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OOP

Define a class

Declare a class named Greeter that takes a string on creation and greets using this string if you call the "greet" method.
ruby
class Greeter
def initialize(whom) @whom = whom end
def greet() puts "Hello, #{@whom}!" end
end

(Greeter.new("world")).greet()
csharp
using System;

class Greeter
{
private string name {get;set;}

public void Greet(){
Console.WriteLine("Hello, {0}",name);
}

public Greeter(string name){
this.name = name;
}
}

class Test
{
static void Main()
{
new Greeter("Dante").Greet();
}
}
cpp
class Greeter
{
public:
Greeter(const std::string& whom);
void greet() const;

private:
std::string whom;
};

int main()
{
Greeter* gp = new Greeter("world");
gp->greet();
delete gp;
}

Greeter::Greeter(const std::string& whom) : whom(whom) {}

void Greeter::greet() const
{
std::cout << "Hello, " << whom << std::endl;
}
public ref class Greeter
{
public:
Greeter(String^ whom);
void greet();

private:
initonly String^ whom;
};

int main()
{
(gcnew Greeter(L"world"))->greet();
}

Greeter::Greeter(String^ whom) : whom(whom) {}

void Greeter::greet()
{
Console::WriteLine(L"Hello, {0}", whom);
}
fantom
class Greeter
{
private Str whom
new make(Str whom) { this.whom = whom }
Void greet() { echo("Hello, $whom") }
}

Greeter("world").greet
erlang
Greeter = make_greeter("world!"),
Greeter(greet).
groovy
// version using named parameters
class Greeter {
def whom
def greet() { println "Hello, $whom" }
}
new Greeter(whom:'world').greet()
// version using traditional constructor
class Greeter {
private whom
Greeter(whom) { this.whom = whom }
def greet() { println "Hello, $whom" }
}
new Greeter('world').greet()
clojure
(defprotocol IGreeter
(greet [this]))

(deftype Greeter [whom]
IGreeter
(greet [this]
(println (str "Hello, " whom))))

(greet (Greeter. "world"))
(defn greeter [whom]
{:whom whom})

(defn greet [g]
(println (str "Hello, " (:whom g))))

(greet (greeter "world"))

Instantiate object with mutable state

Reimplement the Greeter class so that the 'whom' property or data member remains private but is mutable, and is provided with getter and setter methods. Invoke the setter to change the greetee, invoke 'greet', then use the getter in displaying the line, "I have just greeted {whom}.".

For example, if the greetee is changed to 'Tommy' using the setter, the 'greet' method would display:

Hello, Tommy!

The getter would then be used to display the line:

I have just greeted Tommy.
ruby
class Greeter
attr_accessor :whom
def initialize(whom) @whom = whom end
def greet() puts "Hello, #{@whom}!" end
end

greeter = Greeter.new("world") ; greeter.greet()

greeter.whom = 'Tommy' ; greeter.greet()
puts "I have just greeted %s" % greeter.whom
csharp
class Greeter
{
public string Name {get;set;}

public void Greet(){
Console.WriteLine("Hello, {0}",Name);
}

public Greeter(string name){
this.Name = name;
}

// Driver
public static void Main()
{
var g = new Greeter("Dante");

g.Name = "Tommy";
g.Greet();
Console.Write("I have just greated {0}", g.Name);
}
}
cpp
#include <iostream>

using namespace std;

class Greeter {
string whom_;

public:
Greeter(const string &whom) : whom_(whom) {}

string get_whom() const {
return whom_;
}

void set_whom(const string &whom) {
whom_ = whom;
}

void greet() const {
cout << "Hello " << whom_ << "!" << endl;
}
};

int main()
{
Greeter greeter("world");
greeter.greet();
greeter.set_whom("Tommy");
greeter.greet();
cout << "I have just greeted " + greeter.get_whom() << "." << endl;
}
fantom
class Greeter
{
new make(Str whom) { this.whom = whom }
Void greet() { echo("Hello, $whom!") }
Str whom
}

greeter := Greeter("world")
greeter.greet
greeter.whom = "Tommy"
echo("I have just greeted ${greeter.whom}.")
groovy
class Greeter {
def whom
def greet() { println "Hello, $whom!" }
}

greeter = new Greeter(whom:"world"); greeter.greet()

greeter.whom = 'Tommy'; greeter.greet()
println "I have just greeted $greeter.whom"
clojure
(defn greeter [whom]
(atom {:whom whom}))

(defn get-whom [g]
(:whom @g))

(defn set-whom [g whom]
(swap! g #(conj % {:whom whom})))

(defn greet [g]
(println (str "Hello, " (:whom @g) "!")))

; using the "class"
(let [g (greeter "world")]
(greet g)
(set-whom g "Tommy")
(greet g)
(println (str "I have just greeted " (get-whom g) ".")))

