feat: Add CircleDemo and CylinderDemo to demonstrate inheritance and geometry methods

WHAT the code does:
Defines CircleDemo with:
- radius field.
- area(): computes circle area (πr²).
- perimeter(): computes circle perimeter (2πr).
- circumference(): delegates to perimeter().
Defines CylinderDemo extending CircleDemo with:
- height field.
- volume(): computes cylinder volume using area() × height.
Defines Inheritance with main():
- Creates CylinderDemo object.
- Assigns radius = 7 and height = 10.
- Prints cylinder volume and circle area.

WHY this matters:
Demonstrates **inheritance** in Java:
- CylinderDemo reuses CircleDemo’s area() for its volume calculation.
- Highlights code reuse: circle properties directly extend into cylinder computations.
Shows how subclass methods can build on superclass methods.
Provides a practical geometry-based example of inheritance.

HOW it works:
CylinderDemo inherits radius and area() from CircleDemo.
c.radius = 7, c.height = 10.
volume() = area() × height = (π × 7²) × 10 = 1539.38.
area() = π × 7² = 153.94.

Tips and gotchas:
Fields radius and height are public, breaking encapsulation—prefer private with getters/setters.
circumference() is redundant since it directly calls perimeter(); the two could be merged or one removed.
Class names should follow convention: Inheritance could be renamed GeometryInheritance for clarity.
Inheritance here models a “is-a” relationship, but mathematically, a cylinder is not a circle—it has-a circle base. Composition would be more semantically correct.

Use-cases:
Educational demonstration of inheritance and method reuse.
Geometry-based examples for teaching OOP principles.
Foundation for extending into more advanced shape hierarchies (e.g., abstract Shape or interface).

Short key: class-circledemo cylinderdemo inheritance geometry.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section12Inheritance/src/Inheritance.java

@@ -1,43 +1,33 @@
-class CircleDemo
-{
+class CircleDemo {
     public double radius;
 
-    public double area()
-    {
+    public double area() {
         return Math.PI * radius *radius;
     }
-
-    public double perimeter()
-    {
+    public double perimeter() {
         return 2*Math.PI*radius;
     }
-    public double circumference()
-    {
+    public double circumference() {
         return perimeter();
     }
 }
 
-class CylinderDemo extends CircleDemo
-{
+class CylinderDemo extends CircleDemo {
     public double height;
 
-    public double volume()
-    {
+    public double volume() {
         return area()*height;
     }
 
 }
 
-public class Inheritance
-{
-    public static void main(String[] args)
-    {
+public class Inheritance {
+    public static void main(String[] args) {
         CylinderDemo c = new CylinderDemo();
-
         c.radius = 7;
         c.height = 10;
 
         System.out.println("Volume " + c.volume());
         System.out.println("Area " + c.area());
     }
-}
+}