问个今天上午面试的题目？

Question

实习代码
Public class StudentGrade{
 Public String name;
 Public String lesson;
 Public float grade;
}
现在有一个2000个studentGrade的对象放在一个ArrayList中，为arrayList，现在我们要把每个学生的总成绩，和平均成绩求出来，并且按平均成绩排序输出，
比如：
Name  Totalgrade  avgGrade
John    400        80
Tom     360        75
请给出实现
没有做出来，不知道怎么实现？：（，大概想了想，就是找出每个人选了多少课，但是不知道怎么在ArrayList中做

Answer 1

1,弄个类来存储Name  Totalgrade  avgGrade，设为类A2,然后弄个关于1步的List<A>3, 遍历arrayList，取出学生名字，如果list中已经有该学生，数值相加，否则添加新类A－－－－－－－－－－－－－－以上学生统计做好了，下面进行排序
1 前戏
两种方法，一种A实现Compilable，要么用到Comparator2 重点戏
Collections.sort()

Answer 2

用HashMap的什么都行
其实就两个重点的地方一，根据名字统计学生总成绩，平均成绩
二，排序

Answer 3

用循环搞定总成绩和平均成绩，
然后用Collections.sort()方法搞定排序……

Answer 4

也可以直接对StudentGrade进行排序然后统计再排序

Answer 5

Where will u store Students' scores, if u are goint to use class StudentGrade?

Answer 6

Where will u store Students' scores, if u are goint to use class StudentGrade?

Answer 7

How about a array or HashMap?

Answer 8

这个是JAVA集合里的java.util.Collections.sort(list)应该可以帮到你

Answer 9

我当时也是这样想的，但不知道怎么在里面实现，比如，tom,选择了5门课，假如2000个studentgrade对象为s1-s2000
tom肯定占了5个对象，假如为s10-s14,怎么求他的总成绩

Answer 10

准备工作
A{
name, total, number
}List<A> list=============================
for(StudentGrade s : arrayList){
boolean contain;
for(A a : list){
if(a.name == s.name){
// 分数相加, number++
contian = true;
}
}
if(!contain){
list.add(new A(name, score, 1))
}
}

Answer 11

以下是我的笨方法，应该还有更好的算法吧？欢迎指教public static void main(String[] args) {
    List students = new ArrayList();
    students.add(new StudentGrade("John", "PE", 90));
    students.add(new StudentGrade("Mary", "Math", 90));
    students.add(new StudentGrade("John", "English", 70));
    students.add(new StudentGrade("Mary", "Music", 90));
    students.add(new StudentGrade("Iris", "Article", 60));
    students.add(new StudentGrade("Mary", "English", 70));
    students.add(new StudentGrade("Iris", "PE", 90));
    students.add(new StudentGrade("John", "Math", 80));    //先排序
     Collections.sort(students, new Comparator() {
        public int compare(Object obj1, Object obj2) {
        StudentGrade studentGrade1 = (StudentGrade) obj1;
        StudentGrade studentGrade2 = (StudentGrade) obj2;
        return studentGrade1.getName().compareTo(studentGrade2.getName());
        }
    });    System.out.println("Name\tTotalGrade\tavgGrade");
    float totalGrade = 0;
    int lessonCount = 0;
    String lastName = "";
    String name = "";
    for (int i = 0; i < students.size(); i++) {
        StudentGrade studentGrade = (StudentGrade) students.get(i);
        name = studentGrade.getName();
        // 比较姓名是否发生变化，若没变化，则继续累加总成绩和科目数
         if (name.equals(lastName) || i == 0) {
            totalGrade += studentGrade.getGrade();
            lessonCount++;
        }
        // 若姓名发生变化，则打印上一人的成绩，并重新开始累加总成绩和科目数
         else {
            System.out.println(lastName + "\t" + totalGrade + "\t" + totalGrade / lessonCount);
            totalGrade = studentGrade.getGrade();
            lessonCount = 1;
        }
        lastName = name;
    }
    System.out.println(lastName + "\t" + totalGrade + "\t" + totalGrade / lessonCount);
}
结果是：
Name TotalGrade avgGrade
Iris 150.0 75.0
John 240.0 80.0
Mary 250.0 83.333336

