Java基础之基于HashMap的分挑存储例子

按班级统计学生的平均成绩时，为了减少工作量，计划使用计算机来做这样的统计工作。

下面给出一个类Score用来表示每条考试成绩。

  

   

    

     

    
    

     

      package com.test;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      /**
     
    
   

    

     

    
    

     

       * 学生成绩。
     
    
   

    

     

    
    

     

       */
     
    
   

    

     

    
    

     

      class Score {
     
    
   

    

     

    
    

     
 /**
     
    
   

    

     

    
    

     

       * 学生姓名。
     
    
   

    

     

    
    

     

       */
     
    
   

    

     

    
    

     
 public String stdName;
     
    
   

    

     

    
    

     
 /**
     
    
   

    

     

    
    

     

       * 班级号。
     
    
   

    

     

    
    

     

       */
     
    
   

    

     

    
    

     
 public String classNumber;
     
    
   

    

     

    
    

     
 /**
     
    
   

    

     

    
    

     

       * 分数。
     
    
   

    

     

    
    

     

       */
     
    
   

    

     

    
    

     
 public int mark;
     
    
   

    

     

    
    

     
	public String getStdName() {
     
    
   

    

     

    
    

     
		return stdName;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
	public void setStdName(String stdName) {
     
    
   

    

     

    
    

     
		this.stdName = stdName;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
	public String getClassNumber() {
     
    
   

    

     

    
    

     
		return classNumber;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
	public void setClassNumber(String classNumber) {
     
    
   

    

     

    
    

     
		this.classNumber = classNumber;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
	public int getMark() {
     
    
   

    

     

    
    

     
		return mark;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
	public void setMark(int mark) {
     
    
   

    

     

    
    

     
		this.mark = mark;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      }
     
    
  
 

编写一个类ScoreStatistic，在类里实现以下方法：

  

   

    

     

    
    

     

      package com.test;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      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 ScoreStatistic{
     
    
   

    

     

    
    

     
 public ScoreStatistic(){
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 public Map<String,Integer> statistic1(List<Score> scores){
     
    
   

    

     

    
    

     

      		Map<String,Integer> classcountMap = new HashMap<String, Integer>();
     
    
   

    

     

    
    

     

      		Map<String,Integer> classsumMap = new HashMap<String, Integer>();
     
    
   

    

     

    
    

     

      		Iterator<Score> it = scores.iterator();
     
    
   

    

     

    
    

     
		while (it.hasNext()) {
     
    
   

    

     

    
    

     

      			Score temp = it.next();
     
    
   

    

     

    
    

     

      			String cn = temp.classNumber;
     
    
   

    

     

    
    

     
			int cm = temp.mark;
     
    
   

    

     

    
    

     

      // System.out.println(it.next().classNumber+"+"+it.next().mark);
     
    
   

    

     

    
    

     
			if(classcountMap.get(cn)!=null){System.out.println("1");
     
    
   

    

     

    
    

     

       classcountMap.put(cn, classcountMap.get(cn)+1);
     
    
   

    

     

    
    

     

       classsumMap.put(cn, classsumMap.get(cn)+cm);
     
    
   

    

     

    
    

     

      			}else{
     
    
   

    

     

    
    

     

       classcountMap.put(cn, 1);
     
    
   

    

     

    
    

     

       classsumMap.put(cn,cm);
     
    
   

    

     

    
    

     

      			}
     
    
   

    

     

    
    

     
			
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     

      		Map<String, Integer> finalMap = new HashMap<String, Integer>();
     
    
   

    

     

    
    

     

      		Iterator it1=classcountMap.keySet().iterator(); 
     
    
   

    

     

    
    

     
		while(it1.hasNext()){ 
     
    
   

    

     

    
    

     

       String key; 
     
    
   

    

     

    
    

     

       Integer value; 
     
    
   

    

     

    
    

     

       Integer marksum;
     
    
   

    

     

    
    

     

       key=it1.next().toString(); 
     
    
   

    

     

    
    

     

       value=classcountMap.get(key); 
     
    
   

    

     

    
    

