[英]Collectors.toSet() and HashSet
Take the following line of sample code:获取以下示例代码行:
Set<String> someSet = someColletion.stream().map(p -> p.toString()).collect(Collectors.toSet());
I want a HashSet
.我想要一个HashSet
。 Taking a debugger to the code, I am indeed getting a HashSet
.将调试器带到代码中,我确实得到了一个HashSet
。 I had a look at java.util.stream.Collectors.toSet()
to observe the following code:我查看了java.util.stream.Collectors.toSet()
以观察以下代码:
public static <T> Collector<T, ?, Set<T>> toSet() {
return new CollectorImpl<>((Supplier<Set<T>>) HashSet::new, Set::add,
(left, right) -> { left.addAll(right); return left; },
CH_UNORDERED_ID);
}
The contract guarantees a Set
, and implementation decides on a HashSet
;合约保证一个Set
,实现决定一个HashSet
; seems reasonable.似乎合理。 However, my implementation needs the constant time lookup guaranteed by a HashSet
, not just any old Set
.但是,我的实现需要由HashSet
保证的恒定时间查找,而不仅仅是任何旧的Set
。 If the implementation of toSet()
decides to use say a FooSet
, which is perfectly within its rights, my implementation is compromised.如果toSet()
的实现决定使用一个FooSet
,这完全在它的权利范围内,我的实现就会受到影响。
What is the best practise solution to this problem?这个问题的最佳实践解决方案是什么?
如果您想要有保证的HashSet
,请使用Collectors.toCollection(HashSet::new)
。
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