java8 list stream 排序计算排名

import java.util.*;
import java.util.stream.Collectors;

public class RankTest {
    public static void main(String[] args) {
        List<Person> list = new ArrayList<Person>() {{
            add(new Person(10, "北京"));
            add(new Person(10, "西安"));
            add(new Person(20, "呼市"));
            add(new Person(20, "上海"));
            add(new Person(40, "南京"));
            add(new Person(60, "青海"));
            add(new Person(70, "长春"));
            add(new Person(70, "黑龙江"));
            add(new Person(80, "沈阳"));
        }};
        //从小到大正序
        list = list.stream()
                .sorted(Comparator.comparing(Person::getAge))
                .collect(Collectors.toList());
        //从大到小逆序
        //  list = list.stream()
        //        .sorted(Comparator.comparing(Person::getAge).reversed())
        //      .collect(Collectors.toList());
        //从大到小
//        list.sort((s1, s2) -> -Double.compare(s1.getAge(), s2.getAge()));

        int index = 0;
        double lastAge = -1;
        /**
         * 方法1: 出现并列排名后名次不间断
         */
       /* for (Person bean : list) {
            if (Double.compare(lastAge, bean.getAge()) != 0) {
                lastAge = bean.getAge();
                index++;
            }
            bean.setRank(index);
        }
*/
        /**
         * 方法2.1: 出现并列排名后名次间断，后续名次按实际数据位置累计
         */
                for (int i = 0; i < list.size(); i++) {
            if (list.get(i).getAge() == lastAge ){
                list.get(i).setRank(index);
                if (i + 1 < list.size() && list.get(i + 1).getAge() !=  lastAge){
                    index = i + 1 ;
                }
            }else{
                list.get(i).setRank(++index);
            }
            lastAge = list.get(i).getAge();
        }

        /**
         * 方法2.2: 出现并列排名后名次间断，后续名次按实际数据位置累计(业务在name唯一的前提下使用)
         */
//        Map<String, Integer> rankMap = new HashMap<>();
//        for (int i = 1; i <= list.size(); i++) {
//            if (i != 1) {
//                if (list.get(i - 1).getAge().equals(list.get(i - 2).getAge())) {
//                    rankMap.put(list.get(i - 1).getName(), rankMap.get(list.get(i - 2).getName()));
//                } else {
//                    rankMap.put(list.get(i - 1).getName(), i);
//                }
//            } else {
//                rankMap.put(list.get(0).getName(), i);
//            }
//        }
//        for (Person person : list) {
//            person.setRank(rankMap.get(person.getName()));
//        }

        //打印结果
        list.forEach(p -> {
            System.out.println(p);
        });

    }
}

class Person {
    private Integer age;
    private Integer rank;
    private String name;

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

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Integer getRank() {
        return rank;
    }

    public void setRank(Integer rank) {
        this.rank = rank;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

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