package com.example.demo;

import lombok.extern.log4j.Log4j2;

import org.junit.Test;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;

@Log4j2

public class EmployeeTestCase extends BaseTestCase {

    @Test

    public void groudBy(){

        //根据薪酬获取员工列表

        Map<Double,List<Employee>> map = list.stream()

                .collect(Collectors.groupingBy(Employee::getSalary));

        System.out.println("map:"+map);

        //根据薪酬获取员工数量

        Map<Double,Long> map2 = list.stream()

                .collect(Collectors.groupingBy(Employee::getSalary,Collectors.counting()));

        System.out.println("map2:"+map2);

        //根据薪酬获取员工薪酬总数

        Map<Double,Double> map3 = list.stream()

                .collect(Collectors.groupingBy(Employee::getSalary,Collectors.summingDouble(Employee::getSalary)));

        System.out.println("map3:"+map3);

    }

}

package com.example.demo;

import java.util.Arrays;

import java.util.List;

public class BaseTestCase {

    protected static final List<Employee> list = Arrays.asList(

            new Employee(1, "Alex", 1000),

            new Employee(2, "Michael", 2000),

            new Employee(3, "Jack", 1500),

            new Employee(4, "Owen", 1500),

            new Employee(5, "Denny", 2000));

}

map:{1500.0=[Employee(id=3, name=Jack, salary=1500.0), Employee(id=4, name=Owen, salary=1500.0)], 2000.0=[Employee(id=2, name=Michael, salary=2000.0), Employee(id=5, name=Denny, salary=2000.0)], 1000.0=[Employee(id=1, name=Alex, salary=1000.0)]}

map2:{1500.0=2, 2000.0=2, 1000.0=1}

map3:{1500.0=3000.0, 2000.0=4000.0, 1000.0=1000.0}