The Collectors.reducing Method

//The following example retrieves the total age of members of each gender:

	
Map<Person.Sex, Integer> totalAgeByGender =
    roster
        .stream()
        .collect(
            Collectors.groupingBy(
                Person::getGender,                      
                Collectors.reducing(
                    0,
                    Person::getAge,
                    Integer::sum)));

The reducing operation takes three parameters: identity, mapper and operation.

The Collectors.reducing Method — Structure map

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The Collectors.reducing Method — Related pages: