The first / was causing a problem in the string. You have to get the full string without that.

I have tried with my class to achieve it :

String path = Test.class.getProtectionDomain().getCodeSource().getLocation().getPath();
path = path.substring(1, path.length()) + "file.txt";
System.out.println(path);
Path out = Paths.get(path);
System.out.println(out.isAbsolute());

Output :

F:/software/workspace/file.txt
true

Java is pretty friendly with IO. Try something like this:

File file = new File("/some/absolute/path/myfile.ext");
OutputStream out = new FileOutputStream(file);
// Write your data
out.close();

Notes:

• Your program needs permission to write to the directory.
• If the first character of your path string is not /, it will be relative to your "current" directory
• If you're writing text, you might find a BufferedWriter easier: BufferedWriter writer = new BufferedWriter(new FileWriter(file));. It has newLine() and write(String) methods

You should use the secondary constructor for File to specify the directory in which it is to be symbolically created. This is important because the answers that say to create a file by prepending the directory name to original name, are not as system independent as this method.

Sample code:

String dirName = /* something to pull specified dir from input */;

String fileName = "test.txt";
File dir = new File (dirName);
File actualFile = new File (dir, fileName);

/* rest is the same */

Hope it helps.

You could also use java.nio.file.Paths:

URL url = Paths.get("target", "results.csv").toUri().toURL();

If you want to access the current directory you should reference the file directly, and use try with resources to clean up the output stream:

public static void main(String args[]) throws IOException {
    int max=10;
    File output = new File("output.txt");
    System.out.println("Writing to: "+output.getAbsolutePath());
    try(BufferedWriter writer = new BufferedWriter(new FileWriter(output))) {
        writer.write(Integer.toString(max));
    }
}

The code is simpler in later JDKs using Path and Files:

public static void main(String ... args) throws IOException {
    int max = 10;
    Path output = Path.of("output.txt"); // Use Paths.get in JDK9
    System.out.println("Writing to: "+output.toAbsolutePath());
    Files.writeString(output, Integer.toString(max));
}