What is the reason for

Map<K, V>.filterValues

working directly on the values (i.e. it expects

(V) -> T

) as opposed to

Map<K, V>.mapValues

working on the entire entry (i.e. it expects

(Map.Entry<K, V>) -> T

)? Same question applies to the signature of

filterKeys

vs.

mapKeys

and similar functions.

Isn't it what

Map.filter

is working on?

An observation is it is the only difference with filterValues and filterKeys, filter is the parameter. I assume the reason you have different methods with

map

is to avoid returning pairs where the one component is always the same.

The reason is simply convenience. There is Map.filter for filtering the entries as @voddan pointed out.