FileOutput Stream delets text file contents

Question

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;

public class FileIoStream {

    public static void main(String[] args) throws IOException {
        File f = new File("C:\\Users\\rs\\IO\\myfile.txt");
        FileInputStream fis = new FileInputStream(f);
        FileOutputStream fos = new FileOutputStream(f);
    }
}

Every time I make an object for FileOutputStream the contents in myfile.txt get deleted and I do not know why? But when I just new FileInputStream it does not happen.

By the way i do not use any method of this fileout or in classes.i just new them. — Rsp, Aug 21 '20 at 13:34
The real answer here: read the javadoc of the classes you are using. Seriously, that is the essence of all of programming: you have to understand what you are doing. Dont just use some library class you heard of. Research what it does, and how it does things. Your first stop is always the javadoc of such classes. — GhostCat, Aug 21 '20 at 13:47

score 1 · Answer 1 · answered Aug 21 '20 at 13:36

1

FileOutputStream by default overwrites the file if it exists. You can use the overloaded constructor to append to that file instead of overwriting it:

FileInputStream fis = new FileInputStream(f, true);
// Here -------------------------------------^

answered Aug 21 '20 at 13:36

Mureinik

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It would be so nice if there were other answers on this site one could duplicate to ... ;-) – GhostCat Aug 21 '20 at 13:48

score 1 · Accepted Answer · answered Aug 21 '20 at 13:37

1

You should try with this constructor :

FileOutputStream fos = new FileOutputStream(f, true);

So what you have to add to the file will be appended if it already exists.

Doc available here

answered Aug 21 '20 at 13:37

BenjaminD

488
3
13

Giorgi Tsiklauri · Answer 3 · 2020-08-21T13:57:05.937

If gets deleted, because it actually gets overwritten. Every time you create a new FileOutputStream object with new FileOutputStream(File file) constructor, a new FileDescriptor is created, and therefore:

bytes are written to the beginning of the file.

_{You can think of it, like it starts writing to the file by overwriting everything that previously existed in that file.}

You can alternatively create your FileOutputStream object with the FileOutputStream(File f, boolean append) constructor, passing true as a boolean argument into that constructor, and in this case:

bytes will be written to the end of the file rather than the beginning.

_{You will maintain whatever had been written into the file and your data will be appended to the existing data in the file.}

FileOutput Stream delets text file contents

3 Answers3