Ruby/C3/Object-Oriented-Programming-Methods/English-timed

Time	Narration
00:01	Welcome to this spoken tutorial on Object Oriented Programming – Methods in Ruby.
00:07	In this tutorial, we will learn to use:
00:09	* instance methods
00:11	* class methods
00:14	* accessor methods.
00:15	Here, we are using: Ubuntu version 12.04
00:19	* Ruby 1.9.3
00:22	To follow this tutorial, you must have a working Internet connection.
00:27	You must also have knowledge of Linux commands, Terminal and Text-editor.
00:31	If not, for relevant tutorials, please visit our website.
00:36	Before we begin, recall that we had created “ttt” directory earlier.
00:41	Let's go to that directory.
00:44	Then to ruby-tutorial.
00:47	Create a directory named oop-methods and cd into it.
00:54	What are Instance methods?
00:56	Instance methods are those methods that are available to all instances of the class.
01:03	Earlier we had studied how to create objects or instances of a class.
01:09	Create a new file in gedit as shown in the basic level Ruby tutorials.
01:14	Name it instance_methods.rb.
01:19	I have a working example of implementing instance methods.
01:24	You can pause the tutorial and type the code as we go through it.
01:29	I have defined a class named Product in this example.
01:33	I have called an initialize method to initialize the instance variables, "name" and "price".
01:41	I have also defined instance methods named "name" and "price".
01:47	Each of them return instance variables "name" and "price" respectively.
01:54	Instance methods are defined just like normal methods.
01:58	Earlier we had studied how to create methods in Ruby.
02:02	Shortly, we will see how these methods will be available to all instances.
02:07	Now, let us implement the logic we have.
02:11	Here, I have initialized a Product object and named it as "product_object_1".
02:18	I have initialized it with a name value and a price value.
02:24	The initializer block passes the values to the instance variables "@name" and "@price".
02:31	Now, this product instance or object can use the instance methods name and price.
02:37	On invoking these methods, we get the values stored in the instance variables.
02:43	Now, let us execute this code.
02:46	Switch to the terminal and type: ruby instance_methods.rb and press Enter to see the output.
02:56	You will see that it will print the values you initialized the object with.
03:02	Namely, "laptop" and "35,000".
03:07	Next, initialize another instance or object.
03:12	Let us name this object product_object_2.
03:18	This time, let us give a different set of values for name and price.
03:23	Now, let us call the instance methods- "name" and "price" for this object.
03:35	Next, let us switch back to the terminal and execute the code like before.
03:41	You will notice that it executes successfully and it prints out the new values.
03:48	This proves that instance methods are available to all objects of the class Product.
03:55	You should now be able to write your own instance methods.
03:59	Next, let us look at what class methods are.
04:04	Class methods are methods available only to the class.
04:09	These methods are not available to instances of the class.
04:14	There are different ways you can define class methods.
04:16	Let us look at an example.
04:18	Create a new file in gedit as shown in the basic level Ruby tutorials.
04:24	Name it class_methods.rb.
04:28	I have a working example of class methods.
04:32	You can pause the tutorial and type the code as we go through it.
04:36	I have defined a Product class like before.
04:40	I have also called an initializer, like before.
04:44	However, this time I have added an extra argument called description.
04:48	I am also using class variables to hold the values, unlike instance variables earlier.
04:55	This class will demonstrate to you the 3 different ways one can define class methods.
05:01	Checkout the class method declaration for name.
05:06	Here, it is defined using the class name "Product".
05:10	Then, checkout the second class methods declaration.
05:14	Here I have used the "self" keyword.
05:18	Next, checkout the third way you can define class methods.
05:23	Now let us implement these class methods.
05:27	Let us first initialize an object of Product, like before.
05:32	This time we are also giving a value for the description.
05:37	Now, let us invoke the class methods as shown here.
05:42	Now, let us execute the code and inspect the output.
05:47	Switch to the terminal and execute the code like before.
05:54	You will notice that it will print the values for name, price and description.
05:59	Now, you should be able to write your own class methods.
06:03	Next we shall see what accessor methods are.
06:07	Ruby uses accessor methods to access data, defined within classes.
06:13	Accessor methods comprise of setter methods and getter methods.
06:18	Setter methods set the values.
06:22	Getter methods get those values.
06:24	Ruby uses the word attr_accessor to declare these methods.
06:31	Let us look at an example of accessor methods.
06:35	Create a new file in gedit as shown in the basic level Ruby tutorials.
06:39	Name it accessor_methods.rb
06:43	I have a working example of implementing accessor methods.
06:47	You can pause the tutorial and type the code as we go through it.
06:52	I have defined a class named Product, in this example.
06:56	I have declared attr_accessor for 'name' and 'price'.
07:01	That is all that is required to use these types of methods.
07:05	Now let us put it to action.
07:07	I have initialized a Product object.
07:10	Then, I have set the name and price of the product object.
07:14	This is possible because the attr_declaration, by default, creates methods for setting values.
07:22	I have then attempted to print the values using the getter methods for 'name' and 'price'.
07:28	These getter methods were also generated by the declaration of attr_accessor.
07:35	Now let us execute the code like before.
07:40	You will notice that it prints the values that were set.
07:44	By now, you should be able to write your own accessor methods.
07:50	One thing to note is that accessor methods are, by default, instance methods.
07:55	Thus they can be accessed by different instances of the class Product.
08:00	In this tutorial, we have learnt about: instance methods, class methods and accessor methods.
08:06	As an assignment: define a class named Temperature.
08:10	Write an instance method using Ruby's accessor method syntax.
08:15	This method should calculate the Celsius for the given Fahrenheit.
08:20	Watch the video available at the following link.
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08:26	If you do not have good bandwidth, you can download and watch it.
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09:03	This is Anjana Nair, signing off. Thank you.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14