8 List求和(sum)

package com.gp6.list.sum;

import com.gp6.bean.Employee;
import com.gp6.list.utils.ListUtil;

import java.math.BigDecimal;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.LongSummaryStatistics;
import java.util.Map;
import java.util.stream.Collectors;

/**
 * 列表 求和
 *
 * @author gp6
 * @date 2019-07-23
 */
public class TestSum {
    public static void main(String[] args) {
        List<Employee> employeeList = ListUtil.packEmployeeList();

        // 对list中,对年龄求和
        Integer ageSum = employeeList.stream().mapToInt(Employee::getAge).sum();
        // 121
        System.out.println(ageSum);

        // 对list中,对薪资求和
        long salarySum = employeeList.stream().mapToLong(Employee::getSalary).sum();
        // 56000
        System.out.println(salarySum);

        // 先将 重量 取出,在计算总和
        BigDecimal weightSum = employeeList.stream().map(Employee::getWeight).reduce(BigDecimal.ZERO, BigDecimal::add);
        // 416.45000000000000994759830064140260219573974609375(精度问题)
        System.out.println(weightSum);

        // 根据 性别 分组,再计算出 年龄 信息
        Map<Integer, IntSummaryStatistics> map = employeeList.stream().collect(Collectors.groupingBy(Employee::getSex, Collectors.summarizingInt(Employee::getAge)));
        //Map<Integer, LongSummaryStatistics> map = employeeList.stream().collect(Collectors.groupingBy(Employee::getSex, Collectors.summarizingLong(Employee::getAge)));
        map.forEach((sex, value) -> {
            // 年龄总和
            long ageTmpSum = value.getSum();
            // 最大年龄
            long ageMax = value.getMax();
            // 最小年龄
            long ageMin = value.getMin();
            // 年龄平均值
            double averageAge = value.getAverage();

            System.out.println(ageTmpSum);
            System.out.println(ageMax);
            System.out.println(ageMin);
            System.out.println(averageAge);
        });
    }
}