人们已经问过同样的问题 在邮件列表中 ☺.主要原因是Iterable也有可重迭代的语义，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, whereas Stream is something that can only be used once — more like an Iterator.

如果 Stream 扩展了 Iterable 则现有代码在收到抛出 Exception 的 Iterable 时可能会感到惊讶这他们第二次 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).