How to write an int to the same file we are reading from?

Question

I am trying to read from a file and then writing back to that same while while appending it.

The file to be read has 5,10 and after writing, it the file should have 5,10"\n" 15.

But instead of that it has 5,10"\n" SI.

here is my source code -

 import java.io.*;
 import java.util.*;


public class Ash  {



public static void main(String[] args) throws IOException{

File file = new File("ashray.txt");
BufferedReader reader = new BufferedReader(new FileReader(file));
Scanner input = new Scanner(reader);

    String str = input.nextLine();

    String [] sc = str.split(",");

    int x = Integer.parseInt(sc[0]);
    int y = Integer.parseInt(sc[1]);
    int z = x+y;
    input.close();

    FileWriter fw = new FileWriter(file,true);
    BufferedWriter writer = new BufferedWriter(fw);     
    writer.write(Integer.toString(z));

    fw.close();     

   }    
}

you need to close the reader.. – Anoop LL Apr 26 '16 at 13:57 — Anoop LL, Apr 26 '16 at 13:57
@AnoopLL - no he doesn't. Closing the Scanner closes it. – Stephen C Apr 26 '16 at 14:51 — Stephen C, Apr 26 '16 at 14:51

score 0 · Answer 1 · answered Apr 26 '16 at 13:57

0

Use the PrintWriter

PrintWriter writer = new PrintWriter(file, "UTF-8");
writer.println("print content here");
writer.close();

answered Apr 26 '16 at 13:57

CodeWizard

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why can't i use filewriter wrapped in buffered writer? – shiwchiz Apr 26 '16 at 14:03
You can but you have to know hoe Buffer write to file. how does he converter content. (utf-8? ansi?) – CodeWizard Apr 26 '16 at 14:05
can u please tell me how to write with filewriter and buffered writer? – shiwchiz Apr 26 '16 at 14:07
1

Read this out: http://stackoverflow.com/questions/5759925/printwriter-vs-filewriter-in-java – CodeWizard Apr 26 '16 at 14:09
if i write on some other file its writing `15` but not on the same file. why is it so? – shiwchiz Apr 26 '16 at 14:19
Since the reader is open. close it and write to it and it will be fine. You need to close it before you can write to it if you have it opened in the reader. – CodeWizard Apr 26 '16 at 14:20
thanks! ..so i guess just closing bufferedreader won't work i need to close filereader ! – shiwchiz Apr 26 '16 at 14:25

Stephen C · Answer 2 · 2016-04-26T14:51:13.277

The problem is that you are closing the FileWriter rather than the BufferedWriter. This means that your application is exiting with unwritten characters in the BufferedWriter's buffer.

Solution: change

 fw.close();

to

 writer.close();

Closing the BufferedWriter is going to close the Writer that it wraps. The javadoc says so.

(You don't need to close the Reader. Closing the Scanner will close the source that it wraps. And besides, neither is strictly necessary in this context. But see below.)

Also note that if this was production code, it would be advisable to use try with resources to ensure that the file descriptors were always closed, irrespective of how the method terminated. The issue is that if the method terminated because an exception was thrown, you could skip over the statements that close the Reader or Writer stacks. That could lead to a resource leak and unexpected errors when opening files ... later on.

How to write an int to the same file we are reading from?

2 Answers2