Java SE (Java Platform, Standard Edition)

Hi,

i want to delete a panel when a button is clicked. The problem is, parent panel is not refreshing for some reason. When i resize my application, the panel disappears. I also get some exceptions when i delete the panel:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javax.swing.JComponent._paintImmediately(JComponent.java:5085)
        at javax.swing.JComponent.paintImmediately(JComponent.java:4880)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:803)

I am kind of embarrased because I know that I am obviously doing something wrong while validating parent panel. I tried validate, revalidate, invalidate-validate but none of them worked. Here is the related code segment:

                // delete channel panel
                panels.elementAt(pIndex).remove(channels.elementAt(i).getChannelPanel());
                
                // delete vertical separator if exists
                if(channels.elementAt(i).getSeparator() != null)
                    panels.elementAt(pIndex).remove(channels.elementAt(i).getSeparator());
                
                // validate panel
                panels.elementAt(pIndex).revalidate();
                channels.remove(i);
                
                // delete row panel if it is empty
                if(panels.elementAt(pIndex).getComponentCount() == 0)
                {
                    System.out.println("deleting panel and seperator");
                    
                    // remove row panel & horizontal separator
                    jPanel1.remove(panels.elementAt(pIndex));
                    jPanel1.remove(horSep.elementAt(pIndex));
                    
                    // validate main panel
                    jPanel1.revalidate();
                    
                    horSep.remove(pIndex);
                    panels.remove(pIndex);
                    
                }

If you find the code confusing here is a summary of my layout:

On top there is main panel (jPanel1 - boxlayout), i add row panels to main panel (members of panels vector - flow layout) , i put 4 channel panel to a row panel (channels.getChannelpanel)

i remove channel panels one by one and if row panel is empty i remove it from main panel

thanks in advance