Chandrika: Created page with ''''Title of script''': Instance Fields '''Author: '''arya '''Keywords: '''video''' '''tutorial,''' '''dot operator, instance fields {| style="border-spacing:0;" ! Vi…'

2012-11-27T10:15:13Z

Created page with ''''Title of script''': Instance Fields '''Author: '''arya '''Keywords: '''video''' '''tutorial,''' '''dot operator, instance fields {| style="border-spacing:0;" ! <center>Vi…'

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'''Title of script''': Instance Fields

'''Author: '''arya

'''Keywords: '''video''' '''tutorial,''' '''dot operator, instance fields

{| 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 '''Instance Fields''' 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 '''instance fields'''

- To access the '''instance fields '''of a '''class'''

-'''Modifiers''' for '''instance fields'''

-Why '''instance fields''' are called so?

|-
| 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 '''class '''in '''Java '''using '''Eclipse'''.

You must also know how to create an '''object '''for the '''class'''.

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

'''Instance 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;"| We know that objects store their individual states in''' fields'''.

These fields are declared without the <tt>'''static'''</tt> keyword.

We will learn about''' static fields''' in the coming tutorials.

'''Non-static fields''' are also known as '''''instance variables '''''or''''' instance fields.'''''

|-
| 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

Open Student.java file.
| 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 go back to the '''Student class''' we had already created.

We can see that here''' roll_no''' and '''name''' are the '''instance fields''' of this '''class'''.

Now, we will learn how to access these '''fields'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open TestStudent.java file
| 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 the '''TestStudent class '''which we had already created.

We can remove the statement for creating the second '''object'''.

We will also remove the '''println '''statements.

Now we will access the fields '''roll_no''' and '''name''' using '''stud1 '''and the''' dot operator'''.

So type '''System''' ''dot'' '''out''' ''dot'' '''println''' within brackets and double quotes '''The roll number is''', then ''plus '''''stud1''''' dot '''''roll_no''''' ''and then ''semicolon''.

Next line type '''System''' ''dot'' '''out''' ''dot'' '''println''' within brackets and double quotes '''The name is''', then ''plus '''''stud1''''' dot '''''name''''' ''and then ''semicolon''.

Now, '''save''' and '''run''' the file '''TestStudent.java'''.

|-
| 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

'''The roll number is 0.'''

'''The name is null.'''

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open Student.java file and highlight the variables
| 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 is because, we have not initialized the '''variables''' to any value.

In '''Java''', the '''fields''' cannot have random values.

After the '''memory''' is allocated for the '''object''' the '''fields''' are initialized to '''null '''or '''zero'''.

This work is done by the '''constructor'''.

We will learn about '''constructor''' in the coming tutorials.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Initalize roll_no and name

Save and run the file
| 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, we will initialize the '''fields''' and see the '''output'''.

Type''' roll_no''' equal to '''50''' and '''name''' equal to within double quotes '''Raju'''.

|-
| 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, '''save '''and '''run '''the file.

We get the '''output''' as '''The roll number is 50'''.

'''The name is Raju'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open Student.java
| 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.

We can see that here the '''fields '''have no '''modifier '''or''' '''the''' default modifier'''.

Recall '''modifiers''' we had discussed in '''Creating Classes.'''

We can access the fields because both '''Student.java''' and '''TestStudent.java''' are in the same '''package'''.

We can see that here they are in the same '''default package'''.

We will learn about '''packages''' in the later tutorials.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Type private before every 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;"| We will now change the modifier to '''private'''.

So before the '''field''' declarations type '''private'''.

Now '''save''' the file '''Student.java'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open TestStudent.java

Hover the mouse over the error.
| 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 see that we get errors in '''TestStudent.java'''.

Hover the mouse over the error symbol.

It says '''The field Student '''''dot '''''roll '''''underscore '''''number '''is not visible.

'''The field Student '''''dot '''''name '''is not visible.

This is because private fields can be accessed only within its own class.

You can try accessing '''roll_no''' and '''name''' from the '''Student class '''itself.

You will find that you can access them without any error.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open Student.java
| 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, come back to '''Student''' '''class'''.

Let us change the '''modifier''' to '''protected'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| '''Save''' and '''Run'''
| 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;"| '''Save''' and '''Run''' the program

|-
| 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 '''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 see the '''output''' on the console.

This is because '''protected fields''' can be accessed within the same '''package'''.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Slide 6
| 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;"| '''Instance fields''' are called so because their values are unique to each '''''instance''''' of a class.

In other words each object of a class will have unique values.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open TestStudent 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 go to the '''TestStudent class'''.

Here, we will create one more object of the '''TestStudent class'''.

So type '''Student''' space '''stud2''' equal to '''new''' space '''Student''' , opening and closing brackets semicolon.

We will now initialize both the objects here.

So next line type '''stud1''' ''dot '''''roll_no''' equal to '''20 '''and ''semicolon.''

Then type '''stud1''' ''dot'' '''name''' equal to within double quotes '''Ramu '''''semicolon''.

Thus we have initialized the fields for the first object.

Now, we will initialize the fields for the second object.

So type '''stud2''' ''dot'' '''roll_no''' equal to '''30 '''and ''semicolon''.

Then type '''stud2''' ''dot'' '''name''' equal to within double quotes''' Shyamu '''''semicolon'''''.'''

Now, type System dot out dot println within brackets and double quotes '''The roll number is''', then ''plus '''''stud2 '''''dot '''''roll_no''''' ''and then ''semicolon''.

Next line type '''System''' ''dot'' '''out''' ''dot'' '''println''' within brackets and double quotes '''The name is''', then ''plus '''''stud2 '''''dot '''''name''''' ''and then ''semicolon''.

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 follows.

Here both '''stud1''' and '''stud2''' are referring to two different '''objects'''.

This means that the two '''objects''' have unique values.

We can see that here.

The first object has values 20 and Ramu.

The second object has values 30 and Shyamu.

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open TestStudent.java
| 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 create one more '''object.'''

So type '''Student''' space '''stud3''' equal to '''new''' space '''Student''' and then opening and closing brackets.

We will now, print the values the third '''object''' contains.

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 see that the third '''object''' contains the values''' 50''' and '''Raju.'''

|-
| style="border-top:none;border-bottom:0.035cm solid #000000;border-left:0.035cm solid #000000;border-right:none;padding:0.097cm;"| Open Student.java
| 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 is because we had explicitly initialized the fields of the '''Student''' class.

Now, try de-initializing the fields and see the output for the third object.

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

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

* About instance fields.
* Accessing the fields using dot operator.

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

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,

Create another object stud2 in the TestStudent class already created.

Then initialize the values of the two objects using dot operator.

Use 55 and Priya as values for first object.

Use 45 and Sandeep as values for second object.

Display the values for both the objects in the output.

|-
| 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/Instance-fields/English - Revision history

Chandrika: Created page with ''''Title of script''': Instance Fields '''Author: '''arya '''Keywords: '''video''' '''tutorial,''' '''dot operator, instance fields {| style="border-spacing:0;" ! Vi…'