一个学生类的实体类

@Data
public class Student {private Long id;private String name;private int age;private Double height;public Student(Long id, String name, int age, Double height) {this.id = id;this.name = name;this.age = age;this.height = height;}

然后我们测试下三种排序方式：

• 按照id升序排列
• 按照id逆序排列
• 按照age排序，然后按照height排序

public class ListStreamSortTest {public static void main(String[] args) {// 一个集合中放入4个学生对象List<Student> list = new ArrayList<>();list.add(new Student(10002L, "ZhangSan", 19, 175.2));list.add(new Student(10003L, "LiSi", 18, 180.1));list.add(new Student(10004L, "Peter", 19, 170.8));list.add(new Student(10001L, "KangKang", 18, 167.4));// 打印默认顺序System.out.println("默认顺序：");list.stream().forEach(System.out::println);// 按照id排序System.out.println("id升序：");list.stream().sorted(Comparator.comparing(Student::getId)).forEach(System.out::println);// 按照id逆序排列System.out.println("id逆序：");list.stream().sorted(Comparator.comparing(Student::getId).reversed()).forEach(System.out::println);// 按照年龄排序，再按照升高排序System.out.println("age和height排序：");list.stream().sorted(Comparator.comparing(Student::getAge).thenComparing(Student::getHeight)).forEach(System.out::println);}
}

执行结果：

默认顺序：
Student{id=10002, name='ZhangSan', age=19, height=175.2}
Student{id=10003, name='LiSi', age=18, height=180.1}
Student{id=10004, name='Peter', age=19, height=170.8}
Student{id=10001, name='KangKang', age=18, height=167.4}
id升序：
Student{id=10001, name='KangKang', age=18, height=167.4}
Student{id=10002, name='ZhangSan', age=19, height=175.2}
Student{id=10003, name='LiSi', age=18, height=180.1}
Student{id=10004, name='Peter', age=19, height=170.8}
id逆序：
Student{id=10004, name='Peter', age=19, height=170.8}
Student{id=10003, name='LiSi', age=18, height=180.1}
Student{id=10002, name='ZhangSan', age=19, height=175.2}
Student{id=10001, name='KangKang', age=18, height=167.4}
age和height排序：
Student{id=10001, name='KangKang', age=18, height=167.4}
Student{id=10003, name='LiSi', age=18, height=180.1}
Student{id=10004, name='Peter', age=19, height=170.8}
Student{id=10002, name='ZhangSan', age=19, height=175.2}

需求： 需要对List中的每个student对象按照birthday顺序排序，时间由小到大排列

1. 刚开始用的是冒泡排序，出现数据覆盖的情况

		for (int i = 0; i < list.size() - 1; i++) {for (int j = 0; j < list.size() - 1 - i; j++) {long time = list.get(j).getCreateAt().getTime();long time1 = list.get(j + 1).getCreateAt().getTime();if (time >time1) {Object temp = list.get(j+1);BeanUtils.copyProperties(list.get(j), list.get(j+1));BeanUtils.copyProperties(temp, list.get(j));}}

2. 之后想到了Comparator比较器

public static <T> void sort(List<T> list，Comparator<? super T> )

这个里面就涉及到了Comparator 这个接口，位于java.util包下，排序是comparator能实现的功能之一,通俗地讲需要比较两个对象 谁排在前谁排在后，那么比较的方法就是：

• public int compare(String o1, String o2)：比较其两个参数的顺序

两个对象比较的结果有三种：大于，等于，小于。 
如果要按照升序排序， 则o1 小于o2，返回（负数），相等返回0，01大于02返回（正数） 
如果要按照降序排序 则o1 小于o2，返回（正数），相等返回0，01大于02返回（负数）

操作如下

package com.hbsi.test;import java.text.SimpleDateFormat;
import java.util.*;/*** @author lbq* @date 2020 10  15:07*/
public class ListSort {static class Student {private String userName;private String birthday;}public static void main(String[] args) {Student s1 = new Student();Student s2 = new Student();Student s3 = new Student();List<Student> list = new ArrayList<Student>();s1.setUserName("aa");s1.setBirthday("1997-01-08");s2.setUserName("bb");s2.setBirthday("1990-11-08");s3.setUserName("cc");s3.setBirthday("1957-05-08");list.add(s1);list.add(s2);list.add(s3);System.out.println("排序前:");for (Student o : list) {System.out.println(o);}listSort(list);System.out.println("排序后:");for (Student o : list) {System.out.println(o);}}private static void listSort(List<Student> list) {Collections.sort(list, new Comparator<Student>() {SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");public int compare(Student o1, Student o2) {try {Date dt1 = sf.parse(o1.getBirthday());Date dt2 = sf.parse(o2.getBirthday());if (dt1.getTime() > dt2.getTime()) {return 1;} else if (dt1.getTime() < dt2.getTime()) {return -1;} else {return 0;}} catch (Exception e) {e.printStackTrace();}return 0;}});}
}