stream分组求和

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分类专栏： java基本知识文章标签： java

于 2022-01-17 21:19:50 首次发布

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本文介绍如何利用Java StreamAPI的Collectors.groupby结合summingInt方法，实现数据的分组与求和操作，提供了一种高效的数据处理方式。

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如何用Streamapi进行分组求和，可以使用Collectors.groupby(**, Collectors.summingInt(**))来进行分组求和。

public class Test {

    public static void main(String[] args) {

        Student student1 = new Student(1, 1);
        Student student2 = new Student(1, 1);
        Student student3 = new Student(2, 2);
        Student student4 = new Student(2, 3);
        Student student5 = new Student(3, 3);
        Student student6 = new Student(3, 4);
        Student student7 = new Student(4, 1);

        List<Student> list = Arrays.asList(student1, student2, student3, student4, student5, student6, student7);

        Map<Integer, Integer> collect = list.stream().collect(Collectors.groupingBy(Student::getId, Collectors.summingInt(Student::getScore)));
        System.out.println(collect);
    }
}

class Student{

    private Integer id;

    private Integer score;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getScore() {
        return score;
    }

    public void setScore(Integer score) {
        this.score = score;
    }

    public Student(Integer id, Integer score) {
        this.id = id;
        this.score = score;
    }
}