NullPointerException when running program...

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I am create a software app, and I am using NetBeans with MySQL as my database.

I've created a login screen, where the user inputs user and password and has access to the main software. The user and password is saved in the MySQL database. Everytime I enter the user and password, it just throws a nullpointerexception, but the compile time is fine.

Heres the login code: -

Code :

package software;
 
import java.sql.*;
import javax.swing.*;
 
/**
 *
 * @author RiskyShenanigan
 */
public class Login extends javax.swing.JFrame {
 
    DatabaseConnect dc = new DatabaseConnect();
    Connection con = null;
 
 
    /** Creates new form Login */
   public Login() {
 
 
        initComponents();
    }
 
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {
 
        jPanel1 = new javax.swing.JPanel();
        jTextField1 = new javax.swing.JTextField();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jPasswordField1 = new javax.swing.JPasswordField();
 
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Aquarium Maintenance System");
        setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));
        setForeground(java.awt.Color.white);
        setIconImages(null);
        setResizable(false);
 
        jPanel1.setBorder(javax.swing.BorderFactory.createTitledBorder("Login"));
 
        jButton1.setText("OK");
        jButton1.setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });
 
        jButton2.setText("Cancel");
 
        jLabel1.setText("Username:");
 
        jLabel2.setText("Password:");
 
        jPasswordField1.setHorizontalAlignment(javax.swing.JTextField.LEFT);
 
        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGap(112, 112, 112)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 105, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(30, 30, 30)
                        .addComponent(jButton2, javax.swing.GroupLayout.PREFERRED_SIZE, 104, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                        .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(jLabel1)
                            .addComponent(jLabel2))
                        .addGap(32, 32, 32)
                        .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                            .addComponent(jPasswordField1)
                            .addComponent(jTextField1, javax.swing.GroupLayout.DEFAULT_SIZE, 139, Short.MAX_VALUE))
                        .addGap(16, 16, 16)))
                .addContainerGap(119, Short.MAX_VALUE))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel1)
                    .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(18, 18, 18)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel2)
                    .addComponent(jPasswordField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(28, 28, 28)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1)
                    .addComponent(jButton2))
                .addContainerGap(30, Short.MAX_VALUE))
        );
 
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(14, Short.MAX_VALUE))
        );
 
        pack();
    }// </editor-fold>                        
 
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
 
        String userName = jTextField1.getText();
        String password = jPasswordField1.getName();
        String passwordCheck = null;
        String userNameCheck = null;
        boolean loginFail = true;
 
          try {
            Statement st = con.createStatement();
            ResultSet rt = st.executeQuery("SELECT * " + "FROM type");
            while(rt.next()){
               passwordCheck = rt.getString(3);
               userNameCheck = rt.getString(2);
               if (passwordCheck.equals(password) && userNameCheck.equals(userName)) {
                   new Menu().setVisible(true);
                   this.dispose();
                   loginFail = false;
               }
            }
        } catch (SQLException e) {System.out.println("error login frame"); }
 
        if (loginFail == true){
            System.out.println("IncorrectLogin");
           }
 
    }                                        
 
    /**
    * @param args the command line arguments
    */
  public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
               new Login().setVisible(true);
              }
        });
    }
 
}

Heres is the DatabaseConnect class: -

Code :

package software;
 
 import java.sql.*;
 
/**
 *
 * @author RiskyShenanigan
 */
public class DatabaseConnect {
 
 
public static void main(String[] args) {
System.out.println("MySQL Connect Example");
Connection con = null;
String url = "jdbc:mysql://localhost:3306/";
String dbName = "software"; /*I created this database for me*/
String driver = "com.mysql.jdbc.Driver";
String userName = "root";
String password = "cake";
 
try {
Class.forName(driver).newInstance();
con = DriverManager.getConnection(url+dbName,userName,password);
System.out.println("Connected to the database");
con.close();
System.out.println("Disconnected from database");
}
 
catch (Exception e) {
e.printStackTrace();
        }
    }
}

March 12th, 2011, 12:13 AM
JJeng

Re: NullPointerException when running program...

Haven't Compiled the code, but first thing, the con variable in the Login class is never set. You have a con variable in DatabaseConnect Class, but that variable only exists inside a main method in DatabaseConnect. Essentially the DatabaseConnect Class is Empty. What you want to do is move the code in the main to the DatabaseConnect constructor, then make a getCon() method to use and assign the con variable in the Login class. Even then, I'm not sure if the sql connection is being setup correctly(lack of exp.) I hope this helps with the NullPointerException, good luck

Re: NullPointerException when running program...

