System.err.println(">>DFS: visiting " + u);
      private void DFS()      {         for (Iterator i = graph.keySet().iterator(); i.hasNext(); ) {            colors.put(i.next(), WHITE);         }         for (Iterator i = graph.keySet().iterator(); i.hasNext(); ) {            Object u = i.next();            if (colors.get(u).equals(WHITE)) {               System.err.println(">>DFS: visiting " + u);               DFSVisit(u);            }         }      }