Nancyvarkey at 10:06, 12 March 2014

2014-03-12T10:06:05Z

Arya Ratish: Created page with ''''Title of script''': Subclassing and Method overriding '''Author: arya ''' '''Keywords: '''subclassing, extends keyword, overriding, method overriding, Java, Eclipse IDE, vid…'

2014-03-12T07:33:50Z

Created page with ''''Title of script''': Subclassing and Method overriding '''Author: arya ''' '''Keywords: '''subclassing, extends keyword, overriding, method overriding, Java, Eclipse IDE, vid…'

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'''Title of script''': Subclassing and Method overriding

'''Author: arya '''

'''Keywords: '''subclassing, extends keyword, overriding, method overriding, Java, Eclipse IDE, video tutorial

{| style="border-spacing:0;"
| style="border:1pt solid #000000;padding:0.097cm;"| <center>'''Visual Cue'''</center>
| style="border:1pt solid #000000;padding:0.097cm;"| <center>'''Narration'''</center>

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 1'''
| style="border:1pt solid #000000;padding:0.097cm;"| Welcome to the spoken-tutorial on''' Subclassing and Method overriding.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 2'''
| style="border:1pt solid #000000;padding:0.097cm;"| In this tutorial we will learn about :

* '''subclassing'''
* '''extends '''keyword and
* '''method overriding'''

|-
| style="border:1pt solid #000000;padding:0.106cm;"| '''Slide 3'''

'''Software Requirements'''
| style="border:1pt solid #000000;padding:0.106cm;"| Here we are using

* '''Ubuntu''' '''Linux '''version 12.04
* '''JDK '''1.7
* '''Eclipse '''4.3.1

|-
| style="border:1pt solid #000000;padding:0.106cm;"| '''Slide 4'''

'''Prerequisites'''
| style="border:1pt solid #000000;padding:0.106cm;"| To follow this tutorial, you must have knowledge of

'''basics of Java and Eclipse IDE.'''

If not, for relevant '''Java '''tutorials, please visit our website.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 5'''

'''Subclassing'''
| style="border:1pt solid #000000;padding:0.097cm;"| First of all, we will learn what '''subclassing '''is.

* It is a way to create a new '''class''' from an existing '''class.'''

* The new class created is called '''subclass '''or''' derived class '''or''' child class.'''

* The already existing class is called '''superclass '''or''' base class '''or''' parent class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Go to the '''Eclipse''' '''IDE.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let me show you how to create a '''sub-class. '''

So, go to the '''Eclipse''' '''IDE.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''Employee class.'''

'''public class Employee {'''
| style="border:1pt solid #000000;padding:0.097cm;"| I have already created a '''class '''called '''Employee.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''variables'''.

'''public String name<nowiki>="";</nowiki>'''

'''public String email_address<nowiki>;</nowiki>'''
| style="border:1pt solid #000000;padding:0.097cm;"| It has '''variables name '''and '''email_address.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''setter '''and '''getter methods.'''

'''public void setName(String newName) {'''

''' name<nowiki>=</nowiki>newName<nowiki>;</nowiki>'''

'''}'''

'''public String getName() {'''

''' return name<nowiki>;</nowiki>'''

'''}'''

'''public void setEmail(String newEmail) {'''

''' email_address<nowiki>=</nowiki>newEmail<nowiki>;</nowiki>'''

'''}'''

'''public String getEmail() {'''

''' return email_address<nowiki>;</nowiki>'''

'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| It also has the '''setter '''and '''getter methods '''for the '''class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''method getDetails().'''

'''public String getDetails() '''

'''{'''

''' '''

'''return("Name: " + getName() + "\n" + "Email: " + getEmail());'''

'''}'''

''' '''

'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| It has a '''method getDetails().'''

This '''method '''returns the '''name '''and''' email_address.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''Manager class.'''

'''public class Manager {'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us come to the '''class '''called '''Manager.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''variables.'''

'''public String name<nowiki>="";</nowiki>'''

'''public String email_address<nowiki>;</nowiki>'''

'''public String department<nowiki>="";</nowiki>'''
| style="border:1pt solid #000000;padding:0.097cm;"| It has '''variables name, email_address '''and '''department.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight '''name and email_address '''in both the '''Employee '''and '''Manager class.'''

