HashSet和Set之间有什么区别? [英] What's the difference between HashSet and Set?
问题描述
看到类似代码片段
Set<Record> instances = new HashSet<Record>();
我想知道Hashset是否是一种特殊的集合。它们之间有什么区别吗?
I am wondering if Hashset is a special kind of set. Any difference between them?
推荐答案
A 集合
代表一个通用的集合价值观。 TreeSet
是一个元素排序(因而有序)的集合, HashSet
是一个元素集合是不排序或订购。
A Set
represents a generic "set of values". A TreeSet
is a set where the elements are sorted (and thus ordered), a HashSet
is a set where the elements are not sorted or ordered.
A HashSet
通常比a快很多 TreeSet
。
A HashSet
is typically a lot faster than a TreeSet
.
A TreeSet
通常实现为红黑树(见 http://en.wikipedia.org/wiki/Red-black_tree - 我没有验证sun / oracle的 TreeSet
的实际实现,而 HashSet
使用 Object.hashCode()
在数组中创建索引。红黑树的访问时间为 O(log(n))
,而 HashSet
的访问时间范围为恒定时间到最坏的情况(每个项目都有相同的hashCode),你可以在线性搜索时间 O(n)
。
A TreeSet
is typically implemented as a red-black tree (See http://en.wikipedia.org/wiki/Red-black_tree - I've not validated the actual implementation of sun/oracle's TreeSet
), whereas a HashSet
uses Object.hashCode()
to create an index in an array. Access time for a red-black tree is O(log(n))
whereas access time for a HashSet
ranges from constant-time to the worst case (every item has the same hashCode) where you can have a linear search time O(n)
.
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