I've getting a ClassNotFoundException

Code java:

 
 
 import java.sql.*;
 
 
/**
 *
 * @author RiskyShenanigan
 */
public class DatabaseConnect {
 
  Connection con = null;
 
 public DatabaseConnect()
 {
 System.out.println("MySQL Connect Example");
 
String url = "jdbc:mysql://localhost:3306/";
String dbName = "software"; /*I created this database for me*/
String driver = "com.mysql.jdbc.Driver";
String userName = "root";
String password = "cake";
 
try {
Class.forName(driver).newInstance();
con = DriverManager.getConnection(url+dbName,userName,password);
System.out.println(con);
System.out.println("Connected to the database");
setConnection(con);
con.close();
 
System.out.println("Disconnected from database");
}
 
catch (Exception e) {
e.printStackTrace();
        }
 
 }
 
public static void main(String[] args) {
DatabaseConnect dbc = new DatabaseConnect();
    }
 
	 public  void setConnection(Connection con2)
	 {
	 con = con2;
	 }
 
	 public  Connection getConnection()
	 {
	 return con;
	 }
}



java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

	at java.net.URLClassLoader$1.run(URLClassLoader.java:  202)

	at java.security.AccessController.doPrivileged(Native Method)

	at java.net.URLClassLoader.findClass(URLClassLoader.j  ava:190)

	at java.lang.ClassLoader.loadClass(ClassLoader.java:3  07)

	at sun.misc.Launcher$AppClassLoader.loadClass(Launche  r.java:301)

	at java.lang.ClassLoader.loadClass(ClassLoader.java:2  48)

	at java.lang.Class.forName0(Native Method)

	at java.lang.Class.forName(Class.java:169)

	at DatabaseConnect.<init>(DatabaseConnect.java:25)

	at DatabaseConnect.main(DatabaseConnect.java:42)

Code java:

import java.sql.*;
import javax.swing.*;
import java.awt.*;
 
/**
 *
 * @author RiskyShenanigan
 */
public class Login extends javax.swing.JFrame {
 
 
    Connection con = new DatabaseConnect().getConnection();
    JPanel jPanel1;
	 JTextField jTextField1;
	 JButton jButton1, jButton2;
	 JLabel jLabel1, jLabel2;
	 JPasswordField jPasswordField1;
 
    /** Creates new form Login */
   public Login() {
 
 
        initComponents();
    }
 
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {
 
        jPanel1 = new javax.swing.JPanel();
        jTextField1 = new javax.swing.JTextField();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jPasswordField1 = new javax.swing.JPasswordField();
 
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Aquarium Maintenance System");
        setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));
        setForeground(java.awt.Color.white);
        setIconImages(null);
        setResizable(false);
 
        jPanel1.setBorder(javax.swing.BorderFactory.createTitledBorder("Login"));
 
        jButton1.setText("OK");
        jButton1.setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });
 
        jButton2.setText("Cancel");
 
        jLabel1.setText("Username:");
 
        jLabel2.setText("Password:");
 
        jPasswordField1.setHorizontalAlignment(javax.swing.JTextField.LEFT);
 
        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGap(112, 112, 112)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 105, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(30, 30, 30)
                        .addComponent(jButton2, javax.swing.GroupLayout.PREFERRED_SIZE, 104, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                        .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(jLabel1)
                            .addComponent(jLabel2))
                        .addGap(32, 32, 32)
                        .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                            .addComponent(jPasswordField1)
                            .addComponent(jTextField1, javax.swing.GroupLayout.DEFAULT_SIZE, 139, Short.MAX_VALUE))
                        .addGap(16, 16, 16)))
                .addContainerGap(119, Short.MAX_VALUE))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel1)
                    .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(18, 18, 18)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel2)
                    .addComponent(jPasswordField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(28, 28, 28)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1)
                    .addComponent(jButton2))
                .addContainerGap(30, Short.MAX_VALUE))
        );
 
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(14, Short.MAX_VALUE))
        );
 
        pack();
    }// </editor-fold>                        
 
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
 
        String userName = jTextField1.getText();
        String password = jPasswordField1.getName();
        String passwordCheck = null;
        String userNameCheck = null;
        boolean loginFail = true;
 
          try {
 
			 DatabaseConnect temp = new DatabaseConnect();
			 con = temp.getConnection();
			 System.out.println(con);
			            Statement st = con.createStatement();
            ResultSet rt = st.executeQuery("SELECT * " + "FROM type");
            while(rt.next()){
               passwordCheck = rt.getString(3);
               userNameCheck = rt.getString(2);
               if (passwordCheck.equals(password) && userNameCheck.equals(userName)) {
                   new JMenu().setVisible(true);
                   this.dispose();
                   loginFail = false;
               }
            }
        } catch (SQLException e) {System.out.println("error login frame"); }
 
        if (loginFail == true){
            System.out.println("IncorrectLogin");
           }
 
    }                                        
 
    /**
    * @param args the command line arguments
    */
  public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
               new Login().setVisible(true);
              }
        });
    }
 
}

March 12th, 2011, 03:30 PM
newbie

Re: NullPointerException when running program...

@javapenguin...
Because maybe you don't have the driver installed?