'''public String name<nowiki>="";</nowiki>'''

'''public String email_address<nowiki>;</nowiki>'''
| style="border:1pt solid #000000;padding:0.097cm;"| We can see that some '''variables''' are common to both '''Employee '''and '''Manager class.'''

'''name '''and''' email_address '''are there in '''Employee class.'''

We can see that its also there in '''Manager class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Thus, '''Manager class '''can be made a '''subclass''' of '''Employee class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| For that, we have to make some changes in the '''Manager class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Type '''public class Manager extends Employee{'''
| style="border:1pt solid #000000;padding:0.097cm;"| After '''public class Manager, '''type '''extends Employee.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''extends keyword.'''
| style="border:1pt solid #000000;padding:0.097cm;"| We use the '''extends keyword '''to create a '''subclass '''from an existing '''class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Remove '''name, email_address '''from '''Manager class.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Remove the duplicate '''variables '''common to both the '''classes.'''

So, remove '''name '''and''' email_address '''from '''Manager class.'''

Also remove '''setter '''and '''getter methods '''of the same.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight '''variable department.'''
| style="border:1pt solid #000000;padding:0.097cm;"| In the '''class Manager, '''we will have only one '''variable department.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''setter '''and '''getter method.'''

'''public void setDepartment(String newDepartment) {'''

''' department<nowiki>=</nowiki>newDepartment<nowiki>;</nowiki>'''

'''}'''

'''public String getDepartment() {'''

''' return department<nowiki>;</nowiki>'''

'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| We also have the '''setter '''and '''getter method '''for '''department.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| In this way, the '''Manager class '''inherits the members of '''Employee class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| This way of extending one '''class '''from another is called '''single inheritance.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Open the '''class TestEmployee.'''

'''public class TestEmployee {'''
| style="border:1pt solid #000000;padding:0.097cm;"| I have also created another '''class '''named '''TestEmployee.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight '''object '''of the '''Manager class.'''

'''public static void main(String<nowiki>[] </nowiki>args) {'''

'''Manager manager = new Manager();'''
| style="border:1pt solid #000000;padding:0.097cm;"| Inside the '''main method, '''we will create the '''object '''of the '''Manager class.'''

So inside the '''main method''', type

'''Manager manager ''equal to''''' '''new Manager parentheses'''.''' '''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight

'''manager.setName("Nikkita Dinesh");'''

'''manager.setEmail("[mailto:abc@gmail.com abc][mailto:abc@gmail.com @][mailto:abc@gmail.com gmail][mailto:abc@gmail.com .][mailto:abc@gmail.com com]");'''

'''manager.setDepartment(“Accounts”);'''
| style="border:1pt solid #000000;padding:0.097cm;"| Next, we will call the '''setter methods '''of the '''Manager class.'''

So type,

'''manager ''dot ''setName ''within brackets and double quotes ''Nikkita Dinesh ''semicolon.'''''

Then type,

'''manager ''dot ''setEmail ''within brackets and double quotes ''[mailto:abc@gmail.com abc][mailto:abc@gmail.com @][mailto:abc@gmail.com gmail][mailto:abc@gmail.com .][mailto:abc@gmail.com com] ''semicolon.'''''

Then type,

'''manager ''dot ''setDepartment ''within brackets and double quotes ''Accounts ''semicolon.'''''

You can use any '''name, emailaddress''' and '''department'''.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Type

'''System.out.println(manager.getDetails());'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us call the '''getDetails() method '''using the '''Manager object.'''

So, type

'''System.out.println ''within brackets ''manager ''dot ''getDetails ''parentheses'''''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Run the program.
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us run the program.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output

'''Name: Nikkita Dinesh'''

'''Email: abc@gmail.com'''
| style="border:1pt solid #000000;padding:0.097cm;"| We can see that we get the '''output '''as ''':'''

'''Name: Nikkita Dinesh'''

'''Email: abc@gmail.com'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''println statement '''in '''TestEmployee class.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Here, the '''object '''of '''Manager class '''calls the '''getDetails() method.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Come to the '''Manager class.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, come to the '''Manager class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Point that there is no '''getDetails() method.'''
| style="border:1pt solid #000000;padding:0.097cm;"| We can see that there is no '''getDetails() method '''here.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''Manager class.'''
| style="border:1pt solid #000000;padding:0.097cm;"| But, we still got the output.

