code: public void push(int line, Vertex vertex)
      {
          Iterator<Vertex> iterator = vertexes[line].iterator();
          while (iterator.hasNext())
          {
              if (iterator.next().realWord.length() == vertex.realWord.length())
              {
                  iterator.remove();
                  --size;
                  break;
              }
          }
          vertexes[line].add(vertex);
          ++size;
      }
docs: 强行添加，替换已有的顶点
  
  @param line
  @param vertex