做一个Student类，有sno、sname、score3个属性；实现Comparable接口，按照score降序排序；在测试类的main方法中创建3个Studeng对象放入一个TreeSet，然后遍历看输出

好的，以下是实现代码：

import java.util.*;

class Student implements Comparable<Student> {
    private int sno;
    private String sname;
    private int score;

    public Student(int sno, String sname, int score) {
        this.sno = sno;
        this.sname = sname;
        this.score = score;
    }

    public int getSno() {
        return sno;
    }

    public void setSno(int sno) {
        this.sno = sno;
    }

    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

    public int getScore() {
        return score;
    }

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

    @Override
    public int compareTo(Student o) {
        return o.score - this.score;
    }

    @Override
    public String toString() {
        return "Student{" +
                "sno=" + sno +
                ", sname='" + sname + '\'' +
                ", score=" + score +
                '}';
    }
}

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student(1, "张三", 80);
        Student s2 = new Student(2, "李四", 90);
        Student s3 = new Student(3, "王五", 85);

        Set<Student> set = new TreeSet<>();
        set.add(s1);
        set.add(s2);
        set.add(s3);

        for (Student s : set) {
            System.out.println(s);
        }
    }
}

运行结果：

Student{sno=2, sname='李四', score=90}
Student{sno=3, sname='王五', score=85}
Student{sno=1, sname='张三', score=80}