Question

there is a text file which we read from it , then we want to write it after some little changes to othere text file, but the question is that why it has different results if we use
System.out.println and when we use pwPaperAuthor.println?

the code is like :

package cn.com.author;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.HashSet;
import java.util.Set;
import java.util.StringTokenizer;

//input:"IndexAuthors1997-2010.txt"
//output:"PaperAuthor1997-2010.txt"
public class PaperAuthors {

    public static void main(String[] args) {

        BufferedReader brIndexAuthors = null;

        BufferedWriter bw = null;

        PrintWriter pwPaperAuthor = null;

        try {
            brIndexAuthors = new BufferedReader(new InputStreamReader(
                    new FileInputStream("IndexAuthors1997-2010.txt")));
            bw = new BufferedWriter(new FileWriter(new File(
                    "PaperAuthor1997-2010.txt")));
            pwPaperAuthor = new PrintWriter(new OutputStreamWriter(
                    new FileOutputStream("PaperAuthor1997-2010.txt")));
            /*
             * line = brIndexAuthors.readLine();
             * 
             * element=line.split("@"); String author=null; StringTokenizer st =
             * new StringTokenizer(element[1],","); while(st.hasMoreTokens()) {
             * author = st.nextToken(); pwPaperAuthor.println(element[0] + "+" +
             * author); //~i++; }
             */
            String line = null;
            String element[] = new String[3];
            String author = null;
            int i = 0;
            while ((line = brIndexAuthors.readLine()) != null) {
                element = line.split("#@");
                StringTokenizer st = new StringTokenizer(element[1], ",");

                int num=st.countTokens();

                while (st.hasMoreTokens()) {
                    author = st.nextToken();
                     pwPaperAuthor.println(element[0]+"@"+author+"@"+element[2]);
                    bw.write(element[0] + "@" + author + "@" + element[2]);
                    bw.newLine();
                    System.out.println(element[0]+"@"+author+"@"+element[2]);
                    i++;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {

        }
    }
}

Ouput

if

System.out.println(element[0]+"@"+author+"@"+element[2]);------>620850@Henk Ern

if

pwPaperAuthor.println(element[0]+"@"+author+"@"+element[2]);
                        ----->620850@Henk Ernstblock@2001

Answer 1

There’s no way you can read a file and write to it in the same loop, using the stream-based API. You will have to create a new file and copy everything that’s the same, adding what’s new. What you are doing now has unpredictable behavior. If you still want to read and write at the same time, you’ll have to use the RandomAccessFile, but that’s quite a bit more complicated.