0926-----homework

Posted 2020-08-11 风林山火

 

 1 /**
 2   *homework0926
 3   *@author:kai li
 4   */
 5 package com.kai.li.homework0926;
 6 import java.util.List;
 7 import java.util.ArrayList;
 8 import java.util.Arrays;
 9 import java.util.Map;
10 import static java.util.stream.Collectors.groupingBy;
11 /**
12   *following class is client 
13   */
14 public class HomeWork0926{
15     public static void main(String[] args)throws Exception{
16         
17         /**
18           *question three
19           */
20 
21         /*create data source*/
22 
23     List<Student> students=Arrays.asList(new Student("小明",18,100,"class04"),new Student("小黄",22,70,"class04"),new Student("小真",25,90,"class03"),new Student("小花",30,80,"class02"),new Student("tom",28,66,"class02"),new Student("jerry",24,100,"class02")); 
24     
25     /*operate*/
26     int sumAge=students.stream().mapToInt(Student::getAge).sum();
27     int sumScore=students.stream().mapToInt(Student::getScore).sum();
28     System.out.println("学生的平均年龄是："+sumAge/students.size()+"，平均分数是："+sumScore/students.size());
29 
30     Map<String,List<Student>> studentsByClass=students.stream().collect(groupingBy(Student::getClassNum));
31     System.out.println("class average score is fllowing:");
32 
33     studentsByClass.keySet().stream()                        //get stream
34             .mapToInt(i->(studentsByClass.get(i).stream()        //map to int
35                         .mapToInt(Student::getScore)    //map to int from the level 2
36                         .sum())                //sum
37                         /studentsByClass.get(i).size()) //average
38             .forEach(System.out::println);                //iterator and println
39 
40     }
41 }
42 /**
43   *following class for question three
44   *create data source class
45   *student class
46   */
47 class Student{
48     private String name;
49     private int age;
50     private int score;
51     private String classNum;
52     Student(String name,int age,int score,String classNum){
53         this.name=name;
54         this.age=age;
55         this.score=score;
56         this.classNum=classNum;
57     }
58     public String getName(){
59         return name;
60     }
61     public int getAge(){
62         return age;
63     }
64     public int getScore(){
65         return score;
66     }
67     public String getClassNum(){
68         return classNum;
69     }
70 }