Java 9，Set.of（）和Map.of（）varargs重载 [英] Java 9, Set.of() and Map.of() varargs overloads

问题描述

我正在研究不可变集合的工厂方法。
我看到 Set.of（）方法有10个varargs重载（同样适用于 Map.of（））。我真的不明白为什么会这么多。最后，无论如何都会调用函数 ImmutableCollections.SetN<>（元素）。

I'm studying the factory methods for Immutable collections. I see the Set.of() method has 10 varargs overloading (same for Map.of()). I really can't understand why there are so many. In the end the function ImmutableCollections.SetN<>(elements) gets called anyway.

在文档中我发现这个：

虽然这会在API中引入一些混乱，但它避免了varargs引起的数组分配，初始化和垃圾收集开销调用。

While this introduces some clutter in the API, it avoids array allocation, initialization, and garbage collection overhead that is incurred by varargs calls.

杂乱的确是否值得获得性能提升？如果是，理想情况下是否会为任何 N 元素创建单独的方法？

Is the clutter indeed worth the performance gain? If yes, would that ideally do create a separate method for any N elements?

推荐答案

目前无论如何调用该方法 - 这可能会改变。例如，它可能会创建一个 Set ，只有三个元素，4等等。

At the moment that method is called anyway - this could change. For example it could be that it creates a Set with only three elements, 4 and so on.

此外并非所有委托给 SetN - 那些零，一个和两个元素的实际类别为 ImmutableCollections.Set0 ， ImmutableCollections.Set1 和 ImmutableCollections。 Set2

Also not all of them delegate to SetN - the ones that have zero, one and two elements have actual classes of ImmutableCollections.Set0, ImmutableCollections.Set1 and ImmutableCollections.Set2

或您可以阅读有关此问题的实际问题... where 阅读 Stuart Marks 在那个问题中 - 他是创建这些收藏的人。

Or you can read the actual question regarding this ... here Read the comments from Stuart Marks in that question -as he is the person that created these Collections.

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