HashMap的运用 计算3个班级的总成绩和平均成绩

TestStudent.java

package com.sxt.home;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

/*
 * 计算三个不同班学生的的总成绩和平均成绩
 * 存储在集合中
 */
public class TestStudent {
    public static void main(String[] args) {
        //定义一个Hashmap存储每个班  定义一个ArrayList存储每个班的成绩
        Map<Integer,List<Student>> map = new HashMap<>();    

        //第一个班
        List<Student> list1 = new ArrayList<>();
        list1.add(new Student("小花", "男", 77.5));
        list1.add(new Student("小明", "女", 43.5));
        list1.add(new Student("小刚", "男", 33.5));
        map.put(1, list1);
        //第二个班
        List<Student> list2 = new ArrayList<>();
        list2.add(new Student("小明", "男", 43.5));
        list2.add(new Student("小明", "男", 43.5));
        list2.add(new Student("小明", "男", 43.5));
        list2.add(new Student("小明", "男", 99.5));
        map.put(2, list2);
        //第三个班
        List<Student> list3 = new ArrayList<>();
        list3.add(new Student("刚刚", "女", 43.5));
        list3.add(new Student("小明", "男", 43.5));
        map.put(3, list3);

        //遍历集合取出数据
        //entrySet取出键值对
        Set<Entry<Integer, List<Student>>> entrySet = map.entrySet();
        Iterator<Entry<Integer, List<Student>>> iterator = entrySet.iterator();
        double sum = 0;//成绩总和
        int num = 0;//人数统计
        //迭代器遍历循环HashMap 取出每个ArrayList
        while(iterator.hasNext()){
            Entry<Integer, List<Student>> next = iterator.next();
            List<Student> value = next.getValue();
            //增强for循环遍历ArrayList：遍历每个班的成绩
            for(Student s : value){
                sum += s.getScore();
                num++;
            }
            System.out.println(next);
        }
        System.out.println("三个班总成绩:"+sum);
        System.out.println("三个班级的平均成绩："+sum/num);
    }
}

Student.java

package com.sxt.home;

public class Student {
    private String name;
    private String sex;
    private double score;
    public Student(String name, String sex, double score) {
        super();
        this.name = name;
        this.sex = sex;
        this.score = score;
    }
    public Student() {
        super();
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public double getScore() {
        return score;
    }
    public void setScore(double score) {
        this.score = score;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", sex=" + sex + ", score=" + score + "]";
    }

}