鼠标事件响应问题求助！！
我初学java，正在看core java2，看到第8章鼠标事件那节，有个例子，编写一个简单的图形处理编辑器程序，允许用户在画布上放置、移动和擦除小方块，点下鼠标就放置，在方块内双击鼠标就删除，按住鼠标就可拖动小方块（如果鼠标点在小方块内的话），我仿照书中的源程序，做了些小改动(主要修改的find函数)，就不能实现删除和拖放功能了，我检查了一天也没发现哪里有问题，郁闷啊，请各位高手帮我看看，谢谢了哈，以下是我的源程序：

/**
 * 
 */

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.awt.geom.*;
import javax.swing.*;
public class MouseTest 
{
public static void main(String[] args) 
{
MouseFrame MF = new MouseFrame();
MF.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MF.setVisible(true);
}
}

class MouseFrame extends JFrame
{
public MouseFrame()
{
setTitle("MouseTest");
Container contentPane = getContentPane();
MousePanel SP = new MousePanel();
contentPane.add(SP);
Toolkit kit = Toolkit.getDefaultToolkit();
Dimension screenSize = kit.getScreenSize();
int screenWidth = screenSize.width;
int screenHeight = screenSize.height;
setSize(screenWidth/2,screenHeight/2);
setLocation(screenWidth/4,screenHeight/4);
}
}

class MousePanel extends JPanel
{
public MousePanel()
{
all_rectangle = new ArrayList<Rectangle2D>();

addMouseListener(new ML());

addMouseMotionListener(new MML());
}


public void paintComponent(Graphics g)
{
super.paintComponents(g);
Graphics2D g2 = (Graphics2D)g;
for (int i = 0; i < all_rectangle.size(); i++)
{
g2.draw((Rectangle2D)all_rectangle.get(i));
}
}

public int find(Point2D p)
{
for (int i = 0; i < all_rectangle.size(); i++)
{
if (all_rectangle.get(i).contains(p))
{
return i; 
}
}
return -1;
}

public void add_Rect(Point2D p)
{
double x = p.getX();
double y = p.getY();
Rectangle2D s = new Rectangle2D.Double(
x - Rectangle_length / 2, 
y - Rectangle_length / 2, 
Rectangle_length, 
Rectangle_length);
all_rectangle.add(s);
repaint();
}

public void del_Rect(int p)
{
all_rectangle.remove(p);
repaint();
}

private ArrayList<Rectangle2D> all_rectangle;
private static final int Rectangle_length = 10;

private class ML extends MouseAdapter
{
public void mousePressed(MouseEvent e)
{
if (find(e.getPoint()) == -1)
{
add_Rect(e.getPoint());
}
}

public void mouseClicked(MouseEvent e)
{
int flag = find(e.getPoint());
if ( e.getClickCount() >= 2 && flag >= 0)
{
del_Rect(flag);
}
}
}

private class MML implements MouseMotionListener
{
public void mouseMoved(MouseEvent e)
{
if (find(e.getPoint()) < 0)
{
setCursor(Cursor.getDefaultCursor());
}
else
{
setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
}

}

public void mouseDragged(MouseEvent e)
{
int flag = find(e.getPoint());
if (flag >= 0)
{
int x = e.getY();
int y = e.getY();
all_rectangle.get(flag).setFrame(
x - Rectangle_length / 2, 
y - Rectangle_length / 2, 
Rectangle_length, 
Rectangle_length);
repaint();
}

}
}

}