why map.keyset() returns set view but map.values() returns collections in Java?

Question

This question is more about design implementation by Java developers. I want to know (if there any vital reason that I cannot think of) why Keyset() returns a set-view but values() returns Collection-view. why not return Values() as a ValueSet with set-view. I can cast to set if needed, but why it is chosen the way it is.

Maybe this could help in deciding what data structures to use when it comes to building our custom ones.

Map<String, Integer> map = new HashMap<String,Integer>();
map.put("hello",1);
map.put("world",2);

Collection <Integer> i = map.values();
Set<String> s = map.keySet();

Answer 1

By definition the keys of a Map form a Set, that is a collection of unique keys. The values of a Map can be duplicates however. So it is possible to have the same value for different keys in a Map.