Repository

https://github.com/ruby/ruby 

What Will I Learn?

• You will learn the Heritage.
• You will learn the Visibility.
• You will learn Overriding and Polymorphism.

Requirements

• You need to have Ruby installed on your computer

Difficulty

• Basic

Tutorial Contents

1- Heritage 

Heritage is one concept in all programming languages. It is derived from real life, where the child inherits from his father the qualities and actions and everything that is specific to him. From this concept the heritage was applied to programming languages.

Assuming that people are a classes, when a son inherits from his father is the same thing when the class inherits from another class, it will take all the variables and functions and the constructors of the father.

We will give a simple example, we have a class Human and we want to create a class professor where the professor is also a human , what can we understand? Since the professor is also a human , he has a name, age and sex and some of the functions he performs. Moreover, the professor has other things such as the salary.

class Professor < Human  # Heritage

  def initialize(name, sex, age, salary) # creation of constructor       

    super(name, sex, age)    // call to the super method for the super constuctor

    @salary=salary  // add the salary to the salary variable

end

When creating an object from a human class, we create the name, the sex and the age of the person, since the professor class is also a human. When we create it we do not add another constructor, but we call the function super and only add information about the professor.

The constructor of the human class contains the " name, age and sex ", when we create the professor we need to add just the " salary " and for that we don't need to create new constructor with all these parameters but we will add just the salary to the super constructor of " Human ".

I want to give you three functions that we will use :

a- is_a(class) Function

This function will test if the object is an object from the class passed as parameter or not, it return a boolean value.

b- instance_of?(class) Function

This function also will test if the object is an instance of the class passed as parameter or not, so if we have an object from the human class " h1 " and we want to see if this object is from human or not we will call this function and see the result ( True/False).

c- kind_of?(class) Function

This function also the same concept of the other functions , will test the relation of the class passed as parameter and the object, it returns a boolean value.

Let's apply these functions and see the result of the heritage

h1=Human.new("Alex", "m", 20) #creation of object from Human class
puts "h1 is an instance of human" if h1.instance_of?(Human) #an Object of the Human class 
puts h1.class #Human
prof1=Professor.new("Alex", "m", 20, 2000) 
puts "prof1 is an instance of Professor class" if prof1.instance_of?(Professor)
puts prof1.class #Professor 
puts h1.is_a?(Human) #is h1 a human ? 
puts h1.is_a?(Professor) # is h1 an professor ?
puts prof1.is_a?(Professor) # is prof1 an professor? 
puts prof1.is_a?(Human) # is prof1 a human ? 
puts prof1.instance_of?(Human)

We've created two objects " h1 " from " human" and " prof1 " from " professor ". I have applied the functions

is_a : 

I have tested if h1 is a human or not and if prof1 is professor or not.

instance_of :

 I have tested if the prof1 is an instance of human or not.

This is the output, the functions has returned " true and false " you can understand from the output how to use these functions  :

h1 is an instance of human 
Human 
prof1 is an instance of Professor class 
Professor 
true 
false 
true 
true 
false 

Let's now create a complete example with the human, professor and university classes

