使用streams统计对象的多个字段

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

public class ObjectStatistics {
    public static void main(String[] args) {
        // 创建一个包含对象的列表
        List<Person> people = Arrays.asList(
                new Person("John", 25, "Male"),
                new Person("Jane", 30, "Female"),
                new Person("Tom", 35, "Male"),
                new Person("Emily", 28, "Female"),
                new Person("Mike", 32, "Male")
        );

        // 使用Streams进行统计
        Map<String, Long> genderCount = people.stream()
                .collect(Collectors.groupingBy(Person::getGender, Collectors.counting()));

        // 输出统计结果
        genderCount.forEach((gender, count) -> System.out.println(gender + ": " + count));
    }

    // 定义一个Person类
    static class Person {
        private String name;
        private int age;
        private String gender;

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

        public String getGender() {
            return gender;
        }
    }
}