题目要求：定义一个Student类，属性有，name名字，no班级，score成绩，现在将若干不同班级的Student对象放入List中，统计每个班的总分和平均分

题目分析：首先需要一个student类是毋庸置疑的，采用javabean模式设计一个student类，接下来就是选择集合容器来装对象了，我们可以选择List〈student〉来装student对象，然后利用泛型嵌套把List〈student〉嵌套到Map中，
即Map〈String，List〈student〉〉，Map中的key存放班级，List〈student〉存放对应班级的学生，这也是一种办法，这里采用另外一种方式，创建一个新的类，ClassRoom，这就是一个班级类，属性有班级和学生列表，以及总成绩

代码实现：

/*** 学生类* @author wwyDEPP**/
public class Student {private String name;private String no;private double score;public Student() {}public Student(String name, String no, double score) {super();this.name = name;this.no = no;this.score = score;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getNo() {return no;}public void setNo(String no) {this.no = no;}public double getScore() {return score;}public void setScore(double score) {this.score = score;}}

import java.util.ArrayList;
import java.util.List;
/*** 班级类* @author wwyDEPP**/
public class ClassRoom {private String no;private List<Student> stuList;private double total;public ClassRoom() {//避免出现空指针异常stuList=new ArrayList<Student>();}public ClassRoom(String no) {this.no=no;//避免出现空指针异常stuList=new ArrayList<Student>();}public ClassRoom(String no, List<Student> stuList, double total) {super();this.no = no;this.stuList = stuList;this.total = total;}public String getNo() {return no;}public void setNo(String no) {this.no = no;}public List<Student> getStuList() {return stuList;}public void setStuList(List<Student> stuList) {this.stuList = stuList;}public double getTotal() {return total;}public void setTotal(double total) {this.total = total;}}

核心代码：
把给出的Student对象添加到List集合中后，利用Map集合，key是班级，value是ClassRoom类对象，封装了班级总分和学生对象List Map<String,ClassRoom> map =new HashMap<String,ClassRoom>();
接下来就需要便利存放student对象的list，进行分班，获取学生对象的班级和成绩属性
String no=stu.getNo(); double score=stu.getScore();
这里就遇到了分拣存储一对多的问题，一个班级对应很多个学生，像在之前博客分拣存储中提到的快递问题一样，我们也要判断有没有这个班级编号，有的话往里面添加数据，没有的话就新创建一个，然后计算总分

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;public class Mytest {public static void main(String[] args) {Mytest test=new Mytest();test.view(test.count(test.exam()));}//模拟考试输入学生成绩public List<Student> exam(){List<Student> list=new ArrayList<Student>();list.add(new Student("depp","a",90));list.add(new Student("depp","a",90));list.add(new Student("depp","a",90));list.add(new Student("jack","b",70));return list;}//统计分析数据public Map<String,ClassRoom> count(List<Student> list){Map<String,ClassRoom> map =new HashMap<String,ClassRoom>();for(Student stu:list){String no=stu.getNo();double score=stu.getScore();ClassRoom room=map.get(no);//不存在班级编号，新建一个if(room==null){room=new ClassRoom(no);map.put(no, room);}//存在则放入room.getStuList().add(stu);//计算总分room.setTotal(room.getTotal()+score);}return map;}//查看班级总分平均分public void view(Map<String,ClassRoom> map){Set<String> keys=map.keySet();Iterator<String> keysIt=keys.iterator();while(keysIt.hasNext()){String no=keysIt.next();ClassRoom room=map.get(no);double total=room.getTotal();double avg=Math.round(room.getTotal()/room.getStuList().size());System.out.println("total="+total+",avg="+avg);}}
}