Java 8 Stream API收集器问题

Question

我正在遍历图形的边缘,并希望得到所有源和目标的列表.这是我到目前为止:

public Set<Vertex> getVertices(){

    Set<Vertex> vertices = this.edges.stream().map(edge -> edge.getSource()).collect(Collectors.toSet());
    vertices.addAll(this.edges.stream().map(edge -> edge.getTarget()).collect(Collectors.toSet()));
    return vertices;
}

有没有办法在同一个映射/收集步骤中获取源和目标？像(PSEUDO-CODE)这样的东西:

edges.stream().collect(edge.getSource()).collect(edge.getTarget())

或普通的旧Java 7

for ( Edge e : edges ){
    vertices.add(e.getSource());
    vertices.add(e.getTarget());
}

干杯,丹尼尔

Answer 1

Set<Vertex> vertices = edges.stream()
    .flatMap(e -> Stream.of(e.getSource(), e.getTarget()))
    .collect(Collectors.toSet());

Answer 2

Yoy可以使用Misha的建议或手动编写收集器:

Set<String> vertices = this.edges.stream()
       .collect(HashSet::new, (set, edge) -> {
            set.add(edge.getSource());
            set.add(edge.getTarget());
          }, Set::addAll);