package common;

import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.Stream;

// Stream 案例2
public class StreamE2 {
 // 生成count个随机的学生信息
 List<Student> newStudents(int count) {
 return Stream.generate(Student::new).limit(count).collect(Collectors.toList());
 }

 void print(List<Student> list) {
 list.forEach(System.out::println);
 }

 // 输出年龄大于20的学生
 void printAgeThan20(List<Student> list) {
 System.out.println("出年龄大于20的学生");
 list.stream().filter(s -> s.age > 20).forEach(System.out::println);
 }

 // 输出年龄大于19学生
 void printAgeThan19(List<Student> list) {
 }

 // 输出专业是计科的学生
 void printMajorIsComputer(List<Student> list) {
 System.out.println("输出专业是计科的学生");
 list.stream().filter(s -> "计科".equals(s.major)).forEach(System.out::println);
 }

 // 输出专业是通信的学生的姓名
 void printNameOfMajorIsComputer(List<Student> list) {
 System.out.println("输出专业是计科的学生的姓名");
 list.stream().filter(s -> "计科".equals(s.major))
 .map(s -> s.name)
 .forEach(System.out::println);
 }

 // 输出专业是电气的学生
 void printMajorIsDq(List<Student> list) {
 }

 // 输出专业是电气的学生的姓名
 void printNameOfMajorIsDq(List<Student> list) {
 }

 // 按专业分组
 void groupMajor(List<Student> list) {
 System.out.println("按专业分组");
 Map<String, List<Student>> byMajor = list.stream().collect(Collectors.groupingBy(s -> s.major));
 byMajor.forEach((key, value) -> {
 System.out.println("专业: " + key);
 value.forEach(System.out::println);
 });
 }

 // 按年龄分组
 void groupAge(List<Student> list) {
 }

 // 按专业分组, 输出各专业人数
 void countGroupMajor(List<Student> list) {
 System.out.println("按专业分组, 输出各专业人数");
 Map<String, Long> byMajor = list.stream().collect(Collectors.groupingBy(
 s->s.major, Collectors.counting()));
 byMajor.forEach((key, value) -> System.out.println(key + " : " + value));
 }

 // 按年龄分组, 输出各年龄段人数
 void countGroupAge(List<Student> list) {
 }

 // 用逗号拼接姓名
 void joinName(List<Student> list) {
 System.out.println("用逗号拼接姓名");
 String joined = list.stream().map(s -> s.name).collect(Collectors.joining(",", "[", "]"));
 System.out.println(joined);
 }

 // 用逗号拼接专业,输出时去掉重复专业
 void joinMajor(List<Student> list) {
 }

 public static void main(String[] args) {
 StreamE2 e2 = new StreamE2();
 List<Student> list = e2.newStudents(10);
 e2.print(list);

 e2.printAgeThan20(list);
 e2.printMajorIsComputer(list);
 e2.printNameOfMajorIsComputer(list);

 e2.groupMajor(list);
 e2.countGroupMajor(list);
 e2.joinName(list);
 }
}


class Student {
 static int id = 1;
 static String[] majors = {
 "计科","机械","电气","通信","信息安全"
 };
 // 学号
 String no;
 // 姓名
 String name;
 // 专业
 String major;
 // 年龄
 int age;

 Student() {
 Random r = new Random();
 // 使用随机值初始化类
 no = String.format("20%02d%02d%06d", 10+r.nextInt(10), r.nextInt(10), r.nextInt(200));
 name = "学生" + id++;
 major = majors[r.nextInt(majors.length)];
 age = 18 + r.nextInt(4);
 }

 @Override
 public String toString() {
 return "Student{" +
 "no='" + no + '\'' +
 ", name='" + name + '\'' +
 ", major='" + major + '\'' +
 ", age=" + age +
 '}';
 }
}