Library System Login Logout

Question

class Test{
    public static void main(String args[])
    {
        Patron list[] = new PatronData().getPatronData();

        /*for(Patron p: list)
        {
            System.out.println(p);
        }*/
    }
    }


    class PatronData{
    //Patron patron[] = {new     Patron("Daniel","A001","15WAD00001","A4701,Jalan Kepong,     Pahang","JK01",0.00,"012-8765432"),
    //               new Patron("Chiam","A002","15WAD00002","A4702,Jalan     Akar,Pahang","JK02",0.00,"0102288554")};
    Patron patron[] = new Patron[2];

    public Patron[] getPatronData()
    {
        patron[0] = new Patron("Daniel","A001","15WAD00001","A4701,Jalan     Kepong, Pahang","JK01",0.00,"012-8765432");
        patron[1] = new Patron("Chiam","A002","15WAD00002","A4702,Jalan     Akar,Pahang","JK02",0.00,"0102288554");
        return patron;
    }
}

class Patron{
    private String userName;
    private String password;
    private String userCode;
    private String streetAddress;
    private String postCode;
    private double overdueBalance;
    private String phoneNumber;

    Patron(String userName[], String password[], String userCode, 
    String streetAddress, String postCode, double overdueBalance, String     phoneNumber)
    {
        this.userName = userName;
        this.password = password;
        this.userCode = userCode;
        this.streetAddress = streetAddress;
        this.postCode = postCode;
        this.overdueBalance = overdueBalance;
        this.phoneNumber = phoneNumber;

        int logNMatch = 0;

        Scanner scan = new Scanner(System.in);
        do{

            System.out.print("Please Enter Your User Name > ");
            String inputUserName=scan.nextLine();
            System.out.println();
            System.out.print("Please Enter Your Password  > ");
            String inputPassword = scan.nextLine();

            if(userName.compareTo(inputUserName) == 0 &&     password.compareTo(inputPassword) == 0)
            {
                System.out.println("Logging Successful");
                System.out.print("\n\n");

            }
            else
            {
                System.out.println("Loging fail");
                System.out.println("Please again later");
                logNMatch++;
            }
        }while(logNMatch > 0);
    }
    }

Hey guys, I am learning Java in Diploma Level. I have a question. Please, I have no idea why I cannot straight away logging into "Chiam Account"I expected is when i log in the compiler will automatically check whether is the login detail match with the data in library system.

Answer 1

You are requesting the login information inside the constructor. Meaning that whenever you make a new Patron it will prompt you to login with that user's information.

Instead remove everything inside that do/while loop and add a method like loginFromLibrary() that will prompt the user to input their name and password. Then check all of the Patron s to see if any of their names match the username given. Then just make sure that the username matches the password.

This example will require some getter ( getPassword() and getUsername() ):

public void loginFromLibrary(Patron[] patrons){
    Scanner scan = new Scanner(System.in);
    while (true){
        // get usernmae
        System.out.println("Username > ");
        String username = scan.nextLine();
        Patron user = null;
        // check array to see if username exists
        for (Patron p : patrons){
            if (p.getUsername().equals(username)){
                user = p;
                break;
            }
        }
        if (user == null){
            // username not found
            System.out.println("Username not found");
            continue;
        }
        // get password
        System.out.println("Password > ");
        String pass = scan.nextLine();
        // check password
        if (pass.equals(user.getPassword())){
            // logged in
            break;
        } else {
            // wrong password
        }
    }
    scan.close();
}