Exceptions while using version 13 (after upgrading from 10)

[pskowronek]

While updating muCommander to use VAqua 13 (from version 10) we see stacktraces in logs that cause both visual and behavioral issues as described here: mucommander/mucommander#1459 (comment)

Any hope for feedback if this could be fixed in VAqua?

Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
        at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1230)
        at org.violetlib.aqua.AppearanceColorsBuilder.getSystemColors(Unknown Source)
        at org.violetlib.aqua.AppearanceColorsBuilder.<init>(Unknown Source)
        at org.violetlib.aqua.AquaAppearances.getAquaAppearance(Unknown Source)
        at org.violetlib.aqua.AquaAppearances.appearanceChanged(Unknown Source)
        at org.violetlib.vappearances.VAppearances.invokeListeners(Unknown Source)
        at org.violetlib.vappearances.VAppearances.lambda$installAppearance$1(Unknown Source)
        at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:318)
        at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
        at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:720)
        at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:714)
        at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
        at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
        at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
        at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
        at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
        at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
        at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
        at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

java.lang.IllegalArgumentException: listener mismatch
        at java.desktop/java.awt.dnd.DropTarget.removeDropTargetListener(DropTarget.java:334)
        at org.violetlib.aqua.AquaTableUI.uninstallListeners(Unknown Source)
        at java.desktop/javax.swing.plaf.basic.BasicTableUI.uninstallUI(BasicTableUI.java:1653)
        at java.desktop/javax.swing.JComponent.uninstallUIAndProperties(JComponent.java:755)
        at java.desktop/javax.swing.JComponent.setUI(JComponent.java:730)
        at java.desktop/javax.swing.JTable.setUI(JTable.java:3662)
        at java.desktop/javax.swing.JTable.updateUI(JTable.java:3711)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1363)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI0(SwingUtilities.java:1378)
        at java.desktop/javax.swing.SwingUtilities.updateComponentTreeUI(SwingUtilities.java:1354)
        at com.mucommander.ui.main.WindowManager.lambda$setLookAndFeel$2(WindowManager.java:309)
        at java.base/java.util.Vector.forEach(Vector.java:1359)
        at com.mucommander.ui.main.WindowManager.setLookAndFeel(WindowManager.java:308)

[cbfiddle]

I believe the java.util.ConcurrentModificationException issue is a problem in VAppearances that has been fixed in the latest sources on GitHub. Alan

[cbfiddle]

I’m not getting anywhere on the listener mismatch issue. Can you insert a breakpoint where that exception is thrown at tell me what the parameter value is, what the field dtListener value is, and what the DropTarget instance class is?

[pskowronek]

I believe the java.util.ConcurrentModificationException issue is a problem in VAppearances that has been fixed in the latest sources on GitHub.

Thanks! Is a new release planned?

Can you insert a breakpoint where that exception is thrown at tell me what the parameter value is, what the field dtListener value is, and what the DropTarget instance class is?

I will try and return with results.

[pskowronek]

And more detailed screenshots:

If you need anything more please let me know!

[cbfiddle]

OK, I think what is going on is that you are using an instance of java.awt.dnd.DropTarget, which has the misfeature of supporting only one drop target listener. In this case, your app and VAqua are both trying to add drop target listeners, but only one can be stored. You would be better off letting TransferHandler install its own drop target, which handles multiple listeners. The remaining issues probably result from AquaTableUI not being fully uninstalled due to the unhandled exception. Alan

[pskowronek]

Thanks for information!

So, hm, why other LaFs behave correctly?

[cbfiddle]

They don’t install a drop target listener.

…

On Apr 8, 2026, at 10:42 AM, Piotr Skowronek ***@***.***> wrote: pskowronek left a comment (violetlib/vaqua#53) <#53 (comment)> Thanks for information! So, hm, why other LaFs behave correctly? — Reply to this email directly, view it on GitHub <#53 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABSSJGKNLNF26KQ4FBZRTE34U2FQHAVCNFSM6AAAAACXOUVXTGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DEMBYGI2TGMJYHE>. You are receiving this because you commented.

[pskowronek]

They don’t install a drop target listener.

Excuse my silly questions :) but ... why VAqua install one then? I mean, it is LaF... I assume that there's some custom implementation of Tree which requires that for drag-n-drop, right?

BTW, do you have any plans soon to release a new version of VAqua with a fix for #53 (comment) ?

[cbfiddle]

On Apr 8, 2026, at 12:15 PM, Piotr Skowronek ***@***.***> wrote: pskowronek left a comment (violetlib/vaqua#53) <#53 (comment)> They don’t install a drop target listener. Excuse my silly questions :) but ... why VAqua install one then? I mean, it is LaF... I assume that there's some custom implementation of Tree which requires that for drag-n-drop, right?

It affects how table cells are displayed by configuring the cell renderer.

BTW, do you have any plans soon to release a new version of VAqua with a fix for #53 (comment) <#53 (comment)> ?

It will be a new release of VAppearances, and “soon” is probably accurate.

…

— Reply to this email directly, view it on GitHub <#53 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABSSJGPAKY3AAF54MGZXTSD4U2QNZAVCNFSM6AAAAACXOUVXTGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DEMBYHE2TSNJZG4>. You are receiving this because you commented.