How do I make a Register and Login example in Java and store the registration records without using database languages? - authentication

Question

I'm trying to make a project which includes the Registration Form and Login Form that the program will check if the user is registered or not and will log in if the user is registered.
I'm using FileWriter to store data like usernames and passwords "separately"
try {
FileWriter fw = new FileWriter("C:\\Users\\Krayst\\Documents\\NetBeansProjects\\Cashiering and Sales System\\src\\"+fName+"\\Full Name.txt", false);
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter out = new PrintWriter(bw);
out.print(fName);
out.close();
bw.close();
fw.close();
} catch(IOException no) {
System.out.println("Error processing data!");
}
And by the way, I created a folder to store specific data like The Full Name of the registered user so the data can be organized well
File regUser = new File("C:\\Users\\Krayst\\Documents\\NetBeansProjects\\Cashiering and Sales System\\src\\" + name);
if (!regUser.exists()) {
if (regUser.mkdir()) {
System.out.println("User Folder created");
} else {
System.out.println("User Folder not created");
}
}
The problem is I cannot access to these files because it has been "newly" created and written by the program so if I try to access its directory, it doesn't work. Plus, it has to be accessed to the other class because I created another class which is the Login JFrame and I'm using Netbeans IDE (The Registration Form is also a JFrame though). All I wanted to do is to read these Records (registration files) from another JFrame class so it can check in the Login Form whether the user is already registered or not.
I am sorry if I made some confusing statements and questions but I can accept any clarifications.
I'm a student and a beginner of programming so I would appreciate all the help from everyone. :)