如何从B类中获取A类窗体的画布并调用paint()在A类的窗体背景画图？

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源代码如下所示：

package Test6;
import java.awt.*;
import java.awt.event.*;


public class BridgeThroughOut {
	BridgePanel winframe;
	public BridgeThroughOut(){}
	public BridgeThroughOut(String wintitle){
		winframe=new BridgePanel(wintitle);
	}//过桥类，其中包括桥面板类，过桥人的类
	
	public static class BridgePanel extends Frame{
		Graphics g;
		public BridgePanel(){}
		public BridgePanel(String wintitle){
			super(wintitle);
			setSize(500,500);
			setLayout(new FlowLayout(FlowLayout.CENTER,10,10));
			addWindowListener(new WindowAdapter(){
				public void windowClosing(WindowEvent e){
					dispose();
				}
			});
			this.setVisible(true);
		}
		
		public class Person extends Thread{
			int x,y;
			Color color;
			int sleeptime;//人过桥的速度
			String direction;//方向
			BridgePanel BP;
			
			public Person(){}
			public Person(BridgePanel BP,int x,int y,int v,String direct,Color color){
				this.BP=BP;
				this.x=x;
				this.y=y;
				this.color=color;
				sleeptime=v;
				direction=direct;
			}//创建人的构造函数
			public void run(){
				if(direction=="North")
				while(y>50){
					y--;
				 try{
						Thread.sleep(sleeptime);
					}catch(Exception e){
						System.out.println(e);
					}
					repaint();
				}
				else if(direction=="South")
				while(y<450){
					y++;
				 try{
						Thread.sleep(sleeptime);
					}catch(Exception e){
						System.out.println(e);
					}
					repaint();
				}
			}
	
			public void setGraphics(BridgePanel BP){
			}
			public void paint(Graphics g){
				Graphics g1=BP.getGraphics();
				g1.setColor(color);
				g1.fillOval(x, y, 20, 20);
			}
		}//过桥人的类，把人当做质点，以颜色的不同区分南北桥上的人
		
		public void addPerson(BridgePanel BP,int x,int y,int v,String direct,Color color){
			new Person(BP,x,y, v,direct,color).start();
                   //new Thread(new Person(x,y, v,direct,color).start();
		}//添加过桥人的方法
	}// 过桥面板的创建
	
	public static void main(String[] args){
		//添加人的参数分别是所选面板,横坐标、纵坐标、方向（South或者North）、描绘颜色
		BridgePanel BP=new BridgePanel("过桥问题");
		BP.addPerson(BP,250,450,10,"North",Color.red);
		BP.addPerson(BP,250,50,100,"South",Color.green);
	}
}

我想问的是怎么能够在BridgePanel中的addPerson中创建线程的时候能够在调用Person中的paint()方法，然后在BridgePanel中画出来？