用鼠标绘图

package _11;

import java.awt.Color;

import java.awt.Graphics;

import java.awt.event.ComponentAdapter;

import java.awt.event.ComponentEvent;

import java.awt.event.MouseAdapter;

import java.awt.event.MouseEvent;

import java.awt.image.BufferedImage;

import javax.swing.JFrame;

public class PaintFrame extends JFrame {

// 记录绘图内容的缓冲区

private BufferedImage canvas;

// 记录上一次鼠标的x、y位置

private int lastX = -1;

private int lastY = -1;

public PaintFrame() {

// 窗口大小改变事件：适配缓冲区大小并保留原有绘图

this.addComponentListener(new ComponentAdapter() {

public void componentResized(ComponentEvent e) {

BufferedImage newCanvas = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);

if (canvas != null) {

Graphics g = newCanvas.getGraphics();

g.drawImage(canvas, 0, 0, null);

}

canvas = newCanvas;

}

});

// 鼠标移动事件：绘制连续红线

this.addMouseMotionListener(new MouseAdapter() {

public void mouseMoved(MouseEvent e) {

int x = e.getX();

int y = e.getY();

if (lastX == -1 && lastY == -1) {

// 初始化首次鼠标位置

lastX = x;

lastY = y;

} else {

// 在缓冲区绘制红线

Graphics g = canvas.getGraphics();

g.setColor(Color.RED);

g.drawLine(lastX, lastY, x, y);

// 更新鼠标位置

lastX = x;

lastY = y;

// 触发界面重绘

repaint();

}

}

});

}

// 重写paint方法：将缓冲区内容绘制到窗口

@Override

public void paint(Graphics g) {

super.paint(g);

g.drawImage(canvas, 0, 0, null);

}

public static void main(String[] args) {

PaintFrame frame = new PaintFrame();

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setSize(500, 500);

frame.setVisible(true);

}

}