protected void doDispose(){
  xSetVisible(false);
  SurfaceData oldData=surfaceData;
  surfaceData=null;
  if (oldData != null) {
    oldData.invalidate();
  }
  destroy();
}

protected void doDispose ( ) { xSetVisible ( false ) ; SurfaceData oldData = surfaceData ; surfaceData = null ; if ( oldData != null ) { oldData . invalidate ( ) ; } destroy ( ) ; }
performs disposal of menu window . should be called only on eventhandlerthread
