1、首先介绍Stream流排序, 因为这个玩意真的太方便了

public class SortDemo {

    public static void main(String[] args) {
	    List<User> list = new ArrayList<>();
        list.add(new User(5, "张三"));
        list.add(new User(2, "李四"));
        list.add(new User(3, "王五"));
        List<User> result = list.stream().sorted(Comparator.comparingInt(u -> u.id)).collect(Collectors.toList());
        System.out.println(result); 
    }

    static class User{
        private Integer id;
        private String name;
        public User(Integer id, String name) {
            this.id = id;
            this.name = name;
        }
    }
}

2、自己项目中类可以是实现Comparable接口, 这样就可以借用java自带的排序api, 比如Collections, TreeSet等

public class SortDemo {
    public static void main(String[] args) {
        TreeSet<User> treeSet = new TreeSet<>();
        treeSet.add(new User(5, "张三"));
        treeSet.add(new User(2, "李四"));
        treeSet.add(new User(3, "王五"));
        System.out.println(treeSet);
    }


    static class User implements Comparable<User>{

        private Integer id;

        private String name;

        public User(Integer id, String name) {
            this.id = id;
            this.name = name;
        }

        @Override
        public int compareTo(User o) {
            return this.id - o.id;
        }

        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }
}

3、如果是二方/三方包中类可以基于Comparator接口, 这样也可以借用java自带的排序api

// 1中stream流中就是借用了这个接口
public static void main(String[] args) {
 List<User> list = new ArrayList<>();
    list.add(new User(5, "张三"));
    list.add(new User(2, "李四"));
    list.add(new User(3, "王五"));
    List<User> result = list.stream().sorted(Comparator.comparingInt(u -> u.id)).collect(Collectors.toList());
    System.out.println(result); 
}