有登录窗口的Java简单画图板

以下是一个简单的Java画图板示例，包含登录窗口：

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

public class SimplePaint extends JFrame implements ActionListener {

    private JButton btnClear;
    private JPanel drawingPanel;
    private Graphics graphics;
    private Color currentColor;

    public SimplePaint() {
        super("Simple Paint");
        setLayout(new BorderLayout());

        // 创建登录窗口
        String username = JOptionPane.showInputDialog(null, "请输入用户名：", "登录", JOptionPane.PLAIN_MESSAGE);
        String password = JOptionPane.showInputDialog(null, "请输入密码：", "登录", JOptionPane.PLAIN_MESSAGE | JOptionPane.OK_CANCEL_OPTION);
        if (password == null) {
            System.exit(0);
        } else if (!password.equals("123456")) {
            JOptionPane.showMessageDialog(null, "密码错误！", "错误", JOptionPane.ERROR_MESSAGE);
            System.exit(0);
        }

        // 创建画图面板
        drawingPanel = new JPanel();
        drawingPanel.setBackground(Color.WHITE);
        add(drawingPanel, BorderLayout.CENTER);

        // 创建清除按钮
        btnClear = new JButton("清除");
        btnClear.addActionListener(this);
        add(btnClear, BorderLayout.SOUTH);

        // 设置窗口大小和可见性
        setSize(400, 400);
        setVisible(true);
    }

    // 监听按钮点击事件
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == btnClear) {
            graphics.setColor(Color.WHITE);
            graphics.fillRect(0, 0, drawingPanel.getWidth(), drawingPanel.getHeight());
            graphics.setColor(currentColor);
        }
    }

    public static void main(String[] args) {
        new SimplePaint();
    }
    
    // 初始化画笔
    public void initGraphics() {
        graphics = drawingPanel.getGraphics();
        currentColor = Color.BLACK;
        graphics.setColor(currentColor);

        // 监听鼠标事件
        drawingPanel.addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                graphics.drawLine(e.getX(), e.getY(), e.getX(), e.getY());
            }
        });
        drawingPanel.addMouseMotionListener(new MouseMotionAdapter() {
            public void mouseDragged(MouseEvent e) {
                graphics.drawLine(e.getX(), e.getY(), e.getX(), e.getY());
            }
        });
    }

    // 初始化窗口
    public void initWindow() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
        setResizable(false);

        // 初始化画笔
        initGraphics();
    }
}

这个程序会在启动时弹出一个登录窗口，要求输入用户名和密码。如果密码输入正确，就会打开一个简单的画图面板。画图面板中有一个清除按钮，可以清除画板上的内容。用户可以使用鼠标在画板上绘制图形。