Course类：

package com.goodprg.d1207.que1;

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

public class Course

{

private String name;

//选中此课程的学生成绩

private List stuList = new ArrayList();

public Course()

{

super();

}

public Course(String name)

{

super();

this.name = name;

}

public String getName()

{

return name;

}

public void setName(String name)

{

this.name = name;

}

public List getStuList()

{

return stuList;

}

public void setStuList(List stuList)

{

this.stuList = stuList;

}

public void stuChoose(Student s)

{

this.stuList.add(s);

}

/**

* 计算平均值

*

* @return [参数说明]

*

* @return float [返回类型说明]

* @exception throws [违例类型] [违例说明]

* @see [类、类#方法、类#成员]

*/

public float getAvg()

{

int count = 0;

float total = 0;

for(Student s : stuList)

{

total = total + s.getScore();

count++;

}

if(count==0)

{

return 0;

}

return total / count;

}

/**

* 计算方差

*

* @return [参数说明]

*

* @return float [返回类型说明]

* @exception throws [违例类型] [违例说明]

* @see [类、类#方法、类#成员]

*/

public float getVariance()

{

if(stuList.size()==0)

{

return 0;

}

float avg = getAvg();

float totalTmp = 0;

for(Student s : stuList)

{

float sub = s.getScore() - avg;

totalTmp = sub * sub + totalTmp;

}

return totalTmp / stuList.size();

}

/**

* 求中位数

*

* @return [参数说明]

*

* @return float [返回类型说明]

* @exception throws [违例类型] [违例说明]

* @see [类、类#方法、类#成员]

*/

public float getMedian()

{

if(stuList.size()==0)

{

return 0;

}

int inx = stuList.size() / 2;

int mod = stuList.size() % 2;

//排序集合

Collections.sort(stuList);

//个数为奇数

if(mod==1)

{

return stuList.get(inx).getScore();

}

//个数为偶数

else

{

float s1 = stuList.get(inx-1).getScore();

float s2 = stuList.get(inx).getScore();

return (s1+s2)/2;

}

}

/**

* 排序后，返回的list

*

* @return [参数说明]

*

* @return List [返回类型说明]

* @exception throws [违例类型] [违例说明]

* @see [类、类#方法、类#成员]

*/

public List sortStudents()

{

Collections.sort(stuList);

return stuList;

}

public static void main(String[] args)

{

int a = 9/2;

System.out.println(a);

}

}

Student类：

package com.goodprg.d1207.que1;

public class Student implements Comparable

{

//学生姓名

private String name;

//课程成绩

private float score;

public Student()

{

super();

}

public Student(String name, float score)

{

super();

this.name = name;

this.score = score;

}

public String getName()

{

return name;

}

public void setName(String name)

{

this.name = name;

}

public float getScore()

{

return score;

}

public void setScore(float score)

{

this.score = score;

}

@Override

public int compareTo(Student o)

{

int res = this.score>o.score ? 1 : (this.score==o.score ? 0 : -1);

return res;

}

@Override

public String toString()

{

return "学生：【" + name + "】成绩为：" + score;

}

}

测试类：

package com.goodprg.d1207.que1;

import java.util.List;

public class Test

{

public static void main(String[] args)

{

Student s1 = new Student("张一",92);

Student s2 = new Student("张二",83);

Student s3 = new Student("张三",77);

Student s4 = new Student("张四",99);

Course cs = new Course("马列主义");

cs.stuChoose(s1);

cs.stuChoose(s2);

cs.stuChoose(s3);

cs.stuChoose(s4);

//平均值

System.out.println("课程【"+cs.getName()+"】学生平均值："+cs.getAvg());

System.out.println("课程【"+cs.getName()+"】学生成绩方差："+cs.getVariance());

System.out.println("课程【"+cs.getName()+"】学生成绩中位数："+cs.getMedian());

System.out.println("课程【"+cs.getName()+"】学生成绩排序如下：");

List sortStus = cs.sortStudents();

for(Student s : sortStus)

{

System.out.println(s);

}

}

}

运行结果

课程【马列主义】学生平均值：87.75

课程【马列主义】学生成绩方差：70.6875

课程【马列主义】学生成绩中位数：87.5

课程【马列主义】学生成绩排序如下：

学生：【张三】成绩为：77.0

学生：【张二】成绩为：83.0

学生：【张一】成绩为：92.0

学生：【张四】成绩为：99.0

追问

学生成绩存储在文件中，每行一个学生成绩，形如：

20151201 85 84 91.5

20151202 70 85 65

。。。

请编程读入学生成绩，并计算各门课程的均值和方差，写入文件最后的最后一行

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