关于JDK8中stream的用法小总结。

import java.io.Serializable;
import java.util.*;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        List<Student> studentList = new ArrayList<>();

        studentList.add(new Student(1,2,1000,88));
        studentList.add(new Student(2,2,1000,76));
        studentList.add(new Student(3,1,2000,79));
        studentList.add(new Student(4,2,3000,88));
        studentList.add(new Student(5,2,3000,49));
        studentList.add(new Student(5,1,4000,69));
        studentList.add(new Student(5,1,4000,96));
        // 按照班级分组，性别为女，分数降序

        Map<String, List<Student>> groupList = new HashMap<String, List<Student>>();

        studentList.stream().filter(student ->
                student.getSex() == 2
        ).collect(Collectors.groupingBy(Student::getClassNo,
                Collectors.toList())).forEach(
                (classNo, listByClassNo) -> {
                    groupList.put(classNo + "",
                            listByClassNo.stream().sorted(Comparator.comparing(Student::getScore).reversed()).collect(Collectors.toList()));
    }

        );

        System.out.println("Hello World!");
    }

    private static class Student implements Serializable {

        private int id;

        private int sex;

        private int classNo;

        private int score;

        public Student(int id, int sex, int classNo, int score) {

            this.id = id;

            this.sex = sex;

            this.classNo = classNo;

            this.score = score;

        }

        public int getId() {
            return id;
        }

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

        public int getSex() {
            return sex;
        }

        public void setSex(int sex) {
            this.sex = sex;
        }

        public int getClassNo() {
            return classNo;
        }

        public void setClassNo(int classNo) {
            this.classNo = classNo;
        }

        public int getScore() {
            return score;
        }

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

}