class Shape {
    public void draw() {
        System.out.println("绘制一个形状");
    }
}

class Circle extends Shape {
    @Override
    public void draw() {
        System.out.println("绘制一个圆形");
    }
}

class Rectangle extends Shape {
    @Override
    public void draw() {
        System.out.println("绘制一个矩形");
    }
}

public class ShapeTest {
    public static void drawShape(Shape s) {
        s.draw();
    }

    public static void main(String[] args) {
        Shape shape1 = new Circle();
        Shape shape2 = new Rectangle();
        Shape shape3 = new Shape();

        drawShape(shape1);
        drawShape(shape2);
        drawShape(shape3);
    }
}