class Human      
  @@NUMBER_OF_HUMANS=0  
  #The Constructor  
  def initialize(name, sex, age)    
    @name =name    
    @sex  =sex    
    @age=age      
    @legs=2    
    @eyes=2    
    @@NUMBER_OF_HUMANS += 1  
  end    
  attr_accessor :name, :age  
  attr_reader :sex   
  def move()    
    #moving code  
  end    
  def sleep()    
    #sleeping code  
  end    
  def drink()    
    #drinking code  
  end    
  def Human.numberOfHumans    
    return @@NUMBER_OF_HUMANS
  end
end
class Professor < Human  
  attr_accessor :salary  
  def initialize(name, sex, age, salary)    
    super(name, sex, age)    
    @salary=salary    
    @state=""  
  end    
  def work    
    #working code  
  end    
  def getHired(salary)    
    @salary=salary    
    @state="hired"  
  end   
  def getFired    
    @salary=0
    @state="fired"      
  end    
  def profInfo    
    s="Name: " << @name    
    s << ", State: " << @state     
    s << ", Salary: " << @salary.to_s    
    return s  
  end  
end
class University  
  def initialize(university_name, administrator)      
    @university_name=university_name      
    @administrator=administrator         
    @profs=[]        
  end    
  def raiseProfessor(prof, raise)    
    prof.salary += raise    
    puts @administrator  + ": " + prof.name + " is raised!\n"  
  end    
  def hire(prof, salary)    
    prof.getHired(salary)    
    @profs.push(prof)    
    puts @administrator  + ": " + prof.name + " is hired.\n"   
  end    
  def fire(prof)    
    prof.getFired    
    @profs.delete(prof)
    puts @administrator + prof.name + ": " + "is fired.\n"  
  end    
  def profsList    
    return @profs  
  end 
end
#demo 
university=University.new("Oxford", "Alex Harry") 
$Alex=Professor.new("Alex", "m", 20, 2000) 
$Tina =Professor.new("Christina", "f", 35, 4000) 
$Sordin = Professor.new("Sordin", "m", 32, 3000) 
def profsInfo  
  puts "----------------"  
  lst=[$Alex, $tina, $Sordin]  
  for prof in lst    
    puts prof.profInfo  
  end  
  puts "----------------" 
end
puts "Hiring..." 
university.hire($Alex, 2500) 
university.hire($Tina, 2500) 
university.hire($Sordin, 3000) 
$Alex.profInfo
$Tina.profInfo
$Sordin.profInfo
puts "Firing Sordin..."
university.fire($Sordin) 
profsInfo 
university.raiseProfessor($Alex, 1000) 
profsInfo 
puts "--------------" 
puts "The list of professors: "
for prof in university.profsList
  puts prof.name
end

Human Class :

In the human class I have created the constructor with 3 variables " name, sex and age", and inside I have added some constants variables " eyes and legs ", and also when the constructor has been executed the number of humans will be +1

And I have created also 4 functions " move, sleep, drink and the number of humans that return the number of humans created ".

Professor Class :

In the professor class I have added another variable which is " salary ", as we mentioned because the professor is also a human so he will take the " name,sex and age", I have added the salary to the constructor and I have used the " super " method.

I have created 4 functions for the professor " work, getHired that changes the state to " hired ", getFired that changes the state to "fired " and sets the salary to 0 and finally profInfo that combine between the informations of the user and returns them in a variable called " s ".

University Class :

In the university class we have other variables so we have a new constructor with the ' university_name and administrator ' as parameters to the constructor and an array " profs " .

I have created 4 functions for the university " raiseProfessor to raise the salary of the professor by the value passed as parameter, hire to add the professor to the list of professors and to call getHired, fire to delete a professor from the list of professors and to call getFired, and finally profsList to return the list of professors ".

Alex Harry: Alex is hired. 
Alex Harry: Christina is hired. 
Alex Harry: Sordin is hired. 
---------------
Name: Alex, State: hired, Salary: 2500
Name: Christina, State: hired, Salary: 2500
Name: Sordin, State: hired, Salary: 3000
--------------
Firing Sordin... 
Alex Harry Sordin: is fired.
---------------
Name: Alex, State: hired, Salary: 2500 
Name: Christina, State: hired, Salary: 2500 
Name: Sordin, State: fired, Salary: 0 
---------------
Alex Harry: Alex is raised! 
---------------
Name: Alex, State: hired, Salary: 3500
Name: Christina, State: hired, Salary: 2500 
Name: Sordin, State: fired, Salary: 0 
---------------------------
The list of professors: 
Alex
Christina

I have created a university object from University class and 3 profs " Alex,Tina and Sordin", I have created a list of these professors and I have called the function " profInfo " to get the informations about each professor.

I have called the function " Hire " with 3 different names " Alex,Christina and Sordin", I have called " Fire " for Sordin so its salary is now 0, when we call " profsInfo " it will return the professors and Sordin with a salary 0, Than I have raised the professor Alex with 1000$ , finally I have printed the professors with and without Sordin after deleting him from the list.

