ADDITIONAL SYSTEM INFORMATION :
Windows 10
Java 21 or later
JavaFX 21 or later


A DESCRIPTION OF THE PROBLEM :
Adding, then removing, and then adding a JFXPanel to the same component in the Swing scene graph leads to a NullPointerException in GlassScene because the sceneState is null. The use case and where this bug was noticed is to show and hide tabs in a JTabbedPane, but the bug appears to be reproducible for any Swing component that can take children.

REGRESSION : Last worked in version 20

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create an instance of a JFXPanel.
2. Add the JFXPanel to a Swing component X as a child.
3. Remove the JFXPanel instance from X.
4. Add the JFXPanel instance again to Swing component X as a child.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The JFXPanel is visible to the user of the application and no Exceptions are thrown.
ACTUAL -
The JFXPanel is visible but the following Exception is thrown:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException: Cannot invoke "com.sun.javafx.tk.quantum.SceneState.update()" because "this.sceneState" is null
at javafx.graphics/com.sun.javafx.tk.quantum.GlassScene.updateSceneState(GlassScene.java:285)
at javafx.graphics/com.sun.javafx.tk.quantum.EmbeddedScene.lambda$setPixelScaleFactors$1(EmbeddedScene.java:159)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithRenderLock(QuantumToolkit.java:448)
at javafx.graphics/com.sun.javafx.tk.quantum.EmbeddedScene.lambda$setPixelScaleFactors$2(EmbeddedScene.java:158)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:456)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:455)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
at java.base/java.lang.Thread.run(Thread.java:1570)

---------- BEGIN SOURCE ----------
import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Scene;
import javafx.scene.control.Button;

import javax.swing.*;

public class FxTest {

    private static void initAndShowGUI() {
        JFrame frame = new JFrame("FX");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        final JFXPanel fxPanel = new JFXPanel();
        // fxPanel added to frame for the first time
        frame.add(fxPanel);
        frame.setVisible(true);

        Platform.runLater(() -> {
            initFX(fxPanel);
            SwingUtilities.invokeLater(() -> {
                // fxPanel removed from frame
                frame.remove(fxPanel);
                // fxPanel added to frame again
                frame.add(fxPanel); // <-- leads to NullPointerException
            });
        });
    }

    private static void initFX(JFXPanel fxPanel) {
        Scene scene = new Scene(new Button("Testbutton"));
        fxPanel.setScene(scene);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> initAndShowGUI());
    }

}
---------- END SOURCE ----------

FREQUENCY : always