Can't write data into renamed file

Question

The task is to rename some existing file and after that write some data into it.
There is a special handmade class for renaming, which uses File.renameTo method. But that's what program does: New file with new name appears in directory and nothing writes into it, but old file with previose name stays in that directory also (it shouldn't I suppose). And all data writes into that old file.

Here is that handmade class:

public class FileUtils {

    public static void renameFile(File source, File destination) {
        if (!source.renameTo(destination)) {
            System.out.println("Can not rename file with name " + source.getName());
        }
    }
}

And here is my code:

public class Solution {

    public static void main(String[] args) throws IOException {
        //args[0] = "D:/Java_Projects/FileJob";
        //args[1] = "D:/Java_Projects/result.txt";
        Path path = Paths.get(args[0]);
        File resultFileAbsolutePath = new File(args[1]);
        //File allFilesContent = new File("D:/Java_Projects/allFilesContent.txt");
        FileUtils.renameFile(resultFileAbsolutePath, new File("D:/Java_Projects/allFilesContent.txt"));

        List<String> filesToWrite = getContent(path);
        try (FileOutputStream writeToFile = new FileOutputStream(resultFileAbsolutePath)) {
            for (String file : filesToWrite) {
                FileInputStream readFile = new FileInputStream(file);
                while (readFile.available() > 0) {
                    writeToFile.write(readFile.read());
                }
                writeToFile.write('\n');
            }
        }
    }

    public static List<String> getContent(Path file) throws IOException {
        Path path = Paths.get(file.toString());
        Iterator iterator = new Iterator();
        Files.walkFileTree(path, iterator);
        return iterator.suitableFiles;
    }

    public static class Iterator extends SimpleFileVisitor<Path> {
        List<String> suitableFiles = new ArrayList<>();
        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
            if (file.toFile().length() <= 50) {
                suitableFiles.add(file.toFile().getAbsolutePath());
            }
            return CONTINUE;
        }
    }
}

I tried to use File.renameTo directly in main. Nothing.
I tried to initialese new variable and asign old ref to it. But it seemse to me that File object is immutable. So nothing. Any ideas?