lambda列求和

学习成绩汇总

创建对象
public class Student {
    public Student(Integer chinese, Integer math, Integer english, Integer physics) {
        Chinese = chinese;
        this.math = math;
        English = english;
        this.physics = physics;
    }
    private Integer Chinese;
    private Integer math;
    private Integer English;
    private Integer physics;
}
测试
public class Test {
    public static void main(String[] args) {
        ## 准备数据
        Student student1 = new Student(100, 90, 80, 89);
        Student student2 = new Student(83, 80, 75, 73);
        Student student3 = new Student(90, 100, 80, 80);
        Student student4 = new Student(60, 98, 98, 79);
        List<Student> list = new ArrayList();
        list.add(student1);
        list.add(student2);
        list.add(student3);
        list.add(student4);
        // reduce使用 acc中间结果(会使用第一个元素的地址)、bb是Stream的元素
        // 方式一 
        Student student5 = list.stream().reduce((acc, bb) -> {
            acc.setChinese(acc.getChinese() + bb.getChinese());
            acc.setEnglish(acc.getEnglish() + bb.getEnglish());
            acc.setMath(acc.getMath() + bb.getEnglish());
            acc.setPhysics(acc.getPhysics() + bb.getPhysics());
            return acc;
        }).get();
        list.add(student5);
        System.out.println(list);
        // 此上方式会修改student1对象中的值 不推荐
        //方式二  初始化一个对象，中间结果使用此地址
        Student stu0 = new Student(0, 0, 0, 0);
        Student reduce = list.stream().reduce(stu0, (stu1, stu2) -> {
            stu1.setChinese(stu1.getChinese() + stu2.getChinese());
            stu1.setEnglish(stu1.getEnglish() + stu2.getEnglish());
            stu1.setMath(stu1.getMath() + stu2.getMath());
            stu1.setPhysics(stu1.getPhysics() + stu2.getPhysics());
            return stu1;
        });
    }
}