how to prevent inheritance chain in java - oop

Question

I have a problem with inheritance chain in java
I have an interface Geometry, a class Circle implements Geometry,and a class Cylinder extends Circle. Because Circle haven't Volume, I return it to 0. When Cylinder extends Circle, Volume return V = PI * Radius * Radius * Height
But I create instance of Cylinder is cy, when it call getVolume(), it return 0 of Circle. How does it call getVolume() itself, not Circle??
Thanks. This is my code:
public interface Geometry {
public double getArea();
public double getVolume();
}
class Circle implements Geometry {
public double R;
public double getArea() {
return Math.pow(R, 2) * Math.PI;
}
public double getVolume() {
return 0; // because not volume of Circle
}
}
class Cylinder extends Circle {
public double Height;
//lateral area of Cylinder
public double getArea() {
double s = super.getArea();
return 2 * s + 2 * Math.PI * super.R * this.Height;
}
public double getVolume() {
return Math.PI * Math.pow(R, 2) * Height;
}
}
public class Main {
public static void main(String[] args) {
Cylinder cy = new Cylinder();
cy.R = 1;
System.out.println(cy.getArea()); // 6.28
System.out.println(cy.getVolume()); // 0 Wrong!!!
}
}

Answer 1

Its not returning the getVolume() of circle, but as you have not set the height the volume is coming as Zero return Math.PI * Math.pow(R, 2) * Height;
You can confirm this by putting a system.out.println statement in the method.
But in any case this hierarchy is incorrect, you should not extend Cylinder with circle as cylinder is not a circle. Inheritance is used to make a specific type from a generic type like dog out of animal, cylinder and circle are not related in that sense , so you are misusing inheritence

Answer 2

I think your problem is not the Circle's getVolume called. The method called is the Cylinder's, but the Height property is 0, hence the 0 return value.
You need to set the Height property of your Cylinder instance (cy), as in:
cy.Height = 3.00;

Answer 3

Inheritance is overused by beginner programmers
Your idea to use inheritance here breaks many many rules in OOP. The most basic of which is that, a cylinder is not a cycle.
There are other mechanisms for code re-usage in OOP, but beginners gravitate towards inheritance because it is obviously FOR re-usage.
Encapsulation and Composition
In this case, I would encourage you to use composition, which is a consequence of encapsulation.
In this case I would encourage you to make a class called Prism that contains two properties, Height and Face, the second of which is where you place your Circle.