Workswing und for Swing exceptions during lookandfeel switchover

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: javax.swing.plaf.ColorUIResource cannot be cast to java.util.Listat javax.swing.plaf.metal.MetalUtils.drawGradient(Unknown Source)at javax.swing.plaf.metal.MetalInternalFrameTitlePane.paintComponent(Unknown Source)at javax.swing.JComponent.paint(Unknown Source)at javax.swing.JComponent.paintChildren(Unknown Source)at javax.swing.JComponent.paint(Unknown Source)at javax.swing.JComponent.paintChildren(Unknown Source)at javax.swing.JComponent.paint(Unknown Source)at javax.swing.JLayeredPane.paint(Unknown Source)at javax.swing.JComponent.paintChildren(Unknown Source)at javax.swing.JComponent.paint(Unknown Source)at javax.swing.JComponent.paintChildren(Unknown Source)at javax.swing.JComponent.paint(Unknown Source)at javax.swing.JLayeredPane.paint(Unknown Source)at javax.swing.JComponent.paintChildren(Unknown Source)at javax.swing.JComponent.paint(Unknown Source)at javax.swing.JComponent.paintToOffscreen(Unknown Source)at javax.swing.BufferStrategyPaintManager.paint(Unknown Source)at javax.swing.RepaintManager.paint(Unknown Source)at javax.swing.JComponent._paintImmediately(Unknown Source)at javax.swing.JComponent.paintImmediately(Unknown Source)at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)at javax.swing.RepaintManager.access$700(Unknown Source)at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)at java.awt.event.InvocationEvent.dispatch(Unknown Source)at java.awt.EventQueue.dispatchEventImpl(Unknown Source)at java.awt.EventQueue.access$000(Unknown Source)at java.awt.EventQueue$3.run(Unknown Source)at java.awt.EventQueue$3.run(Unknown Source)at java.security.AccessController.doPrivileged(Native Method)at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)at java.awt.EventQueue.dispatchEvent(Unknown Source)at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)at java.awt.EventDispatchThread.pumpEvents(Unknown Source)at java.awt.EventDispatchThread.pumpEvents(Unknown Source)at java.awt.EventDispatchThread.run(Unknown Source)

The cause of this exception in my program is:

The program adds a japplet to the jframe. During lookandfeel switching, the input parameter is a japplet object, not a jframe object:

Swingutilities. updatecomponenttreeui (applet); // there is an error. If it is a jframe application, a jframe object should be passed in. If it is an applet, A japplet object should be passed in.