Why Guava does not provide a way to transform map keys

Question

This question is kind of already posted here: How to convert Map to Map using guava

I think the answer of CollinD is appropriat

Answer 1

As @CollinD suggests, there's no way to do this in a lazy way. To implement get, you have to convert all the keys with your transformation function (to ensure any duplicates are discovered).

So applying Function<K,NewK> to Map<K,V> is out.

You could safely apply Function<NewK,K> to the map:

V value = innerMap.get( fn.apply(newK) );

I don't see a Guava shorthand for that--it may just not be useful enough. You could get similar results with:

Function<NewK,V> newFn = Functions.compose(Functions.forMap(map), fn);