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OOP
Inheritance

Implement Inheritance Heirarchy

Implement a Shape abstract class which will form the base of an inheritance hierarchy that models 2D geometric shapes. It will have:

* A non-mutable 'name' property or data member set by derived or descendant classes at construction time
* A 'area' method intended to be overridden by derived or descendant classes ( double precision floating point return value)
* A 'print' method (also for overriding) will display the shape's name, area, and all shape-specific values

Two derived or descendant classes will be created:
* Circle    -> Constructor requires a 'radius' argument, and a 'circumference' method to be implemented  
* Rectangle -> Constructor requires 'length' and 'breadth' arguments, and a 'perimeter' method to be implemented 

Instantiate an object of each class, and invoke each objects 'print' method to show relevant details.
ruby
class Shape
def initialize(name="") @name = name end
end

class Circle < Shape
def initialize(radius) super("circle") ; @radius = radius end

def area() 3.14159 * @radius * @radius end
def circumference() 2 * 3.14159 * @radius end

def print()
puts "I am a #{@name} with ->"
puts "Radius: %.2f" % @radius
puts "Area: %.2f" % self.area()
puts "Circumference: %.2f\n" % self.circumference()
end

end

class Rectangle < Shape
def initialize(length, breadth) super("rectangle") ; @length = length ; @breadth = breadth end

def area() @length * @breadth end
def perimeter() 2 * @length + 2 * @breadth end

def print()
puts "I am a #{@name} with ->"
printf("Length, Width: %.2f, %.2f\n", @length, @breadth)
puts "Area: %.2f" % self.area()
puts "Perimeter: %.2f\n" % self.perimeter()
end
end

# ------

shapes = [Circle.new(4.2), Rectangle.new(2.7, 3.1), Rectangle.new(6.2, 2.6), Circle.new(17.3)]
shapes.each {|shape| shape.print}

cpp
#include <string>
#include <iostream>

using namespace std;

static const double PI = 3.141592;

class Shape {
protected:
string name_;
public:
Shape(const string& name) : name_(name) { }
virtual double area() const = 0;
virtual void print() const = 0;
};

class Circle : public Shape {
double radius_;
public:
Circle(double radius) : Shape("circle"), radius_(radius) { }
double area() const {
return PI * radius_ * radius_;
}
void print() const {
cout << "A " << name_ << " with radius " << radius_ << ", area "
<< area() << " and circumference " << circumference() << "."
<< endl;
}
double circumference() const {
return 2 * PI * radius_;
}
};

class Rectangle : public Shape {
double length_;
double breadth_;
public:
Rectangle(double length, double breadth) :
Shape("rectangle"), length_(length), breadth_(breadth) { }
double area() const {
return length_ * breadth_;
}
void print() const {
cout << "A " << name_ << " with length " << length_ << ", breadth "
<< breadth_ << ", area " << area() << " and perimeter "
<< perimeter() << "." << endl;
}
double perimeter() const {
return 2 * length_ + 2 * breadth_;
}
};

int main(int argc, char *argv[])
{
Circle circle(4);
circle.print();
Rectangle rectangle(2, 5.5);
rectangle.print();
}
fsharp
[<AbstractClass>]
type Shape(name:string) =
member this.Name = name
abstract Area : float
abstract Print : unit -> unit

type Circle(name, radius:float) =
inherit Shape(name)
member this.Radius = radius
member this.Circumference =
System.Math.PI * radius * 2.
override this.Area =
System.Math.PI * radius * radius
override this.Print() =
printfn "Circle: %s" this.Name
printfn "Area: %f" this.Area
printfn "Circumference: %f" this.Circumference
printfn "Radius: %f" this.Radius

type Rectangle(name, length:float, breadth:float) =
inherit Shape(name)
member this.Length = length
member this.Breadth = breadth
member this.Perimiter =
(length * 2.) + (breadth * 2.)
override this.Area =
length * breadth
override this.Print() =
printfn "Rectangle: %s" this.Name
printfn "Area: %f" this.Area
printfn "Perimiter: %f" this.Perimiter
printfn "Length: %f" this.Length
printfn "Breadth: %f" this.Breadth

let c = Circle("Foo", 2.1)
let r = Rectangle("Bar", 2.2, 3.3)

c.Print()
printfn ""
r.Print()
clojure
(defmulti area :Shape)
(defmulti print :Shape)

