Java8学习笔记-09：flatMap操作

flatMap:flatMap方法可用 Stream 替换值,然后将多个 Stream 连接成一个 Stream
图示例如下：

flatMap.png

 List together = Stream.of(asList(1, 2), asList(3, 4))
                                    .flatMap(numbers -> numbers.stream())
                                    .collect(toList());
     assertEquals(asList(1, 2, 3, 4), together);