Getting NullPointerException when trying to modify JavaFX gui components in controller

Question

So I am trying to create a JavaFX GUI. I have added a button onto the screen, and have set up a controller which I want to access the button and output the text of the button. Here is the code:

The FXML:

    ...
   <children>
      <Button fx:id="btnSubmit" layoutX="321.0" layoutY="185.0" mnemonicParsing="false" onMouseClicked="#graphClick" text="Submit" />
   </children>
...

The Controller:

public class GraphController implements Initializable {

private Button btnSubmit;

public void graphClick() {
    System.out.println(btnSubmit.getText());
}

@Override
public void initialize(URL location, ResourceBundle resources) {
    System.out.println("hello");

}

The Driver class:

public class Graph extends Application {
    public static void main(String[] args) {
        launch(args);

    }

    public static Stage stage;

    @Override
    public void start(Stage stage) throws Exception {
        Graph.stage = stage; // initialize value of stage.
        Parent root = FXMLLoader.load(getClass().getResource("MeansGUI.fxml"));
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();

        stage.setResizable(false);
    }
}

And finally, the error:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3470)
    at javafx.scene.Scene$ClickGenerator.access$8100(Scene.java:3398)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3766)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:417)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.Trampoline.invoke(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 31 more
Caused by: java.lang.NullPointerException
    at gui.GraphController.graphClick(GraphController.java:26)
    ... 41 more

From the console output, what I have understood so far is that the button - btnSubmit - is null, but I'm not sure how to make it not null.

Also, the initialize method works.

Can someone please point me in the right direction?

Many thanks,

See https://stackoverflow.com/questions/30210170/is-fxml-needed-for-every-declaration — James_D, Jun 24 '17 at 17:58

Nabin Bhandari · Accepted Answer · 2017-06-24T17:42:11.770

1

Private fields cannot be accessed by the FXML loader. If you really need it to be private, you can use @FXML annotation which uses java reflection to access private field.

Either use

public Button btnSubmit;

or

@FXML
private Button btnSubmit;

edited Jun 24 '17 at 17:42

answered Jun 24 '17 at 17:38

Nabin Bhandari

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Yes, that seemed to have worked. Thank you (I shall mark it as the answer when possible) – user_90 Jun 24 '17 at 17:41
you are welcome. you can mark it right now. just click the tick mark. – Nabin Bhandari Jun 24 '17 at 17:42

Getting NullPointerException when trying to modify JavaFX gui components in controller

1 Answers1