Difference between revisions of "Java/C3/Java-Interfaces/English-timed"

| Welcome to the''' Spoken Tutorial''' on''' Java Interfaces.'''

| In this tutorial we will learn about:

* Creating an''' interface'''

* Creating an''' Implementation class''' and

* Usage of''' Interfaces'''

| For this tutorial, I am using

| 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'''.

| 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

 

| 01:46

| But an''' abstract class''' can have all these inside it.

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| 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().'''

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| 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.'''

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| So it must provide implementations for the '''methods talk(), see()''' and''' move().'''  

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| A '''class''' can also implement''' multiple interfaces'''.

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| As shown in the example, the''' class Human '''implements two''' interfaces Animal''' and''' Action.'''

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| 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.'''

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| The''' Human '''and''' Snake classes''' are the two '''implementation classes'''.

| The '''Human class''' provides its own different implementations for''' talk(), see()''' and''' move() methods.'''

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| 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'''.

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| Here we will create the necessary''' classes''' and''' interface''' to demonstrate the usage of''' interfaces.'''

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| Now, right click on''' src''' folder and click''' new-> interface'''.

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| Type the name as''' Animal''' and press '''Enter'''.

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| 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'''

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| 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'''

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| We should also define the''' move() method'''

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| So type''' public void move( )''' Within curly brackets type '''System.out.println''' within quotes''' I move by walking semicolon'''

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| Note that the error disappears, once all the '''methods''' are implemented.

| 06:36

| Next we will see how to define the''' Snake class.'''

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| 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.

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| Now let us go through the code.

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| We can see that all the '''methods''' of the''' Animal interface talk(), see()''' and''' move()''' are implemented inside this '''class'''.

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| 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”'''

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| Here the''' see() method''' prints “'''I can see only in black and white”'''

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| The''' move() method''' prints''' "I move by crawling"'''

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| Note that the''' Human class''' has its own implementations of''' talk(), see()''' and''' move() methods'''.

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| And the''' Snake class''' has its own implementations of''' talk(), see()''' and''' move() methods'''.

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| Now right click on the '''default package''' click''' new-> class''' and then type name as''' Demo.'''

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| Inside this '''class''', we will have the''' main method''', So type''' main''' and then press ctrl+space to generate the''' main method.'''

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| Type the following code as displayed on the screen. In this line, we instantiate the''' Human class''' using the''' Animal interface.'''

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| This is represented as '''Animal h equals new Human();'''

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| Now we can invoke the different '''methods''' using this object as

'''h.talk()'''

'''h.see();'''

'''h.move();'''

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| Next, we instantiate the''' Snake class''' using the''' Animal interface.'''

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| This is represented as '''Animal s equals new Snake()'''

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| 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.'''

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| We can see the output as '''I am a human and I belong to Mammal family'''

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| '''I can see all colors''' and '''I move by walking'''

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| 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.

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| 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)'''

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| 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”.'''

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| 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.

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| 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”'''.

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| Next, implement the '''fill()''' and '''pay() methods''' as explained earlier.

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| Finally, create a '''Demo class''' containing the '''main method''' to verify the results.

| 11:16

| The video at the following link summarizes the''' '''Spoken Tutorial Project. Please download and watch it.

| 11:25

| The Spoken Tutorial Project Team

| 11:34

| For more details, please write to us.

| 11:37

| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

 

| 11:48

| This script has been contributed by:

 

 

This is Priya from IIT Bombay signing off. Thank you for joining.