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POJava MVC DAO implementation getting NullPointerException error
 

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  1. POJava MVC DAO implementation getting NullPointerException error
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    <p>I'm trying to learn how to do MVC and DAO but my implementation is failing right now and I can't get around it.</p> <p>Here is my view, or the relevant parts of it: </p> <pre><code>package gui; import javax.swing.JFrame; public class LoginFrame{ private JPanel contentPane; private final JLabel credentialsLabel = new JLabel("Credentials"); private JTextField usernameField; private JPasswordField passwordField; private JButton btnLogin; /** * Create the frame. */ public LoginFrame() { createAndShowGUI(); } private void createAndShowGUI() { EventQueue.invokeLater(new Runnable() { public void run() { try { JFrame frame = new JFrame(); frame.setTitle("Login"); frame.setContentPane(createContentPane()); frame.setBounds(100, 100, 480, 237); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); } catch (Exception e) { e.printStackTrace(); } } }); } //A function that sets up the basic structure of the GUI. private JPanel createContentPane() { contentPane = new JPanel(); contentPane.setForeground(Color.LIGHT_GRAY); contentPane.setBackground(Color.DARK_GRAY); contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); GridBagLayout gbl_contentPane = new GridBagLayout(); gbl_contentPane.columnWidths = new int[]{106, 0, 0, 153, 0}; gbl_contentPane.rowHeights = new int[]{65, 27, 39, 36, 0, 0}; gbl_contentPane.columnWeights = new double[]{0.0, 0.0, 0.0, 1.0, Double.MIN_VALUE}; gbl_contentPane.rowWeights = new double[]{0.0, 0.0, 0.0, 0.0, 0.0, Double.MIN_VALUE}; contentPane.setLayout(gbl_contentPane); //login button btnLogin = new JButton("login"); GridBagConstraints gbc_btnLogin = new GridBagConstraints(); gbc_btnLogin.anchor = GridBagConstraints.WEST; gbc_btnLogin.insets = new Insets(0, 0, 5, 5); gbc_btnLogin.gridx = 2; gbc_btnLogin.gridy = 3; contentPane.add(btnLogin, gbc_btnLogin); //register button JButton btnRegister = new JButton("register"); btnRegister.setFont(new Font("Helvetica", Font.PLAIN, 13)); GridBagConstraints gbc_btnRegister = new GridBagConstraints(); gbc_btnRegister.anchor = GridBagConstraints.WEST; gbc_btnRegister.insets = new Insets(0, 0, 5, 0); gbc_btnRegister.gridx = 3; gbc_btnRegister.gridy = 3; contentPane.add(btnRegister, gbc_btnRegister); return contentPane; } //the Action Listener for the Login Button passed by controller public void buttonActionListeners(ActionListener al) { btnLogin.setActionCommand("login"); btnLogin.addActionListener(al); } } </code></pre> <p>My Model: </p> <pre><code>package functions; import database.LoginDAO; public class LoginModel { LoginDAO logindao; public LoginModel(LoginDAO logindao){ this.logindao = logindao; } public void attemptLogin(String username, char[] password) { System.out.println("Testing login attempt"); logindao.attemptLogin(username, password); } } </code></pre> <p>My controller:</p> <pre><code>package controller; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import functions.LoginModel; import gui.LoginFrame; public class LoginControl implements ActionListener { LoginModel model; LoginFrame view; public LoginControl(LoginModel model, LoginFrame view){ this.model = model; this.view = view; //add action listener from control to view. view.buttonActionListeners(this); } //action performed by view public void actionPerformed(ActionEvent ae) { System.out.println("Testing Action Performed"); String action = ae.getActionCommand(); if(action.equals("login")){ System.out.println("Testing Action Performed"); model.attemptLogin(view.getUsername(),view.getPassword()); } } } </code></pre> <p>Main: </p> <pre><code>import functions.LoginModel; import java.io.IOException; import java.sql.SQLException; import controller.LoginControl; import database.LoginDAO; import gui.LoginFrame; public class Main { public static void main(String[] args) throws IOException, SQLException { LoginFrame frame = new LoginFrame(); LoginDAO loginDao = new LoginDAO(); LoginModel model = new LoginModel(loginDao); LoginControl controller = new LoginControl(model, frame); } } </code></pre> <p>The Error: </p> <pre><code>Exception in thread "main" java.lang.NullPointerException at gui.LoginFrame.buttonActionListeners(LoginFrame.java:160) at controller.LoginControl.&lt;init&gt;(LoginControl.java:16) at Main.main(Main.java:14) </code></pre> <p>The lines that the error references: </p> <pre><code>btnLogin.setActionCommand("login"); //in View view.buttonActionListeners(this); //in Control LoginControl controller = new LoginControl(model, frame); //in main. </code></pre> <p>So from what I've tried to understand: view.buttonActionListeners(this); somewhere in here I'm passing a null, so either this is null or view is null? how can view be null if we initiated LoginFrame view; </p> <p>Thanks for helping me solve this bug. </p>
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    1. PO
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    1. PTQuestion
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    1. USHarrison
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    1. PO
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    1. COI think you btnLogin property is null to you get this error. But I did not identify how it can be null yet.
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      1. POJava MVC DAO implementation getting NullPointerException error
      1. USdigao_mb
 

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