我已经使用mysql与eclipse进行了数据库连接。执行我的代码时，我得到空指针异常错误。当我单击“添加”按钮在数据库中添加新记录时，会发生这种情况。请帮忙
import javax.swing.JFrame;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import javax.swing.BorderFactory;
import javax.swing.ButtonGroup;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JLabel;
import javax.swing.JTabbedPane;
import javax.swing.border.TitledBorder;
import org.eclipse.wb.swing.FocusTraversalOnArray;
import com.toedter.calendar.JDateChooser;
import java.awt.Component;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.Statement;
import javax.swing.JCheckBox;
import javax.swing.JButton;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.JComboBox;
import javax.swing.JRadioButton;
import javax.swing.DefaultComboBoxModel;
public class PassF extends JFrame{
private JTextField fname;
private JTextField lname;
private JTextField address;
private JTextField resId;
private JComboBox ori, des;
private JButton btnAdd, btnUpdate, btnDelete, btnClear;
private JRadioButton premium, economy, business;
private JDateChooser dt;
private Connection con;
String url = "jdbc:mysql://localhost:3306/";
String user = "root";
String password = "root";
public PassF(){
super("Passenger Details");
setBounds(100, 100, 792, 631);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLayout(null);
JPanel panel = new JPanel();
panel.setBounds(0, 0, 831, 78);
add(panel);
JLabel l1 = new JLabel();
l1.setIcon(new ImageIcon("C:\\Users\\Yetin\\workspace\\Assignment\\src\\passenger.png"));
panel.setBackground(Color.WHITE);
panel.add(l1);
JLabel lblFirstName = new JLabel("First Name ");
lblFirstName.setForeground(new Color(25, 25, 112));
lblFirstName.setFont(new Font("Candara", Font.BOLD, 15));
lblFirstName.setBounds(34, 132, 95, 23);
add(lblFirstName);
JLabel lblLastName = new JLabel("Last Name ");
lblLastName.setForeground(new Color(25, 25, 112));
lblLastName.setFont(new Font("Candara", Font.BOLD, 15));
lblLastName.setBounds(316, 132, 80, 23);
add(lblLastName);
fname = new JTextField();
setBounds(239, 132, 126, 22);
add(fname);
fname.setColumns(10);
lname = new JTextField();
lname.setBounds(432, 132, 126, 22);
add(lname);
lname.setColumns(10);
JLabel lblAddress = new JLabel("Address");
lblAddress.setForeground(new Color(25, 25, 112));
lblAddress.setFont(new Font("Candara", Font.BOLD, 15));
lblAddress.setBounds(34, 177, 95, 23);
add(lblAddress);
address = new JTextField();
address.setBounds(139, 178, 126, 56);
add(address);
address.setColumns(10);
JLabel lblReservationId = new JLabel("Reservation ID");
lblReservationId.setForeground(new Color(25, 25, 112));
lblReservationId.setFont(new Font("Candara", Font.BOLD, 15));
lblReservationId.setBounds(316, 173, 107, 31);
add(lblReservationId);
resId = new JTextField();
resId.setBounds(432, 178, 126, 22);
add(resId);
resId.setColumns(10);
JLabel origin= new JLabel("Origin");
origin.setForeground(new Color(25, 25, 112));
origin.setFont(new Font("Candara", Font.BOLD, 15));
origin.setBounds(34, 273, 95, 23);
add(origin);
JLabel lblDestination = new JLabel("Destination");
lblDestination.setForeground(new Color(25, 25, 112));
lblDestination.setFont(new Font("Candara", Font.BOLD, 15));
lblDestination.setBounds(34, 316, 95, 23);
add(lblDestination);
ori = new JComboBox();
ori.setModel(new DefaultComboBoxModel(new String[] {"Afghanistan", "Albania", "Algeria", "Andorra", "Angola", "Bangladesh", "Barbados", "Belarus", "Belgium", "Brazil", "China", "Egypt", "France", "Germany", "Hong Kong", "India", "Maldives", "Madagascar", "Mauritius", "Nigeria ", "Russia", "Seychelles", "Singapore ", "United Arab Emirates"}));
ori.setBounds(139, 273, 126, 22);
add(ori);
des = new JComboBox();
des.setModel(new DefaultComboBoxModel(new String[] {"Afghanistan", "Albania", "Algeria", "Andorra", "Angola", "Bangladesh", "Barbados", "Belarus", "Belgium", "Brazil", "China", "Egypt", "France", "Germany", "Hong Kong", "India", "Maldives", "Madagascar", "Mauritius", "Nigeria ", "Russia", "Seychelles", "Singapore ", "United Arab Emirates"}));
des.setBounds(139, 317, 126, 22);
add(des);
JLabel clas = new JLabel();
clas.setForeground(new Color(25, 25, 112));
clas.setBounds(316, 231, 246, 132);
