难题求解

我编了一个程序，从图片文件中导入图像，黑块为障碍物。我想让小圆碰上障碍物后能沿着障碍物的边走，怎么办？（障碍物为任意图形）
以下为一部分代码，请求更正（红字为重点修改对象）：
    class PaintThread extends JPanel implements Runnable
    {
      int x = 30, y = 50,f=0,n,i;
      final ImageIcon imageIcon = new ImageIcon("bb.jpg");
      Image image = imageIcon.getImage();
          public void paint(Graphics g)
              {
              super.paint(g);
              g.drawImage(image,0,0,this);
              g.fillOval(x, y, 30, 30);
              g.drawRect(0,0,1100,600);
            }            
          public void run()
              {
            try {
               BufferedImage bi = ImageIO.read(new File("bb.jpg"));
              do{   for(i=0;i<=120;i++)         
                    {
                        n=bi.getRGB((int)(x+15*Math.cos(i*Math.PI/60-Math.PI/2)+15),(int)(y+15*Math.sin(i*Math.PI/60-Math.PI/2)+15));
                      if(n!=-16777216)
                          {
                           x=(int)(Math.cos((i+10)*Math.PI/60+Math.PI)*2+x+15);
                             y=(int)(Math.sin((i+10)*Math.PI/60+Math.PI)*2+y+15);
                           
                          }
                    }
               
                    repaint();
                    try{Thread.sleep(10);}
                    catch(InterruptedException e){e.printStackTrace();}
                    }while(true);
                    } catch (IOException e)     {e.printStackTrace();}
        
            }
        }
求大神！！
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