Map with long as key in Java

Question

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

My point is that wrapping takes time and is uselessly costly here according to the profiler. That's why I want to avoid it in the first place — Arthur Rainbow, Oct 24 '20 at 09:15

score 1 · Accepted Answer · answered Oct 31 '20 at 22:55

1

http://fastutil.di.unimi.it/ is a class of library doing exactly what I was asking for here

answered Oct 31 '20 at 22:55

Arthur Rainbow

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Thiyagu · Answer 2 · 2020-10-27T06:07:10.303

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 Long in 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.

Map with long as key in Java

2 Answers2