对象排序得到方式

        java实现 list 排序的方式，有三种

        ① 对象实现Comparable 接口，然后代码里直接调用Collections.sort(list)

        ②使用内部类Comparator

        ③使用stream.sort

代码如下

        实现Comparable接口的实体类

@Data
public class Student implements Comparable<Student>{

    private String name;

    private int age;

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

    @Override
    public int compareTo(Student s1) {
        return this.age - s1.age;
    }
}

        没实现Comparable接口的实体类

@Data
public class Bag {

    private int num;

    private String name;

    public Bag(int num, String name) {
        this.num = num;
        this.name = name;
    }
}

        几种排序的方式都在下面了：

public class testSort {

    public static void main(String[] args) {

        List<Student> list1 = new ArrayList<>();
        Student s1 = new Student("张三", 15);
        Student s2 = new Student("李四", 13);
        Student s3 = new Student("王五", 14);
        Student s4 = new Student("李二麻子", 22);
        Student s5 = new Student("赵六", 31);
        list1.add(s1);
        list1.add(s2);
        list1.add(s3);
        list1.add(s4);
        list1.add(s5);
        Collections.sort(list1);
        for (Student student : list1) {
            System.out.println(student.getName() + "----" + student.getAge());
        }
        System.out.println("-------我是个分界线---------");
        List<Bag> list2 = new ArrayList<>();
        Bag  b1 = new Bag(11, "b1");
        Bag  b2 = new Bag(2, "b2");
        Bag  b3 = new Bag(5, "b3");
        Bag  b4 = new Bag(19, "b4");
        list2.add(b1);
        list2.add(b2);
        list2.add(b3);
        list2.add(b4);
        // 可以使用lamda表达式写法
        Collections.sort(list2 ,(p1, p2) ->{return p1.getNum()-p2.getNum();});

        /* 可以采取匿名内部类写法
        Collections.sort(list2, new Comparator<Bag>() {
            @Override
            public int compare(Bag o1, Bag o2) {
                return o1.getNum() - o2.getNum();
            }
        });
         */
        for (Bag bag : list2) {
            System.out.println(bag.getName() + "----" + bag.getNum());
        }

        List<Bag> list3 = new ArrayList<>();
        Bag  b11 = new Bag(11, "b1");
        Bag  b21 = new Bag(2, "b2");
        Bag  b31 = new Bag(5, "b3");
        Bag  b41 = new Bag(19, "b4");
        list3.add(b11);
        list3.add(b21);
        list3.add(b31);
        list3.add(b41);
        // 这个stream。sort一定要接受返回值，否则源对象不变
        list3 = list3.stream().sorted(Comparator.comparing(p -> p.getNum())).collect(Collectors.toList());
        // 或者直接stream流里直接操作打印啥的
        //list3.stream().sorted(Comparator.comparing(p -> p.getNum())).forEach(System.out::println);
        System.out.println("--------我是个分界线--------");
        for (Bag bag : list3) {
            System.out.println(bag.getName() + "----" + bag.getNum());
        }
    }
}