'Why does introducing a FileWriter delete all the content in the file?

I have a text file with some text in it and i'm planning on replacing certain characters in the text file. So for this i have to read the file using a buffered reader which wraps a file reader.

File file = new File("new.txt");
BufferedReader br = new BufferedReader(new FileReader(file));

String line = null;
while ((line = br.readLine()) != null) {
    System.out.println(line);
}

But since i have to edit characters i have to introduce a file writer and add the code which has a string method called replace all. so the overall code will look as given below.

File file = new File("new.txt");

FileWriter fw = new FileWriter(file);
BufferedReader br = new BufferedReader(new FileReader(file));

String line = null;
while ((line = br.readLine()) != null) {
    System.out.println(line);
    fw.write(br.readLine().replaceAll("t", "1") + "\n");
}

Problem is when i introduce a file writer to the code (By just having the initialization part and when i run the program it deletes the content in the file regardless of adding the following line)

fw.write(br.readLine().replaceAll("t", "1") + "\n");

Why is this occurring? am i following the correct approach to edit characters in a text file?

Or is there any other way of doing this?

Thank you.

javabufferedreaderfilewriter


Solution 1:[1]

public FileWriter(String fileName, boolean append)

Parameters:

fileName - String The system-dependent filename.

append - boolean if true, then data will be written to the end of the file rather than the beginning.

To append data use 

new FileWriter(file, true);

Solution 2:[2]

The problem is that you're trying to write to the file while you're reading from it. A better solution would be to create a second file, put the transformed data into it, then replace the first file with it when you're done. Or if you don't want to do that, read all of the data out of the file first, then open it for writing and write the transformed data.

Also, have you considered using a text-processing language solution such as awk, sed or perl: https://unix.stackexchange.com/questions/112023/how-can-i-replace-a-string-in-a-files

Solution 3:[3]

You need to read the file first, and then, only after you read the entire file, you can write to it.

Or you open a different file for writing and then afterwards you replace the old file with the new one.

The reason is that once you start writing to a file, it is truncated (the data that was in the file is deleted). The only way to avoid that is to open the file in "append" mode. With that mode, you start writing at the end of the file, so you don't delete its content. However, you won't be able to modify the existing content, you will only add content.

Solution 4:[4]

Maybe like this

public static void main(String[] args) throws IOException {
        try {
            File file = new File("/Users/alexanderkrum/IdeaProjects/printerTest/src/atmDep.txt");
            Scanner myReader = new Scanner(file);
            ArrayList<Integer> numbers = new ArrayList<>();
            while (myReader.hasNextLine()) {
                numbers.add(myReader.nextInt() + 1);
            }
            myReader.close();

            FileWriter myWriter = new FileWriter(file);
            for (Integer number :
                    numbers) {
                myWriter.write(number.toString() + '\n');
            }
            myWriter.close();

        } catch (FileNotFoundException e) {
            System.out.println("An error occurred.");
            e.printStackTrace();
        }
    }

Solution 5:[5]

Just add at last :

fw.close();

this will close it ,then it will not delete anything in the file. :)

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Priyath Gregory
Solution 2 Community
Solution 3 Olivier
Solution 4 Alexander Krum
Solution 5 jizhihaoSAMA

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