Answer 12

可不可以写数据库啊？
用SQL的话求和、排序是不是更方便点啊

Answer 13

class StudentGrade {
public String name; public String lesson; public float grade; public StudentGrade(String name, String lesson, float grade) {
this.name = name;
this.lesson = lesson;
this.grade = grade;
}
}public class Count{
public Map countGrade(ArrayList sc){
String name="";
ArrayList<Float> smap = new ArrayList<Float>();
Map<String,List> pmap = new HashMap<String,List>();


for(Iterator isc = sc.iterator();isc.hasNext(); ){
StudentGrade s = (StudentGrade)isc.next();
name = s.name;

float perSum=0;
int sum =0;
float avg =0;
smap.clear();
for(Iterator it = sc.iterator();it.hasNext(); ){
StudentGrade sn = (StudentGrade)it.next();
if(name.equals(sn.name)){
sum +=1;
perSum += sn.grade;
avg = perSum / sum;
}
}
smap.add(perSum);
smap.add(avg);

ArrayList<Float> a = new ArrayList<Float>();
for(Float f :smap){
a.add(f);
}
pmap.put(name,a);

}
return pmap;

}
public static void main(String[] args){
StudentGrade[] arr = {new StudentGrade("yr","A",80),new StudentGrade("yr","A",69),new StudentGrade("yr","e",85),new StudentGrade("yr1","A1",90),new StudentGrade("yr1","A1",98),new StudentGrade("yr5","A1",98)};
ArrayList arrl = new ArrayList();
Collections.addAll(arrl, arr);

Map s = new Count().countGrade(arrl);
System.out.println(s);
}
原版，还没来得及优化，没时间了。。应该对 的

Answer 14

2000*2000+的,效率~~~~~,
计算完A的分数和平均分,将ArrayList里边的信息remove();

Answer 15

恕我直言  这个问题  是excel做 就很简单

Answer 16

package com.test.app;import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;public class Count
{
    public String name;
    public float totalGrade = 0f;
    public float avgGrade = 0f;
    /**
     * @param args
     */
    public static void main(String[] args)
    {
        StudentGrade[] arr = {
                        new StudentGrade("yr", "A", 80),
                        new StudentGrade("yr", "A", 69),
                        new StudentGrade("yr", "e", 85),
                        new StudentGrade("yr1", "A1", 90),
                        new StudentGrade("yr1", "A1", 98),
                        new StudentGrade("yr5", "A1", 70)
        };
        ArrayList arrl = new ArrayList();
        Collections.addAll(arrl, arr);// 将所有指定元素添加到指定 collection 中。        Count obj = new Count();
        List list = obj.countGrade(arrl);        for(Iterator iterator = list.iterator(); iterator.hasNext();)
        {
            Count count = (Count) iterator.next();
            System.out.println(count.name + "\t" + count.avgGrade + "\t" + count.totalGrade);
        }    }
    public List countGrade(ArrayList list)
    {
        String name = "";
        Count count = null;
        ArrayList gradeList = new ArrayList();        for(Iterator it = list.iterator(); it.hasNext();)
        {
            StudentGrade st = (StudentGrade) it.next();            name = st.name;
            int lessonNum = 0;
            float totalGrade = 0f;
            float avgGrade = 0f;            for(Iterator it2 = list.iterator(); it2.hasNext();)
            {
                StudentGrade st2 = (StudentGrade) it2.next();                if(name.equals(st2.name))
                {
                    lessonNum += 1;
                    totalGrade += st2.grade;
                    avgGrade = totalGrade / lessonNum;
                }
            }
            count = new Count();
            count.name = name;
            count.avgGrade = avgGrade;
            count.totalGrade = totalGrade;            if(!gradeList.contains(count))
            {
                gradeList.add(count);
            }        }        //排序
        Collections.sort(gradeList, new Comparator()
        {            public int compare(Object o1, Object o2)
            {
                Count obj = (Count) o1;
                Count other = (Count) o2;
                if(obj.avgGrade > other.avgGrade)
                {
                    return 1;
                }
                if(obj.avgGrade == other.avgGrade)
                {
                    return 0;
                }
                else
                {
                    return -1;
                }
            }        });
        return gradeList;
    }
    public boolean equals(Object obj)
    {
        if(obj == null)
        {
            return false;
        }        if(obj instanceof Count)
        {
            Count other = (Count) obj;            return (this.name == other.name);
        }
        else
        {
            return false;
        }    }
    public int hashCode()
    {
        return super.hashCode();
    }}class StudentGrade
{
    public String name;
    public String lesson;
    public float grade;
    public StudentGrade(String name, String lesson, float grade)
    {
        this.name = name;
        this.lesson = lesson;
        this.grade = grade;
    }}

