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OOP
Basics

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();
}
}
erlang
Greeter = make_greeter("world!"),
Greeter(greet).

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);
}
}
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}

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();
}
}

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'))