     

       marksum=classsumMap.get(key); System.out.println(value);
     
    
   

    

     

    
    

     

       finalMap.put(key, marksum/value);
     
    
   

    

     

    
    

     

       System.out.println(key+":"+marksum/value); 
     
    
   

    

     

    
    

     

      		}   
     
    
   

    

     

    
    

     
		return classsumMap;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public Map<String,Integer> statistic(List<Score> scores){
     
    
   

    

     

    
    

     

      		Map<String,Integer> map = new HashMap<String,Integer>();
     
    
   

    

     

    
    

     
		
     
    
   

    

     

    
    

     

      		Map<String,ClassRoom> roomMap = new HashMap<String,ClassRoom>();
     
    
   

    

     

    
    

     
		int avg;
     
    
   

    

     

    
    

     

      		ClassRoom room = null;
     
    
   

    

     

    
    

     
		for(Score score:scores){
     
    
   

    

     

    
    

     

      			String classNumber = score.getClassNumber();
     
    
   

    

     

    
    

     
			int mark = score.getMark();
     
    
   

    

     

    
    

     

      			room = roomMap.get(classNumber); 
     
    
   

    

     

    
    

     
			if(room == null){
     
    
   

    

     

    
    

     

       room = new ClassRoom(classNumber);
     
    
   

    

     

    
    

     

       roomMap.put(classNumber, room);
     
    
   

    

     

    
    

     

      			}
     
    
   

    

     

    
    

     

      			room.setTotal(room.getTotal()+mark);
     
    
   

    

     

    
    

     

      			room.getList().add(score);
     
    
   

    

     

    
    

     
			//System.out.println(score.getClassNumber()+":"+avg);
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
		
     
    
   

    

     

    
    

     

      		Set<Map.Entry<String,ClassRoom>> set = roomMap.entrySet();
     
    
   

    

     

    
    

     

      		Iterator<Map.Entry<String, ClassRoom>> it = set.iterator();
     
    
   

    

     

    
    

     
		while(it.hasNext()){
     
    
   

    

     

    
    

     

      			Map.Entry<String, ClassRoom> entry = it.next();
     
    
   

    

     

    
    

     

      			ClassRoom ro = entry.getValue();
     
    
   

    

     

    
    

     

      			avg = ro.getTotal()/ro.getList().size();
     
    
   

    

     

    
    

     

      			map.put(ro.getClassNumber(), avg);
     
    
   

    

     

    
    

     

      			System.out.println(ro.getClassNumber()+":"+avg);
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
		
     
    
   

    

     

    
    

     
		return map;
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 class ClassRoom{
     
    
   

    

     

    
    

     
 /**
     
    
   

    

     

    
    

     

       * 班级号。
     
    
   

    

     

    
    

     

       */
     
    
   

    

     

    
    

     
 public String classNumber;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 /**
     
    
   

    

     

    
    

     

       * 总分
     
    
   

    

     

    
    

     

       */
     
    
   

    

     

    
    

     
 private int total;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 private List<Score> list;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public ClassRoom(){
     
    
   

    

     

    
    

     

       list = new ArrayList<Score>();
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public ClassRoom(String classNumber){
     
    
   

    

     

    
    

     
 this();
     
    
   

    

     

    
    

     
 this.classNumber = classNumber;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
		public String getClassNumber() {
     
    
   

    

     

    
    

     
			return classNumber;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
		public void setClassNumber(String classNumber) {
     
    
   

    

     

    
    

     
			this.classNumber = classNumber;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
		public int getTotal() {
     
    
   

    

     

    
    

     
			return total;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
		public void setTotal(int total) {
     
    
   

    

     

    
    

     
			this.total = total;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
		public List<Score> getList() {
     
    
   

    

     

    
    

     
			return list;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
		public void setList(List<Score> list) {
     
    
   

    

     

    
    

     
			this.list = list;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      }
     
    
  
 

文章来源: smilenicky.blog.csdn.net，作者：smileNicky，版权归原作者所有，如需转载，请联系作者。

原文链接：smilenicky.blog.csdn.net/article/details/53183675