Java8 集合元素使用Stream Api进行分组

import java.util.ArrayList;import java.util.List;import java.util.Map;import java.util.stream.Collectors;import static java.util.stream.Collectors.groupingBy;public class Student {    private int id;    private String sex;    private String name;    public static void main(String[] args) {        List<Student> list = new ArrayList();        for (int i = 0; i < 5; i++) {            Student student = new Student();            student.setId(i);            student.setSex(i % 2 == 0 ? "男" : "女");            student.setName("zhangsan" + i);            list.add(student);        }        //将所有的学生按照性别进行分组        Map<String, List<Student>> collect = list.stream().collect(Collectors.groupingBy(Student::getSex));        //用方法引用可读性更好        Map<String, List<Student>> collect2 = list.stream().collect(groupingBy(Student::getSex));        //按照Id分组        Map<Integer, List<Student>> collect3 = list.stream().collect(groupingBy(Student::getId));        //自定义函数分组        Map<Integer, List<Student>> collect4 = list.stream().collect(groupingBy(stu -> stu.hashCode() % 5));        System.out.println(collect);        System.out.println(collect2);        System.out.println(collect3);        System.out.println(collect4);    }    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getSex() {        return sex;    }    public void setSex(String sex) {        this.sex = sex;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}