jdk8 新特性之 List 排序

一、排序示例

• 升序–> 從小到大
• 降序–> 從大到小
• age --> 排序字段
• jdk8 -> Lambda 循環打印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）

//  不帶參  
list.sort((u1, u2) -> u1.getAge().compareTo(u2.getAge()));        
//  帶參
list.sort((User u1, User u2) -> u1.getAge().compareTo(u2.getAge()));  

3、jdk8 -> Comparator 提供的靜態方法排序（ 升序）

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

4、jdk8 -> Comparator 提供的靜態方法排序（ 降序）.reversed()

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

5、jdk8 -> 組合排序

支持每個排序字段的結尾添加.reversed() 改爲降序

// 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、完整測試代碼參考

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 --> 從小到大");
        list = initList();
        list.sort((u1, u2) -> u1.getAge().compareTo(u2.getAge()));   //不帶參  帶參: 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 --> 從小到大，Comparator提供的靜態方法");
        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 --> 從大到小，Comparator提供的靜態方法");
        list = initList();
        Collections.sort(list, Comparator.comparing(User::getAge).reversed());
        list.forEach(System.out::println);
        System.out.println();


        // TODO jdk8 組合排序
        System.out.println("============jdk8 組合排序，Comparator提供的靜態方法，先按年紀排序，年紀相同的按名稱排序");
        list = initList();
        Collections.sort(list, Comparator.comparing(User::getAge).thenComparing(User::getName));
        list.forEach(System.out::println);

    }


    /**
     * TODO  初始化List數據
     *
     * @return java.util.List<com.ws.ldy.common.utils.JDK8ListSort.User>
     * @author ws
     * @mail [email protected]
     * @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  測試對象
     *
     * @author ws
     * @mail [email protected]
     * @date 2020/5/10 0010 22:49
     */
    @Data
    @AllArgsConstructor
    public static class User implements Serializable {
        private String name;
        private Integer age;
    }
}