class Shape {
    public void draw(){
        System.out.println("画一个形状");
    }
}

class Circle extends Shape{
    @Override
    public void draw(){
        System.out.println("画一个圆形");
    }
}

class Rectangle extends Shape{
    @Override
    public void draw(){
        System.out.println("画一个矩形");
    }
}

public class ShapeTest{
    public static void main(String[]args){
        Shape s1 = new Circle();
        Shape s2 = new Rectangle();

        s1.draw();
        s2.draw();

        Shape[]shapes={new Circle(),new Rectangle(),new Circle()};//两个new Circle 是为了演示数组中可以有多个相同类型对象共存
        for(Shape s:shapes){
            s.draw();//每个对象调用自己的draw版本
        }
    }
}