Java/C3/Java-Interfaces/English

Title of script: Java Interfaces

Author: Joms Antony

Keywords: Java Interfaces, Implementation Classes, implements keyword, abstract method, video tutorial, Java tutorial

Visual Cue	Narration
Slide 1:	Welcome to the Spoken Tutorial on Java Interfaces.
Slide 2: Learning Objectives	In this tutorial we will learn about: Creating an interface Creating an Implementation class and Usage of Interfaces
Slide 3: Software Requirements	For this tutorial, I am using Ubuntu 12.04 JDK 1.7 and Eclipse 4.3.1
Slide 4: Prerequisites	To follow this tutorial, you should have knowledge of basics of Java and Eclipse IDE. You should also have the knowledge of subclassing and Abstract classes in Java. If not, for relevant Java tutorials, please visit the link shown.
	First let's understand what is an interface.
Slide 5: What is an interface?	An Interface contains a set of abstract methods and static data members. It defines the signatures of a set of methods, without the body. It is declared using the interface keyword.
Slide 6: Implementing the interface	A class can implement an interface using the implements keyword. A class can implement more than one interface. All the abstract methods defined in the interface or interfaces must be implemented in such classes.
	Now let us explore the differences between an interface and an abstract class.
Slide 7: Interface Vs Abstract Classes	All the methods in an interface should be abstract. Within interface there should not be any constructors concrete methods static methods and main method But an abstract class can have all these inside it. The variables in an interface should be static and final. There are no such restrictions for an abstract class.
	Next we will see an example for an interface.
Slide 8: Interface: Example: Highlight the methods	Here the interface name is Animal. It contains three abstract methods talk(), see() and move(). All such methods in an interface are implicitly public and abstract. An interface can also contain constant variable declarations. Here, the constant string value “Mammal” is assigned to the variable “type1”. And “Reptiles” is assigned to the variable “type2”. All constant values defined in an interface are implicitly public, static and final.
	Next we will see how to create an implementation class for an interface with an example.
Slide 9: Implementation class: Example:	Here Human is a class which implements the Animal interface. So it must provide implementations for the methods talk(), see() and move().
Slide 10: Implementing multiple interfaces Example: Highlight the syntax and the usage of comma operator	A class can also implement multiple interfaces. As shown in the example, the class Human implements two interfaces Animal and Action. Note that a comma operator used in the syntax is to identify the different interfaces. Now this class should provide implementations to all the abstract methods in both Animal and Action interfaces.
Slide 11: Interface Usage - Example	The figure here represents an implements relation. The Animal class is an interface. The Human and Snake classes are the two implementation classes. The Human class provides its own different implementations for talk(), see() and move() methods. And the Snake class provides its own different implementations for talk(), see() and move() methods.
	Let us understand the usage of interfaces with a sample program.
In Ecilpse IDE a project called InterfaceDemo is created,	Now we will switch to Eclipse and create a new project called InterfaceDemo. Here we will create the necessary classes and interface to demonstrate the usage of interfaces.
The interface Animal is created in the src folder. Code is copied	Now, right click on src folder and click new-> interface. Type the name as Animal and press Enter. Note that the “interface” keyword is used for defining an interface. Now type the code as displayed on the screen.
	Next let us create the implementation classes.
Right click on the default package and create a class called Human. Type implements Animal	Right click on the default package and create a class called Human. Now to make this an implementation class of Animal, type implements Animal.
Point to the error message	Now we can see an error comes up in the Eclipse IDE. This error indicates that, we should provide an implementations to the Animal interface.
	Let us see how to rectify this error.
public void talk(){ System.out.println("I am a Human, I belong to the "+Animal.type1+" Family"); } public void see(){ System.out.println("I CAN SEE ALL COLORS "); } public void move(){ System.out.println("I MOVE BY WALKING"); }	Now let us define the methods talk(), see() and move(). So type public void talk( ) within curly brackets type System.out.println within quotes I am a human and I belong to Now we can use the value of the static, final variable type1 declared in the Animal interface So type + Animal.type1+ within quotes family semicolon. 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 We should also define the move() method So type public void move( ) within curly brackets type System.out.println within quotes I move by walking semicolon Note that the error disappears, once all the methods are implemented.
	Next we will see how to define the Snake class.
Show and highlight the code for Snake Class.	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. Now let us go through the code.
Highlight the code public void talk(){ System.out.println("I am a Snake, I belong to the "+Animal.type2+" Family"); } public void see(){ System.out.println("I CAN SEE ONLY IN BLACK AND WHITE"); } public void move(){ System.out.println("I MOVE BY CRAWLING"); }	We can see that all the methods of the Animal interface talk() , see() and move() are implemented inside this class. 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” Here the see() method prints “I can see only in black and white” The move() method prints "I move by crawling"
Highlight the talk(), see() and move() methods of Human class Highlight the talk(), see() and move() methods of Snake class	Note that the Human class has its own implementations of talk(), see() and move() methods. And the Snake class has its own implementations of talk(), see() and move() methods
click new-> class and then type name as Demo.	Now right click on the default package click new-> class and then type name as Demo. Inside this class we will have the main method, So type main and then press ctrl+space to generate the main method.
Highlight the code line by line Highlight the second line Animal h=new Human(); h.talk() h.see(); h.move();	Type the following code as displayed on the screen. In this line, we instantiate the Human class using the Animal interface. This is represented as Animal h equals new Human();. Now we can invoke the different methods using this object as h.talk() h.see(); h.move();
Highlight the code Animal s =new Snake(); s.talk(); s.see(); s.move();	Next, we instantiate the Snake class using the Animal interface. This is represented as Animal s equals new Snake(). Now we can invoke the different methods using this object as s.talk(); s.see(); s.move();
	Now let us run this Demo program.
Right click on the class Demo and then select Run as -> Java Application	So right click on the class Demo and then select Run as -> Java Application.
Highlight code and the output	We can see the output as I am a human and I belong to Mammal family I can see all colors and I move by walking These are printed by the talk(), see() and move() methods invoked using the Human class object h.
Highlight code and the output	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 These are printed by the talk(), see() and move() methods invoked using the Snake class object s.
	This brings us to the end of this tutorial. Let us summarize.
Slide 10: Summary	In this tutorial we have learnt about Creating an Interface Creating an implementation class and Usage of interfaces
Slide 11: Assignment	As an assignment Create an interface Vehicle which contains the methods brake() and run(). Create another interface Fuel which contains the following methods. fill(String type, int quantity) pay(int quantity, int price)
Assignment	Create a subclass Car which implements both the interfaces Vehicle and Fuel. Here brake method should print ”Car Applies Power brake” and the run method should print ”Car is running on 4 wheels”.
Assignment	Similarly fill() method can print the the type and quantity of the fuel filled. For example: 10 Litres of Petrol pay() method can be used to print the price to be paid. For example: Pay Rs.640
Assignment	Create another subclass Bike which again implements both the interfaces Vehicle and Fuel. Here brake method can print ”Bike Applies hand brake” and the run method can print “Bike is running on 2 wheels”
	Next, implement the fill() and pay() methods as explained earlier. Finally create a Demo class containing the main method to verify the results.
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Contributor slide	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

Nancyvarkey, Priyacst