Java求和元素_实现一个List集合中的某个元素的求和

List userlist = userService.findAll();

Integer sum= userlist .stream().collect(Collectors.summingInt(User::getAge));

package com.example.list_test;

import java.util.ArrayList;

import java.util.List;

/**

* 描述:ListTest3

*

* @author 何志鹏

* @ClassName:ListTest3

* @create 2019-05-30 18:49

* Version 1.0

*/

public class ListTest3 {undefined

public static void main(String[] args) {undefined

List list = new ArrayList<>();

Student s1 = new Student();

s1.setId(1);

s1.setName("张三");

s1.setAge(28);

Student s2 = new Student();

s2.setId(2);

s2.setName("李四");

s2.setAge(29);

Student s3 = new Student();

s3.setId(3);

s3.setName("网二");

s3.setAge(30);

list.add(s1);

list.add(s2);

list.add(s3);

System.out.println("=========第一种方式================");

int suma = list.stream().map(e -> e.getAge()).reduce(Integer::sum).get();//求和

System.out.println(suma);

int maxa = list.stream().map(e -> e.getAge()).reduce(Integer::max).get();//最大

System.out.println(maxa);

int mina = list.stream().map(e -> e.getAge()).reduce(Integer::min).get();//最小

System.out.println(mina);

System.out.println("=========第二种方式================");

double doublesum = list.stream().mapToDouble(Student::getAge).sum();//和

System.out.println(doublesum);

int intmax = list.stream().mapToInt(Student::getAge).max().getAsInt();//最大

System.out.println(intmax);

int intmin = list.stream().mapToInt(Student::getAge).min().getAsInt();//最小

System.out.println(intmin);

double avg = list.stream().mapToDouble(Student::getAge).average().getAsDouble();//平均

System.out.println(avg);

}

}