blocks|key|1012186|text|也许你应该先用“外部迭代”一词来定义你所理解的东西。由于在调用filter、map或reduce时不编写循环程序，所以从定义上讲，它不是外部迭代。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1012187|您可以尝试更改您的观点，并查看filter、map或reduce方法。但是，在试图理解这个概念时，查看实现并不一定有用。|1012188|在执行filter、map或reduce时，您是根据Predicate、Function、BiFunction或BinaryOperator定义操作。而且它们都不会使用Iterator实现一个循环，因此它仍然不是一个外部循环。|1012189|您似乎想知道迭代代码是碰巧在Collection类中还是在Stream类中，但这并不是一个重要的实现细节，因为这些都是同一个库/框架的一部分，因此在任何情况下迭代都被认为是“内部的”。|1012190|即使是第三个选项，即有另一方，执行循环的Spliterator也不会改变迭代的性质。对于内部迭代来说，这是典型的，您第一眼就看不出迭代在哪里发生。|1012191|entityMap^0|V|6|12|3|16|6|0|F|6|M|3|Q|6|0|3|6|A|3|E|6|Q|9|10|8|19|A|1K|E|2C|8|0|E|A|T|6|0|K|B|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1K|8|@$9|1L|A|1M|B|C]|$9|1N|A|1O|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|1P|8|@$9|1Q|A|1R|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1S|8|@]|D|@]|E|$]]]|O|$]]

Maybe you should first define what you understand by the term “external iteration”. Since you don’t program a loop when invoking <code>filter</code>, <code>map</code>, or <code>reduce</code>, it’s not an external iteration by definition.

You may try to change your point of view and look inside the <code>filter</code>, <code>map</code>, or <code>reduce</code> methods. But it’s not necessarily useful to look at an implementation when trying to understand the concept.

When performing <code>filter</code>, <code>map</code>, or <code>reduce</code> you are defining an operation in terms of <code>Predicate</code>, <code>Function</code>, <code>BiFunction</code>, or <code>BinaryOperator</code>. And none of them will implement a loop using an <code>Iterator</code> therefore it’s still not an external loop.

It seems that you want to know whether the iteration code happens to be inside the <code>Collection</code> class or within the <code>Stream</code> class but that’s an unimportant implementation detail as these are parts of the same library/framework and hence the iteration is to be considered “internal” regarding this library/framework in either case.

Even the third option, having another party, the <code>Spliterator</code> performing the loop doesn’t change the nature of the iteration. It’s typical for an internal iteration that you can’t see at the first glance where the iteration actually happens.

blocks|key|693417|text|从根本上说，要对集合的所有成员进行操作，需要对它们进行迭代。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|693418|它的确切方式可能会根据集合和操作而改变，但它需要发生的事实是不可避免的。|693419|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Fundamentally to operate on all the members of a collection something needs to iterate over them.

The exact way it does that may change based on the collection and the operation but the fact that it needs to happen is inescapable.

blocks|key|1012654|text|正如@Tim+B指出的那样，存在内部迭代，但并非所有项都会被处理。有过滤和短路，当你链几个操作，以避免不必要的计算.|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1012655|参考这里。|1012656|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/21313711/270349|1|https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html#StreamOps^0|2|6|0|0|2|2|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]]]

There is internal iteration as pointed by <a href="https://stackoverflow.com/a/21313711/270349">@Tim B</a> but not all items are always processed. There is filtering and short-circuiting when you chain several operations to avoid unnecessary computation.

Reference <a href="https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html#StreamOps" rel="nofollow noreferrer">here</a>.

blocks|key|2866249|text|流操作基于Spliterator的顶部，这是内部迭代和外部迭代之间的一个奇怪的混合。Spliterator是集合的spliterator()方法返回的外部对象，但是Spliterator本身接受回调以将方法传递给，就像内部迭代一样。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2866250|例如，collection.stream().forEach(consumer)将(本质上)等同于collection.spliterator().forEachRemaining(consumer)，或者它可能用于|2866251|Spliterator<T>+spliterator+=+collection.spliterator();
while+(spliterator.tryAdvance(consumer))+{
+++//+do+something
}|code-block|syntax|javascript|2866252|entityMap|0|LINK|mutability|MUTABLE|url|http://download.java.net/jdk8/docs/api/java/util/Spliterator.html^0|5|B|16|B|1L|D|2A|B|5|B|0|0|3|11|1D|1F|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|1B|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Stream operations are based on top of <a href="http://download.java.net/jdk8/docs/api/java/util/Spliterator.html" rel="nofollow"><code>Spliterator</code></a>s, which are a weird mix somewhere between internal and external iteration. A <code>Spliterator</code> is an external object returned by the collection's <code>spliterator()</code> method, but the <code>Spliterator</code> itself accepts callbacks to pass the methods to, like internal iteration would.

For example, <code>collection.stream().forEach(consumer)</code> would be (essentially) equivalent to <code>collection.spliterator().forEachRemaining(consumer)</code>, or it might be used like

<pre><code>Spliterator&lt;T&gt; spliterator = collection.spliterator();
while (spliterator.tryAdvance(consumer)) {
 // do something
}
</code></pre>

Is the internal iteration executed only with the <code>forEach</code> method of a <code>Collection</code>
object or also with <code>Stream</code>'s methods like <code>filter</code>, <code>reduce</code>, etc. ?

Java 8 internal iteration

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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内部迭代是只使用Collection对象的Collection方法执行，还是使用Stream的方法(如filter、reduce等)执行？

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