Java 8 grouping using custom collector?

Question

I have the following class.

class Person {

    String name;
    LocalDate birthday;
    Sex gender;
    String emailAddress;

    public int getAge() {
             


        

Answer 1

You can use a mapping Collector to map the list of Person to a list of person names :

Map> collect = 
    members.stream()
           .collect(Collectors.groupingBy(Person::getAge,
                                          Collectors.mapping(Person::getName, Collectors.toList())));