This is the output of this code :

2-Public/Private/Protected

When we say " public, private and protected " you will think directly to the accessibility, these indicators will protect your variables, classes and functions ..etc.

Public : 

It's accessible by all, it's in the public without any obstructions and protection.

Private :

When the visibility is " private " means that the variables , functions ..etc accessible just in the class.

Protected : 

It's like the "private", but it's accessible only through the class or from the classes that derived from it or let's say its children.

Let's now create an example to see the difference between these indicators.

class Human  
  def move      
  end    
  def sleep      
  end    
  def drink    
  end  
end
class Professor < Human
end

So I have created two classes " Human and Professor " as the previous example, the Human class contains 3 public methods " move, sleep and drink", and the class Professor which inherits from Human.

Let's create two object, the first from Human and the second from Professor.

h1=Human.new() 
prof1=Professor.new()

We can simply call the methods in the Human class because they are " public ", we know in many languages that we use " private and protected " to protect the accessibility, in Ruby "private = protected" it means they have the same effect.

class Human  
  def move 
    puts "The Human is moving"     
  end   
  def sleep 
    puts "The human is sleeping"     
  end   
  def drink
    puts "The human is drinking"    
  end
  private :move, :drink  
end
class Professor < Human
  def method
    drink
  end
end

Let's create two object, the first from Human and the second from Professor and I will call the method of the professor object.

h1=Human.new()
prof1=Professor.new()
prof1.method

We can see that the object "prof1" can access to the function " drink " although its a private function.

3- Overriding and Polymorphism

a- Overriding

The redefinition of a method exists in the parent or in the original class to be defined in the child class in a different way compatible with the work of the class.

class A  
  def method1    
    puts "A's method1 is called"  
  end    
  def method2    
    puts "A's method2 calling method3.."    
    method3  
  end   
  def method3 
    puts "A's method3 is called"  
  end    
  private :method1, :method3  
end 
class B < A
  def method2 #override the protected method
    puts "B's method2 is called"    
  end      
  def method4
    puts "Calling method1..."    
    method1
  end  
end

We have two classes A and B, the class A contains 3 methods " method1, method2 and method3" two of them are privates, the class B extends from A so it can call any method in the parent class " A ", in the class B I have created " method2 " or in other words I have copied the method and change in it and this action called " Overriding ".

a=A.new()
#Calling the parent's method2
a.method2
b=B.new()
#Calling the overriden method2 in the child b.method2

I have created two object a from A and b from B, I have called method2 by " a and b ", if I call method3 for example by " b " we will get " A's method3 is called ", but we have used " overriding " so the method called by " b" will be the method in the class "B", and this is the result :

output => 
A's method2 calling method3.. 
A's method3 is called 
B's method2 is called 

b- Polymorphism

The polymorphism is very known in programming, it means one method with many different forms, for example in Java the polymorphism is a method duplicated but with different parameters or types of parameters, in Ruby is the same thing a method duplicated but with different content.

class A   
def method1     
puts "A's method1 is called.."   
end
end
class B
def method1     
puts "B's method2 is called.."   
end 
end

We have two classes A and B, each one contains a method called " method1 ", the content of method1 in class A is not the same content of the method in the class B, " A's method1 is called.. " and " B's method2 is called.. ".

a=A.new() 
b=B.new()

I have created two objects " a from A " and " b from B ", I can simply call the methods using these objects and I want to give you two different ways to call the methods:

a.method1 
b.method1
# or
objects=[a, b]
for obj in objects  
  obj.method1
end

The first way is the simple way so we can directly call the method using the object.

The second way is to create an array [a,b], to use a " for " loop and call the method1 by each object.

This is the result : 

#output =>
#A's method1 is called.. 
#B's method2 is called..

Curriculum

Part1

Proof of Work Done

 https://github.com/alex-harry/rubyTutorial/blob/master/ruby2.rb