Nancyvarkey at 09:57, 12 January 2017

2017-01-12T09:57:04Z

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Priyacst at 06:36, 12 January 2017

2017-01-12T06:36:03Z

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Nirmala Venkat at 05:25, 9 March 2016

2016-03-09T05:25:10Z

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Priyacst: Created page with "'''Title of script:''' Static Variables '''Author:''' Joms Antony '''Keywords:''' Static Variables, Class variables, Instance Variables, static keyword, final keyword, stati..."

2016-03-02T11:12:12Z

Created page with "'''Title of script:''' Static Variables '''Author:''' Joms Antony '''Keywords:''' Static Variables, Class variables, Instance Variables, static keyword, final keyword, stati..."

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'''Title of script:''' Static Variables

'''Author:''' Joms Antony

'''Keywords:''' Static Variables, Class variables, Instance Variables, static keyword, final keyword, static constants, video tutorial

{| style="border-spacing:0;"
| style="background-color:#ffffff;border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <center>'''Visual Cue'''</center>
| style="background-color:#ffffff;border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <center>'''Narration'''</center>

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 1'''
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Welcome to the Spoken Tutorial on '''Static Variables.'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 2'''

'''Learning Objectives'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| In this tutorial we will learn about:

* What are''' static variables'''
* Creating''' static variables '''and
* How to''' '''use''' static variables'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 3'''

'''Software Requirements'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Here we are using

* '''Ubuntu 12.04'''
* '''JDK 1.7 '''and
* '''Eclipse 4.3.1'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 4'''

'''Prerequisites'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| To follow this tutorial, you must have knowledge of basics of''' Java''' and''' Eclipse IDE.'''

You should also have the knowledge of''' classes, objects '''and''' instance variables''' in''' Java.'''

If not, for relevant''' Java '''tutorials, please visit the link shown.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 5'''

'''What is a static variable?'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| A''' static variable''' is a variable which is associated with the entire''' class.'''

It is also called a '''class variable.'''

It is declared using the''' static keyword.'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 6'''

'''Static Variable-Example'''

(Proceed with the Slide)
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| We have seen about static variable briefly in the earlier tutorial.

In this tutorial we will see it in detail.

Let us illustrate the usage of''' static variables''' with an example.

Consider a''' class''' created to represent student enrollments in an organization.

This class contains the '''Name, Id , Branch''' and''' Total Count''' of students enrolled.

Now let us visualize what happens when student enrollments are done.

The''' Name''' of the first student is '''ADIL.'''

'''Id''' is''' IT101. Branch''' is''' IT.'''

Now the''' Total Count''' is updated as 1.

Similarly when the second student''' AMAL '''gets enrolled, '''Total Count''' is updated to 2.

When the third student''' CAROL''' gets enrolled,''' Total Count''' is updated to 3.

Now we can identify that the variable''' Total Count''' is common to all the objects and has a single value.

So the variable''' Total Count''' can be represented as a''' static variable'''.

We can also see that the variables''' Name, Id''' and''' Branch''' have their own copies for each object.

Also they have specific values for each object.

So these variables can be treated as''' instance variables.'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 7'''

'''Instance Vs Static Variable'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now let us explore the differences between''' instance variables''' and''' static variables.'''

Every object has its own copies for '''instance variables.'''

'''Id, Name, Branch''' are examples of instance variables.

'''Static variables''' in a class share a single

copy with all objects in that class.

'''Total Count''' is an example of static variable.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 7(A)'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| When a class is loaded

A''' static variable''' occupies a single fixed memory location

whereas

'''Instance variables''' of each object occupy separate''' '''memory locations.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 8'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now let us look at the sample code representing the student enrollment class.

The name of the class is''' StudentEnroll.'''

The instance variables are declared as''' id, name''' and''' branch.'''

The variable''' count''' is declared as static since it is common to the whole class.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| In Eclipse IDE, create a class StaticVariableDemo

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now we will switch to''' Eclipse''' and create a new project called '''StaticVariableDemo'''.

Inside this project we will create the necessary classes to demonstrate the usage of''' Static variables.'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Right click on '''src''' folder -> '''new '''-> '''class''', type '''StudentEnroll''' and hit Enter

Go back to slide 8 and show the code

Copy and paste the code
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| So right click on '''src''' folder and click on '''new '''-> '''class''', and type the name of the class as''' StudentEnroll''' and Press '''Enter'''.

Now type the code which was shown in the earlier slide.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| click on''' source ->''' and select''' Generate Constructor using Fields'''

Delete the''' super''' keyword
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now click on''' source ->''' and select''' Generate Constructor using Fields.'''

Delete the''' super''' keyword from the generated code.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Constructor''' code

public StudentEnroll(String id, String name, String branch) {

this.id = id;

this.name = name;

this.branch = branch;

count++;

}

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This '''constructor''' can initialize the values of the''' id, name''' and''' branch '''fields.

We also need to increment the value of the variable''' count''' by one every time an object is created.

So inside the constructor type,

'''count ++ semicolon.'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Type, public void showData()

{// Copy the code below

System.out.println(id+" " +name+" "+branch+" "+count);

}
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now we will add a''' '''method '''showData'''( ) to this class to print the values of all the variables.