; Circle methods
(defn circle [r]
{:Shape :Circle
:name "Circle"
:radius r})

(defn circumference [c]
(* 2 Math/PI (:radius c)))

(defmethod area :Circle [c]
(* Math/PI (:radius c) (:radius c)))

(defmethod print :Circle [c]
(println (format "I am a %s with ->" (:name c)))
(println (format "Radius: %.2f" (:radius c)))
(println (format "Area: %.2f" (area c)))
(println (format "Circumference: %.2f" (circumference c))))

; Rectangle methods
(defn rectangle [l b]
{:Shape :Rectangle
:name "Rectangle"
:length l
:breadth b})

(defn perimeter [r]
(+ (* 2 (:length r)) (* 2 (:breadth r))))

(defmethod area :Rectangle [r]
(* (:length r) (:breadth r)))

(defmethod print :Rectangle [r]
(println (format "I am a %s with ->" (:name r)))
(println (format "Length, Width: %.2f, %.2f" (:length r) (:breadth r)))
(println (format "Area: %.2f" (area r)))
(println (format "Perimeter: %.2f" (perimeter r))))

; usage of the "classes"
(let [shapes (list (circle 4.2) (rectangle 2.7 3.1) (rectangle 6.2 2.6) (circle 17.3))]
(doseq [shape shapes]
(print shape)))

Implement and use an Interface

Create a Serializable interface consisting of 'save' and 'restore' methods, each of which:

* Accept a stream or handle or descriptor argument for the source or destination
* Save to destination or restore from source the properties or data members of the implementing class (restrict yourself to the primitive types 'int' and 'string')

Next, create a Person class which has 'name' and 'age' properties or data members and implements this interface. Instantiate a Person object, save it to a serial stream, and instantiate a new Person object by restoring it from the serial stream.
ruby
class Person
def initialize(name, age)
@name, @age = name, age
end
end

tom = Person.new("Tom Bones", 23)

File.open('tommy.dump', 'w+') {|f| f.write(Marshal.dump(tommy)) }
toms_clone = Marshal.load(File.read('tommy.dump'))
cpp
struct person
{
person(){}
person(const string &name, int age) : name_(name), age_(age) {}

string name_;
int age_;

template<typename Archive>
void serialize(Archive &ar, const unsigned int version) {
ar & name_ & age_;
}
};


int main()
{
const char *fn = "filename.txt";

person k("Ken", 38);
{
ofstream ofs(fn);
archive::text_oarchive oa(ofs);
oa << k;
}

person restored_person;
{
ifstream ifs(fn);
archive::text_iarchive ia(ifs);
ia >> restored_person;
}

cout << "Name : " << restored_person.name_ << endl
<< "Age : " << restored_person.age_ << endl;
}
fsharp
// Since everyone else is using built-in functionality instead of
// defining an interface as required, I won't buck the trend.
// Maybe this problem should be named "Use serialization features" instead
// of "Implement and use an Interface"

open System
open System.IO
open System.Runtime.Serialization.Formatters.Binary

[<Serializable>]
type Person(name:string, age:int) =
member this.Name = name
member this.Age = age

let serialize x =
use ms = new MemoryStream()
let bf = new BinaryFormatter()
bf.Serialize(ms, x)
ms.ToArray()

let deserialize<'a> bytes =
use ms = new MemoryStream(bytes:byte[])
let bf = new BinaryFormatter()
bf.Deserialize(ms) :?> 'a

let before = Person("Joel", 35)
let bytes = serialize before
let after = deserialize<Person> bytes

printfn "Before: %s, %i" before.Name before.Age
printfn "After: %s, %i" after.Name after.Age
clojure
(defn person [name age]
{:name name :age age})

(defn show [p]
(println (format "Name=%s Age=%d" (:name p) (:age p))))

(defn save [p filename]
(with-out-writer filename (pr p)))

(defn restore [filename]
(read (PushbackReader. (reader filename))))

(let [p (person "Ken" 38)]
(show p)
(save p *person-fn*))

(let [ser-p (restore *person-fn*)]
(show ser-p))