1package collenction;
 2
 3/**
 4 * @author Administrator
 5 *
 6 */
 7public class Student {
 8
 9	private String name;
10	private String classno;
11	private double score;
12
13
14	public Student(String name, String classno, double score) {
15		super();
16		this.name = name;
17		this.classno = classno;
18		this.score = score;
19	}
20
21	public String getName() {
22		return name;
23	}
24
25	public void setName(String name) {
26		this.name = name;
27	}
28
29	public double getScore() {
30		return score;
31	}
32
33	public void setScore(double score) {
34		this.score = score;
35	}
36
37	public String getClassno() {
38		return classno;
39	}
40
41	public void setClassno(String classno) {
42		this.classno = classno;
43	}
44
45}

 1package collenction;
 2
 3import java.util.ArrayList;
 4import java.util.List;
 5
 6/**
 7 * 班级
 8 * 
 9 * @author Administrator
10 *
11 */
12public class ClassRoom {
13	private String no;
14	private List<Student> sut; // 学生列表
15	private double total; // 总分数
16
17	public ClassRoom() {
18		System.out.println("aslfjlsadk");
19		sut = new ArrayList<Student>();
20	}
21	
22	public ClassRoom(String no) {
23		this.no = no;
24		sut = new ArrayList<Student>();
25	}
26
27	public String getNo() {
28		return no;
29	}
30
31	public void setNo(String no) {
32		this.no = no;
33	}
34
35	public List<Student> getSut() {
36		return sut;
37	}
38
39	public void setSut(List<Student> sut) {
40		this.sut = sut;
41	}
42
43	public double getTotal() {
44		return total;
45	}
46
47	public void setTotal(double total) {
48		this.total = total;
49	}
50
51}

1public static void exam(List<Student> list){
2	list.add(new Student("张三","001",30));
3	list.add(new Student("张四","001",95));
4	list.add(new Student("张五","002",790));
5	list.add(new Student("张六","003",80));
6	list.add(new Student("张七","003",90));
7	
8}

 1public static void count(Map<String,ClassRoom> rooms,List<Student> list){
 2	//循环处理所有的学生
 3	for(Student stu:list) {
 4		//获取学生信息
 5		String no = stu.getClassno();
 6		double score = stu.getScore();
 7		ClassRoom room = rooms.get(no);
 8		//判断该学生对应的班级是否存在
 9		if(null == room) {
10			//班级不存在，创建一个，然后把学生放进来
11			room = new ClassRoom(no);
12			rooms.put(no, room);
13		}
14			//若班级存在，则把学生放进来
15			room.setTotal(room.getTotal()+score); //把当前学生的分数加到总分
16			room.getSut().add(stu);//先获取当前班级的学生list，然后把当前学生放进来
17	}
18}

 1public static void printScore(Map<String,ClassRoom> rooms) {
 2	Set<Entry<String, ClassRoom>> entrySet = rooms.entrySet();//这里使用entrySet，不使用keySet，是因为entrySet会减少一次循环，效率更高
 3	Iterator<Entry<String,ClassRoom>> it = entrySet.iterator();
 4	while(it.hasNext()) {
 5		Entry<String, ClassRoom> entry = it.next();
 6		ClassRoom room  = entry.getValue();
 7		double avg = room.getTotal()/room.getSut().size();
 8		//占位符 %s：字符串   %d：整数   %f：浮点   %b：boolean   %%：表示一个%
 9		System.out.printf("班级号为%s的班级共%s个学生，总分是%.2f分，平均分是%.2f \n" , room.getNo(),room.getSut().size(),room.getTotal(),avg);
10	}
11}

 1package collenction;
 2
 3import java.util.ArrayList;
 4import java.util.HashMap;
 5import java.util.Iterator;
 6import java.util.List;
 7import java.util.Map;
 8import java.util.Map.Entry;
 9import java.util.Set;
10
11public class HashMapTest02 {
12
13	public static void main(String[] args) {
14		//创建学生对象list
15		List<Student> list = new ArrayList<Student>();
16		//初始化一些学生
17		exam(list);
18		
19		//创建班级
20		Map<String,ClassRoom> rooms  = new HashMap<String, ClassRoom>();
21		//统计分数
22		count(rooms,list);
23		
24		printScore(rooms);
25	}
26}