This is because, the '''Manager class extends '''the '''Employee class.'''

The '''Manager class '''automatically '''inherits '''the '''variables '''and '''methods '''of the '''Employee class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''getDetails() method '''in the '''Employee class.'''

Highlight the '''return statement.'''

| style="border:1pt solid #000000;padding:0.097cm;"| So it checks in the '''parent class '''which is '''Employee.'''

Let us come to the '''Employee class.'''

It finds the '''getDetails() method '''here.

Note that we have not returned the '''department.'''

As a result, it did not print the '''department '''in the '''output.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Change '''getDetails method '''to '''private.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us change the '''getDetails method '''here''' '''to '''private.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Point to the '''error.'''
| style="border:1pt solid #000000;padding:0.097cm;"| We can see that we get a compilation error in the '''TestEmployee class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| It says '''The method getDetails() from the type Employee is not visible.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| This means that '''getDetails() method '''cannot be accessed.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Come to the '''Employee class. '''Highlight '''getDetails() method.'''
| style="border:1pt solid #000000;padding:0.097cm;"| This is because we have declared '''getDetails() method '''as '''private.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 6'''

'''Private members in a superclass'''
| style="border:1pt solid #000000;padding:0.097cm;"| * A '''subclass''' does not inherit the private members of its '''superclass'''.
* '''Subclass '''cannot directly access the private members of the '''superclass.'''
* However, the superclass can have public or protected methods.
* These methods can access its private fields.
* Then the subclass can also access the private fields through these methods.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Change the '''getDetails() method '''from '''private '''to '''public.'''
| style="border:1pt solid #000000;padding:0.097cm;"| So, let us change it back to '''public.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us include '''method getDetails '''in the '''Manager class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Type

'''public String getDetails() '''

'''{'''

'''return ( "Name: " + getName() + "\n" + "Email: " +getEmail()+"\n"'''

'''+"Manager of: " + getDepartment());'''

'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| This '''method '''will return the '''name, email_address '''and '''department.'''

So type,

'''public String getDetails ''parentheses.'''''

Inside the method we will return '''name, email''' and '''department'''.

So type'' ''

'''return “Name:” ''plus ''getName() ''plus ''“Email:” ''plus ''getEmail() ''plus ''“Manager of:” ''plus ''getDepartment() '''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''method getDetails '''in both '''Employee '''and '''Manager class.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Note that now, we have the '''method getDetails '''in both '''Employee '''and '''Manager class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the '''method declaration '''in both the '''classes.'''

'''public String getDetails() '''
| style="border:1pt solid #000000;padding:0.097cm;"| The '''name, return type '''and '''argument list '''of the''' method '''is same in both the '''classes.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 7'''

'''Method overriding'''
| style="border:1pt solid #000000;padding:0.097cm;"| A''' method '''in the '''subclass '''is said to '''override '''the '''method '''in the '''parent class '''if:

* '''name'''
* '''return type'''
* '''argument list'''

matches exactly.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Come back to the '''IDE.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us come back to the '''IDE.'''

Come back to the '''Manager class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Type '''@Override.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Before, the '''getDetails() method '''type '''@Override.'''

This is an '''override''' '''annotation.'''

It''' '''indicates that a method is intended to '''override''' a '''method''' in '''superclass'''.

Now, let us see what an '''annotation '''is.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 8'''

'''Annotation'''
| style="border:1pt solid #000000;padding:0.097cm;"| '''Annotations:'''

* start with at sign character(@)
* provide data about a program
* have no direct effect on the operation of the code.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 9'''

'''@Override Annotation'''

| style="border:1pt solid #000000;padding:0.097cm;"| If a '''method '''is '''annotated '''with '''@Override compiler '''generates '''error message '''if:

* the''' method''' does '''override''' a '''method''' declared in a '''superclass'''.
* the '''method signature '''is different in its '''superclass.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Come back to the '''IDE.'''

