如何在不使用foreach的情况下合并两个列表? [英] How to combine two lists without using foreach?

问题描述

最初，我有以下代码:

String[] A;
String[] B;
//...
List<String> myList= new ArrayList<>(A.length + B.length);
for (int i= 0; i< B.length; i++){
   myList.add(A[i]);
   myList.add("*".equals(B[i]) ? B[i] : doSomethingWith(B[i]));
}

如果最好使用Java 8，如何重构?

How to refactor if using, preferably, Java 8?

例如，如果我有这些数组

If for instance I have these arrays

A = {一个"，两个"，三个"，四个"}

B = {五个"，六个"，七个"，八个"}

在代码结尾，myList将为:

At the end of the code, myList will be:

myList = {一个"，五个"，两个"，六个"，三个"，七个"，四个"，八个"}

推荐答案

我个人认为这不需要进行重构，因为任何流式"代码都不会比您现有的代码更具可读性和直观性，但是作为一个纯粹的证明，概念:

I personally don't think this needs refactoring as any "streamed" code will be less readable and less intuitive than your existing code, but as a pure proof-of-concept:

String[] A;
String[] B;
List<String> myList;

myList = IntStream.range(0, B.length)
                  .mapToObj(i -> new String[]
                      {
                          A[i],
                          "*".equals(B[i]) ? B[i] : doSomethingWith(B[i])
                      })
                  .flatMap(Arrays::stream)
                  .collect(Collectors.toList());

工作演示.

• 我们使用IntStream.range将索引提供到数组中.

• We use IntStream.range to provide the indices into our arrays.

mapToObj将每个索引映射到包含我们想要的元素的数组(也需要此阶段，因为IntStream::flatMap只能转换为另一个IntStream，我们希望将其转换为Stream String s).

mapToObj maps each index to an array containing the elements we want (this stage is also needed as IntStream::flatMap can only convert to another IntStream, we want to convert it to a Stream of Strings).

flatMap将每个数组映射到一个流，然后展平"所得的流.

flatMap maps each array to a stream, then "flattens" the resulting stream of streams.

最后，我们只是collect结果.

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