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Revision as of 11:02, 18 August 2014


Time Narration
00:01 Welcome to this spoken tutorial on Object Oriented Concept in Ruby.
00:06 In this tutorial we will learn to use-
00:08 classes
00:09 creating objects
00:10 different ways of defining methods in Ruby
00:13 Here we are using
00:14 Ubuntu version 12.04
00:16 Ruby 1.9.3
00:19 To follow this tutorial, you must have knowledge of Linux commands, Terminal and Text-editor.
00:24 If not, for relevant tutorials, please visit our website.
00:28 Before we begin, recall that we had created a “ttt” directory earlier.
00:33 Let's go to that directory.
00:35 To ruby hyphen tutorial and classes directory.
00:41 Ruby is an object oriented language.
00:44 Everything in Ruby is an object; from a value to a string or number.


00:49 A class' is a collection of related data and functions.
00:53 It can serve to keep information organized.
00:56 An object is an instantiation of a class.
01:00 A class definition begins with the keyword class.
01:05 It is followed by the name of the class.
01:08 It is delimited with an “end”.


01:11 Let us look at an example of a class.
01:14 class Product
01:16 ruby code
01:17 end
01:20 The name of the class must begin with a capital letter.
01:24 Names that contain more than one word should be camelcased.
01:28 For example,
01:30 UserInformation
01:32 ProductInformation
01:34 The subsequent file names will have underscore separating the words:


01:37 user underscore information
01:40 product underscore information
01:45 Create a new file in gedit as shown in the basic level Ruby tutorials.
01:48 Name it class_definition.rb
01:52 I have a working example of the implementation of classes.
01:57 You can pause the tutorial, and type the code as we go through it.
02:02 I have defined a class named Order in this example.
02:05 Now let us make the class useful by adding some variables.
02:11 Then I have defined an instance variable “myinstance”.
02:15 And I have assigned a value to it.
02:18 I have also defined a class variable “myclassvar”
02:21 And I have assigned a value to it.
02:24 Now let us add some code that will make use of this class.
02:30 Type puts Order dot instance underscore variables.


02:36 Before this line, add puts some characters slash n for a new line.
02:43 Let us copy and paste that and add it just below the line we added and save it.
02:51 Now let us execute this code
02:53 Switch to the terminal and type
02:56 ruby space class underscore definition dot rb
03:02 and see the output.
03:05 You will see the instance variable you defined.
03:09 Now let us type puts Order dot class underscore variables.
03:15 Let us copy and paste the demarcation, just below the line and save it.
03:21 Now let us switch to the terminal and execute the file like before.
03:26 You will notice the class variable you defined, also show up.
03:32 To now be able to write your own class.
03:35 Next, let us look at what an object is.
03:40 An object is an instance of a class.
03:43 Which means an object is created from a class.
03:46 An object will have the properties and methods defined in the class.
03:52 How do you declare an object
03:54 We declare an object of a class using the new keyword.


03:58 Here we are declaring an object of the Product class.
04:02 Here an object gets created.
04:05 product = Product.new
04:09 This process is called initialization of an object.
04:12 This object is of type: Product.


04:16 Now let is look at what an “initialize” method is.
04:20 An initialize method is called at the time of object creation.


04:26 On calling new on an object, we invoke the initialize method.
04:31 An initialize method may take a list of parameters.
04:37 Like other Ruby methods, it is preceded by the “def” keyword.
04:43 Let us look at an example.
04:46 Create a new file in gedit as shown in the basic level Ruby tutorials.
04:50 And name it object undescore initialize dot rb
04:55 I have a working example of the object initialization code.
05:00 You can pause the tutorial, and type the code as we go through it.
05:04 Here I have defined a class called “Order”
05:08 Then I have defined the initialize method, with no argument.
05:13 I have defined a puts method to display the message “I have created an object”.
05:20 Next, I have defined Order dot new.
05:24 This will invoke the initialize method.
05:27 Switch to the terminal and type
05:31 ruby space object underscore initialize dot rb
05:36 and see the output.
05:39 You will see the message “I have created an object” .
05:43 Now let us go back to gedit and add an argument to the method.
05:48 Let us modify the puts .
05:51 It should display the value of the argument passed.
05:55 Next let us type
05:56 Order dot new(“I have created an object”).
06:04 Here we have given an argument to the new method.
06:08 This argument gets passed on to the initialize method.
06:13 Switch to the terminal and type
06:16 ruby space object underscore initialize dot rb
06:20 and see the output.
06:22 You will see the message “I have created an object” printed out.
06:29 Now, you would have understood what object initialization means.
06:33 Recall that in Ruby, methods are the functions that a class performs.
06:39 Each method in a class is defined within the “def” and “end” block.


