HashMap经典存储案例，分拣思路_与面向对象组合解题

最新推荐文章于 2019-02-21 15:52:38 发布

原创最新推荐文章于 2019-02-21 15:52:38 发布 · 893 阅读

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CC 4.0 BY-SA版权

本文介绍了一个使用Java实现的学生成绩统计程序。程序通过List存储多个Student对象，并利用HashMap统计每个班级的成绩总分及平均分。

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package com.pkushutong.Collection;

/**
 * 定义一个Student类，属性：名字、班号、成绩
 * 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
 */
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 Test09 {
	public static void main(String[] args) {
		List<Student> list = new ArrayList<Student>();
		exam(list);
		
		//统计
		Map<String,ClassRoom> rooms = new HashMap<String, ClassRoom>();
		count(rooms,list);
		
		//打印
		printStudent(rooms);
	}
	
	//打印总分和平均分
	public static void printStudent(Map<String,ClassRoom> rooms){
		Set<Map.Entry<String, ClassRoom>> entrySet = rooms.entrySet();
		Iterator<Map.Entry<String, ClassRoom>> it = entrySet.iterator();
		while(it.hasNext()){
			Map.Entry<String, ClassRoom> entry = it.next();
			ClassRoom room = entry.getValue();
			double avg = room.getTotal()/room.getStu().size();
			System.out.println("班号为："+room.getNo()+"，总分："+room.getTotal()+"，平均分"+avg);
		}
	}
	
	//统计分数
	public static void count(Map<String,ClassRoom> rooms,List<Student> list){
		for(Student stu : list){
			String no = stu.getno();
			double score = stu.getScore();
			
			//根据班级编号 查看Map是否存在该班级
			ClassRoom room = rooms.get(no);
			if(room == null){	//第一次创建
				room = new ClassRoom(no);
				rooms.put(no, room);
			}
			//存储总分
			room.setTotal(room.getTotal()+score);
			room.getStu().add(stu);		//加入学生
		}
	}
	
	//现在将若干Student对象放入List
	public static void exam(List<Student> list){
		list.add(new Student("a","001",80));
		list.add(new Student("b","002",85));
		list.add(new Student("a","001",90));
		list.add(new Student("d","004",85));
	}
}

package com.pkushutong.Collection;

public class Student {
	private String name;
	private String no;
	private double score;
	
	@Override
	public String toString() {
		return "Student [name=" + name + ", no=" + no
				+ ", score=" + 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;
	}
	
	
}

package com.pkushutong.Collection;

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

/**
 * 班级
 * @author dell
 *
 */
public class ClassRoom {
	private String no;
	private List<Student> stu;	//学生
	private double total;		//总分
	
	public ClassRoom() {
		stu = new ArrayList<Student>();
	}
	
	public ClassRoom(String no) {
		this();
		this.no = no;
	}

	public String getNo() {
		return no;
	}
	public void setNo(String no) {
		this.no = no;
	}
	public List<Student> getStu() {
		return stu;
	}
	public void setStu(List<Student> stu) {
		this.stu = stu;
	}
	public double getTotal() {
		return total;
	}
	public void setTotal(double total) {
		this.total = total;
	}
	
	
}