Arrays.stream(array) vs Arrays.asList(array).stream()

问题描述

在这个问题中已经有人回答了两个表达式是相等的，但在这种情况下它们产生不同的结果.对于给定的 int[] 分数，为什么会这样:

In this question it has already been answered that both expressions are equal, but in this case they produce different results. For a given int[] scores, why does this work:

Arrays.stream(scores)
        .forEach(System.out::println);

...但这不会:

Arrays.asList(scores).stream()
        .forEach(System.out::println);

据我所知 .stream() 可以在任何集合上调用，列表肯定是.第二个代码片段只返回一个包含整个数组而不是元素的流.

As far as I know .stream() can be called on any Collection, which Lists definitely are. The second code snippet just returns a stream containing the array as a whole instead of the elements.

推荐答案

您看到的行为并非特定于 Stream.Arrays.asList(scores) 当你传递给它一个 int[] 时返回一个 List，因为一个泛型类型参数不能被原始类型替换.因此，当您调用 asList(T... a) 时，编译器使用 int[] 代替 T.

The behavior you see is not specific to Streams.Arrays.asList(scores) returns a List<int[]> when you pass to it an int[], since a generic type parameter can't be replaced by a primitive type. Therefore, when you call asList(T... a), the compiler uses int[] in place of T.

如果您将 scores 更改为 Integer[]，您将得到您期望的输出(即 Arrays.asList(scores)返回一个 List).

If you change scores to Integer[], you'll get the output you expect (i.e. Arrays.asList(scores) will return a List<Integer>).

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