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  • 实现一个List集合中的某个元素的求和

    List<User> 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 {
    public static void main(String[] args) {
    List<Student> 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);


    }
    }
    ————————————————
    版权声明:本文为CSDN博主「浅唱~幸福」的原创文章,遵循 CC 4.0 BY-SA 版权协议,转载请附上原文出处链接及本声明。
    原文链接:https://blog.csdn.net/weixin_39643007/article/details/90703329

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  • 原文地址:https://www.cnblogs.com/jishumonkey/p/12166541.html
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