第三题 有如下Student 对象， private String name; private int age; private int score; private String classNum; 其中，classNum 表示学生的班号，例如“class05”。 有如下List List list = new ArrayList();

list.add(new Student(“Tom”, 18, 100, “class05”));

list.add(new Student(“Jerry”, 22, 70, “class04”));

list.add(new Student(“Owen”, 25, 90, “class05”));

list.add(new Student(“Jim”, 30,80 , “class05”));

list.add(new Student(“Steve”, 28, 66, “class06”));

list.add(new Student(“Kevin”, 24, 100, “class04”));

在这个list 的基础上，完成下列要求：

1） 计算所有学生的平均年龄

2） 计算各个班级的平均分

package com.hanqi.test;

public class Student {
     private String name;
        private int age;
        private int score;
    private String classNum;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public int getScore() {
        return score;
    }
    public void setScore(int score) {
        this.score = score;
    }
    public String getClassNum() {
        return classNum;
    }
    public void setClassNum(String classNum) {
        this.classNum = classNum;
    }
    public Student() {
        super();

    }
    public Student(String name, int age, int score, String classNum) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
        this.classNum = classNum;
    }

}

package com.hanqi.test;

import java.util.ArrayList;
import java.util.List;

public class TestStudent {

    public static void main(String[] args) {

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

        list.add(new Student("Tom",18,100,"class05"));
        list.add(new Student("Jerry",22,70,"class04"));
        list.add(new Student("Owen",25,90,"class05"));
        list.add(new Student("Jim",30,80,"class05"));
        list.add(new Student("Steve",28,66,"class06"));
        list.add(new Student("Kevin",24,100,"class04"));

        int sum=0;
        for(int i=0;i<list.size();i++)
        {
            sum+=list.get(i).getAge();
        }
        System.out.println("所有学生的平均分是："+sum/list.size());

        int score4=0;
        int score5=0;
        int score6=0;
        int num4=0;
        int num5=0;
        int num6=0;
        for(int j=0;j<list.size();j++)
        {
        Student st=list.get(j);

        if(st.getClassNum()=="class04")
        {
            num4++;
            score4 +=st.getScore();
        }
        else if(st.getClassNum()=="class05")
        {
            num5++;
            score5+=st.getScore();
        }
        else
        {
            num6++;
            score6+=st.getScore();
        }

        }
        System.out.println("class04的平均分数是："+score4/num4);
        System.out.println("class05的平均分数是："+score5/num5);
        System.out.println("class06的平均分数是："+score6/num6);

    }

}