java - HashSet 上的迭代成本还取决于支持映射的容量吗？

Question

来自 HashSet 的 JavaDocs :

This class offers constant time performance for the basic operations (add, remove, contains and size), assuming the hash function disperses the elements properly among the buckets. Iterating over this set requires time proportional to the sum of the HashSet instance's size (the number of elements) plus the "capacity" of the backing HashMap instance (the number of buckets). Thus, it's very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important

为什么迭代花费的时间与总和(集合中的元素数 + 支持映射的容量)成正比，而不仅仅是集合本身的元素数？

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Answer 1

HashSet 是使用 HashMap 实现的，其中元素是映射键。由于 map 具有定义数量的桶，可以包含一个或多个元素，因此迭代需要检查每个桶，无论它是否包含元素。