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;
}
}