/**
  * Add the graph item to the graph.
  *
  * @param graphItem Item to be added to the graph.
  */
 public void addGraphItem(GraphItem graphItem) {
   if (graphItem != null) {
     graphItems.addElement(graphItem);
     graphItem.addGraphItemListener(graphItemListener);
   }
   repaint();
 }
 /**
  * Remove the graph item from the graph.
  *
  * @param graphItem Item to be removed from the graph.
  */
 public void removeGraphItem(GraphItem graphItem) {
   graphItems.removeElement(graphItem);
   graphItem.removeGraphItemListener(graphItemListener);
   repaint();
 }