jdk8 新特性之 List 排序

傷城~ 2023-03-13 03:53 4阅读 0赞

### 一、排序示例 ###

*  升序–> 从小到大
 *  降序–> 从大到小
 *  age --> 排序字段
 *  jdk8 -> Lambda 循环打印println -> `list.forEach(System.out::println)`;

#### 1、jdk8 -> 之前的排序(升序) ####

Collections.sort(list, new Comparator<User>() {
                @Override
                public int compare(User o1, User o2) {
                    return o1.getAge().compareTo(o2.getAge());
                }
            });

#### 2、jdk8 -> Lambda排序（升序） ####

//  不带参  
    list.sort((u1, u2) -> u1.getAge().compareTo(u2.getAge()));        
    //  带参
    list.sort((User u1, User u2) -> u1.getAge().compareTo(u2.getAge()));

#### 3、jdk8 -> Comparator 提供的静态方法排序（ 升序） ####

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

#### 4、jdk8 -> Comparator 提供的静态方法排序（ 降序）.reversed() ####

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

#### 5、jdk8 -> 组合排序 ####

支持每个排序字段的结尾添加.reversed() 改为降序

// Age-升序   Name-升序
    Collections.sort(list, Comparator.comparing(User::getAge).thenComparing(User::getName));
    
    // Age-升序   Name-降序
    Collections.sort(list, Comparator.comparing(User::getAge).thenComparing(User::getName).reversed());
    
    // Age-降序   Name-升序
    Collections.sort(list, Comparator.comparing(User::getAge).reversed() .thenComparing(User::getName));
    
    // Age-降序   Name-降序
    Collections.sort(list, Comparator.comparing(User::getAge).reversed() .thenComparing(User::getName).reversed());

### 二、完整测试代码参考 ###

package com.ws.ldy.common.utils;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    
    import java.io.Serializable;
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.List;
    
    public class JDK8ListSort {
    
        public static void main(String[] args) {
    
    
            // TODO jdk8 之前的排序
            System.out.println("============jdk8 之前的排序");
            List<User> list = initList();
            Collections.sort(list, new Comparator<User>() {
                @Override
                public int compare(User o1, User o2) {
                    return o1.getAge().compareTo(o2.getAge());
                }
            });
            list.forEach(System.out::println);
    
    
            // TODO jdk8 lambda 排序-升序
            System.out.println("============jdk8 lambda排序，升序排序 --> 从小到大");
            list = initList();
            list.sort((u1, u2) -> u1.getAge().compareTo(u2.getAge()));   //不带参  带参: list.sort((User u1, User u2) -> u1.getAge().compareTo(u2.getAge()));
            list.forEach(System.out::println);
    
    
            // TODO jdk8 升序排序
            System.out.println("============jdk8 升序排序 --> 从小到大，Comparator提供的静态方法");
            list = initList();
            Collections.sort(list, Comparator.comparing(User::getAge));
            list.forEach(System.out::println);
    
    
            // TODO jdk8 降序排序
            System.out.println("============jdk8 降序排序 --> 从大到小，Comparator提供的静态方法");
            list = initList();
            Collections.sort(list, Comparator.comparing(User::getAge).reversed());
            list.forEach(System.out::println);
            System.out.println();
    
    
            // TODO jdk8 组合排序
            System.out.println("============jdk8 组合排序，Comparator提供的静态方法，先按年纪排序，年纪相同的按名称排序");
            list = initList();
            Collections.sort(list, Comparator.comparing(User::getAge).thenComparing(User::getName));
            list.forEach(System.out::println);
    
        }
    
    
        /**
         * TODO  初始化List数据
         *
         * @return java.util.List<com.ws.ldy.common.utils.JDK8ListSort.User>
         * @author ws
         * @mail 1720696548@qq.com
         * @date 2020/5/10 0010 22:49
         */
        private static List<User> initList() {
            List<User> list = new ArrayList<>();
            list.add(new User("lisa", 23));
            list.add(new User("tom", 11));
            list.add(new User("john", 16));
            list.add(new User("jennis", 26));
            list.add(new User("tin", 26));
            list.add(new User("army", 26));
            list.add(new User("mack", 19));
            list.add(new User("jobs", 65));
            return list;
        }
    
    
        /**
         * TODO  测试对象
         *
         * @author ws
         * @mail 1720696548@qq.com
         * @date 2020/5/10 0010 22:49
         */
        @Data
        @AllArgsConstructor
        public static class User implements Serializable {
            private String name;
            private Integer age;
        }
    }