我是 java 和 JDBC 用法的新手。我正在编写我的第一个连接到数据库的 Java 应用程序。但是当我单击执行数据库创建的 JButton 时出现此错误。但我得到这个错误：
$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)
这是我的代码：
$/** 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
}
这是与我的数据库通信的 DBOptions 类：
$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
}
}
}
请帮我...