Java 如何将两个 arrays 与减少 function 合并为一个，如果可能的话？

Question

I have this code:

String[] arr1 = {"asd1", "asd2", "asd3", "asd4", "asd5", "asd6", "asd7"};
    String[] arr2 = {"asd8", "asd9", "asd10", "asd11", "asd12", "asd13", "asd14"};

    String[] concatenated = Stream.of(arr1, arr2)
           .flatMap(Stream::of)
           .toArray(String[]::new);

    String[] concatenated = Stream
            .concat(Arrays.stream(arr1), Arrays.stream(arr2))
            .toArray(String[]::new);

    String[] concatenated = Stream.of(arr1, arr2)
            .reduce(new String[arr1.length + arr2.length],
                    (String[] a, String[] b) -> )); ///// how to proceed from here?

    System.out.println(Arrays.toString(concatenated));

I am playing around and i didn't managed to find how to use the reduce function to combine them both to get this result:

[asd1, asd2, asd3, asd4, asd5, asd6, asd7, asd8, asd9, asd10, asd11, asd12, asd13, asd14]

note: The order doesn't really matter, the important thing is to get them both into one array with the reduce function..

Is it possible to do it with the reduce?

Answer 1

Well for the moment this is the best i come up with, if someone is interested:

String[] concatenated = Stream
            .of(arr1, arr2)
            .reduce((a, b) -> {
                String[] result = Arrays.copyOf(a, a.length + b.length);
                System.arraycopy(b, 0, result, a.length, b.length);
                return result;
            })
            .orElseThrow();

    Stream.of(arr1, arr2)
            .reduce((a, b) -> {
                String[] result = Arrays.copyOf(a, a.length + b.length);
                System.arraycopy(b, 0, result, a.length, b.length);
                return result;
            })
            .ifPresent(strings -> System.out.println(Arrays.toString(strings)));

    Optional<String[]> concatenated2 = Stream
            .of(arr1, arr2)
            .reduce((a, b) -> {
                String[] result = Arrays.copyOf(a, a.length + b.length);
                System.arraycopy(b, 0, result, a.length, b.length);
                return result;
            });

    System.out.println(Arrays.toString(concatenated));

    concatenated2.ifPresent(strings -> System.out.println(Arrays.toString(strings)));

Not exactly what i am looking for. I would be glad to see if someone can come up with a cleaner solution using reduce to solve this problem. I know i can make it cleaner if i put the body of the reduce in a method reference or something, but that's not really the case.

Answer 2

This works. It is contrived. But then any way of doing this with reduce would, imho, be contrived since there are much better ways.

String[] result = Stream.of(arr1, arr2)
                .flatMap(Arrays::stream)
                .reduce("", (s1, s2) -> s1 + s2 + ",").split(",");

System.out.println(Arrays.toString(result));