Java: PrintWriter object does not output the text on my file?

I'm trying to print out the usernames of a certain program into a file but PrintWriter is not printing anything on my file. I've tried everything mentioned on stackOverFlow none of them worked.

Users Class

private File usersListFile;
private PrintWriter usersListPrintWriter;
private Scanner usersListScanner;

Constructor:

Users(){
    try {
        this.usersListFile = new File("D:\\Dairy\\usersList.txt");
        if(usersListFile.exists()){
            this.usersListPrintWriter = new PrintWriter(new BufferedWriter(new FileWriter("D:\\Dairy\\usersList.txt", true)));
            this.usersListScanner = new Scanner("D:\\Dairy\\usersList.txt");
        }
        else
            System.err.println("File does not exist !");
    }
    catch(Exception e){
        System.err.println("Error: Users Class!");                   
    }
}

Method:

public void addToUsersList(String username){
        usersListPrintWriter.print(username);           
    }

Main Method:

public static void main(String[] args) {

    Users usersObject = new Users();
    usersObject.addToUsersList("USERNAME");

    }

via Chebli Mohamed