Java8 introduced those nice methods getOrDefault() and putIfAbsent() , allowing to write code like: Map<Foo, List<Bar>> itemsByFoo = ... List<Bar> bars = itemsByFoo.getOrDefault(key, new ArrayList<>()); bars.add(someNewBar); Now I am wondering if there are good factual reasons to either do: itemsByFoo.put(key, bars); or itemsByFoo.putIfAbsent(key, bars); Both would work: option 1 might do a lot of unnecessary "put" calls when adding elements to lists happens often option2 might do a lot of unnecessary "containsKey" calls when adding new entries for new keys is dominant SO: are the good reasons to go for option 1 or option 2 "always"?

Should I use put() or putIfAbsent() after using getOrDefault()?

Java8 introduced those nice methods getOrDefault() and putIfAbsent(), allowing to write code like:

Map<Foo, List<Bar>> itemsByFoo = ...
List<Bar> bars = itemsByFoo.getOrDefault(key, new ArrayList<>());
bars.add(someNewBar);

Now I am wondering if there are good factual reasons to either do:

itemsByFoo.put(key, bars);

itemsByFoo.putIfAbsent(key, bars);

Both would work:

option 1 might do a lot of unnecessary "put" calls when adding elements to lists happens often
option2 might do a lot of unnecessary "containsKey" calls when adding new entries for new keys is dominant

SO: are the good reasons to go for option 1 or option 2 "always"?