Java Login program using a class

Question

I have to create a simple login program using a public class and the main driver console.

Here's my code:

Main

import java.util.Scanner;
public class main  
{

    public static void main(String[] args) 
    {

      Scanner input = new Scanner (System.in);  

      String username;
      String password;


      System.out.println("Welcome to your Social network site!");
      System.out.println("\nEnter your username and password to login to your account.");    

      System.out.println("Username: ");
        username = input.nextLine();

      System.out.println("Password: ");
        password = input.nextLine();

        UserAccount login = new UserAccount(username, password);

        if(login.checkPassword())
            System.out.println("You are logged in!");
        else
            System.out.println("The username and password you entered are incorrect.");
    }


}

User Class

public class UserAccount 
{

    private String username;
    private String password;
    private String[][] accounts = {{"anthony", "supernova"},{"steve", "java1"}};

    public UserAccount(String username, String password) 
    {
        String user = username;
        String pass = password;
        boolean active;
    }

    public boolean checkPassword()
    {

        if((username.equals(accounts[0][0])) && (password.equals(accounts[0][1])))
            return true;
        else
            return false;
    }

    public void deactivateAccount()
    {
        boolean active = false;
    }

}

The problem is I keep getting this error after I input the correct info: Exception in thread "main" java.lang.NullPointerException at UserAccount.checkPassword(UserAccount.java:19)at main.main(main.java:25)

Robby Cornelissen · Accepted Answer · 2014-09-01T05:12:47.103

You're not assigning your object properties in your UserAccount constructor. Change as follows:

public UserAccount(String username, String password) {
    this.username = username;
    this.password = password;
}

Furthermore, if you plan to do something with that active boolean, you'll have to add it as a property to your class as well. Just declaring it in your constructor/methods like you're doing now will have no effect.

score 0 · Answer 2 · edited Sep 01 '14 at 05:17

0

Your UserAccount constructor should be initializing the class variables. Like this -

 public UserAccount(String username, String password) 
    {
        this.username = username;
        this.password = password;
        boolean active;
    }

HTH

edited Sep 01 '14 at 05:17

Robby Cornelissen

91,784
22
134
156

answered Sep 01 '14 at 05:05

NewBie

1
1

score 0 · Answer 3 · edited May 23 '17 at 11:49

public UserAccount(String username, String password) 
{
   this.username = username;
   this.password = password;
   // boolean active;   //not a good coding standard 
   //in constructor only initialization of class variables  must be done

}

this will show how to use constructor-- good coding standard (important : constructor must be used only for initialization not for delcaration)

Java Login program using a class

3 Answers3