Student类

package test;

public class Student {
    private String classId;
    private String name;
    private Integer age;
    private String sex;

    public Student() {
        super();
    }

    public Student(String classId, String name, Integer age, String sex) {
        super();
        this.classId = classId;
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public String getClassId() {
        return classId;
    }

    public void setClassId(String classId) {
        this.classId = classId;
    }

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "Student [classId=" + classId + ", name=" + name + ", age=" + age + ", sex=" + sex + "]";
    }

}

MapTest 类(测试用例)

package test;

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

import org.junit.Test;
public class TestList {
    @Test
    public void testList() throws Exception{
        Student student1=new Student("四年级", "小夫", 12, "男");
        Student student2=new Student("三年级", "大熊", 11, "男");
        Student student3=new Student("一年级", "静香", 8, "女");
        Student student4=new Student("二年级", "胖虎", 9, "未知");
        List<Student> stuentList =new ArrayList<>();
        stuentList.add(student1);
        stuentList.add(student2);
        stuentList.add(student3);
        stuentList.add(student4);
        System.out.println("=================原始输出=====================");
        for (Integer i = 0; i <stuentList.size(); i++) {
            System.out.println(stuentList.get(i).toString());
        }
        Collections.sort(stuentList, new Comparator<Student>(){
            //排序
            public int compare(Student p1, Student p2) {
                //按照Student的age进行升序排列
                if(p1.getAge() > p2.getAge()){
                    return 1;
                }
                if(p1.getAge() == p2.getAge()){
                    return 0;
                }
                return -1;
            }
        });
        System.out.println("=================升序输出=====================");
        for (Integer i = 0; i <stuentList.size(); i++) {
            System.out.println(stuentList.get(i).toString());
        }
        Collections.sort(stuentList, new Comparator<Student>(){
            //排序
            public int compare(Student p1, Student p2) {
                //按照Student的年进行降序排列
                if(p1.getAge() < p2.getAge()){
                    return 1;
                }
                if(p1.getAge() == p2.getAge()){
                    return 0;
                }
                return -1;
            }
        });
        System.out.println("=================降序输出=====================");
        for (Integer i = 0; i <stuentList.size(); i++) {
            System.out.println(stuentList.get(i).toString());
        }
    }

}

Console:输出

=================原始输出=====================
Student [classId=四年级, name=小夫, age=12, sex=男]
Student [classId=三年级, name=大熊, age=11, sex=男]
Student [classId=一年级, name=静香, age=8, sex=女]
Student [classId=二年级, name=胖虎, age=9, sex=未知]
=================升序输出=====================
Student [classId=一年级, name=静香, age=8, sex=女]
Student [classId=二年级, name=胖虎, age=9, sex=未知]
Student [classId=三年级, name=大熊, age=11, sex=男]
Student [classId=四年级, name=小夫, age=12, sex=男]
=================降序输出=====================
Student [classId=四年级, name=小夫, age=12, sex=男]
Student [classId=三年级, name=大熊, age=11, sex=男]
Student [classId=二年级, name=胖虎, age=9, sex=未知]
Student [classId=一年级, name=静香, age=8, sex=女]