• Ruby is pure object-oriented language, Everything appears to Ruby, is an object.
• Every value in Ruby is an object, even the most primitive things: strings, numbers and even true and false

• It's constructor in ruby
• useful when you want to initialize some class variables at the time of object creation. 
  
• This method may take a list of parameters
  

class Box
  def initialize
    # do something
  end
end

• private means the method(s) are accessible only when they can be called without an explicit receiver. Only self is allowed to be the receiver of a private method call.

• A protected method can be called from a class or descendant class instances, but also with another instance as its receiver.

#class with variable types
$global_var = "global"
class Greeter
  attr_accessor :surname
  def initialize(name = "World")
    @name = name
    @surname = "joshi"
    @@company = "WGBL"
    local_name = "local"
  end
  
  def access
    puts "Access global variable #{$global_var}"
    puts "Access class variable #{@@company}"
    puts "Access instance variable #{@name}"
    puts "Access instance variable #{local_name}"
  end
end

• Why? The answer is encapsulation and security
• What's this? nothing but methods for accessing data members
• Getter: method for 'getting' the data member's value
• Setter: method for 'setting' the data member's value

 #getter method
def width
  @width
end

#setter method
def width=(w)
   @width = w
end

class Box
  # generate getter method for width
  attr_reader :width

  # generate setter method for width
  attr_writer :width

  # generate getter and setter methods for   
  #height
  attr_accessor :height
end
 

class Box
  def initialize(w,h)
    @width, @height = w, h
    @@count +=1
  end

  def self.count  # class method
     @@count
  end

  def area  # instance method
     @width * @height
  end
end

• Does not directly support multiple inheritance but can be achieved using mixins

class Animal
   def make_noise
      “awww……”
   end
end

class Dog < Animal
  def make_noise # overriding method 
     “bhow bhow”
  end
end

class Cat < Animal
  def walk
     “walking”
  end
end

• Modules are a way of grouping together methods, classes, and constants. analogous to package in Java
  
• Modules give you two major benefits.
  

1. Modules provide a namespace and prevent name clashes.
   
2. Modules implement the mixin facility.
   

module Utility
   def self.sin(a)
      # do something
   end

  class Language
    def hindi_hello
       puts “namaste”
    end
  end
end

f = File.new(“filename”, “mode”)

# process file

# closing the file after  performing options is important

f.close

• You can use File.open method to create a new file object and assign that file object to a file
  
• File.open method can be associated with a block, whereas you cannot do the same using the File.new method
• There are many methods that can be used to perform action on file like readline , write, readlines, read_char, read_byte etc

File.open(“filename”, “mode”) do |file|
  # process files
end

• All files are contained within various directories, and Ruby has no problem handling these too. Whereas the File class handles files, directories are handled with the Dir class.

Dir.pwd # gives current directory

Dir.chdir(“path”) # change current directory to specified path

Dir.entries(“path”) # gives list of entries in given path

Dir.mkdir “path” #creates directory specified in path

• https://www.ruby-lang.org/en/documentation/quickstart/
  
• https://www.ruby-lang.org/en/documentation/ruby-from-other-languages/
  

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• Email id: datt@cart91.com
• Phone: 8446353453