Java Collectors.toSet() 和 HashSet
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Collectors.toSet() and HashSet
提问by Robert Bain
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. Taking a debugger to the code, I am indeed getting a HashSet. I had a look at java.util.stream.Collectors.toSet()to observe the following code:
我想要一个HashSet. 将调试器带到代码中，我确实得到了一个HashSet. 我查看java.util.stream.Collectors.toSet()了以下代码：
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 guaranteesa Set, and implementation decides on a HashSet; seems reasonable. However, my implementation needs the constant time lookup guaranteed by a HashSet, not just any old Set. If the implementation of toSet()decides to use say a FooSet, which is perfectly within its rights, my implementation is compromised.
合约保证a Set，执行决定 a HashSet；似乎合理。但是，我的实现需要由 a 保证的恒定时间查找HashSet，而不仅仅是任何旧的Set. 如果 的实现toSet()决定使用 say a FooSet，这完全在其权利范围内，我的实现就会受到损害。
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？
采纳答案by Tagir Valeev
If you want a guaranteed HashSet, use Collectors.toCollection(HashSet::new).
如果你想要一个有保证的HashSet，使用Collectors.toCollection(HashSet::new).
