请问一下，FileWriter为什么不能写入文件

import java.io.*;import java.util.*;import java.util.regex.Matcher;import java.util.regex.Pattern;public class TestEmail {    public static int i = 0;    public static void main(String[] args) throws IOException{                FileReader fr = new FileReader("c://hello.txt");        BufferedReader br = new BufferedReader(fr);        String line = "";        while((line = br.readLine()) != null){            email(line);        }        fr.close();        br.close();        System.out.print("i == " + i);            }    public static void email(String s) throws IOException{        FileWriter fw = new FileWriter("c://hello2.txt");//        BufferedWriter bw = new BufferedWriter(fw);        String str = "";        Pattern p = Pattern.compile("\\w*+\\@\\w*\\.[\\w]*");        Matcher m = p.matcher(s);                if(m.find()){            ++i;            str = m.group();            System.out.println(str);            fw.write(str);        }      }    }