Question

我是Java的新手，我正在尝试做这个练习;但我只是坚持这个新问题。我整天都在google搜索这个错误--Java.lang.NullPointerException - 我尝试解决它，但我找不到它;有人请？

**我有一个BankDB_Final.db文件;它有一个名为Bank_001的表 **我已经安装了sqlite连接器（连接正常）和 rs2xml.jar文件位于名为“lib”的同一文件夹中。 **登录：Abbas ..密码：root。

以下是方法代码： //启动应用程序。

import java.awt.*;
import java.sql.*;

import javax.swing.*;
import javax.swing.border.EmptyBorder;
import javax.swing.border.TitledBorder;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;


public class Login_jFrame extends JFrame {

Connection conn = null;
ResultSet rs = null;
PreparedStatement pst = null;

private JPanel contentPane;
private JPasswordField txt_password;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {

        public void run() {
            try {
                Login_jFrame frame = new Login_jFrame();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public Login_jFrame() {

    conn = javaconnect.ConnectrDB();


    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    JLabel lblNewLabel = new JLabel("Username");
    lblNewLabel.setFont(new Font("Tahoma", Font.PLAIN, 12));
    lblNewLabel.setBounds(177, 93, 70, 14);
    contentPane.add(lblNewLabel);

    JLabel lblNewLabel_1 = new JLabel("Password");
    lblNewLabel_1.setFont(new Font("Tahoma", Font.PLAIN, 12));
    lblNewLabel_1.setBounds(177, 139, 70, 14);
    contentPane.add(lblNewLabel_1);

    txt_password = new JPasswordField();
    txt_password.setBounds(253, 133, 100, 20);
    contentPane.add(txt_password);

    TextField txt_username = new TextField();
    txt_username.setBounds(253, 85, 100, 22);
    contentPane.add(txt_username);

    JPanel panel = new JPanel();
    panel.setBorder(new TitledBorder(new TitledBorder(new TitledBorder(UIManager.getBorder("TitledBorder.border"), "Login", TitledBorder.LEADING, TitledBorder.TOP, null, new Color(0, 0, 0)), "Login:", TitledBorder.LEADING, TitledBorder.TOP, null, new Color(64, 64, 64)), "Login:", TitledBorder.LEADING, TitledBorder.TOP, null, Color.DARK_GRAY));
    panel.setBounds(160, 50, 219, 160);

    contentPane.add(panel);
    panel.setLayout(null);

    JButton cmdLogin = new JButton("Login");
    cmdLogin.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            String sql = "select * from bank_001 where AccountName=? and Password=?";
            try{
                pst = conn.prepareStatement(sql);
                pst.setString(1, txt_username.getText());
                pst.setString(2, txt_password.getText());

                rs= pst.executeQuery();
                if(rs.next()) {
                    Employee_info s = new Employee_info();
                    s.setVisible(true);

                    JOptionPane.showMessageDialog(null, "Username and Password is correct!");

                }else {
                    JOptionPane.showMessageDialog(null, "Username or Password is Not correct!");
                }

            }catch(Exception e) {

                JOptionPane.showMessageDialog(null, e);

            }

        }
    });
    cmdLogin.setBounds(90, 126, 89, 23);
    panel.add(cmdLogin);

    JLabel icon = new JLabel("");
    icon.setIcon(new ImageIcon("C:\\Users\\User\\Downloads\\DB SQLITE\\Project123\\img\\icon.jpg"));
    icon.setBounds(40, 56, 90, 90);
    contentPane.add(icon);
}

}

JavaConnect类：

import java.sql.*;

import javax.swing.*;


public class javaconnect {

Connection conn = null;

public static Connection ConnectrDB() {

    // 1- Get a connection to Database
    try {

        Class.forName("org.sqlite.JDBC");
        Connection conn = DriverManager.getConnection("jdbc:sqlite:c:\\users\\user\\downloads\\db sqlite\\bankdb_final.db");
        //Connection conn = DriverManager.getConnection("jdbc:sqlite:C:\\Users\\User\\Downloads\\DB SQLITE\\BankDB_Final.db");

        JOptionPane.showMessageDialog(null, "Connection Established");

        return conn;
    } catch(Exception e) {

     JOptionPane.showMessageDialog(null, e);
   return null;

    }

}

}

和最后（我认为这是错误）Employee_info类

import java.awt.BorderLayout;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JTable;
import javax.swing.border.LineBorder;

import java.awt.Color;

import javax.swing.table.DefaultTableModel;

import java.sql.*;
import javax.swing.*;

import net.proteanit.sql.DbUtils;                 

public class Employee_info extends JFrame {



private JPanel contentPane;
private JTable table_employee;



/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Employee_info frame = new Employee_info();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}
Connection conn = null;
ResultSet rs = null;
PreparedStatement pst = null;             

/**
 * Create the frame.
 */
public Employee_info() {


    conn = javaconnect.ConnectrDB();
    Update_Table();


    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    JScrollPane scrollPane = new JScrollPane();
    scrollPane.setBounds(21, 11, 389, 230);
    contentPane.add(scrollPane);

    table_employee = new JTable();
    scrollPane.setViewportView(table_employee);
    table_employee.setModel(new DefaultTableModel(
        new Object[][] {
        },
        new String[] {
        }
    ));
}


private void Update_Table() {
    try {

    String sql = "select * from Bank_001";
    pst = conn.prepareStatement(sql);
    rs = pst.executeQuery();
    table_employee.setModel(DbUtils.resultSetToTableModel(rs));
    conn.close();

    }catch(Exception e) {
         JOptionPane.showMessageDialog(null, e);

    }

}

}

屏幕：

Eclipse Jtable不显示错误，但也不显示数据

0 个答案: