question: private void contextMenu ( LogicalVisualizationEx visualization , MouseEvent mouseEvent ) { JComponent menu = new JPopupMenu ( ) ; JMenuItem restore = new JMenuItem ( "Restore Logical View" ) ; restore . addActionListener ( null ) ; JMenuItem collapse = new JMenuItem ( "Collapse all" ) ; collapse . addActionListener ( null ) ; JMenuItem expand = new JMenuItem ( "Expand all" ) ; expand . addActionListener ( null ) ; menu . add ( restore ) ; menu . add ( collapse ) ; menu . add ( expand ) ; getVisibilityMenuItems ( menu , visualization ) ; if ( menu instanceof JPopupMenu ) { JPopupMenu popup = ( JPopupMenu ) menu ; popup . setLocation ( mouseEvent . getLocationOnScreen ( ) ) ; popup . setInvoker ( getDisplay ( ) ) ; popup . setVisible ( true ) ; popup . requestFocus ( ) ; } }
target:  creates and displays a context menu for the blank space on the graph.