来自对象集的流API对象

Question

I started learning Stream API, but can't make through this one.

I'm implementing graphs, so I have classes like so:

Graph -> Node -> Edge

Nodes in graph are stored in Hashset; Edges in Nodes too.

Here's code:

    Graph g = new Graph("Graph 1");
    g.addNode(new Node("A"));
    g.addNode(new Node("B"));
    g.connectNodes("A","B", true); //nodeA, nodeB, bidirectional

    System.out.println(g);

    g.getNodes().stream().map(Node::getConnections);

I dunno what do next with last line. At this moment it returns HashSet of edges.

I tried

    g.getNodes().stream().map(Node::getConnections).map(x->x.getNodeB().getName()).forEach(System.out::println);

to get second connected via edge node name, but IDE don't allow me to do next map.

Can you give some hints?

Answer 1

Serghey建议使用flatMap就像一个魅力。

g.getNodes().stream().map(Node::getConnections).flatMap(x->x.stream()).map(x->x.getNodeB().getName()).forEach(System.out::println);