创建一个Java GUI界面，包含两个选项：注册和登录。 当用户点击注册选项时，弹出一个新的窗口，要求用户输入用户名和密码。将这些信息存储到mysql数据库中的用户表中。

当用户点击登录选项时，弹出一个新的窗口，要求用户输入用户名和密码。从mysql数据库中的用户表中查询该用户是否存在，如果存在则跳转到主页面，否则弹出错误提示。

以下是示例代码：

Main.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Main {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Login/Register");

        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(2, 1));

        JButton loginButton = new JButton("Login");
        loginButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                LoginDialog loginDialog = new LoginDialog(frame);
                loginDialog.setVisible(true);
            }
        });
        panel.add(loginButton);

        JButton registerButton = new JButton("Register");
        registerButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                RegisterDialog registerDialog = new RegisterDialog(frame);
                registerDialog.setVisible(true);
            }
        });
        panel.add(registerButton);

        frame.add(panel);
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

LoginDialog.java

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

public class LoginDialog extends JDialog {
    private JTextField usernameField;
    private JPasswordField passwordField;

    public LoginDialog(Frame parent) {
        super(parent, "Login", true);

        JPanel panel = new JPanel(new GridLayout(2, 2));

        JLabel usernameLabel = new JLabel("Username:");
        panel.add(usernameLabel);

        usernameField = new JTextField();
        panel.add(usernameField);

        JLabel passwordLabel = new JLabel("Password:");
        panel.add(passwordLabel);

        passwordField = new JPasswordField();
        panel.add(passwordField);

        JButton loginButton = new JButton("Login");
        loginButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String username = usernameField.getText();
                String password = new String(passwordField.getPassword());

                try {
                    Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydatabase", "root", "password");
                    Statement statement = connection.createStatement();
                    ResultSet resultSet = statement.executeQuery("SELECT * FROM users WHERE username='" + username + "' AND password='" + password + "'");
                    if (resultSet.next()) {
                        JOptionPane.showMessageDialog(LoginDialog.this, "Login successful!");
                        dispose();
                        // TODO: Jump to main page
                    } else {
                        JOptionPane.showMessageDialog(LoginDialog.this, "Invalid username or password!", "Error", JOptionPane.ERROR_MESSAGE);
                    }
                    resultSet.close();
                    statement.close();
                    connection.close();
                } catch (SQLException ex) {
                    ex.printStackTrace();
                }
            }
        });
        panel.add(loginButton);

        JButton cancelButton = new JButton("Cancel");
        cancelButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                dispose();
            }
        });
        panel.add(cancelButton);

        add(panel);
        pack();
        setLocationRelativeTo(parent);
    }
}

RegisterDialog.java

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

public class RegisterDialog extends JDialog {
    private JTextField usernameField;
    private JPasswordField passwordField;

    public RegisterDialog(Frame parent) {
        super(parent, "Register", true);

        JPanel panel = new JPanel(new GridLayout(2, 2));

        JLabel usernameLabel = new JLabel("Username:");
        panel.add(usernameLabel);

        usernameField = new JTextField();
        panel.add(usernameField);

        JLabel passwordLabel = new JLabel("Password:");
        panel.add(passwordLabel);

        passwordField = new JPasswordField();
        panel.add(passwordField);

        JButton registerButton = new JButton("Register");
        registerButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String username = usernameField.getText();
                String password = new String(passwordField.getPassword());

                if (username.isEmpty() || password.isEmpty()) {
                    JOptionPane.showMessageDialog(RegisterDialog.this, "Username and password cannot be empty!", "Error", JOptionPane.ERROR_MESSAGE);
                    return;
                }

                try {
                    Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydatabase", "root", "password");
                    Statement statement = connection.createStatement();
                    ResultSet resultSet = statement.executeQuery("SELECT * FROM users WHERE username='" + username + "'");
                    if (resultSet.next()) {
                        JOptionPane.showMessageDialog(RegisterDialog.this, "Username already exists!", "Error", JOptionPane.ERROR_MESSAGE);
                    } else {
                        statement.executeUpdate("INSERT INTO users (username, password) VALUES ('" + username + "', '" + password + "')");
                        JOptionPane.showMessageDialog(RegisterDialog.this, "Registration successful!");
                        dispose();
                    }
                    resultSet.close();
                    statement.close();
                    connection.close();
                } catch (SQLException ex) {
                    ex.printStackTrace();
                }
            }
        });
        panel.add(registerButton);

        JButton cancelButton = new JButton("Cancel");
        cancelButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                dispose();
            }
        });
        panel.add(cancelButton);

        add(panel);
        pack();
        setLocationRelativeTo(parent);
    }
}