帮小弟我看看这个简单的有关问题.

帮我看看这个简单的问题..!
import   java.io.*;

public   class   temp  
{
public   static   void   main(String   []   args)  
{
try
{
String   head   =   "Name,ID,DS,DB ";
byte[]   c   =   new   byte[40];
c   =   head.getBytes();
System.out.println(new   String(c));
String   record   =   "\n ";

BufferedWriter   fo   =   new   BufferedWriter(new   FileWriter( "c:\\student.txt ",true));
String[]   info   =   new   String[4];
BufferedReader   reader   =   new   BufferedReader(new   InputStreamReader(System.in));
for   (int   i   =   0;   i   <   info.length;   i++)
{
info[i]   =   reader.readLine();
record   +=   info[i];
}
System.out.println(record);
fo.write(record);
fo.close();
}
catch   (FileNotFoundException   fe)
{
System.out.println( "File   Not   Found ");
}
catch   (IOException   ie)
{
System.out.println( "IO   Exception ");
}
}
}


我想让程序实现输出字符保存到文本文件里
其格式为
Name,ID,DS,DB
a   001   90   90
b   002   90   96

当我输入两组数据以后,程序执行结果与预期结果不同,我搞了半天也没搞懂为什么,

a   001   90   90b   002   99   99null
nullnullnullnull


上面为程序执行,为什么会是这种结果

------解决方案--------------------
修改如下：

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;

// 注意类名要大写
public class Temp
{
public static void main(String [] args)
{
try
{
String head = "Name,ID,DS,DB ";
byte[] c = new byte[40];
c = head.getBytes();
System.out.println(new String(c));
String record = " ";

// 判断文件是否存在
File dir = new File( "c:\\student.txt ");
if(dir.exists())
{
// 是否有内容
FileInputStream infile = new FileInputStream(dir);
if(infile.read() < 0)
{
record = "Name ID DS DB " + "\r\n ";
}
infile.close();
}

BufferedWriter fo = new BufferedWriter(new FileWriter( "c:\\student.txt ",true));
String[] info = new String[4];
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
for (int i = 0; i < info.length; i++)
{
info[i] = reader.readLine();
record += info[i] + "\t\n ";
}
System.out.println(record);

fo.write(record);

// 换行
fo.write( "\r\n ");
fo.close();
}
catch (FileNotFoundException fe)
{
System.out.println( "File Not Found ");
}
catch (IOException ie)