java - Sum attributes of an element in a stream

Question

This question already has an answer here: question from:https://stackoverflow.com/questions/65852927/sum-attributes-of-an-element-in-a-stream

Answer 1

Map<String, Integer> result = 
foos.stream()
    .collect(
        Collectors.groupingBy(
            Foo::getName, 
            Collectors.summingInt(x -> x.getPrice() + x.getFees())
        )
);

collect to a Map with a Collectors::groupingBy and a downstream collector : Collectors::summingInt.

Or you can use toMap:

foos.stream()
    .collect(
        Collectors.toMap(
               Foo::getName,
               x -> x.getPrice() + x.getFees(),
               Integer::sum
        )
    );

This is rather easy to achieve if you just read the documentation a bit.