有一次在课上无意中看了东哥演示的隐形画图板，感觉比较有趣，于是头脑发热，回去就马上动手，话了 一晚上时间，编出一个比较丑陋的所谓的隐形画图板。其实说吧，这个画图板就是一个骗人的东西，它的原理就是先把当前屏幕图片截下来，然后再画到窗体上，把窗体大小设置成屏幕大小，去掉窗体上的关闭按钮，就得到了一个隐形画图板了。接下来逐步介绍怎么实现这个画图板的几个窗用的功能。
一、将窗体设置成屏幕大小，该过程使用了Java中的一个工具Toolkit 代码如下：
Toolkit toolkit = Toolkit.getDefaultToolkit();
Dimension dm = toolkit.getScreenSize();
this.setSize(dm);二、去掉窗体的关闭按钮，用到了Java自带的一个窗体修饰方法setUndecorated(true)，参数true表示不可修饰，得到一个空白窗体，代码很简单，就一行：
this.setUndecorated(true);
三、获取当前屏幕背景图片，并保存到工程下，该过程用到了Java自带的Robot和ImageIO方法；具体代码实现如下：
Rectangle rect = new Rectangle(dm);
Robot robot = new Robot();
BufferedImageimage=robot.createScreenCapture（rect）;
try {
ImageIO.write(image, "jpg", new File("C:\\Users\\Administrator\\workspace\\隐形画图板\\img\\" + "a" + ".jpg"));
} catch (IOException ef) {
// TODO Auto-generated catch block
ef.printStackTrace();
}
g.drawImage(image, 0 , 0, dm.width, dm.height,Color.white, null);
} catch (AWTException ea) {
// TODO Auto-generated catch block
ea.printStackTrace();
}
//主窗体
package cjl.deaw1;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.image.RenderedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
/**
* 画图板界面类
*
* @author Administrator
*
*/
public class DrawUI extends JFrame {
BufferedImage image;
Image image1;
public static void main(String args[]) {
new DrawUI();
}
/**
* 初始化界面的方法
*/
public DrawUI() {
Toolkit toolkit = Toolkit.getDefaultToolkit();
Dimension dm = toolkit.getScreenSize();
JPanel panel=new JPanel();
panel.setBackground(Color.WHITE);
panel.setPreferredSize(dm);
this.setSize(dm);
FlowLayout fl = new FlowLayout();
this.setUndecorated(true);
this.setLayout(fl);
this.setAlwaysOnTop(true);
this.setDefaultCloseOperation(3);
this.add(panel );
this.setVisible(true);
// 从窗体上获取画布对象
// 获取窗体在屏幕上所占据的区域，这块区域是允许改变颜色的
Graphics g = this.getGraphics();
// int [] x={100,150,300};
// int [] y={100,200,300};
// g.drawPolygon(x, y, 3);
// Graphics2D g2d = (Graphics2D) this.getGraphics();
// 创建鼠标监听器对象
DrawListener dlis = new DrawListener(g,this);
// 给窗体加上鼠标监听器
this.addMouseListener(dlis);
try {
Rectangle rect = new Rectangle(dm);
Robot robot = new Robot();
BufferedImage image = robot.createScreenCapture(rect);
try {
ImageIO.write(image, "jpg", new File("C:\\Users\\Administrator\\workspace\\隐形画图板\\img\\" + "a" + ".jpg"));
} catch (IOException ef) {
// TODO Auto-generated catch block
ef.printStackTrace();
}
g.drawImage(image, 0 , 0, dm.width, dm.height,Color.white, null);
} catch (AWTException ea) {
// TODO Auto-generated catch block
ea.printStackTrace();
}
}
}
//监听器
package cjl.deaw1;
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JOptionPane;
/**
* 画板的监听器，实现鼠标监听器接口
*
* @author Administrator
*
*/
public class DrawListener implements MouseListener {
private int x1, y1, x2, y2;
private Graphics gr;
public float stroke;
DrawUI drawUI;
public DrawListener(Graphics gr, DrawUI drawUI) {
this.gr = gr;
this.drawUI=drawUI;
}
public void mousePressed(MouseEvent e) {
// 获取鼠标按下时候光标的位置
x1 = e.getX();
y1 = e.getY();
if (e.isMetaDown()) {
JOptionPane.showMessageDialog(drawUI, "你你确定要退出吗？");
System.exit(0);
}
if (e.isControlDown())
System.out.println();
// draw(x1, y1, 100, 1);
}
public void mouseReleased(MouseEvent e) {
// 获取鼠标释放时候光标的位置
x2 = e.getX();
y2 = e.getY();
for (int i = 0; i <= 50; i++) {
gr.setColor(new Color(155 + 2 * i, 100 + 2 * i, 40 + 2 * i));
gr.fillOval(Math.min(x1, x2) + i, Math.min(y1, y2), 100 - 2 * i,
160 - 2 * i);
}
}
public void mouseEntered(MouseEvent e) {
// System.out.println("mouseEntered");
}
public void mouseExited(MouseEvent e) {
// System.out.println("mouseExited");
}
public void mouseClicked(MouseEvent e) {
// System.out.println("mouseClicked");
}
public void draw(double x0, double y0, int L, int n) {
double x1 = 0, y1 = 0;
if (n <= 0) {
return;
} else {
for (int i = 0; i <= 800; i++) {
try {
Thread.sleep(5);
} catch (InterruptedException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
if (i <= 200) {
L = i;
gr.setColor(new Color(255 - i, i, i));
gr.fillOval((int) (x0 + L), (int) y0, 10, 10);
}
if (i >= 200 && i <= 400) {
L = i - 200;
gr.setColor(new Color(455 - i, i - 200, i - 150));
gr.fillOval((int) (x0 + 200), (int) y0 + L, 10, 10);
}
if (i >= 400 && i <= 600) {
L = 600 - i;
gr.setColor(new Color(655 - i, i - 400, i - 350));
gr.fillOval((int) x0 + L, (int) y0 + 200, 10, 10);
}
if (i >= 600 && i <= 800) {
L = 800 - i;
gr.setColor(new Color(855 - i, i - 600, i - 550));
gr.fillOval((int) x0, (int) y0 + L, 10, 10);
}
x1 = Math.sin((x0 + i) / 4) * 100;
y1 = Math.sin((y0 + i) / 4) * 100;
// System.out.println("x1:" + x1 + "\n" + "y1;" + y1);
}
}
draw(y1 + 140, y1 + 140, L, n - 1);
}
}