如何获得整数数组列表的总和? [英] How to get the sum of an Integer arraylist?

问题描述

基本上我试图制作一个程序，允许老师为每个学生输入考试成绩，然后在他们输入成绩后，它会给老师他们输入的所有成绩的总和

Basically Im trying to make a program that allows a teacher to input grades for a test for each student then after they've inputted the grades it gives the teacher a sum of all the grades they inputted

public static void grades(){
    List<Integer> grade = new ArrayList<Integer>();
    int gradetotal = IntStream.of(grades).sum;/* sum */
    int gradelistnumber = 1;
    int inputedgrade = 0;

    while(inputedgrade != -1){
        System.out.println("Enter Grade for student " + gradelistnumber + " (1-50): ");
        inputedgrade = sc.nextInt();
        grade.add(inputedgrade);
        gradelistnumber++;


    }

    System.out.println("Class Average: " + gradetotal / 50 * 100);
}

我想弄清楚如何获得数组列表 grades 的总和.

I'm trying to figure out how to get the sum of the array list grades .

推荐答案

以下是使用 Java 8 对集合求和的方法:

Here's how you sum a Collection using java 8:

import java.util.ArrayList;
import java.util.List;

public class Solution {

    public static void main(String args[]) throws Exception {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(3);
        numbers.add(5);

        System.out.println(numbers.stream().mapToInt(value -> value).sum());
    }
}

在您的代码中，您将对 grade 列表执行此操作.您可以将其设置为 gradetotal after 循环.

In your code, you would do this to the grade list. You can set this to gradetotal after your loop.

<代码>值 ->value 是说获取每个参数并返回它".stream() 返回一个没有 sum() 的 Stream.mapToInt 返回一个 IntStream，它确实具有 sum().那个 值 ->value 告诉代码如何将 Stream 中的每个元素转换为 Integer.因为每个元素已经是一个Integer，所以我们只需要返回每个元素.

value -> value is saying "take each argument and return it". stream() returns a Stream which doesn't have sum(). mapToInt returns an IntStream which does have sum(). That value -> value tells the code how to convert each element in the Stream into an Integer. Because each element is already an Integer, we merely have to return each element.

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