java8 list 去重

我就是我 2022-12-17 11:53 179阅读 0赞

总结： 1.用TreeSet可以根据某一个字段去重 2.根据 distinct 去重 要重写 equals（）和hashCode()==》 根据所有字段去重
 测试数据参考：https://www.cnblogs.com/hooly/p/11612811.html
 
 package cn.banyu.test;
 
 import java.util.*;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
 /**
 * Title: TestList 
 * Description: TestList
 * Copyright (c) 2020 
 * Company: BANYU
 *
 * @author ken
 * @version 1.0
 * @date
 */
 public class TestList {
 
 public static void main(String[] args) {
 List<User> userList = new ArrayList<>();
 userList.add(new User("1","李大锤","23","南京"));
 userList.add(new User("2","张无忌","18","西安"));
 userList.add(new User("3","刘德华","26","苏州"));
 userList.add(new User("4","郭靖","33","上海"));
 
 userList.add(new User("1","李大锤","23","南京")); //id相同，其他数据也相同
 userList.add(new User("3","带头大哥","36","杭州")); //id相同，其他数据不同
 
 userList.add(new User("3","刘德华","26","苏州"));
 userList.add(new User("4","郭靖","33","上海"));
 System.out.println(userList);
 //用TreeSet根据userid去重
 List<User> userList1 = userList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User :: getUserid))), ArrayList::new));
 System.out.println("TreeSet根据userid去重:" + userList1);
 //根据 distinct 去重
 List<User> userList2 = userList.stream().distinct().sorted(Comparator.comparing(User::getUserid)).collect(Collectors.toList());
 System.out.println("根据 distinct 去重:" + userList2);
 }
 
 static class User {
 private String userid;
 private String username;
 private String age;
 private String address;
 
 public User(String userid, String username, String age, String address) {
 super();
 this.userid = userid;
 this.username = username;
 this.age = age;
 this.address = address;
 }
 
 public String getUserid() {
 return userid;
 }
 
 public void setUserid(String userid) {
 this.userid = userid;
 }
 
 public String getUsername() {
 return username;
 }
 
 public void setUsername(String username) {
 this.username = username;
 }
 
 public String getAge() {
 return age;
 }
 
 public void setAge(String age) {
 this.age = age;
 }
 
 public String getAddress() {
 return address;
 }
 
 public void setAddress(String address) {
 this.address = address;
 }
 
 @Override
 public String toString() {
 return "User [userid=" + userid + ", username=" + username + ", age=" + age + ", address=" + address + "]";
 }
 
 //覆写equals userid 和username
 @Override
 public boolean equals(Object obj) {
 if (!(obj instanceof User)) {
 return false;
 }
 User u = (User) obj;
 return this.userid.equals(u.userid)
 && this.username == u.username;
 }
 
 @Override
 public int hashCode() {
 return Objects.hash(getUserid(), getUsername(), getAge(),getAddress());
 }
 }
 }

===============================执行结果=================================  
\[User \[userid=1, username=李大锤, age=23, address=南京\], User \[userid=2, username=张无忌, age=18, address=西安\], User \[userid=3, username=刘德华, age=26, address=苏州\], User \[userid=4, username=郭靖, age=33, address=上海\], User \[userid=1, username=李大锤, age=23, address=南京\], User \[userid=3, username=带头大哥, age=36, address=杭州\], User \[userid=3, username=刘德华, age=26, address=苏州\], User \[userid=4, username=郭靖, age=33, address=上海\]\]

TreeSet根据userid去重:\[User \[userid=1, username=李大锤, age=23, address=南京\], User \[userid=2, username=张无忌, age=18, address=西安\], User \[userid=3, username=刘德华, age=26, address=苏州\], User \[userid=4, username=郭靖, age=33, address=上海\]\]

根据 distinct 去重:\[User \[userid=1, username=李大锤, age=23, address=南京\], User \[userid=2, username=张无忌, age=18, address=西安\], User \[userid=3, username=刘德华, age=26, address=苏州\], User \[userid=3, username=带头大哥, age=36, address=杭州\], User \[userid=4, username=郭靖, age=33, address=上海\]\]