Java8中Iterator和Spliterator的区别 [英] Difference between Iterator and Spliterator in Java8
问题描述
我在学习时了解到Parallelism是Spliterator的主要优势.
I came to know while studying that Parallelism is a main advantage of Spliterator.
这可能是一个基本问题，但谁能解释一下 Iterator 和 Spliterator 之间的主要区别并举例说明?
This may be a basic question but can anyone explain me the main differences between Iterator and Spliterator and give some examples?
推荐答案
对我来说，这些名称几乎一目了然.Spliterator == Splittable Iterator :它可以拆分一些源，也可以迭代它.它具有与 Iterator 大致相同的功能，但有一个额外的东西，它可以拆分成多个部分:这就是 trySplit为了.并行处理需要拆分.
The names are pretty much self-explanatory, to me. Spliterator == Splittable Iterator : it can split some source, and it can iterate it too. It roughly has the same functionality as an Iterator, but with the extra thing that it can potentially split into multiple pieces: this is what trySplit is for. Splitting is needed for parallel processing.
Iterator 总是有一个未知的大小:你只能通过 hasNext/next 遍历元素；Spliterator 可以提供大小(从而也在内部改进其他操作)；通过 getExactSizeIfKnown 获得精确的值或通过 estimateSize 获得的近似值.
An Iterator always has an unknown size: you can traverse elements only via hasNext/next; a Spliterator can provide the size (thus improving other operations too internally); either an exact one via getExactSizeIfKnown or a approximate via estimateSize.
另一方面，tryAdvance 是 hasNext/next 来自 Iterator 的东西，但它是一个单一的方法，更容易推理关于，海事组织.与此相关的是 forEachRemaining，它在默认实现中委托给 tryAdvance，但它不必总是这样(参见 ArrayList例子).
On the other hand, tryAdvance is what hasNext/next is from an Iterator, but it's a single method, much easier to reason about, IMO. Related to this, is forEachRemaining which in the default implementation delegates to tryAdvance, but it does not have to always be like this (see ArrayList for example).
Spliterator 也是一个更智能"的迭代器，通过其内部属性，如 DISTINCT 或 SORTED 等(在实现自己的 Spliterator).这些标志在内部用于禁用不必要的操作；例如，请参阅此优化:
A Spliterator also is a "smarter" Iterator, via its internal properties like DISTINCT or SORTED, etc (which you need to provide correctly when implementing your own Spliterator). These flags are used internally to disable unnecessary operations; see for example this optimization:
someStream().map(x -> y).count();
因为在流的情况下大小不会改变，所以可以完全跳过map，因为我们所做的只是计数.
Because size does not change in the case of the stream, the map can be skipped entirely, since all we do is counting.
如果需要，您可以通过以下方式围绕 Iterator 创建 Spliterator:
You can create a Spliterator around an Iterator if you need to, via:
Spliterators.spliteratorUnknownSize(yourIterator, properties)
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