JDK8中的排序

不念不忘少年蓝@ 2022-05-28 12:53 260阅读 0赞

import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.List;
    
    public class Test {
        public static void main(String[] args){
            List<User> list = initList();
            //JDK8之前的排序
            Collections.sort(list, new Comparator<User>() {
                @Override
                public int compare(User o1, User o2) {
                    return o1.getAge().compareTo(o2.getAge());
                }
            });
    
            //JDK8中 lambda排序，带类型参数
            list = initList();
            list.sort((User u1,User u2)->u1.getAge().compareTo(u2.getAge()));
            list.forEach(System.out::println);
            System.out.println();
    
            //JDK8中 lambda排序，不带类型参数
            list = initList();
            list.sort(( u1, u2)->u1.getAge().compareTo(u2.getAge()));
            list.forEach(System.out::println);
            System.out.println();
    
            //JDK8 升序排序， Comparator提供的静态方法
            list = initList();
            //  Collections.sort(list,Comparator.comparing(User::getAge));
            list.sort(Comparator.comparing(User::getAge));
            list.forEach(System.out::println);
            System.out.println();
    
            //JDK8 降序排序， Comparator提供的静态方法
            list = initList();
            //  Collections.sort(list,Comparator.comparing(User::getAge).reversed());
            list.sort(Comparator.comparing(User::getAge).reversed());
            list.forEach(System.out::println);
            System.out.println();
    
            //JDK8组合排序，先按年纪排序，年纪相同按名字排序
            list = initList();
            //    Collections.sort(list,Comparator.comparing(User::getAge).thenComparing(User::getUsername));
            list.sort(Comparator.comparing(User::getAge).thenComparing(User::getUsername));
            list.forEach(System.out::println);
            System.out.println();
        }
        private static List<User> initList(){
            List<User> list = new ArrayList<>();
            list.add(new User("lisa",23));
            list.add(new User("tom",19));
            list.add(new User("jack",22));
            list.add(new User("lucy",24));
            list.add(new User("mack",26));
            return list;
        }
    }
    class User implements Comparator<User>{
        private String username;
        private Integer age;
    
        @Override
        public int compare(User o1, User o2) {
            return o1.getAge()-o2.getAge();
        }
    
        public User(String username, int age) {
            this.username = username;
            this.age = age;
        }
    
        public String getUsername() {
            return username;
        }
    
        public void setUsername(String username) {
            this.username = username;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "age "+getAge()+"\tname "+getUsername();
        }
    }

进化版：

list.sort(( u1, u2)->u1.getAge().compareTo(u2.getAge()));

究极进化版：

list.sort(Comparator.comparing(User::getAge));

list.sort(Comparator.comparing(User::getAge).reversed());

list.sort(Comparator.comparing(User::getAge).thenComparing(User::getUsername));