我想实现:
        在面板的黑色和红色区域中单击,在单击的地方出现一个白色的圆.单击其他地方,原来的圆消失,在新的地方出现白色的圆.
        我写的程序在下面,有错误,没达到我的要求,那位大侠帮帮忙!!

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JavaTest extends JFrame {
      JButton b=new JButton("button");
      JTextField tf=new JTextField("txet");
      public JavaTest(){
          Container con=this.getContentPane();
          con.setLayout(null);
          PaintRect pr=new PaintRect();
          pr.setBounds(new Rectangle(2,2,290,200));
          pr.setBorder(BorderFactory.createLineBorder(Color.red));
          con.add(pr);
          b.setBounds(new Rectangle(20,220,100,30));
          con.add(b);
          tf.setBounds(new Rectangle(160,220,120,30));
          con.add(tf);
          //面板上有一个矩形区、一个JButton和一个JTextField
          addMouseListener(new MouseAdapter(){
                 public void mouseClicked(MouseEvent e) {
                     int x=e.getX();
                     int y=e.getY();
           //在下面条件下，画白色的圆    
                     if(x>=2 && x<=292 && y>=2 && y<=202){                        
                        PaintCircle pc=new PaintCircle(e.getX(),e.getY());
                        pc.setBounds(new Rectangle(x,y,10,10));
                        getContentPane().add(pc);
                      }
                }
           });
          this.setSize(300,300);
    }
    public static void main(String args[]){
          JavaTest jt=new JavaTest();
          jt.setVisible(true);
    }
}
class PaintCircle extends JPanel{
        int cx;
        int cy;
        public PaintCircle(int x,int y){
               cx=x;cy=y;
        }
        public void paintComponent(Graphics g){
               super.paintComponent(g);
               g.setColor(Color.white);
               g.drawOval(cx,cy,10,10);
        } 
}
class PaintRect extends JPanel{
        public void paintComponent(Graphics g){
               super.paintComponent(g);
               g.setColor(Color.black);
               g.fillRect(2,2,145,195); 
               g.setColor(Color.red);
               g.fillRect(2,147,140,195);                
        } 
}