并列排名的實現(xiàn)

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


class Student {
    private String name;
    private double score;
    private int age;
    private int index;

    public String getName() {
        return name;
    }

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

    public double getScore() {
        return score;
    }

    public void setScore(double score) {
        this.score = score;
    }

    public int getAge() {
        return age;
    }

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

    public Student(String name, double score, int age) {
        this.name = name;
        this.score = score;
        this.age = age;
    }

    public int getIndex() {
        return index;
    }

    public void setIndex(int index) {
        this.index = index;
    }

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

class TestDemo {
    public static void main(String[] args) {
        List<Student> students = Arrays.asList(
                new Student("Jack", 52, 10),
                new Student("Amdy", 79.5, 10),
                new Student("Lucy", 68, 9),
                new Student("Tom", 79.5, 11),
                new Student("Jerry", 52, 8),
                new Student("Cherry", 79.5, 10),
                new Student("Sweet", 91, 12),
                new Student("Lucky", 68, 9),
                new Student("Sim", 79.5, 10),
                new Student("Solem", 65, 10)
        );
        // fun1(students);
        // System.out.println("---------------分割線---------------------");
        // fun2(students);
        // System.out.println("---------------分割線---------------------");
        // fun3(students);
        // System.out.println("---------------分割線---------------------");
        func4(students);
    }

    /**
     * 按照成績排序 ---低級寫法
     */
    public static void fun1(List<Student> students) {
        students.sort((s1, s2) -> -Double.compare(s1.getScore(), s2.getScore()));
        int index = 0;
        double lastScore = -1;

        for (Student s : students) {
            if (Double.compare(lastScore, s.getScore()) != 0) {
                lastScore = s.getScore();
                index++;
            }
            System.out.println("名次:" + index + "\t分數(shù)" + s.getScore() + "\t名字" + s.getName());
        }
    }

    /**
     * 按照成績排序 --- 使用Java 8
     */
    public static void fun2(List<Student> students) {
        List<Entry<Double, List<Student>>> list = students.stream()
                .collect(Collectors.groupingBy(Student::getScore))
                .entrySet()
                .stream()
                .sorted((s1, s2) -> -Double.compare(s1.getKey(), s2.getKey()))
                .collect(Collectors.toList());
        int index = 1;
        for (Entry<Double, List<Student>> entry : list) {
            System.out.print("名次:" + index + "\t分數(shù):" + entry.getKey() + "\t名字");
            entry.getValue().forEach((s) -> System.out.print("  " + s.getName()));
            System.out.println();
            index++;
        }
    }

    /**
     * 按照成績排序 --- 使用Java 8切蟋；并列排名跳到下一名
     */
    public static void fun3(List<Student> students) {
        List<Entry<Double, List<Student>>> list = students.stream()
                .collect(Collectors.groupingBy(Student::getScore))
                .entrySet()
                .stream()
                .sorted((s1, s2) -> -Double.compare(s1.getKey(), s2.getKey()))
                .collect(Collectors.toList());
        int index = 1;
        for (Entry<Double, List<Student>> entry : list) {
            System.out.print("名次:" + index + "\t分數(shù):" + entry.getKey() + "\t名字");
            entry.getValue().forEach((s) -> System.out.print("  " + s.getName()));
            System.out.println();
            index = index + entry.getValue().size();
        }
    }

    /**
     * 按照多條件排序 --- 使用Java 8坐漏；并列排名跳到下一名
     */
    public static void func4(List<Student> students) {
        // students.sort((h1, h2) -> {
        //     // 排名相同苫幢，年齡正序排序
        //     if (Double.compare(h1.getScore(), h2.getScore()) == 0) {
        //         return Double.compare(h1.getAge(), h2.getAge());
        //     }
        //     return -Double.compare(h1.getScore(), h2.getScore());
        // });
        students.sort(Comparator.comparing(Student::getScore).reversed().thenComparing(Student::getAge));
        // students.forEach(System.out::println);
        int index = 0;
        int count = 0;
        double lastScore = -1;
        Map<Integer, Student> rankMap = new HashMap<>(5);
        for (int i = 0; i < students.size(); i++) {
            Student s = students.get(i);
            System.out.println(s.toString() + "，lastScore：" + lastScore + "图张，count：" + count + "锋拖，index：" + index);
            // 如果成績和上一名的成績不相同,那么排名+1
            if (Double.compare(lastScore, s.getScore()) != 0) {
                lastScore = s.getScore();
                index = index + 1 + count;
                count = 0;
            } else {
                // 分數(shù)相同诈悍，如果年齡不同，排名+1
                if (Double.compare(students.get(i - 1).getAge(), s.getAge()) != 0) {
                    index = index + 1 + count;
                    count = 0;
                } else {
                    // 重復(fù)數(shù)+1
                    count++;
                }
            }
            s.setIndex(index);
            System.out.println(s.toString() + "兽埃，lastScore：" + lastScore + "侥钳，count：" + count + "，index：" + index);
            System.out.println("****************");
            rankMap.put(i, s);
        }
        for (Integer key : rankMap.keySet()) {
            System.out.println(rankMap.get(key));
        }
    }

}

最后面貼出并列排名跳到下一名的運行結(jié)果柄错，index即是各個學(xué)生的排名舷夺。

其實如果List<Student> students參數(shù)是從數(shù)據(jù)庫中讀取的，可以通過sql進行一遍排序售貌，

select name, score, age from tb_student order by score desc,age asc;

來替代java排序

students.sort(Comparator.comparing(Student::getScore).reversed().thenComparing(Student::getAge));

然后代碼里面不再排序给猾，只做并列排名計算名次跳到下一名的特殊處理。