Java/C3/Java-Interfaces/English-timed

Time	Narration
00:01	Welcome to the Spoken Tutorial on Java Interfaces
00:05	In this tutorial we will learn about: Creating an interface
00:10	Creating an Implementation classes and Usage of Interface
00:16	For this tutorial, I am using Ubuntu 12.04 JDK 1.7 and Eclipse 4.3.1
00:28	To follow this tutorial, you should have knowledge of basics of Java and Eclipse IDE.
00:36	You should also have the knowledge of subclassing and Abstract classes in Java.
00:42	If not, for relevant Java tutorials, please visit the link shown.
00:48	First let's understand what is an interface.
00:52	An Interface contains a set of abstract methods and static data members.
00:58	It defines the signatures of a set of methods without the body.
01:04	It is declared using the interface keyword.
01:08	Now we will switch to Eclipse and create a new project called InterfaceDemo.
01:15	Here we will create the necessary classes and interface to demonstrate the usage of interfaces.
01:24	Right click on src folder and click New-> Interface.
01:30	Type the name as Animal and press Enter.
01:34	Note that the “interface” keyword is used for defining an interface.
01:39	Now type the code as displayed on the screen
01:43	Here the the interface name is Animal.
01:46	It contains three abstract methods talk(), see() and move().
01:52	All such methods in an interface are implicitly public and abstract.
01:59	An interface can also contain constant variable declarations.
02:04	Here, the constant string value “Mammal” is assigned to the variable “type1”.
02:12	And “Reptiles” is assigned to the variable “type2”.
02:16	All constant values defined in an interface are implicitly public, static and final.
02:25	Next we will see implementation class for an interface with an example.
02:32	Here Human is a class which implements the Animal interface.
02:38	So it must provide implementations for the methods talk(), see() and move().
02:45	A class can also implement multiple interfaces.
02:49	As shown in the example, the class Human implements two interfaces Animal and Action.
02:57	Note that a comma operator used in the syntax is to identify the different interfaces.
03:04	Now this class should provide implementations to all the abstract methods in both Animal and Action interfaces.
03:13	The figure here represents an implement relation.
03:18	The Animal class is an interface.
03:22	The Human and Snake classes are the two implementation classes.
03:28	The Human class provides its own different implementations for talk(), see() and move() methods.
03:36	And the Snake class provides its own different implementations for talk(), see() and move() methods.
03:45	Let us understand the usage of interfaces with a sample program.
03:50	Right click on the default package and create a class called Human.
03:56	Now, to make this an implementation class of Animal, type implements Animal
04:04	Now we can see an error comes up in the Eclipse IDE.
04:09	This error indicates that, we should provide an implementation to the Animal interface.
04:15	Let us see how to rectify this error.
04:19	Now let us define the methods talk(), see() and move().
04:23	So type public void talk( ) within curly brackets type System.out.println within quotes I am a human and I belong to
04:37	Now we can use the value of the static, final variable type1 declared in the Animal interface
04:45	So type, + Animal.type1+ within quotes family semicolon.
04:54	Let us now implement the see() method.
04:57	So type public void see( ) within curly brackets type System.out.println within quotes I can see all colors semicolon
05:11	We should also define the move() method.
05:14	So type public void move( ). within curly brackets type System.out.println within quotes I move by walking semicolon
05:29	Note that the error disappears, once all the methods are implemented.
05:34	Next we will see how to define the Snake class.
05:38	I have already created it in my project.
05:42	Please create the snake class in your project and type the following code as displayed on the screen.
05:49	Now let us go through the code.
05:52	We can see that all the methods of the Animal interface talk() , see() and move() are implemented inside this class.
06:01	Here the talk() method prints “I am a snake and I belong to”
06:07	Then the value of Animal.type2 is to be printed and then “family”
06:13	Here the see() method prints “I can see only in black and white”
06:19	The move() method prints "I move by crawling"
06:23	Note that the Human class has its own implementations of talk(), see() and move() methods.
06:31	And the Snake class has its own implementations of talk(), see() and move() methods.
06:39	Now right click on the default package click new-> class and then type the name as Demo.
06:47	Inside this class we will have the main method,
06:51	So type main and then press ctrl+space to generate the main method.
06:58	Type the following code as displayed on the screen.
07:01	In this line we instantiate the Human class using the Animal interface.
07:07	This is represented as Animal h equals new Human();
07:14	Now we can invoke the different methods using this object as h.talk(), h.see(); h.move();
07:26	Next, we instantiate the Snake class using the Animal interface
07:31	Now we can invoke the different methods using this object as shown
07:38	Now let us run this Demo program.
07:41	So right click on the class Demo and then select Run as -> Java Application
07:48	We can see the output
07:52	These are printed by the talk(), see() and move() methods invoked using the human class object h
08:00	These are printed by the talk(), see() and move() methods invoked using the Snake class object s
08:08	Now let us explore the differences between an interface and an abstract class.
08:14	All the methods in an interface should be abstract.
08:18	Within interface there should not be any constructors
08:23	concrete methods, static methods and main method
08:28	But an abstract class can have all these inside it.
08:32	The variables in an interface should be static and final.
08:38	There are no such restrictions for an abstract class.
08:43	This brings us to the end of this tutorial. Let us summarize.
08:48	In this tutorial we have learnt about - Creating an Interface
08:53	Creating an implementation class and
08:56	Usage of interfaces
08:59	As an assignment Create an interface Vehicle which contains the methods brake() and run()
09:07	Create another interface Fuel which contains the following methods. fill(String type,int quantity) , pay(int quantity,int price)
09:19	Create a subclass Car which implements both interfaces Vehicle and Fuel.
09:26	Here brake method should print ”Car Applies Power brake”
09:30	And the run method must print ”Car is running on 4 wheels”
09:35	Similarly fill() method can print the type and quantity of the fuel filled.
09:41	For example: 10 Litres of Petrol.
09:44	pay() method can be used to print price to be paid. For example: Pay Rs. 640
09:53	Create another subclass Bike which again implements both the interfaces Vehicle and Fuel
10:00	Here brake method can print ”Bike Applies hand brake”
10:05	And the run method can print “Bike is running on 2 wheels”
10:10	Next implement the fill() and pay() methods as explained earlier.
10:15	Finally create a Demo class containing the main method to verify the results.
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10:52	This script has been contributed by: Deptartment of Information Technology, Amal Jyothi College of Engineering
11:01	This is Priya from IIT Bombay signing off. Thanks for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14