java 8流收集最大对象和按属性区分

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

public class Main {
    public static void main(String[] args) {
        // 假设我们有一个Person类，包含name和age属性
        List<Person> persons = List.of(
                new Person("Alice", 25),
                new Person("Bob", 30),
                new Person("Charlie", 20),
                new Person("David", 35)
        );

        // 收集年龄最大的人
        Person oldestPerson = persons.stream()
                .max(Comparator.comparingInt(Person::getAge))
                .orElse(null);
        System.out.println("年龄最大的人：" + oldestPerson);

        // 按年龄区分人员
        Map<Integer, List<Person>> personsByAge = persons.stream()
                .collect(Collectors.groupingBy(Person::getAge));
        System.out.println("按年龄区分的人员：" + personsByAge);
    }

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

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

        public String getName() {
            return name;
        }

        public int getAge() {
            return age;
        }

        @Override
        public String toString() {
            return "Person{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
}