1. Comparable

当使用Comparable接口对学生类进行排序时，需要在Student类中实现Comparable接口，并重写compareTo方法。之后在实例化Student后，对其通过sort进行排序。实现如下：

package com.example.helloworld;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Student implements Comparable<Student> {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public int compareTo(Student otherStudent) {
        // 根据年龄比较学生
        return Integer.compare(this.age, otherStudent.getAge());
        //另一种写法：
        // return this.age - otherStudent.age; 
    }

    public static void main(String[] args) {
        List<Student> students = new ArrayList<>();
        students.add(new Student("Alice", 20));
        students.add(new Student("Bob", 22));
        students.add(new Student("Charlie", 19));

        Collections.sort(students);

        for (Student student : students) {
            System.out.println(student.getName() + " - " + student.getAge());
        }
    }
}

***（return this.age - otherStudent.age）表示升序，同理，（return otherStudent.age-this.age ）***就表示降序！

2. Comparator

public class Student {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public static void main(String[] args) {
        List<Student> students = new ArrayList<>();
        students.add(new Student("Alice", 20));
        students.add(new Student("Bob", 22));
        students.add(new Student("Charlie", 19));

        Comparator<Student> comparator = new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {

               return Integer.compare(s1.getAge(), s2.getAge());
            }
        };
        students.sort(comparator);
        // 使用 Comparator 对学生列表按年龄进行排序
        // 或者使用 lambda 表达式  
//        students.sort(new Comparator<Student>() {
//            @Override
//            public int compare(Student s1, Student s2) {
//
//               return Integer.compare(s1.getAge(), s2.getAge());
//            }
//        });

        for (Student student : students) {
            System.out.println(student.getName() + " - " + student.getAge());
        }
    }
}