clas.setBorder(BorderFactory.createTitledBorder(null, "Class", TitledBorder.LEFT, TitledBorder.TOP, new Font("Candara", Font.BOLD, 15), new Color(25, 25, 112)));
add(clas);
ButtonGroup group = new ButtonGroup();
premium = new JRadioButton("Premium");
premium.setBounds(338, 257, 109, 23);
premium.setForeground(new Color(25, 25, 112));
premium.setFont(new Font("Candara", Font.BOLD, 15));
group.add(premium);
add(premium);
economy = new JRadioButton("Economy");
economy.setBounds(338, 291, 109, 23);
add(economy);
economy.setForeground(new Color(25, 25, 112));
economy.setFont(new Font("Candara", Font.BOLD, 15));
group.add(economy);
add(economy);
business = new JRadioButton("Business");
business.setBounds(338, 324, 109, 23);
business.setForeground(new Color(25, 25, 112));
business.setFont(new Font("Candara", Font.BOLD, 15));
group.add(business);
add(business);
JLabel lblJourneyDate = new JLabel("Journey Date");
lblJourneyDate.setForeground(new Color(25, 25, 112));
lblJourneyDate.setFont(new Font("Candara", Font.BOLD, 15));
lblJourneyDate.setBounds(34, 90, 95, 22);
add(lblJourneyDate);
btnAdd = new JButton();
btnAdd.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
insert();
}
});
btnAdd.setIcon(new ImageIcon("C:\\Users\\Yetin\\workspace\\Assignment\\src\\Icons\\add.jpg"));
btnAdd.setForeground(new Color(34, 139, 34));
btnAdd.setFont(new Font("Copperplate Gothic Bold", Font.BOLD, 15));
btnAdd.setBounds(647, 143, 85, 31);
add(btnAdd);
JButton btnSave = new JButton();
btnSave.setIcon(new ImageIcon("C:\\Users\\Yetin\\workspace\\Assignment\\src\\Icons\\clear.jpg"));
btnSave.setForeground(new Color(34, 139, 34));
btnSave.setFont(new Font("Copperplate Gothic Bold", Font.BOLD, 15));
btnSave.setBounds(647, 203, 85, 31);
add(btnSave);
JButton btnUpdate = new JButton();
btnUpdate.setIcon(new ImageIcon("C:\\Users\\Yetin\\workspace\\Assignment\\src\\Icons\\update.jpg"));
btnUpdate.setForeground(new Color(34, 139, 34));
btnUpdate.setFont(new Font("Copperplate Gothic Bold", Font.BOLD, 15));
btnUpdate.setBounds(647, 257, 85, 31);
add(btnUpdate);
JButton btnDelete = new JButton("");
btnDelete.setIcon(new ImageIcon("C:\\Users\\Yetin\\workspace\\Assignment\\src\\Icons\\delete.jpg"));
btnDelete.setForeground(new Color(34, 139, 34));
btnDelete.setFont(new Font("Copperplate Gothic Bold", Font.BOLD, 15));
btnDelete.setBounds(647, 317, 80, 31);
add(btnDelete);
dt = new JDateChooser();
dt.setBounds(139, 89, 126, 23);
add(dt);
JLabel l2 = new JLabel();
l2.setBounds(0, 75, 831, 547);
add(l2);
l2.setIcon(new ImageIcon("C:\\Users\\Yetin\\workspace\\Assignment\\src\\world.jpg"));
}
public void insert(){
try{
Class.forName("com.mysql.jdbc.Driver").newInstance();
con = DriverManager.getConnection(url, user, password);
System.out.println("Database connection succesful to: " + url);
}catch(Exception e){
System.out.println("Error in connecting");
}
try{
PreparedStatement stmt = con.prepareStatement("insert into passenger"
+ " (ReservID, JourneyDate, FirstName, LastName, Address, ClassType, Origin, Destination)"
+ " values (?, ?, ?, ?, ?, ?, ?, ?");
//set parameters
stmt.setString(1, resId.getText());
stmt.setString(2, dt.getDateFormatString());
stmt.setString(3, fname.getText());
stmt.setString(4, lname.getText());
stmt.setString(5, address.getText());
stmt.setString(6, premium.getText());
stmt.setString(7, ori.getSelectedItem().toString());
stmt.setString(8, des.getSelectedItem().toString());
//execute SQL
stmt.executeUpdate();
}catch(Exception e){
System.out.println("ERROR");
}
}
}
答案 0 :(得分：2)
所以我通过阅读你的代码找到了......你的问题就在这里..
try{
Class.forName("com.mysql.jdbc.Driver").newInstance();
con = DriverManager.getConnection(url, user, password);
System.out.println("Database connection succesful to: " + url);
}catch(Exception e){
System.out.println("Error in connecting");
}
您不会重新抛出异常，因此会吞下它。然后st为null。将其更改为
catch(Exception exp){
throw new Exception(exp);
}
然后您将获得jdbc连接存在的确切原因或问题。可能缺少罐子，错误的路径或认证问题..可能也是其他东西，但你需要先知道原因..
编辑：
我认为它可能是打印“连接错误”..
如果连接失败，也没有必要继续使用PreparedStatement。
答案 1 :(得分：0)
ImageIcon icon=new ImageIcon(getClass().getResource("path Name of image"));
buttonobj.setIcon(icon);