import java.util.*;
/**
 * Description:
 * <br/>Copyright (C), 2005-2008, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@
 * @version  1.0
 */
public class Canvas
{
    //同时在画布上绘制多个形状
    public void drawAll(List<? extends Shape> shapes)
    {
        for (Shape s : shapes)
        {
            s.draw(this);
        }
    }
    public static void main(String[] args)
    {
        List<Circle> circleList = new ArrayList<Circle>();
        circleList.add(new Circle());
        Canvas c = new Canvas();
        c.drawAll(circleList);
    }
}


/**
 * Description:
 * <br/>Copyright (C), 2005-2008, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@
 * @version  1.0
 */
//定义一个抽象类Shape
public abstract class Shape
{
    public abstract void draw(Canvas c);
}
 


/**
 * Description:
 * <br/>Copyright (C), 2005-2008, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@
 * @version  1.0
 */
//定义Shape的子类Circle
public class Circle extends Shape
{
    //实现画图方法，以打印字符串来模拟画图方法实现
    public void draw(Canvas c)
    {
        System.out.println("在画布" + c + "画一个圆");
    }
}

Circle类中的draw函数 接受参数为名为Canvas的类 在Canvas函数中 循环调用所有的从Shape类扩展的类 每次循环用this把当前的所在的Canvas类本身传到draw函数中

circleList.add(new Circle());自动调用public void draw(Canvas c)并把括号里的实参Canvas c传入方法里面吗？Canvas c依我看应该是形参。所以我认为circleList.add(new Circle());这句并没有传入实参。我说的对吗？