Java集合插入：设置与列表 [英] Java collection insertion: Set vs. List

问题描述

我正在考虑用大量的唯一对象填充集合。
与List（比如ArrayList）相比，在Set（比如HashSet）中插入的代价是多少？

I'm thinking about filling a collection with a large amount of unique objects. How is the cost of an insert in a Set (say HashSet) compared to an List (say ArrayList)?

我的感觉是在集合可能会导致一个小的开销。

My feeling is that duplicate elimination in sets might cause a slight overhead.

推荐答案

没有重复消除比如对所有现有元素。如果你插入到哈希集，它真的是一个字典的项目通过哈希码。没有重复检查，除非已经有具有相同散列码的项目。给定一个合理的（分布良好的）散列函数，并不是那么糟糕。

There is no "duplicate elimination" such as comparing to all existing elements. If you insert into hash set, it's really a dictionary of items by hash code. There's no duplicate checking unless there already are items with the same hash code. Given a reasonable (well-distributed) hash function, it's not that bad.

正如Will所说，因为字典结构 HashSet 可能比 ArrayList 慢一点（除非你想插入之间现有元素）。它也有点大。我不知道这是一个重大差异，虽然。

As Will has noted, because of the dictionary structure HashSet is probably a bit slower than an ArrayList (unless you want to insert "between" existing elements). It also is a bit larger. I'm not sure that's a significant difference though.

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