java - Java 8 是否缺少处理可变流的 Stream.concat？

Question

目前我们有以下Stream.concat在 Java 8 中:

public static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b);

我很惊讶为什么没有版本采用 Stream<? extends T> 的可变参数?

目前我的代码如下:

Stream<Integer> resultStream = Stream.concat(stream1, Stream.concat(stream2, Stream.of(element)))
        .filter(x -> x != 0)
        .filter(x -> x != 1)
        .filter(x -> x != 2);

如果此签名的可变参数可用:

public static <T> Stream<T> concat(Stream<? extends T>... streams);

然后我可以更清楚地写成:

Stream<Integer> resultStream = Stream.concat(
                stream1,
                stream2,
                Stream.of(element)
        )
        .filter(x -> x != 0)
        .filter(x -> x != 1)
        .filter(x -> x != 2);

无各种嵌套Stream.concat来电。

还是有其他原因没有提供？
我想不出这样的原因，因为我们现在最终还是做了可变参数调用的工作。

Answer 1

就flatMap吧:

public static void main(final String[] args) throws Exception {
    final Stream<String> stream1 = /*some stream*/
    final Stream<String> stream2 = /*some stream*/
    final Stream<String> stream3 = /*some stream*/
    final Stream<String> stream4 = /*some stream*/
    final Stream<String> stream5 = /*some stream*/

    final Stream<String> stream = Stream.of(stream1, stream2, stream3, stream4, stream5).flatMap(Function.identity());
}

在你的例子中:

Stream<Integer> resultStream = Stream.of(stream1, stream2, Stream.of(element))
        .flatMap(identity())
        .filter(x -> x != 0)
        .filter(x -> x != 1)
        .filter(x -> x != 2);