Answer 17

结果
yr5 70.0 70.0
yr 78.0 234.0
yr1 94.0 188.0

Answer 18

我是java初学者，根据楼主的题目写了下，代码很搓，大家见谅啊~~============================================================================================package test;import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;public class PrintStudent {

public static List<StudentDetail> processStudentGrade(List<StudentGrade> list){
List<StudentDetail> sds = new ArrayList<StudentDetail>();
Map<String,List<Object>> map = new HashMap<String,List<Object>>(); 

for(StudentGrade sg : list){
String name = sg.name;
Integer grade = sg.grade;
if(map.containsKey(name)){
List temp = map.get(name);
Integer totolGrade = (Integer)temp.get(0);
temp.set(0, (totolGrade+grade));
Integer count = (Integer)temp.get(1);
temp.set(1, count+1);

}else{
List save = new ArrayList();
save.add(grade);
save.add(1);
save.add(name);
map.put(name, save);
}
}
Set<String> set = map.keySet();
Iterator it = set.iterator();
while(it.hasNext()){
String name =(String) it.next();
List<Object> l = map.get(name);
StudentDetail sd = new StudentDetail();
sd.setName((String)l.get(2));
int totalGrade = (Integer)l.get(0);
sd.setTotalGrade(totalGrade);
sd.setAveGrade(totalGrade/(Integer)l.get(1));
sds.add(sd);
}
return sds;
}

public static void print(List<StudentDetail> list){
Collections.sort(list);
System.out.println("Name\tTotalgrade\tavgGrade");
for(int i = 0 ;i<list.size();i++ ){
StudentDetail sd = list.get(i);
System.out.println(sd.getName()+"\t"+sd.getTotalGrade()+"\t"+sd.getAveGrade());
}
}
public static void main(String[] args) {
List<StudentGrade> students = new ArrayList<StudentGrade>();
    students.add(new StudentGrade("John", "PE", 90));
    students.add(new StudentGrade("Mary", "Math", 90));
    students.add(new StudentGrade("John", "English", 70));
    students.add(new StudentGrade("Mary", "Music", 90));
    students.add(new StudentGrade("Iris", "Article", 60));
    students.add(new StudentGrade("Mary", "English", 70));
    students.add(new StudentGrade("Iris", "PE", 90));
    students.add(new StudentGrade("John", "Math", 80));
    students.add(new StudentGrade("John", "PE", 90));
    students.add(new StudentGrade("John", "PE", 90));
    students.add(new StudentGrade("Iris", "Article", 100));
    students.add(new StudentGrade("Iris", "Article", 100));
    students.add(new StudentGrade("Iris", "Article", 100));
    students.add(new StudentGrade("Iris", "Article", 100));
    
    PrintStudent.print(PrintStudent.processStudentGrade(students));
    
}
}
============================================================================================
package test;public class StudentDetail implements Comparable {
private String name;
private int totalGrade;
private double aveGrade;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getTotalGrade() {
return totalGrade;
}
public void setTotalGrade(int totalGrade) {
this.totalGrade = totalGrade;
}
public double getAveGrade() {
return aveGrade;
}
public void setAveGrade(double aveGrade) {
this.aveGrade = aveGrade;
}
@Override
public int compareTo(Object o) {
if(o instanceof StudentDetail){
StudentDetail sd = (StudentDetail) o;
return (int) (aveGrade  - (int)sd.getAveGrade());
}
return 0;
}

}