java中流中的重复项

Question

我需要复制一个项目List.

所以,如果列表是:

["firstItem", "secondItem"]

我想返回一个列表:

["firstItem","firstItem","secondItem","secondItem"]

我试图通过flatMap函数来做到这一点,但我不知道如何去做.

List<T> duplicatedList = originalList.stream()
            .flatMap(u -> Stream.of()) // how to duplicate items??
            .collect(Collectors.toList());

Answer 1

创建两个相同项目的流:

List<String> originalList = Arrays.asList("firstItem","secondItem");
List<String> duplicatedList = originalList.stream()
        .flatMap(u -> Stream.of(u,u))
        .collect(Collectors.toList());
System.out.println(duplicatedList);

输出:

[firstItem, firstItem, secondItem, secondItem]