Java8 使用stream().map()提取List对象的某一列值及去重

Java8 使用stream().map()提取List对象的某一列值及去重

Java8 使用stream().map()提取List对象的某一列值及去重

一、对象类User

package com.example.listdemo.entity;

import lombok.Data;

import java.time.LocalDate;
import java.util.List;


@Data
public class User {

    
    private String name;
    
    private String jobNumber;
    
    private Integer age;
    
    private Boolean  gender;
    
    private Double  height;
    
    private LocalDate birthday;

    public User(String name, String jobNumber, Integer age, Boolean gender, Double height, LocalDate birthday){
        this.name = name;
        this.jobNumber = jobNumber;
        this.gender = gender;
        this.age = age;
        this.height = height;
        this.birthday = birthday;
    }
    
    public static void printUsers(List list){
        System.out.println("[姓名]tt[工号]tt[性别]tt[年龄]tt[身高]tt[生日]");
        System.out.println("-----------------------------------------------------------------------");
        list.forEach(u-> System.out.println(printValue(u)));
        System.out.println(" ");
    }

    
    public static String printValue(User user){
        String str=String.format("%sttt%stt%stt%sttt%stt%s",
                user.name,user.jobNumber,user.gender.toString(),user.age.toString(),
                user.height.toString(),user.birthday.toString());
        return str;
    }
}

二、测试数据

 //构建测试数据
 List list = new ArrayList();
 list.add(new User("张三","000001",26,true,1.76, LocalDate.of(1996,1,18)));
 list.add(new User("小莉","000002",21,false,1.61, LocalDate.of(2001,1,18)));
 list.add(new User("李四","000003",22,true,1.83, LocalDate.of(2000,1,18)));
 list.add(new User("程曦","000004",20,false,1.64, LocalDate.of(2002,1,18)));
 list.add(new User("喜喜","000005",20,false,1.67, LocalDate.of(2002,1,18)));

三、提取某一列

 //1.提取某一列
List nameList = list.stream().map(User::getName).collect(Collectors.toList());
System.out.println(JSON.toJSONString(nameList));

四、提取age列并去重（使用distinct()函数）

//2.从列表中提取age并去重
List  ageList = list.stream().map(User::getAge).distinct().collect(Collectors.toList());
System.out.println(JSON.toJSONString(ageList));

五、完成代码

package com.example.listdemo.utils;

import com.alibaba.fastjson.JSON;
import com.example.listdemo.entity.User;
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;


public class ListDistinct {

    public static void main(String[] args) {
        //构建测试数据
        List list = new ArrayList();
        list.add(new User("张三","000001",26,true,1.76, LocalDate.of(1996,1,18)));
        list.add(new User("小莉","000002",21,false,1.61, LocalDate.of(2001,1,18)));
        list.add(new User("李四","000003",22,true,1.83, LocalDate.of(2000,1,18)));
        list.add(new User("程曦","000004",20,false,1.64, LocalDate.of(2002,1,18)));
        list.add(new User("喜喜","000005",20,false,1.67, LocalDate.of(2002,1,18)));

        //输出list列表
//        User.printUsers(list);

        //1.提取某一列
        List nameList = list.stream().map(User::getName).collect(Collectors.toList());
        System.out.println(JSON.toJSONString(nameList));

        //2.从列表中提取age并去重
        List  ageList = list.stream().map(User::getAge).distinct().collect(Collectors.toList());
        System.out.println(JSON.toJSONString(ageList));
    }
}