为什么LinkedHashSet上的迭代时间不取决于其容量？

Question

From the Java Docs of LinkedHashSet(LHS) class :

Iteration over a LinkedHashSet requires time proportional to the size of the set, regardless of its capacity. Iteration over a HashSet is likely to be more expensive, requiring time proportional to its capacity.

My question is why does iteration time over a LHS has no bearing on the capacity of the set ?

Answer 1

Because the LinkedHashSet comprises internally both a LinkedList and a Set. When iterating, you iterate over the (I believe, double) LinkedList, not the HashSet.

Answer 2

创建一个容量为1MB的常规HashSet（新的HashSet（1024 * 1024），添加1个元素并尝试进行迭代。尽管HashSet只有1个元素，但迭代器将必须遍历基础hastable的所有1MB存储桶。它是一个LinkedHashSet，迭代器不会遍历哈希表（该哈希表仅用于get（）和contains（）），但会通过LinkedList（并行结构），并且其中只有一个元素。

Answer 3

Iterating over a HashSet you need (pretty much) iterate over the buckets that contain the elements, then to eliminate empty values, which requires additional time. Briefly - there is some overhead associated with sorting empty elements out.

The nature of Linked collections is so that every element points to the next one. So, you start with the first and without much problems pull the next, and so on - this way you easily iterate them all.