Problems writing to and reading from a file

Question

I am new to programming (Sorry if I ask an easy question) and I have a problem with my program dealing with writing to and reading from a file. To start off I ask the user what they want their username and password to be. Then to simply check if what I was doing was correct, I tried to read the file and then print out the same information. Here is my code:

public void createAccount()
{
    try
    {
        FileWriter doc = new FileWriter("Username.ctxt", true);
        System.out.print("Enter your desired Username: ");
        myUsername = keyboard.next();
        System.out.println();
        System.out.print("Enter your desired Password: ");
        myPassword = keyboard.next();
        System.out.println();
        String doc2 = myUsername + " " + myPassword + "\n";
        doc.write(doc2, 0, doc2.length());
        doc.close();
    }
    catch(IOException e)
    {
        System.out.println("Error: " + e.getMessage());
   }

   retrieveAccount();
}

public void retrieveAccount()
{
    try
    {
        BufferedReader reader = new BufferedReader(new FileReader("Username.ctxt"));//
        String user = new String("");//username
        String pass = new String("");//password
        int stop;
        String line = null;

        System.out.print("Enter your username: ");//allows computer to search through file and find username
        username = keyboard.next();
        while ((line = reader.readLine()) != null) 
        {
            scan = reader.readLine();
            stop = scan.indexOf(" ");
            user = scan.substring(0, stop);
            System.out.println(user);
            pass = scan.substring(stop + 1);
            System.out.println(pass);
            if(user.equals(myUsername))
            {
                System.out.println("Your password is: " + pass);
                break;
            }
        }
    }
    catch(IOException a)
    {
        System.out.println("Error: " + a.getMessage());
    }
}

So what I want to happen is:

Enter desired username: jake101
Enter desired password: coolKid

Enter your username: jake101
your password is: coolKid

But what actually happens is, is and out of bounds exception(-1)

This is happening because when I use indexOf(" "); it searches for a space. And when it returns negative 1 it means there is no space. What i believe is happening is that i am not writing to the same document i am trying to read from. If anybody can help me figure out what i am doing wrong this would help!

Answer 1

I would suggest you to create seperate methods for createAccount,retrieveAccount,writeToFile and readToFile. A method should always be responsible to handle single modules. Is the actual responsibillity of createAccount method to read from a file? I would totally say no. Firstly, because low coupling - high cohesion principles are not followed and secondly, because reusabillity does not exist in this way. There are other issues that occur with your currect approach but since you are still in the beginning is expected.

I will provide you with some parts of the things you could do, however, there will be some parts that you should work on your own, like creating the User Class ( it shouldn't be difficult and it will help you learn)

So let's see.

 public void createAccount(User user, ListInterface<User> userList)
                throws AuthenticationException {
        if (!userList.exists(user)) {
            userList.append(user);
        } else {
            throw new AuthenticationException(
                "You cannot add this user. User already exists!");
        }
    
 }
    
    
public boolean authenticate(User user, ListInterface<User> userList)
                throws AuthenticationException {
        for (int i = 1; i <= userList.size(); i++) {
            if (user.equals(userList.get(i))
            && user.getPassword().equals(
                userList.get(i).getPassword())) {
                return true;
            }
        }
        return false;
}

    public void readFromFile(String fileName, ListInterface<User> userList) {
        String oneLine, oneLine2;
        User user;
        try {
            /*
             * Create a FileWriter object that handles the low-level details of
             * reading
             */
            FileReader theFile = new FileReader(fileName);

            /*
             * Create a BufferedReader object to wrap around the FileWriter
             * object
             */
            /* This allows the use of high-level methods like readline */
            BufferedReader fileIn = new BufferedReader(theFile);

            /* Read the first line of the file */
            oneLine = fileIn.readLine();
            /*
             * Read the rest of the lines of the file and output them on the
             * screen
             */
            while (oneLine != null) /* A null string indicates the end of file */
            {
                oneLine2 = fileIn.readLine();
                user = new User(oneLine, oneLine2);
                oneLine = fileIn.readLine();
                userList.append(user);
            }

            /* Close the file so that it is no longer accessible to the program */
            fileIn.close();
        }

        /*
         * Handle the exception thrown by the FileReader constructor if file is
         * not found
         */
        catch (FileNotFoundException e) {
            System.out.println("Unable to locate the file: " + fileName);
        }

        /* Handle the exception thrown by the FileReader methods */
        catch (IOException e) {
            System.out.println("There was a problem reading the file: "
                    + fileName);
        }
    } /* End of method readFromFile */

    
    public void writeToFile(String fileName, ListInterface<User> userList) {
        try {
            /*
             * Create a FileWriter object that handles the low-level details of
             * writing
             */
            FileWriter theFile = new FileWriter(fileName);

            /* Create a PrintWriter object to wrap around the FileWriter object */
            /* This allows the use of high-level methods like println */
            PrintWriter fileOut = new PrintWriter(theFile);

            /* Print some lines to the file using the println method */
            for (int i = 1; i <= userList.size(); i++) {
                fileOut.println(userList.get(i).getUsername());
                fileOut.println(userList.get(i).getPassword());
            }
            /* Close the file so that it is no longer accessible to the program */
            fileOut.close();
        }

        /* Handle the exception thrown by the FileWriter methods */
        catch (IOException e) {
            System.out.println("Problem writing to the file");
        }
    } /* End of method writeToFile */

Useful Information:

• The userList is a dynamic linked list that uses generics (ListInterface<User>)

  if you dont want to use generics you could just say ListInterface userList, whereever it appears.

• Your User class should implement the comparable and include the methods stated below:

  public int compareTo(User user) {
      
  }
  
  public boolean equals(Object user) {
       
  }
  

• Always try to create "plug-an-play" methods(not hardcoded), that's the reason I pass as a parameter the userList.

• Note that, in case that you dont use generics, typecast might be needed. Otherwise, you will get compilation errors.

• If you have any questions let me know.

Answer 2

The issue is that you are calling readline twice in same loop

    while ((line = reader.readLine()) != null) 
    {
        scan = reader.readLine();

Change the above to following and it will work

    while ((line = reader.readLine()) != null) 
    {
       String scan = line;

Answer 3

The problem seems to be in your retrieveAccount() method, try closing ur reader object. U have opened the file in retrieveAccount() and never closed (so its stil under locked state for other applns/mthds/threads to access).

Try adding reader.close() before end of try block

Answer 4

You're double readling the contents of the file...

You first read a line from the file using...

while ((line = reader.readLine()) != null) {

The, straight after that, you read another line using...

String scan = reader.readLine();

Get rid of the second line read...