Chandrika: Created page with ''''Title of script''': Using this keyword '''Author: '''Arya Ratish '''Keywords: '''video''' '''tutorial,''' '''this, constructor {| style="border-spacing:0;" ! Visu…'

2012-11-27T10:17:59Z

Created page with ''''Title of script''': Using this keyword '''Author: '''Arya Ratish '''Keywords: '''video''' '''tutorial,''' '''this, constructor {| style="border-spacing:0;" ! <center>Visu…'

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'''Title of script''': Using this keyword

'''Author: '''Arya Ratish

'''Keywords: '''video''' '''tutorial,''' '''this, constructor

{| style="border-spacing:0;"
! <center>Visual Cue</center>
! <center>Narration</center>

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 1

Opening slide
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Welcome to the Spoken Tutorial on '''using this keyword''' in '''java'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 2

Learning Objectives
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| In this tutorial we will learn

- About use of '''this''' keyword

- To use '''this''' keyword with '''fields'''

-To use '''this '''keyword for chaining of '''constructors'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 3

System Requirements
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Here we are using

* Ubuntu version 11.10
* Java Development Environment jdk 1.6
* Eclipse 3.7

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 4

Prerequisites
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| To follow this tutorial you must know

how to create a '''default constructor''' in '''java''' using '''eclipse'''.

You must also know how to create a '''parameterized constructor''' in '''java'''.

If not, for relevant tutorials please visit our website which is as shown,

('''http'''://'''www.spoken'''-'''tutorial.org''')

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 5

Use of''' this '''keyword
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Within a '''constructor''', '''this''' is a reference to the current '''object'''.

We can refer any member of the current '''object''' within a''' constructor''' using '''this'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 6

Using '''this''' with '''fields'''
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| '''this '''keyword helps us to avoid name conflicts.

We can see such an example here.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open''' Eclipse'''
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| For that let us open '''Eclipse'''.

Open the '''Student class''' we had created in the earlier tutorial.

Comment the '''default constructor '''and the '''constructor''' with 1 parameter.

Also comment the code for creating the first two '''objects'''.

Now, notice the '''parameterized constructor.'''

'''the_roll_number''' and '''the_name '''are arguments passed in the constructor.

'''roll_number''' and '''name '''are the instance variables.

Now, let me change the arguments to '''roll_number''' and '''name''' itself.

So inside the '''constructor''' we have:

'''roll_number '''equal to''' roll_number''' and '''name '''equal to''' name.'''

'''Save '''and '''run '''the file.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Highlight the output.
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Now, let us see the output.

We get the output as follows:

I am Parameterized Constructor
0
null

We can see 2 warnings in the code.

'''The assignment to variable roll_number has no effect.'''

'''The assignment to variable name has no effect.'''

This is because in the '''constructor roll_number and name''' are '''local variables'''.

'''Local variables''' are '''variables''' accessible within a '''method''' or '''block'''.

Here, '''roll_number''' and '''name''' will be initialized to '''11''' and '''Raju'''.

Once they come out of the '''constructor''', it is not accessible.

Then the only '''roll_number''' and '''name''' we know are the '''instance variables'''.

They have been initialized to '''0 '''and '''null '''already once the '''object''' is created.

So we got the output as '''0 '''and '''null'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Type this.roll_number=roll_number

this.name=name
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Now, let us make a small change inside the constructor.

Type '''this '''''dot '''''roll_number equal to roll_number'''.

Next line type''' this '''''dot '''''name equal to name'''.

Now '''save '''and '''run''' the file.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Highlight the output.
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| We get the output as

I am Parameterized Constructor
11
Raju

This is because '''this '''''dot '''''roll_number '''and '''this '''''dot '''''name''' refers to the '''instance variables''' '''roll_number''' and '''name.'''

'''roll_number '''and '''name '''refers to the arguments passed in the method.

To avoid confliction between '''local''' and '''instance''' variables we use '''this '''keyword.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 7

Using '''this''' for chaining of constructors
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| We can use '''this '''keyword inside a '''constructor''' to call another one.

