Java基础之基于HashMap的分挑存储例子

骑猪看日落 2021-09-11 04:40 214阅读 0赞

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;
    		}
            
        }
    
    }