So type''' public void showData( )'''

within brackets type the following code to print the values of''' id, name, branch '''and '''total number of students enrolled'''.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Right click on the '''default package,''' click new-> class and then type name as''' Demo'''.
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now right click on the '''default package''' click on '''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.'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Type

StudentEnroll s1=new StudentEnroll("IT101","ADIL","IT");

Type s1.showData( );

Click on '''Run '''icon

Highlight the values of s1

Highlight '''1'''

StudentEnroll s2=new StudentEnroll("EC101","AMAL","EC");

copy and paste, s2.showData();

Click on '''Run '''icon

Highlight values

Highlight '''2'''

StudentEnroll s3=new StudentEnroll("CS101","CAROL","CS");

Type, s3.showData();

Click on '''Run '''icon

Hightlight the values

Highlight '''3'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now we need to print the Student Enrollment data.

We will create a few objects of''' StudentEnroll class''' to represent student enrollments.

So type''' '''the following code.

'''StudentEnroll s1 equals new StudentEnroll'''

Now we can pass the values of different arguments.

Within brackets type''' IT101 '''as''' id, ADIL''' as''' name '''and''' IT''' as '''branch.'''

Now let us invoke the''' showData''' method to print the enrollment details. So type

'''s1.showData( )'''.

Now run the '''Demo''' program.

We can see that the values of the instance variables corresponding to''' s1''' get printed.

Also note that the value of the number of student enrollments is 1.

This is because we have created only 1 object.

Now type the following code to create one more object''' s2.'''

The''' showData''' method can be called once again using''' s2.'''

Again run the '''Demo''' Program.

We can see that the values of the instance variables corresponding to''' s2''' get printed.

Also note that the value of''' number of student''' enrollments is updated to 2 for both''' s1''' and''' s2.'''

Now create one more object''' s3.'''

Now Let us Invoke the''' showData''' method again using''' s3.'''

Run the '''Demo''' Program again.

We can see that the values of the instance variables corresponding to''' s3''' get printed.

Also note that the value of''' '''number of student enrollments is now updated to 3 in all the cases.

Now we can understand that the value of the number of student enrollments is common to all the objects.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 9'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Come back to slides.

The''' static''' modifier, is also used along with the final modifier.

It is done to define a''' constant''' which is common to the entire class.

Conventionally, the names of such constant variables are spelled in uppercase letters.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 9(A)'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| If the name is composed of more than one word, the words are separated by '''an underscore.'''

As an Example, if all the students are getting enrolled to the same organisation say''' IITB'''.

It can be represented by using a constant static variable say''' ORG_NAME'''.

Usually we declare such constants

with a '''public''' visibility.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 10'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| A Static variable can be accessed

directly from another class by using its own

class name.

For Example:

StudentEnroll.ORG_NAME;

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Come back to eclipse

In '''StudentEnroll''' class and type,

'''public static final String ORG_NAME = “IITB”;'''

Inside the '''Demo''' class, type '''System.out.println(“ORGANISATION:”+StudentEnroll.ORG_NAME);'''

Highlight '''ORG_NAME '''and''' StudentEnroll'''

Run the '''Demo''' program

Point to '''ORGANISATION: IITB'''
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now come back to eclipse.

Open the '''StudentEnroll''' class and type the variable declaration as

'''public static final String ORG_NAME = “IITB”;'''

Now go to the '''Demo class '''and type the following code

Here you can see that '''ORG_NAME '''is accessed by using its class name '''StudentEnroll.'''

''' '''

Now run the '''Demo''' Program again.

We can see that the '''ORGANISATION''' name is getting printed as''' IITB.'''

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 10'''

Summary

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us summarize.

In this tutorial we have learnt about

* What is a static variable and when it is used
* How to create and invoke the static variables

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Slide 11'''

Assignment
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| As an Assignment.

Design a class''' CarService''' to represent a Car Service Station.

This class should contain variables to represent the following details.

'''Name''' of the Service Station.

Car '''make''', '''model''' and '''reg. no''' - which are in for service.

'''No. of Cars in''' for Service.

Identify the instance variables and static variables.

Declare them using suitable keywords.

Define a''' constructor''' to initialize the values for Car make, model and regno.

Define a method''' show( )''' to print the values of all the variables.

Also create a''' Demo''' class containing the main method to verify the results.

i.e

Create a few objects of''' CarService.'''

Invoke the''' show( ) '''method using these objects.

Also access the static variables directly using the class name.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''About Project'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The video at the following link summarizes the Spoken Tutorial Project.

Please download and watch it.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''About Workshops'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The Spoken Tutorial Project Team

• Conducts workshops using spoken tutorials and

• Gives certificates on passing the online tests.

For more details, please write to us.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''About NMEICT'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Spoken Tutorial Project is funded by the NMEICT, MHRD, Government of India.

More information on this Mission is available at the link shown.

|-
| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Contributor slide'''

| style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This script has been contributed by:

Department of Information Technology, Amal Jyothi College of Engineering.

This is Priya from IIT Bombay signing off. Thanks for joining.

|}

Java/C3/Static-Variables/English - Revision history

Nancyvarkey at 09:57, 12 January 2017

Priyacst at 06:36, 12 January 2017

Nirmala Venkat at 05:25, 9 March 2016

Priyacst: Created page with "'''Title of script:''' Static Variables '''Author:''' Joms Antony '''Keywords:''' Static Variables, Class variables, Instance Variables, static keyword, final keyword, stati..."