如何解决如何解决nullpointer异常
在GUI项目上工作时,我陷入了称为空指针错误的错误。
我无法解决此问题。
显示错误的行两边用双星号(**)闭合。(第80行)
我已将其与SQL数据库连接,并在为Jtable分配其值和结构时发生错误。
package connectsqlite;
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import java.awt.Font;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JTable;
import java.sql.*;
import javax.swing.*;
import net.proteanit.sql.DbUtils;
public class afterLogin extends JFrame {
public JPanel contentPane;
private JTable table;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
afterLogin frame = new afterLogin();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
Connection connect = null;
public afterLogin() {
connect = sqliteConnection.conn();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100,100,695,422);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5,5,5));
setContentPane(contentPane);
contentPane.setLayout(null);
JButton btnBack = new JButton("Log out");
btnBack.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Connecting window = new Connecting();
window.frame.setVisible(true);
}
});
btnBack.setBounds(10,62,114,23);
contentPane.add(btnBack);
JButton btnNewButton = new JButton("Load Details");
btnNewButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try{
String query = "SELECT * FROM Appointments";
PreparedStatement pst = connect.prepareStatement(query);
ResultSet rs = pst.executeQuery();
**table.setModel(DbUtils.resultSetToTableModel(rs));**
}
catch (Exception e1) {
e1.printStackTrace();
}
}
});
btnNewButton.setBounds(10,28,23);
contentPane.add(btnNewButton);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setBounds(162,57,435,305);
contentPane.add(scrollPane);
JScrollPane scrollPane_1 = new JScrollPane();
scrollPane.setViewportView(scrollPane_1);
}
}
解决方法
您尚未实例化表,仅对其进行了声明。因此,当您调用setModel
时,它将导致NullPointerException
。
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