BufferedReader returns null, even though there is text in the file

Question

BufferedReader rea = new BufferedReader(new FileReader("points.txt"));
BufferedWriter writ = new BufferedWriter(new FileWriter("points.txt"));

ArrayList<String> top = new ArrayList<String>();

// checking if file is empty, so it enters imaginary players and scores
// if it is.
if (rea.readLine() == null) {
    for (int i = 1; i < 6; i++) {
        writ.write("Player" + i + "\t\t" + "99:99");
        writ.newLine();
    }
}
while ((readthis = rea.readLine()) != null) {
    top.add(readthis);
}

So what happens is that even though my file "points.txt" already had some made up players inside, it still returns true on that first if sentence, so new players print into the file. But the problem is, when I try to read the file in a while sentence, it doesn't even go through it. I've checked with System.out.println() and found out that it returns null. How can it return null, even if I've seen it fill in the new data? What am I doing wrong? I'm struggling with this one problem for about hour and a half now, tried everything I know. Any help much appreciated.

Answer 1

Please understand that reading and writing to a file simultaneously using a BufferedReader/Writer is not really a good idea.

When using a Buffered reader or writer there is no guarantee when the actual reading and writing will be done.

That being said, one fix is to set a mark on the reader before reaching the end of file and also closing (or at least flushing) the output stream. This will force the BufferedWriter to actually write the contents to the file system and allow the reader to read the new content.

Note: You may find that on some file systems this approach will not work.

rea.mark(4048); // Set mark at beginning of file    
if (rea.readLine() == null) {
    for (int i = 1; i < 6; i++) {
        writ.write("Player" + i + "\t\t" + "99:99");
        writ.newLine();
    }
    writ.close();
    rea.reset();
}

That being said, I think a better approach would be to check the length and existence of the file before trying to read from it. Please see the sample below.

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

// checking if file is empty, so it enters imaginary players and scores
// if it is.'
if ((!file.exists()) || (file.length() == 0)) {
    try (BufferedWriter writ = new BufferedWriter(new FileWriter(file))) {
        for (int i = 1; i < 6; i++) {
            writ.write("Player" + i + "\t\t" + "99:99");
            writ.newLine();
        }
    }
    // writ is closed by the try()
}
try (BufferedReader rea = new BufferedReader(new FileReader(file))) {
    ArrayList<String> top = new ArrayList<String>();

    String readthis;
    while ((readthis = rea.readLine()) != null) {
        top.add(readthis);
    }
}
// rea is safely closed by the try()

The stream creation has been put in try() blocks so that they are safely cleaned up.

I hope this helps.

Answer 2

By using new BufferedWriter(new FileWriter("points.txt")); you are overriding previous content of file. If you want to add new content at end of existing file you need to use constructor with boolean append argument like

new BufferedWriter(new FileWriter("points.txt"),true);

Also don't forget to flush/close your readers/writers.

Answer 3

This code

BufferedWriter writ = new BufferedWriter(new FileWriter("points.txt"));

overwrites the original file.

use

BufferedWriter writ = new BufferedWriter(new FileWriter("points.txt"),true);

to append