06:45 A multiword method name is separated with an underscore.
06:48 Some of the characters that can be appended to a method name are:
06:54  ? (question-mark)
06:56 = (equal to)
06:58 Each of the characters add some meaning to the method.
07:02 Let us look at some examples.


07:05 Create a new file in gedit as shown in the basic level Ruby tutorials.
07:09 And name it class underscore methods dot rb.
07:14 I have a working example of class methods code.
07:17 You can pause the tutorial, and type the code as we go through it.
07:21 Here I have defined a class named “Animal”.
07:23 Then I have two methods “breathe” and “walk”.
07:28 They are both defined with the “def” and “end” keywords.
07:32 I have then initialized the object Animal.
07:36 I have assigned it to a variable called “animal” with lowercase “a”.
07:40 Then I have invoked the methods “breathe” and “walk” consequtively.
07:48 Now let us execute the program.
07:51 Switch to the terminal and type
07:53 ruby space class underscore methods dot rb
07:58 and see the output.
08:00 You will notice the lines:
08:02 “ I breathe”
08:03 “ I walk”
08:04 printed out.
08:05 This is because you have invoked the two methods “breathe” and “walk”.


08:10 A “puts” statement defined within these methods gives the results you see.
08:16 Next, let us look at how to create methods with a trailing question mark.
08:21 Create a new file in gedit as shown in the basic level Ruby tutorials.
08:25 And name it class underscore methods underscore with underscore trailing underscore characters dot rb
08:35 I have a working example of class methods with question mark code.
08:40 You can pause the tutorial, and type the code as we go through it.
08:45 Here I have taken the same class as before as an example.
08:48 Here the breathe method has a trailing “question mark (?)”.
08:52 Such methods are generally used to return boolean values.


08:55 This is based on the method naming convention of Ruby.
09:00 The method gets invoked by declaring animal dot breathe question-mark
09:06 Switch to the terminal and type
09:09 ruby space class underscore methods underscore with underscore trailing underscore characters dot rb and see the output.


09:22 You will notice the output as : “true”


09:26 Next, let us define another method called “walk”.
09:30 Let us place an equal-to sign “=(value)” beside it.
09:36 Let us invoke this method by calling animal dot walk.
09:41 Then let us execute this method.
09:44 Switch to the terminal and type
09:45 ruby class underscore methods underscore with underscore trailing underscore characters dot rb


09:52 and see the output.
09:56 It will give an “undefined method” error.
09:59 This is because the equal to sign has another meaning.
10:03 It is used to assign a value to a method.
10:08 So, let us invoke the method a little differently this time.
10:13 Type puts animal dot walk equal to “ hops”
10:17 Now let give it another try.
10:20 Switch to the terminal and run the command like before and see the output.
10:27 You will notice that the word “hops” get printed.
10:30 This demonstrates that the equal to sign next to a method means assignment.
10:36 Now you should be able to write your own methods.
10:42 In this tutorial we have learnt-
10:44 How to declare classes
10:46 How to create objects of a class
10:48 Different ways of defining methods in Ruby
10:52 As an assignment:
10:54 Define a class Product
10:56 Define methods that you can use to get values of “myvar” and set values for “myvar”.
11:01 To set values, define the method using “=” sign.
11:05 Instantiate the object of the class and set and get values using the above 2 methods.


11:12 Watch the video available at the following link.
11:14 It summarises the Spoken Tutorial project.
11:18 If you do not have good bandwidth, you can download and watch it.
11:22 The Spoken Tutorial Project Team :
11:24 Conducts workshops using spoken tutorials
11:27 Gives certificates to those who pass an online test
11:30 For more details, please write to contact@spoken-tutorial.org
11:36 Spoken Tutorial Project is a part of the Talk to a Teacher project.
11:39 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
11:46 More information on this Mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro
11:56 This is Anjana Nair signing off. Thank you

Contributors and Content Editors

Jyotisolanki, PoojaMoolya, Pratik kamble, Sandhya.np14, Shruti arya

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