Question

I am new to java and JDBC usage. I am writing my first java application that connects to database. But i am getting this error when i click on th JButton that performs database creation. But i get this error:

   $run:Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at data.eceunnrecords.com.DBOptions.executeNonQuery(DBOptions.java:70)
at portal.eceunnrecords.com.CreateDatabase.createButtonActionPerformed(CreateDatabase.java:81)
at portal.eceunnrecords.com.CreateDatabase.access$000(CreateDatabase.java:13)
at portal.eceunnrecords.com.CreateDatabase$1.actionPerformed(CreateDatabase.java:42)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6263)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6028)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2475)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

here is my code:

  $/** To change this template, choose Tools | Templates
  * and open the template in the editor.
  */
  package portal.eceunnrecords.com;
  import portal.eceunnrecords.com.*;
  import data.eceunnrecords.com.*;

 /**
  *
  * @author OPTHINKERS
  */
  public class CreateDatabase extends javax.swing.JFrame {

/**
 * Creates new form CreateDatabase
 */
public CreateDatabase() {
    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() {

    jLabel1 = new javax.swing.JLabel();
    createdbtf = new javax.swing.JTextField();
    createButton = new javax.swing.JButton();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    jLabel1.setText("Database Name:");

    createButton.setText("Create");
    createButton.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            createButtonActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(78, 78, 78)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                .addComponent(createButton)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(jLabel1)
                    .addGap(18, 18, 18)
                    .addComponent(createdbtf, javax.swing.GroupLayout.PREFERRED_SIZE, 80, javax.swing.GroupLayout.PREFERRED_SIZE)))
            .addContainerGap(144, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(110, 110, 110)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(jLabel1)
                .addComponent(createdbtf, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addGap(18, 18, 18)
            .addComponent(createButton)
            .addContainerGap(129, Short.MAX_VALUE))
    );

    pack();
}// </editor-fold>                        

private void createButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
    // TODO add your handling code here:
    String query = "Create Table "+this.createdbtf.getText()+"(REG_NO VARCHAR (10)"
            + "NOT NULL PRIMARY KEY, SURNAME VARCHAR (45) NOT NULL, FIRSTNAME VARCHAR (45) "
            + "NOT NULL, MIDDLENAME VARCHAR (45) NOT NULL, LEVEL INT NOT NULL, STATE_OF_ORIGIN "
            + "VARCHAR (25) NOT NULL, PHONE_NO INT NOT NULL, EMAIL VARCHAR (50) NOT NULL);";
    DBOptions.executeNonQuery(query);
}                                            

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /*
     * Set the Nimbus look and feel
     */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /*
     * If Nimbus (introduced in Java SE 6) is not available, stay with the
     * default look and feel. For details see
     * http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(CreateDatabase.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(CreateDatabase.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(CreateDatabase.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(CreateDatabase.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /*
     * Create and display the form
     */
    java.awt.EventQueue.invokeLater(new Runnable() {

        public void run() {
            new CreateDatabase().setVisible(true);
        }
    });
}
// Variables declaration - do not modify                     
private javax.swing.JButton createButton;
private javax.swing.JTextField createdbtf;
private javax.swing.JLabel jLabel1;
// End of variables declaration                   

}

And here is the class DBOptions that communicates with my database:

 $package data.eceunnrecords.com;
  import java.sql.*;
  import javax.swing.*;


  public class DBOptions {
 /**
 * static variable con is used to hold the active connection information.
 */
 public static Connection con = null;
/**
 *This method is used to make a connection with the database
 * @param strHost holds host name or ip address
 * @param iPort holds port number
 * @param strDBName holds the database name
 * @param strUserName holds username to connect to server
 * @param strPassword holds password to connect to server
 * @return true for establishing connection and false for failure.
 */
public static boolean connect(String strHost, int iPort,String strDBName, String strUserName, String strPassword)
{
    try
    {
        //loading mysql jdbc driver
        Class.forName("com.mysql.jdbc.Driver");
        //connection string
        String url="jdbc:mysql://"+strHost+":"+iPort+"/"+strDBName;
        //establishing connection
        con=DriverManager.getConnection(url, strUserName,strPassword);
        return true; //successfully connected
    }
    catch(Exception e)
    {
        return false; //connection failed
    }
}
/**
 * This method is used to close the database connection
 * @param dbCon holds the active connection information
 */
public static void closeConnection(Connection dbCon)
{
    try
    {
        dbCon.close(); //close connection
    }
    catch(Exception e)
    {

    }
}
/**
 * This method is used to execute an sql non query
 * @param sqlString holds the sql non query to be executed
 * @return the number of rows affected
 */
public static int executeNonQuery(String sqlString)
{
    try
    {
        Statement stmt = con.createStatement();
        return stmt.executeUpdate(sqlString);
        //return the number of rows affected
    }
    catch(SQLException e)
    {
        //display error message
        //JOptionPane.showMessageDialog(null,  e.getMessage()+"\nPlease Try Again","Non Query Execution Failure", 1);
        return -1;
    }
}
/**
 * This method is used to execute an sql query
 * @param sqlQuery holds the sql query
 * @return the ResultSet if successful. Return null on failure
 */
public static ResultSet executeSQLQuery(String sqlQuery)
{
    try
    {
        Statement stmt = con.createStatement();
        return stmt.executeQuery(sqlQuery); //query successfully executed
    }
    catch(SQLException e)
    {
        //display error message
        //JOptionPane.showMessageDialog(null, e.getMessage()+"\nPlease Try Again","Query Execution Failure", 1);
        return null; //sql query execution failed
    }
}

}

please help me…

Answer 1

It seems that the line that is throwing the NullPointerException is this line:

    Statement stmt = con.createStatement();

If this is throwing a NullPointerException, then your static variable con must be null.

I can’t see anywhere where you are creating your database connection function connect(). As far as I can see, you’re getting the error because you’re trying to create a table in a database when you’re not connected to the database.

Alternatively, perhaps you are calling connect() in some code you’ve chosen not to share with us. In which case, I’d guess that you are failing to connect to the database. However, the following code within your connect() method is extremely unhelpful when it comes to finding out what went wrong:

catch(Exception e)
{
    return false; //connection failed
}

There are numerous different reasons why your database connection might be failing, but silently swallowing all exceptions makes it incredibly difficult to find out what is going wrong. Add a line e.printStackTrace(); to this catch block (before the return line) and that will print out the exception that is causing the database connection to fail.