java swing画图板

Java Swing是Java平台的一部分，是一组GUI类库，可以用于创建桌面应用程序。下面是一个简单的Java Swing画图板的实现：

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

public class DrawingBoard extends JFrame implements ActionListener, MouseListener, MouseMotionListener {
    private int x, y, x1, y1;
    private JButton clearButton, redButton, greenButton, blueButton;
    private JPanel buttonPanel, drawingPanel;
    private Graphics g;

    public DrawingBoard() {
        super("Drawing Board");
        setSize(500, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        buttonPanel = new JPanel();
        clearButton = new JButton("Clear");
        redButton = new JButton("Red");
        greenButton = new JButton("Green");
        blueButton = new JButton("Blue");

        buttonPanel.add(clearButton);
        buttonPanel.add(redButton);
        buttonPanel.add(greenButton);
        buttonPanel.add(blueButton);

        drawingPanel = new JPanel();
        drawingPanel.setBackground(Color.WHITE);
        drawingPanel.addMouseListener(this);
        drawingPanel.addMouseMotionListener(this);

        Container contentPane = getContentPane();
        contentPane.add(buttonPanel, BorderLayout.NORTH);
        contentPane.add(drawingPanel, BorderLayout.CENTER);

        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == clearButton) {
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, drawingPanel.getWidth(), drawingPanel.getHeight());
        } else if (e.getSource() == redButton) {
            g.setColor(Color.RED);
        } else if (e.getSource() == greenButton) {
            g.setColor(Color.GREEN);
        } else if (e.getSource() == blueButton) {
            g.setColor(Color.BLUE);
        }
    }

    public void mousePressed(MouseEvent e) {
        x = e.getX();
        y = e.getY();
    }

    public void mouseDragged(MouseEvent e) {
        x1 = e.getX();
        y1 = e.getY();
        g.drawLine(x, y, x1, y1);
        x = x1;
        y = y1;
    }

    public void mouseClicked(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
    public void mouseMoved(MouseEvent e) {}

    public static void main(String[] args) {
        new DrawingBoard();
    }
}