How to sum a list of integers with java streams?

Question

I want to sum a list of integers. It works as follows, but the syntax does not feel right. Could the code be optimized?

Map<String, Integer> integers;

integers.values().stream().mapToInt(i -> i).sum();

Answer 1

This will help, but the i -> i is performing some automatic unboxing which is why it "feels" confusing . You can try both and better explain what the compiler is performing under the hood with your initial syntax:

integers.values().stream().mapToInt(i -> i.intValue()).sum();

integers.values().stream().mapToInt(Integer::intValue).sum();