List Java 8中2个字符串的每个组合 [英] Every combination of 2 strings in List Java 8

问题描述

我想组合列表中的每两个字符串，并使用java8流返回组合列表:

I would like to combine every two strings in the list and return the list of combination using java8 streams:

List<String> list;
Stream.concat(list.stream(), list.stream())
                    .collect(toList());

但是，此代码不会产生组合，而只会产生列表中的元素.我究竟做错了什么.我还希望此代码可以并行化，以便可以在多个内核上运行

However this code doesn't produce combinations but just elements of the lists. What am I doing wrong. I would also like this code to be parallelized so it can run on multiple cores

推荐答案

使用

Use flatMap to combine the strings in a combinatoric manner. Each string will be concatenated with each string in the list.

List<String> combinations =
    list.stream()
        .flatMap(str1 -> list.stream().map(str2 -> str1 + str2))
        .collect(toList());

Ideone演示

要使操作并行，请将.stream()换为.parallelStream().根据您输入的大小，这可能会使操作变慢或变快.

To make the operations parallel, swap out .stream() for .parallelStream(). Depending on your input size, this may make the operation slower or faster.

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