Java 8嵌套(多级)分组依据

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        // 创建一个包含Person对象的列表
        List<Person> persons = Arrays.asList(
                new Person("Alice", "Female", 25),
                new Person("Bob", "Male", 30),
                new Person("Charlie", "Male", 35),
                new Person("Diana", "Female", 40),
                new Person("Eva", "Female", 45)
        );

        // 使用groupingBy()方法进行多级分组
        Map<String, Map<String, List<Person>>> groupedPersons = persons.stream()
                .collect(Collectors.groupingBy(Person::getGender, Collectors.groupingBy(Person::getAgeGroup)));

        // 打印分组结果
        for (Map.Entry<String, Map<String, List<Person>>> entry : groupedPersons.entrySet()) {
            System.out.println("Gender: " + entry.getKey());
            for (Map.Entry<String, List<Person>> subEntry : entry.getValue().entrySet()) {
                System.out.println("Age Group: " + subEntry.getKey());
                for (Person person : subEntry.getValue()) {
                    System.out.println(person.getName());
                }
            }
        }
    }
}

class Person {
    private String name;
    private String gender;
    private int age;

    public Person(String name, String gender, int age) {
        this.name = name;
        this.gender = gender;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public String getGender() {
        return gender;
    }

    public String getAgeGroup() {
        if (age < 30) {
            return "Young";
        } else if (age < 40) {
            return "Middle-aged";
        } else {
            return "Elderly";
        }
    }
}