java怎样监听屏幕，在屏幕上画图

我这里有个监听运行窗口的，你自己再改改吧..希望能帮的上你.. 控制上，下，左，右 或 h,j,k,l来画图... 按住shift键可加速.

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

public class Sketch
{
public static void main(String[] args)
{
SketchFrame frame = new SketchFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}

/**
A frame with a panel for sketching a figure
*/
class SketchFrame extends JFrame
{
public SketchFrame()
{
setTitle("Sketch");
setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

// add panel to frame

SketchPanel panel = new SketchPanel();
add(panel);
}

public static final int DEFAULT_WIDTH = 300;
public static final int DEFAULT_HEIGHT = 200;
}

/**