; or same effect without using any variables
(println (str "I have just greeted "
(get-whom (doto (greeter "world")
(greet)
(set-whom "Tommy")
(greet)))
"."))

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}

csharp
// While abstract classes do exist in C#, it is most common to use
// an interface in this type of situation.
// It is a common idiom to prefix interface names with an I
public interface IShape {
string Name { get; }
double Area { get; }
void Print();
}

public class Circle : IShape {

private double Radius { get; set; }
public Circle(double radius) {
Name = "Circle";
Radius = radius;
}

public string Name { get; private set; }
public double Area {
get {
return Math.PI * Radius * Radius;
}
}
public double Circumference {
get {
return Math.PI * (Radius + Radius);
}
}

public void Print() {
Console.WriteLine( " Name: {0}\n Area: {1}\n Circumference: {2}\n Radius: {3}",
this.Name,
this.Area,
this.Circumference,
this.Radius
);
}
}

public class Rectangle : IShape {

private double Length { get; set; }
private double Breadth { get; set; }
public Rectangle(double length, double breadth) {
Name = "Rectangle";
Length = length;
Breadth = breadth;
}

public string Name { get; private set; }
public double Area {
get {
return Length * Breadth;
}
}
public double Perimeter {
get {
return (Length * 2) + (Breadth * 2 );
}
}

public void Print() {
Console.WriteLine( " Name: {0}\n Area: {1}\n Perimeter: {2}\n Length: {3}\n Breadth: {4}",
this.Name,
this.Area,
this.Perimeter,
this.Length,
this.Breadth
);
}
}

// Driver
public class InheritanceHeirarchy {
public static void _Main() {
var c = new Circle(2.1);
c.Print();

Console.WriteLine();

var r = new Rectangle(2.2, 3.3);
r.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();
}
fantom
abstract class Shape
{
const Str name
new make(Str name) { this.name = name }
abstract Float area()
abstract Void print()
}

class Circle : Shape
{
private Float radius

new make(Float radius) : super("circle") { this.radius = radius }
Float circumference() { return 2 * Float.pi * radius }
override Float area() { return Float.pi * radius.pow(2.0f) }
override Void print()
{
echo("I am a $name with radius $radius, area $area
and circumference $circumference")
}
}

class Rectangle : Shape
{
private Float length
private Float breadth

new make(Float length, Float breadth) : super("rectangle")
{
this.length = length
this.breadth = breadth
}
Float perimeter() { return 2 * (length + breadth) }
override Float area() { return length * breadth }
override Void print()
{
echo("I am a $name with length $length, breadth $breadth,
area $area and perimeter $perimeter")
}
}


circle := Circle(4.0f)
circle.print
rectangle := Rectangle(2.0f, 5.5f)
rectangle.print
groovy
abstract class Shape {
final name
Shape(name) { this.name = name }
abstract area()
abstract print()
}

class Circle extends Shape {
final radius
Circle(radius) {
super('circle')
this.radius = radius
}
def area() { Math.PI * radius * radius }
def circumference() { 2 * Math.PI * radius }
def print() {
println "I am a $name with ->"
printf 'Radius: %.2f\n', radius
printf 'Area: %.2f\n', area()
printf 'Circumference: %.2f\n', circumference()
}
}

class Rectangle extends Shape {
final length, breadth
def Rectangle(length, breadth) {
super("rectangle")
this.length = length
this.breadth = breadth
}
def area() { length * breadth }
def perimeter() { 2 * length + 2 * breadth }
def print() {
println "I am a $name with ->"
printf 'Length, Width: %.2f, %.2f\n', length, breadth
printf 'Area: %.2f\n', area()
printf 'Perimeter: %.2f\n', perimeter()
}
}

shapes = [new Circle(4.2), new Rectangle(2.7, 3.1), new Rectangle(6.2, 2.6), new Circle(17.3)]
shapes.each { shape -> shape.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;
}
fantom
@Serializable
class Person
{
Str name
Int age
new make(|This| f) { f(this) }
}

person := Person() { name="Tom Bones"; age=23 }
File(`tommy.dump`).out.writeObj(person).close
Person tom := File(`tommy.dump`).in.readObj
groovy
// Built-in functionality but with slightly different names. Showing usage:
class Person implements Serializable { String name; int age }
p1 = new Person(name:'John', age:21)
p2 = null
output = new ByteArrayOutputStream() // or FileOutputStream, etc.
output.withObjectOutputStream { oos -> oos << p1 }
input = new ByteArrayInputStream(output.toByteArray())
input.withObjectInputStream(getClass().classLoader){ ois -> p2 = ois.readObject() }
assert p2.name == 'John'
assert p2.age == 21
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))