Java中Map的分拣存储思想--2

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上面一个已经简单的介绍了Map的分拣存储思想，下面通过一个复杂的实例来进一步理解分拣存储思想，虽然在百度的时候，百度分拣存储思想都是尚学堂的，可能我还不知道这个在实际中怎么去用吧。

案例2:定义一个Student类,属性:name 姓名,no班号,score 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

//在解题之前，先建立两个对象，Student1类和Classroom1类import java.util.ArrayList;import java.util.List;public class Classroom1 {    private String no;    private List<Student1> stu;    private double total;    public Classroom1() {        stu = new ArrayList();    }    public Classroom1(String no) {        this();        this.no = no;    }    public Classroom1(String no, List<Student1> stu, double total) {        super();        this.no = no;        this.stu = stu;        this.total = total;    }    public String getNo() {        return no;    }    public void setNo(String no) {        this.no = no;    }    public List<Student1> getStu() {        return stu;    }    public void setStu(List<Student1> stu) {        this.stu = stu;    }    public double getTotal() {        return total;    }    public void setTotal(double total) {        this.total = total;    }}

//在解题之前，先建立两个对象，Student1类和Classroom1类public class Student1 {    private String name;    private String no;    private double score;    public Student1() {    }    public Student1(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;    }    @Override    public String toString() {        return this.name;    }}

//推荐使用Map<String,Classroom1>来建立分拣存储的思想，这里为了操作的方便性，//把学生对象的容器List放入Classroom1中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 TestAverage_2 {    //将数据放入List中    public static List<Student1> exam(){        List<Student1> list = new ArrayList<>();        list.add(new Student1("老裴","a",85));        list.add(new Student1("裴兜兜","a",86));        list.add(new Student1("裴裴","a",89));        list.add(new Student1("高小三","b",80));        list.add(new Student1("高高","b",80));        return list;    }    //统计分析，也就是分拣存储，实现1：N的功能    public static Map<String,Classroom1> count(List<Student1> list){        Map<String,Classroom1> map = new HashMap<String,Classroom1>();        for(Student1 stu:list){            String no = stu.getNo();            double total = stu.getScore();            //查看有班级存在吗？如果没有的话就创建一个班级            Classroom1 room = map.get(no);            if(!map.containsKey(no)){                room = new Classroom1();                map.put(no, room);            }            //已经有班级存在了，剩下的就是把学生放在相应班级中            room.getStu().add(stu);            room.setTotal(room.getTotal()+total);        }        return map;    }    //计算班级的总分和平均分，也就是遍历Map    public static void view(Map<String,Classroom1> map ){        Set<String> set = map.keySet();        Iterator<String> it = set.iterator();        while(it.hasNext()){            String no = it.next();            double total = map.get(no).getTotal();            double avrage = total/(map.get(no).getStu().size());            System.out.println(no+"--"+total+"--"+avrage);        }    }    public static void main(String[] args) {        List<Student1> stu = exam();        Map<String,Classroom1> map = count(stu);        view(map);    }}

import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Set;import cn.feng.test3.Student;/** * 不推荐使用Map<String,List<Student>> 操作不方便，这里只是想试试 * 直接用List当做Map的value值 */public class TestAverage {    //先将需要存储的对象放入List中    public static List<Student1> exam(){        List<Student1> list = new ArrayList<>();        list.add(new Student1("老裴","a",82));        list.add(new Student1("裴兜兜","a",82));        list.add(new Student1("裴裴","a",82));        list.add(new Student1("高小三","b",80));        list.add(new Student1("高高","b",80));        return list;    }    //实现分拣存储的思想，利用map实现1：N的映射，    //其中Key-->String 班级编号；Value-->对应着List<Student>    public static Map<String,List<Student1>> count(List<Student1> list){        Map<String,List<Student1>> map = new HashMap<>();        for(Student1 stu:list){            String no = stu.getNo();            if(!map.containsKey(no)){                List<Student1> value = new ArrayList<>();                map.put(no, value);                value.add(stu);            }else{                List<Student1> value = map.get(no);                value.add(stu);            }        }           return map;    }    public static void view(Map<String,List<Student1>> map){        double total = 0;        Set keyset = map.keySet();        Iterator<String> it = keyset.iterator();        while(it.hasNext()){            String no = it.next();            List<Student1> list = map.get(no);            System.out.println(no+list);            for(int i=0;i<list.size();i++){                Student1 stu = list.get(i);                total = total + stu.getScore();            }            double average = total/list.size();            System.out.println(no+"-->"+total+"-->"+average);            total = 0;        }    }    public static void main(String[] args) {        List<Student1> list = exam();        Map<String,List<Student1>> map = count(list);        view(map);    }}

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