitab.fxml"));          this.scene = new scene(root);         stage.setscene(scene);         stage.settitle("assicurazione");         stage.show();         this.stage = stage;     }     /**      * @param args command line arguments      */     public static void main(string[] args) {         launch(args);     }      public static scene getscene(){         return assicurazionefxgui.scene;     }      public static stage getstage(){         return assicurazionefxgui.stage;     }  } 

can getscene() or getstage()? idea or suggest?

thanks everyone

define stringproperty in mytab1controller, usual methods:

public class mytab1controller {      private final stringproperty leftst = new simplestringproperty();      public stringproperty leftstproperty() {          return leftst ;     }      public final string getleftst() {         return leftstproperty().get();     }      public final void setleftst(string leftst) {         leftstproperty().set(leftst);     }      // ...      @fxml     public void handlebuttonaction() {         setleftst(...);     }      // ... } 

now assign fx:id attribute fx:include tag:

<tab closable="false" text="mytab1">     <content>         <fx:include fx:id="mytab1" source="mytab1.fxml" />     </content> </tab> 

this means can inject controller mytab1.fxml controller fxml included (myprogrammainguitabcontroller):

public class myprogrammainguitabcontroller {      @fxml     private mytab1controller mytab1controller ;  } 

and can observe property , update label when changes:

public class myprogrammainguitabcontroller {      @fxml     private mytab1controller mytab1controller ;      @fxml     private label leftst;      public void initialize() {         leftst.settext("");         mytab1controller.leftstproperty().addlistener((obs, oldvalue, newvalue) ->              leftst.settext(newvalue));     }     } 

note rule here field name controller value of fx:id attribute word "controller" appended: mytab1 in fx:id resolves mytab1controller field controller injected. see nestedcontrollers more information.