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 Creating an Implementation class and Usage of Interfaces
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	A class can implement an interface using the implements keyword.
01:13	A class can implement more than one interface.
01:17	All the abstract methods defined in the interface or interfaces must be implemented in such classes.
01:25	Now let us explore the differences between an interface and an abstract class.
01:32	All the methods in an interface should be abstract.
01:36	Within interface there should not be any constructors concrete methods static methods and main method
01:46	But an abstract class can have all these inside it.
01:50	The variables in an interface should be static and final.
01:55	There are no such restrictions for an abstract class.
02:01	Next we will see an example for an interface.
02:06	Here the interface name is Animal. It contains three abstract methods talk(), see() and move().
02:15	All such methods in an interface are implicitly public and abstract.
02:21	An interface can also contain constant variable declarations.
02:27	Here, the constant string value “Mammal” is assigned to the variable “type1”.
02:34	And “Reptiles” is assigned to the variable “type2”.
02:39	All constant values defined in an interface are implicitly public, static and final.
02:47	Next, we will see how to create an implementation class for an interface with an example.
02:55	Here Human is a class which implements the Animal interface.
03:00	So it must provide implementations for the methods talk(), see() and move().
03:07	A class can also implement multiple interfaces.
03:12	As shown in the example, the class Human implements two interfaces Animal and Action.
03:19	Note that a comma operator used in the syntax is to identify the different interfaces.
03:27	Now this class should provide implementations to all the abstract methods in both Animal and Action interfaces.
03:36	The figure here represents an implements relation.
03:41	The Animal class is an interface.
03:44	The Human and Snake classes are the two implementation classes.
03:50	The Human class provides its own different implementations for talk(), see() and move() methods.
03:59	And the Snake class provides its own different implementations for talk(), see() and move() methods.
04:08	Let us understand the usage of interfaces with a sample program.
04:13	Now we will switch to Eclipse and create a new project called InterfaceDemo.
04:21	Here we will create the necessary classes and interface to demonstrate the usage of interfaces.
04:28	Now, right click on src folder and click new-> interface.
04:35	Type the name as Animal and press Enter.
04:39	Note that the “interface” keyword is used for defining an interface.
04:45	Now type the code as displayed on the screen.
04:48	Next let us create the implementation classes.
04:53	Right click on the default package and create a class called Human.
04:59	Now to make this an implementation class of Animal, type implements Animal.
05:06	Now we can see, an error comes up in the Eclipse IDE.
05:11	This error indicates that, we should provide an implementations to the Animal interface.
05:17	Let us see how to rectify this error.
05:21	Now let us define the methods talk(), see() and move().
05:26	So type public void talk( ) Within curly brackets type System.out.println within quotes I am a human and I belong to
05:39	Now we can use the value of the static, final variable type1 declared in the Animal interface
05:47	So type + Animal.type1+ within quotes family semicolon.
05:56	Let us now implement the see() method. So type public void see( ) Within curly brackets type System.out.println within quotes I can see all colors semicolon
06:13	We should also define the move() method
06:17	So type public void move( ) Within curly brackets type System.out.println within quotes I move by walking semicolon
06:31	Note that the error disappears, once all the methods are implemented.
06:36	Next we will see how to define the Snake class.
06:40	I have already created it in my project. Please create the snake class in your project and type the following code as displayed on the screen.
06:51	Now let us go through the code.
06:55	We can see that all the methods of the Animal interface talk(), see() and move() are implemented inside this class.
07:04	Here the talk() method prints “I am a snake and I belong to. Then the value of Animal.type2 is to be printed and then “family”
07:16	Here the see() method prints “I can see only in black and white”
07:21	The move() method prints "I move by crawling"
07:26	Note that the Human class has its own implementations of talk(), see() and move() methods.
07:33	And the Snake class has its own implementations of talk(), see() and move() methods.
07:41	Now right click on the default package click new-> class and then type name as Demo.
07:49	Inside this class, we will have the main method, So type main and then press ctrl+space to generate the main method.
08:00	Type the following code as displayed on the screen. In this line, we instantiate the Human class using the Animal interface.
08:09	This is represented as Animal h equals new Human();
08:16	Now we can invoke the different methods using this object as h.talk() h.see(); h.move();
08:28	Next, we instantiate the Snake class using the Animal interface.
08:33	This is represented as Animal s equals new Snake()
08:39	Now we can invoke the different methods using this object as s.talk(); s.see(); s.move();
08:50	Now let us run this Demo program. So right click on the class Demo and then select Run as -> Java Application.
09:01	We can see the output as I am a human and I belong to Mammal family
09:07	I can see all colors and I move by walking
09:11	These are printed by the talk(), see() and move() methods invoked using the Human class object h.
09:19	We can also see in the output I am a snake and I belong to Reptiles family. I can see only in black and white and I move by crawling
09:30	These are printed by the talk(), see() and move() methods invoked using the Snake class object s.
09:39	This brings us to the end of this tutorial. Let us summarize.
09:44	In this tutorial we have learnt about Creating an Interface Creating an implementation class and Usage of interfaces
09:54	As an assignment Create an interface Vehicle which contains the methods brake() and run().
10:02	Create another interface Fuel which contains the following methods. fill(String type, int quantity) pay(int quantity, int price)
10:14	Create a subclass Car which implements both the interfaces Vehicle and Fuel.
10:21	Here brake method should print ”Car, Applies Power brake” and the run method should print ”Car is running on 4 wheels”.
10:30	Similarly fill() method can print the type and quantity of the fuel filled.
10:36	For example: 10 Litres of Petrol. pay() method can be used to print the price to be paid. For example: Pay Rs.640
10:48	Create another subclass Bike which again implements both the interfaces- Vehicle and Fuel.
10:56	Here brake method can print ”Bike, Applies hand brake” and the run method can print “Bike is running on 2 wheels”.
11:05	Next, implement the fill() and pay() methods as explained earlier.
11:11	Finally, create a Demo class containing the main method to verify the results.
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11:48	This script has been contributed by: Department of Information Technology, Amal Jyothi College of Engineering. This is Priya from IIT Bombay signing off. Thank you for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14