java - 打印 HashMap 的所有内容> 类型

Question

我在 HGraph 类中有一个如下所示的超图结构

Map<HEdge, ArrayList<HVertex>> hGraph = new HashMap<HEdge, ArrayList<HVertex>>();

并希望使用以下函数打印所有 (key, value) 对。但我得到的只是：

Hypergraph:
e4(2.0)[]
e3(2.0)[]
e1(3.0)[]
e2(2.0)[]
e5(2.0)[]

[] 里面什么都没有，甚至没有我用于调试的“#”符号！我还覆盖了 HEdge 和 HVertex 类中的 toString 方法来打印它们的标签。

public void printHGraph(HGraph hGraph) {
    Set<HEdge> edges = hGraph.getAllHEdges();
    HEdge edge;
    HVertex vertex;
    ArrayList<HVertex> edge_vertices;

    System.out.println("Hypergraph:");

    Iterator<HEdge> edge_iterator = edges.iterator();
    while(edge_iterator.hasNext()) {
        edge = edge_iterator.next();
        System.out.print(edge.toString());

        System.out.print("[");

        edge_vertices = hGraph.getHVertices(edge);
        Iterator<HVertex> vertex_iterator = edge_vertices.iterator();
        while(vertex_iterator.hasNext()) {
            System.out.print("#"); //@debug
            vertex = vertex_iterator.next();
            System.out.print(vertex.toString()+", ");
        }           

        System.out.print("]");
        System.out.println();
    }