read and write file in Java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;



public class Read_Write {

 public static void main(String[] arg) throws IOException{
 String fileName = "data/input/tweet_2012_06";
 BufferedReader in = new BufferedReader(new FileReader(fileName));
 String str;

 FileWriter fstream = new FileWriter("data/output_tweet_2012_06.txt");
 BufferedWriter out = new BufferedWriter(fstream);

 int counter = 0;
 while ((str = in.readLine())!= null){
  System.out.println(counter+"  " + str);
  out.write(str);
  counter++;

 }
    System.out.println("counter is "+counter);
  out.close();
 in.close();
 }

}