Java 8身份映射lambda？

Question

我想在Java 8中使用聚合操作找到几个矩形的平均面积.

Rectangle[] rects = new Rectangle[]{
    new Rectangle(5, 10, 20, 30),
    new Rectangle(10, 20, 30, 40),
    new Rectangle(20, 30, 5, 15)
};

System.out.println("Average area: "
    + Arrays.asList(rects)
    .parallelStream()
    .map((RectangularShape r) -> (r.getWidth() * r.getHeight()))
    .collect(Collectors.averagingDouble(o -> o)));
// I don't like this "o -> o"
System.out.println("Expected: 625");

但是,我找到了一种愚蠢的o -> o要求averagingDouble.是否有更直观的替代这个lambda(甚至可能是某个地方的股票身份lambda)？

Answer 1

没必要:

System.out.println("Average area: "
     + Arrays.asList(rects)
       .parallelStream()
       .mapToDouble((RectangularShape r) -> (r.getWidth() * r.getHeight()))
       .average();

(另外,你可能会觉得Stream.of(rects).parallel())更喜欢Arrays.asList(rects).parallelStream().)