1 package collection.map; 2  3  4 public class Student { 5     private String name; 6     private String classNo; 7     private double score; 8      9     10     public Student(String name, String classNo, double score) {11         super();12         this.name = name;13         this.classNo = classNo;14         this.score = score;15     }16     public String getName() {17         return name;18     }19     public void setName(String name) {20         this.name = name;21     }22     public String getClassNo() {23         return classNo;24     }25     public void setClassNo(String classNo) {26         this.classNo = classNo;27     }28     public double getScore() {29         return score;30     }31     public void setScore(double score) {32         this.score = score;33     }34     35     36 }

package collection.map;import java.util.ArrayList;import java.util.List;public class ClassRoom {	private String roomNo;	private List<Student> stus;		//学生列表	private double total;			//总分		public ClassRoom()	{		stus = new ArrayList<Student>();	}		public ClassRoom(String roomNo)	{		this();		this.roomNo = roomNo;	}	public String getRoomNo() {		return roomNo;	}	public void setRoomNo(String roomNo) {		this.roomNo = roomNo;	}	public List<Student> getStus() {		return stus;	}	public void setStus(List<Student> stus) {		this.stus = stus;	}	public double getTotal() {		return total;	}	public void setTotal(double total) {		this.total = total;	}		}

 1 package collection.map; 2  3 import java.util.ArrayList; 4 import java.util.HashMap; 5 import java.util.Iterator; 6 import java.util.List; 7 import java.util.Map; 8 import java.util.Set; 9 10 11 /*12  *  定义一个Student类,属性:name 姓名,classNumber 班号,score 成绩13  *  现在将若干Student对象放入List,请统计出每个班级的总分和平均分,分别打印出来14  *    以面向对象的思维解决15  * 16  */17 public class MapDemo02 {18 19     //将若干Student放入List20     public static void exam(List<Student> list)21     {22         list.add(new Student("AAA", "301", 88));23         list.add(new Student("BBB", "301", 84));24         list.add(new Student("CCC", "302", 85));25         list.add(new Student("DDD", "302", 86));26         list.add(new Student("EEE", "201", 46));27         list.add(new Student("FFF", "201", 68));28         list.add(new Student("AAA", "301", 88));29     }30     31     //统计分数32     public static void count(Map<String, ClassRoom> rooms,List<Student> list)33     {34         for(Student stu:list)35         {36             String no = stu.getClassNo();37             double score = stu.getScore();38             //根据班级编号 查看 Map是否存在该班级  分拣思路39             ClassRoom room = rooms.get(no);40             if(null == room)41             {42                 room = new ClassRoom(no);43                 rooms.put(no, room);44             }45             //存储总分46             room.setTotal(room.getTotal() + score);47             room.getStus().add(stu);48         }49     }50     51     //打印 总分与平均分52     public static void printScoreAndAvg(Map<String, ClassRoom> rooms)53     {54         Set<Map.Entry<String, ClassRoom>> entrySet = rooms.entrySet();55         Iterator<Map.Entry<String, ClassRoom>> iter = entrySet.iterator();56         while (iter.hasNext()) {57             Map.Entry<String, ClassRoom> entry = iter.next();58             ClassRoom room = entry.getValue();59             double avg = Math.round(room.getTotal() / room.getStus().size());60             System.out.println("班号："+room.getRoomNo()+",总分："+room.getTotal()+"平均分："+avg);61         }62     }63     64     public static void main(String[] args) {65         List<Student> list = new ArrayList<Student>();66         exam(list);67         68         //统计69         Map<String, ClassRoom> rooms = new HashMap<String, ClassRoom>();70         count(rooms, list);71         printScoreAndAvg(rooms);72         73     }74 }