code: private int computeDesktopIconsSpace()
      {
          for (JInternalFrame f : frameToComponent.keySet())
          {
              if (f.isIcon())
              {
                  JDesktopIcon desktopIcon = f.getDesktopIcon();
                  return desktopIcon.getPreferredSize().height;
              }
          }
          return 0;
      }
docs: Compute the space for iconified desktop icons
  
  @return The space