为什么 Stream<T>没有实现 Iterable<T>? [英] Why does Stream<T> not implement Iterable<T>?
问题描述
在 Java 8 中,我们有 Stream
In Java 8 we have the class Stream<T>, which curiously have a method
Iterator<T> iterator()
所以你会期望它实现接口 Iterable
So you would expect it to implement interface Iterable<T>, which requires exactly this method, but that's not the case.
当我想使用 foreach 循环遍历 Stream 时,我必须做类似的事情
When I want to iterate over a Stream using a foreach loop, I have to do something like
public static Iterable<T> getIterable(Stream<T> s) {
return new Iterable<T> {
@Override
public Iterator<T> iterator() {
return s.iterator();
}
};
}
for (T element : getIterable(s)) { ... }
我在这里遗漏了什么吗?
Am I missing something here?
推荐答案
人们已经问过同样的问题 在邮件列表中 ☺.主要原因是 Iterable 也有可重复的语义,而 Stream 没有.
People have already asked the same on the mailing list ☺. The main reason is Iterable also has a re-iterable semantic, while Stream is not.
我认为主要原因是 Iterable
意味着可重用性,而 Stream
是只能使用一次的东西——更像是一个 Iterator
.
I think the main reason is that
Iterable
implies reusability, whereasStream
is something that can only be used once — more like anIterator
.
如果 Stream
扩展了 Iterable
,那么现有代码可能会在收到一个抛出 Exception
的 Iterable
时感到惊讶这他们第二次做 for (element : iterable)
.
If Stream
extended Iterable
then existing code might be surprised when it receives an Iterable
that throws an Exception
the
second time they do for (element : iterable)
.
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