code: private void dumpDAG(Node[][] dag){
          if(LOGGER.isDebugEnabled()) {
              LOGGER.debug("有向无环图：");
              for (int i=0; i<dag.length-1; i++) {
                  Node[] nodes = dag[i];
                  StringBuilder line = new StringBuilder();
                  for (Node node : nodes) {
                      int following = node.getFollowing();
                      StringBuilder followingNodeTexts = new StringBuilder();
                      for (int k = 0; k < dag[following].length; k++) {
                          String followingNodeText = dag[following][k].getText();
                          followingNodeTexts.append("(").append(followingNodeText).append(")");
                      }
                      line.append("【")
                              .append(node.getText())
                              .append("->").append(followingNodeTexts.toString())
                              .append("】\t");
                  }
                  LOGGER.debug(line.toString());
              }
          }
      }
docs: 输出有向无环图的结构
  @param dag