import java.util.*; public class Main { public static void main(String[] args) { TreeMap<String, Student> map = new TreeMap<String,Student>(); Scanner sc = new Scanner(System.in); while(true){ String ID = sc.next(); if(ID.equals("end")){ break; } String name = sc.next(); int score = sc.nextInt(); Student student = new Student(ID,name,score); map.put(ID,student); } Set<String> keyset = new TreeSet<>(); keyset = map.keySet(); for(String key:keyset){ Student student = map.get(key); System.out.println(student.getID() + " " + student.getName() + " " + student.getScore()); } } } class Student{ private String ID;//学号 private String name;//姓名 private int score;//成绩 public Student() { } public Student(String ID, String name, int score) { this.ID = ID; this.name = name; this.score = score; } public String getID() { return ID; } public void setID(String ID) { this.ID = ID; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getScore() { return score; } public void setScore(int score) { this.score = score; } }我这样的代码要改成由从小到大变为由大到小排列，应该怎么处理

可以通过实现 Comparator 接口，并重写 compare 方法来实现 TreeMap 的排序方式的改变。具体的做法是，定义一个新的类 MyComparator 实现 Comparator 接口，在 compare 方法中将两个 Student 对象的成绩 score 进行比较，选择大的那个进行排序。然后在 TreeMap 的构造函数中传入 MyComparator 对象即可。

下面是修改后的代码：

import java.util.*;

public class Main {
    public static void main(String[] args) {
        TreeMap<String, Student> map = new TreeMap<String, Student>(new MyComparator());
        Scanner sc = new Scanner(System.in);
        while (true) {
            String ID = sc.next();
            if (ID.equals("end")) {
                break;
            }
            String name = sc.next();
            int score = sc.nextInt();
            Student student = new Student(ID, name, score);
            map.put(ID, student);
        }
        Set<String> keyset = new TreeSet<>();
        keyset = map.keySet();
        for (String key : keyset) {
            Student student = map.get(key);
            System.out.println(student.getID() + " " + student.getName() + " " + student.getScore());
        }
    }
}

class Student {
    private String ID;//学号
    private String name;//姓名
    private int score;//成绩

    public Student() {
    }

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

    public String getID() {
        return ID;
    }

    public void setID(String ID) {
        this.ID = ID;
    }

    public String getName() {
        return name;
    }

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

    public int getScore() {
        return score;
    }

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

class MyComparator implements Comparator<String> {
    TreeMap<String, Student> map = new TreeMap<String, Student>();

    public MyComparator() {
    }

    public MyComparator(TreeMap<String, Student> map) {
        this.map = map;
    }

    @Override
    public int compare(String o1, String o2) {
        Student s1 = map.get(o1);
        Student s2 = map.get(o2);
        if (s1.getScore() < s2.getScore()) {
            return 1;
        } else if (s1.getScore() > s2.getScore()) {
            return -1;
        } else {
            return 0;
        }
    }
}

在 MyComparator 类中，我们将 TreeMap 对象作为成员变量传入，这样在 compare 方法中就可以通过 map.get() 方法获取到相应的 Student 对象，进而进行比较。通过此方法，就可以实现由大到小的排序方式。