List去除重复数据的五种方式

参考网址:

https://mp.weixin.qq.com/s?__biz=MzI4Njc5NjM1NQ==&mid=2247499540&idx=2&sn=9d7cc14298bd4da9fb2e59dd17101a83&chksm=ebd5c038dca2492efb80e9a849b354bafa7e2290fa82d5af8a802c8611bdaaf13e876420725c&mpshare=1&scene=23&srcid=1110cWvHRB4QeStswgcAM23r&sharer_sharetime=1605534647788&sharer_shareid=9d1e76e919cc0b2f3ca23ed1f5ef67a8#rd

准备测试的实体类

package com.shaoming.pojo;

import lombok.Data;

/**
 * @Auther: shaoming
 * @Date: 2020/11/16 17:35
 * @Description:
 */
@Data
public class User {

    private Integer id;

    private String name;

}

说明:

@Data是lombok(简称小辣椒)的注解

测试代码

package com.shaoming.集合;

import com.shaoming.pojo.User;
import org.junit.Test;

import java.util.*;
import java.util.stream.Collectors;

/**
 * @Auther: shaoming
 * @Date: 2020/11/16 21:55
 * @Description: 测试arraList去重的五种方式
 */
public class ArrayListTestDistinct {
    private static List<User> userList = new ArrayList<User>();
    private static User user1 = new User();
    private static User user2 = new User();

    static {
        user1.setId(1);
        user1.setName("user1的name");
        user2.setId(2);
        user2.setName("user2的name");
        userList.add(user1);
        userList.add(user1);
        userList.add(user1);
        userList.add(user2);
        userList.add(user2);
        userList.add(user2);
    }

    //1.使用LinkedHashSet删除arraylist中的重复数据
    @Test
    public void testquchongByLinkedeHashSet() {
        List<User> userList = new ArrayList<User>();
        LinkedHashSet<User> userLinkedHashSet = new LinkedHashSet<>(userList);
        System.out.println(userLinkedHashSet);
    }

    //2.使用java8新特性stream进行List去重
    @Test
    public void testquchongByJava8ofStream1() {
        ArrayList<Integer> numbersList = new ArrayList<>(Arrays.asList(1, 1, 2, 3, 3, 3, 4, 5, 6, 6, 6, 7, 8));
        System.out.println(numbersList);
        List<Integer> listWithoutDuplicates = numbersList.stream().distinct().collect(Collectors.toList());
        System.out.println(listWithoutDuplicates);
    }
    @Test
    public void testquchongByJava8ofStream2() {
        //获得去重后的list集合
        userList.forEach(user -> System.out.println(user));
        System.out.println("====使用java8的stream api对arrayList数据进行去重===============");
        List<User> userListdistinct = ArrayList去重.userList.stream().distinct().collect(Collectors.toList());
        userListdistinct.forEach(user -> System.out.println(user));
    }
    //3.利用HashSet不能添加重复数据的特性 由于HashSet不能保证添加顺序，所以只能作为判断条件保证顺序：
    @Test
    public void testquzhongByHashSet(){
        HashSet<User> userHashSet = new HashSet<>(userList.size());
        List<User> userArrayList = new ArrayList<>(userList.size());
        for (User user : userList) {
            if(userHashSet.add(user)){
                userArrayList.add(user);
            }
        }
        userList.clear();
        userList.addAll(userArrayList);
        userList.forEach(System.out::println);
    }
    //4.利用List的contains方法循环遍历,重新排序,只添加一次数据,避免重复：
    @Test
    public  void  testByListOfMethodToContains(){
        List<User> userArrayList = new ArrayList<User>(userList.size());
        for (User user : userList) {
            if(!userArrayList.contains(user)){
                userArrayList.add(user);
            }
        }
        userList.clear();
        userList.addAll(userArrayList);
        userList.forEach(System.out::println);
    }
    //5.双重for循环去重
    @Test
    public void testTwoFortoDistinct(){
        for(int i = 0 ; i< userList.size();i++){
            for(int j = 0 ; j< userList.size();j++){
                if(i!=j&&userList.get(i)==userList.get(j)) {
                    userList.remove(userList.get(j));
                }
            }
        }
        userList.forEach(System.out::println);

    }
}

说明:

1.这是我自己的测试方法,如有不当请指正

2.具体细节可以参考我参考的文章连接地址

}
}
userList.forEach(System.out::println);

}

}

> 说明:
>
> 1.这是我自己的测试方法,如有不当请指正
>
> 2.具体细节可以参考我参考的文章连接地址