It is possible to crash Swing by calling Platform.Exit()

import javafx.application.Application;
import javafx.application.Platform;
import javafx.stage.Stage;

import javax.swing.*;

public class PlatformExitCrash extends Application {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(PlatformExitCrash::createSwing);
        Application.launch(args);
    }

    private static void createSwing() {
        JDialog d = new JDialog();
        Platform.runLater(()-> {
            Platform.exit();
        });
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
        }
        d.setVisible(true);
    }

    @Override
    public void start(Stage st) {
    }
}