Starting with Java 8u20, we get this error, when halting the VM:

Exception in thread "Thread-4" java.lang.IllegalStateException: Attempt to call defer when toolkit not running
at com.sun.javafx.tk.quantum.QuantumToolkit.defer(QuantumToolkit.java:646)
at com.sun.javafx.application.PlatformImpl.runLater(PlatformImpl.java:285)
at com.sun.javafx.application.PlatformImpl.runLater(PlatformImpl.java:261)
at javafx.application.Platform.runLater(Platform.java:78)

I don't see a way to check if the Toolkit is running or not. So the only possibility is to wrap the Platform.runLater call in a try-catch?

Testcase: Click Button.

import javafx.application.Application;
import javafx.application.Platform;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.stage.Stage;

public class TestApp2 extends Application {
    public static void main(String[] args) {
        Application.launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {

        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                Platform.runLater(new Runnable() {
                    @Override
                    public void run() {

                    }
                });
            }
        });

        Button button = new Button("Click");
        button.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                System.exit(0);
            }
        });

        Scene scene = new Scene(button);
        stage.setScene(scene);
        stage.show();
    }
}



I also saw this error, after shutting down the VM, but I can't get to reproduce it with the above Testcase:

java.lang.NullPointerException
at com.sun.javafx.tk.quantum.QuantumToolkit.isSupported(QuantumToolkit.java:1044)
at com.sun.javafx.application.PlatformImpl.isSupportedImpl(PlatformImpl.java:713)
at com.sun.javafx.application.PlatformImpl.isSupported(PlatformImpl.java:468)
at javafx.application.Platform.isSupported(Platform.java:163)
at javafx.scene.Scene.getEffectiveCamera(Scene.java:957)
at javafx.scene.Scene.pick(Scene.java:1898)
at javafx.scene.Scene.access$6700(Scene.java:144)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3673)
  at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3447)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1723)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2456)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:348)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:273)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:382)
at com.sun.glass.ui.View.handleMouseEvent(View.java:553)
  at com.sun.glass.ui.View.notifyMouse(View.java:925)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$126(WinApplication.java:102)
at com.sun.glass.ui.win.WinApplication$$Lambda$37/33481228.run(Unknown Source)
at java.lang.Thread.run(Thread.java:745)