英文:
Map with long as key in Java
问题
我的性能分析器显示，我在很大一部分时间里将 long 包装成 Long，而我想避免这样做。我目前这样做是因为我使用了 Map<Long, V>。是否有一种常见的方法可以创建一个键为 long 的 Map 呢？
我知道它不会是 Map<long, V>，因为类型系统不允许这样做，但这并不意味着不能存在从 long 到 V 的映射。实际上，这很容易实现，因为我只需要复制 HashMap<K,V> 的代码，将 K 替换为 long，并进行类型系统所需的所有更改（例如，键的迭代不再是 Iterator<K>）。
我的问题是是否已经存在这样的库，或者我应该自己动手实现？
背景是我的性能分析器显示，在进行批处理时，三分之一的时间用于将 long 转换为 Long，而没有任何理由为了类型系统而支付这个代价。
英文:
My profiler state I spend an important part of the time wrapping long into Long which I want to avoid. I currently do it because I use Map<Long, V>. Is there an usual way to create a Map whose keys are long ?
I know it won't be a Map<long, V> because the type system does not allow it, but that does not mean that a map from long to V can't exists. Actually, it would be quite easy to do, since I would just need to copy the code of HashMap<K,V>, replace K by long, and do all changes required by the type system (E.g. iteration over key would not be an Iterator<K> anymore)
My question is does such a library already exists, or should I do it myself ?
The context is that my profiler state that, when doing batch processing, a third of the time is spent transforming long into Long, and there is really no reason to accept to pay this price for the type system
答案1
得分: 1
http://fastutil.di.unimi.it/ 是一个完全符合我之前提问的库的类。
英文:
http://fastutil.di.unimi.it/ is a class of library doing exactly what I was asking for here
答案2
得分: 0
这是不受支持的，因为泛型不支持原始类型。你也不能创建一个包含原始类型的类（比如 HashMap<int,V>）。
也许JEP 218 - 原始类型上的泛型将在未来尝试解决这个问题。
建议：
- 你能否将代码的其余部分直接使用
Long类型来代替？ - Long 类在范围 -127 到 128 内缓存数值（代码）。探索是否能够为更大范围的值实现类似的内部缓存。
英文:
This is not supported as generics does not support primitive types. You cannot create a class with primitive types as well (like HashMap<int,V>).
Maybe the JEP 218 - Generics over Primitive Types will look to solve this in the future.
Suggestions:
- Can you change the rest of the code to use a
Longin the first place? - The Long class caches values from -127 to 128 (code). Explore if you could have a similar internal cache for a bigger range.
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