I am trying to modify some lines in text files and when I write that line back again to the file, I end up with a blank file

Question

This code is reading a bunch of .java files and finding "public [classname]" or "private [classname]" and adding "System.out.println([classname])" to that line.

The problem is When I write that line back in I end up with a blank file

Can anyone see what I am doing wrong?

private static void work(ArrayList<File> fileList) {
    for (int i = 0; i < fileList.size(); i++) {
        replaceLines(fileList.get(i));
    }

}

public static void replaceLines(File file) {
    String path = file.getPath();
    String fileNameLong = file.getName();
    String fileName = null;
    if (fileNameLong.contains(".java")) {
        fileName = fileNameLong.substring(0, file.getName().indexOf("."));
    }
    if (fileName != null && fileName != "") {
        System.out.println(fileName);
        try {
            //prepare reading
            FileInputStream in = new FileInputStream(path);
            BufferedReader br = new BufferedReader(
                    new InputStreamReader(in));
            //prepare writing
             FileWriter fw = new FileWriter(file);
             PrintWriter out = new PrintWriter(fw);

            String strLine;
            while ((strLine = br.readLine()) != null) {
                // Does it contain a public or private constructor?
                boolean containsPrivateCon = strLine.contains("private "
                        + fileName);
                boolean containsPublicCon = strLine.contains("public "
                        + fileName);

                if (containsPrivateCon || containsPublicCon) {
                    int lastIndexOfBrack = strLine.lastIndexOf("{");

                    while (lastIndexOfBrack == -1) {
                        strLine = br.readLine();
                        lastIndexOfBrack = strLine.lastIndexOf("{");
                    }

                    if (lastIndexOfBrack != -1) {
                        String myAddition = "\n System.out.println(\""
                                + fileName + ".java\"); \n";
                        String strLineModified = strLine.substring(0,
                                lastIndexOfBrack + 1)
                                + myAddition
                                + strLine.substring(lastIndexOfBrack + 1);
                        strLine = strLineModified;
                    }
                }
                out.write(strLine);
            }
        } catch (Exception e) {
            System.out.println(e);
        }
    }

}

Answer 1

If you want to write to the same file you're reading from, you should either write to a copy of the file (different filename) and then rename the output file, or use RandomAccessFile interface to edit a file in-place.

Usually, the first solution will be much easier to implement than the second one; unless the files are huge (which is probably not the case with .java files), there is no real reason to use the second.