The '''constructors''' must be in the same '''class.'''

This is called '''explicit constructor invocation'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Switch to Eclipse

Point to''' Student class'''
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Let us come back to the''' Student '''class which we created.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Remove the comments.

Comment the part to assign the '''instance variables in the first two constructors.'''

Comment the part which creates the''' '''second and third '''objects.'''

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Point to''' default constructor.'''
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Let us first come to the first constructor with no parameters.

After the curly brackets type '''this''' within brackets '''11''' ''semicolon''.

Press '''Enter'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Point to the '''constructor''' with 1 argument.
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Inside the second '''constructor''' type '''this''' within brackets '''11''' ''comma'' '''Raju''' ''semicolon''.

Press '''Enter'''.

'''Save''' and '''Run''' the file.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Highlight the output
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| We get the output as

'''I am Parameterized Constructor'''
'''I am a constructor with a single parameter'''
'''I am Default Constructor'''

'''11'''

'''Raju'''

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Highlight each''' constructor '''as you explain
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Now, I will explain the output.

When the object is created, the respective constructor gets called.

The '''constructor''' here is the '''no argument constructor'''.

The control comes to the first line in the '''constructor'''.

It encounters the '''this '''''within brackets '''''11''' statement.

Hence it calls the constructor that accepts 1 integer argument.

Then the control comes to '''this '''''within brackets''''' 11 '''''comma '''''Raju.'''

Hence it calls the constructor that accepts 1 '''integer''' and 1 '''String''' argument.

So this '''constructor''' is executed and we get the output as '''I am Parameterized Constructor'''.

The instance variables are initialized here to '''11''' and '''Raju.'''

Now, the control goes back to the calling '''constructor'''.

So the second''' constructor '''is executed.

We get the output as''' I am constructor with a single parameter.'''

Then, the control goes to the first constructor and executes it.

So we get output as''' I am default constructor.'''

Then '''studentDetail method''' is executed.

So, we get '''11 '''and '''Raju'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Hover the mouse over the error symbol.
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Now, let us make a small change.

Make the '''this''' statement the last one in the constructor.

We get compiler error.

Hover the mouse over the error symbol.

We get the error as:

'''Constructor''' call must be the first statement in the '''constructor'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| So we must make it the first line of the '''constructor.'''

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| Let us make it the first line of the '''constructor.'''

We can see that the error has gone.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 6

Summary
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| So in this tutorial, we have learnt

To use''' this''' keyword with''' fields.'''

To use''' this''' keyword for chaining '''constructors'''

How '''this '''keyword should be used within a''' constructor.'''

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 7

Assignment
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| For self assessment, in the '''Employee class''' created earlier:

* Create a '''constructor''' with two parameters
* Use''' this '''keyword to initialize the''' instance variables .'''
* Also create a '''constructor''' with 1 and no parameters.
* Try chaining the '''constructors '''using '''this''' as explained in the tutorial.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 8

About Slide
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| To know more about the Spoken Tutorial Project
* Watch the video available at [http://spoken-tutorial.org/What_is_a_Spoken_Tutorial http://spoken-][http://spoken-tutorial.org/What_is_a_Spoken_Tutorial tutorial.org/What_is_a_Spoken_Tutorial]
* It summarizes the Spoken Tutorial project

* If you do not have good bandwidth, you can download and watch it

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 9

About Slide

| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| 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@spoken-tutorial.org

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 10

Acknowledgment
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| 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 http://spoken-tutorial.org/NMEICT-Intro]

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:0.035cm solid #000000;padding:0.097cm;"| We have come to the end of this tutorial.

Thanks for joining.

This is Arya Ratish signing off.

Jai Hind.

|}

Java/C2/Using-this-keyword/English - Revision history

Chandrika: Created page with ''''Title of script''': Using this keyword '''Author: '''Arya Ratish '''Keywords: '''video''' '''tutorial,''' '''this, constructor {| style="border-spacing:0;" ! Visu…'