Highlight the '''annotation.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us come back to the '''IDE.'''

Come back to the '''Manager class.'''

The '''at sign character '''indicates the compiler that what follows is an '''annotation.'''

Here, it shows that the '''getDetails method '''is '''overridden.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Come to the '''TestEmployee class.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Let us come to the '''TestEmployee class.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Right click on '''TestEmployee'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us '''run '''the '''program.'''

For that, right click on '''TestEmployee.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Click on '''Run As.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Then click on '''Run As.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Click on '''Java Application.'''
| style="border:1pt solid #000000;padding:0.097cm;"| Click on '''Java Application.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output.

'''Name: Nikkita Dinesh'''

'''Email:[mailto:abc@gmail.com abc][mailto:abc@gmail.com @][mailto:abc@gmail.com gmail][mailto:abc@gmail.com .][mailto:abc@gmail.com com]

'''Manager of:Accounts'''
| style="border:1pt solid #000000;padding:0.097cm;"| We get the '''output''' as follows.

'''Name: Nikkita Dinesh'''

'''Email:[mailto:abc@gmail.com abc][mailto:abc@gmail.com @][mailto:abc@gmail.com gmail][mailto:abc@gmail.com .][mailto:abc@gmail.com com]

'''Manager of:Accounts'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Here, the '''object '''of the '''Manager class '''calls the '''getDetails() method.'''

But this time, it calls the '''method of Manager class itself.'''

In this way, we override the '''method''' of the '''parent class '''by the '''subclass'''.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 10'''

'''Summary'''
| style="border:1pt solid #000000;padding:0.097cm;"| Let us summarize.

In this tutorial we have learnt about

* '''Subclassing'''
* '''extends '''keyword
* '''Overriding'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 11'''

'''Assignment'''
| style="border:1pt solid #000000;padding:0.097cm;"| As an '''assignment'''

Create a '''class Vehicle '''which has a method '''run '''that prints “'''The Vehicle is running.”'''

Also create a class '''Bike '''which has a method '''run '''that prints “'''The Bike is running safely.”'''

The output should be “'''The Bike is running safely.”'''

|-
| style="border:1pt solid #000000;padding:0.106cm;"| '''Slide 12'''

'''About Spoken Tutorial Project'''
| style="border:1pt solid #000000;padding:0.106cm;"| is this fine check?

To know more about the Spoken Tutorial Project

- Watch the video available at the following link

- It summarizes the Spoken Tutorial project

- If you do not have good bandwidth, you can download and watch itModifiedok do it in previous tutorial as wellTo know more about the Spoken Tutorial Project

* Watch the video available at the following link

* It summarizes the Spoken Tutorial project
* If you do not have good bandwidth, you can download and watch it

|-
| style="border:1pt solid #000000;padding:0.106cm;"| '''Slide 13'''

'''Spoken Tutorial Workshop'''
| style="border:1pt solid #000000;padding:0.106cm;"| The Spoken Tutorial Project Team

* Conducts workshops using spoken tutorials
* Gives certificates for those who pass an online test
* For more details, please write to contact at spoken hyphen tutorial dot org

|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Slide 14'''

'''Acknowledgement'''
| style="border:1pt solid #000000;padding:0.106cm;"| Spoken Tutorial Project is a part of the Talk to a Teacher project

* It is supported by the National Mission on Education through ICT, MHRD, Government of India

* More information on this Mission is available at

* http://spoken-tutorial.org/NMEICT- Intro

This is '''Arya Ratish '''from '''IIT Bombay '''signing off.

Thanks for joining.

|}

Java/C3/Subclassing-and-Method-Overriding/English - Revision history

Nancyvarkey at 10:06, 12 March 2014

Arya Ratish: Created page with ''''Title of script''': Subclassing and Method overriding '''Author: arya ''' '''Keywords: '''subclassing, extends keyword, overriding, method overriding, Java, Eclipse IDE, vid…'