public abstract class Geometry { public abstract double getArea(); } public class Circle extends Geometry { private double r; public Circle( double r){ this .r=r; } public double getArea(){ return ( 3.14 *r*r); } } public class Volume { Geometry botton; double height; public Volume( Geometry botton , double height){ this .botton=botton; this .height=height; } void changeBotton(o botton){ this .botton=botton; } public double getVolume(){ return botton.getArea()*height; } } 关于上述代码的说法,正确的是: