Difference between revisions of "Java/C3/Using-final-keyword/English"

From Script | Spoken-Tutorial
Jump to: navigation, search
 
(One intermediate revision by the same user not shown)
Line 404: Line 404:
 
| style="border:1pt solid #000000;padding:0.097cm;"| Type final keyword before '''getDetails.'''  
 
| style="border:1pt solid #000000;padding:0.097cm;"| Type final keyword before '''getDetails.'''  
 
| style="border:1pt solid #000000;padding:0.097cm;"| Add '''final '''keyword before '''method getDetails'''.  
 
| style="border:1pt solid #000000;padding:0.097cm;"| Add '''final '''keyword before '''method getDetails'''.  
 +
 +
We have made the method as '''final'''.
  
 
|-
 
|-
Line 425: Line 427:
 
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| This is because if you make any '''method''' as '''final''', you cannot '''override''' it.
 
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| This is because if you make any '''method''' as '''final''', you cannot '''override''' it.
  
−
'''Manager class method getDetails overrides getDetails method in Employee class. '''  
+
'''Manager class method getDetails''' overrides '''getDetails method''' in '''Employee class. '''  
  
 
|-
 
|-
Line 481: Line 483:
 
|-
 
|-
 
| style="border:1pt solid #000000;padding:0.097cm;"| Remove the''' final''' keyword before '''Employee()'''
 
| style="border:1pt solid #000000;padding:0.097cm;"| Remove the''' final''' keyword before '''Employee()'''
−
| style="border:1pt solid #000000;padding:0.097cm;"| This is because, '''constructor''' cannot be '''final''' since '''constructors''' are not inherited.  
+
| style="border:1pt solid #000000;padding:0.097cm;"| This is because, '''constructor''' cannot be '''final''' since '''constructors''' cannot not be inherited.  
  
 
We will remove the '''final''' keyword before the '''constructor'''.  
 
We will remove the '''final''' keyword before the '''constructor'''.  
Line 531: Line 533:
 
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Come back to '''Employee''' class and remove the''' final''' keyword
 
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Come back to '''Employee''' class and remove the''' final''' keyword
 
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| So let's come back to''' Employee''' class and remove the '''final '''keyword.  
 
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| So let's come back to''' Employee''' class and remove the '''final '''keyword.  
 +
 +
Save the class.
  
 
|-
 
|-
Line 583: Line 587:
  
 
'''About Spoken Tutorial Project'''  
 
'''About Spoken Tutorial Project'''  
−
| style="border:1pt solid #000000;padding:0.097cm;"| Watch the video available at the following link [http://spoken-tutorial.org/What http://spoken-tutorial.org/What] is a Spoken Tutorial'''
+
| style="border:1pt solid #000000;padding:0.097cm;"| Watch the video available at the following link. It summarizes the Spoken Tutorial project  
−
 
+
−
* It summarizes the Spoken Tutorial project  
+
−
 
+
−
* If you do not have good bandwidth, you can download and watch it
+
  
 
|-
 
|-
Line 596: Line 596:
 
| style="border:1pt solid #000000;padding:0.097cm;"| The Spoken Tutorial Project Team  
 
| style="border:1pt solid #000000;padding:0.097cm;"| The Spoken Tutorial Project Team  
  
−
* Conducts workshops using spoken tutorials
+
* Conducts workshops
 
* Gives certificates for those who pass an online test  
 
* Gives certificates for those who pass an online test  
−
* For more details, please write to contact at spoken hyphen tutorial dot org
+
* For more details, please write to us
  
 
|-
 
|-
Line 606: Line 606:
  
  
−
| style="border:1pt solid #000000;padding:0.097cm;"| Spoken Tutorial Project is a part of the Talk to a Teacher project
+
| style="border:1pt solid #000000;padding:0.097cm;"| Spoken Tutorial Project is supported by the National Mission on Education through ICT, MHRD, Government of India.
  
−
* It is supported by the National Mission on Education through ICT, MHRD, Government of India
+
That's it for this tutorial.
−
* More information on this Mission is available at
+
−
* [http://spoken-tutorial.org/NMEICT- http][http://spoken-tutorial.org/NMEICT- ://][http://spoken-tutorial.org/NMEICT- spoken][http://spoken-tutorial.org/NMEICT- -][http://spoken-tutorial.org/NMEICT- tutorial][http://spoken-tutorial.org/NMEICT- .][http://spoken-tutorial.org/NMEICT- org][http://spoken-tutorial.org/NMEICT- /][http://spoken-tutorial.org/NMEICT- NMEICT][http://spoken-tutorial.org/NMEICT- -] Intro
+
  
−
This is Trupti Kini from '''IIT Bombay''' signing off.  
+
This is Trupti Kini from '''IIT Bombay'''.  
  
−
Thanks for joining.  
+
Thank you very much for watching.  
  
 
|}
 
|}

Latest revision as of 14:54, 24 April 2015

Title of script: USING FINAL KEYWORD

Author: Trupti Rajesh Kini

Keywords: video tutorial, final keyword, final variable, final method, final class


Visual Cue Narration
Slide 1 Welcome to the spoken-tutorial on Using final keyword.
Slide 2 In this tutorial we will learn about

The final keyword and when to invoke it.

We will also learn about -

  • final variables,
  • final methods,
  • final classes
Slide 3

Software Requirements


To record this tutorial, I am using
  • Ubuntu Linux version 12.04
  • JDK 1.7
  • Eclipse 4.3.1
Slide 4

Pre-requisites


To follow this tutorial, you must have,
  • Basic knowledge of Java and Eclipse IDE.
  • and knowledge of Subclassing and Method overriding.

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

Slide 5

final keyword

First of all, we will learn what final keyword is.

final is a keyword or reserved word in Java.

It can be applied to variables, methods or classes.

What is final variable?

Slide 6

Now, let us learn what final variable is.

final variable is a variable whose value cannot be changed.

That is, it will be a constant.

Go to the Eclipse IDE

Point to MyProject

I am switching to Eclipse IDE now.

I had already created a project named MyProject in the previous tutorial.

Go to the Employee class So we will directly go to the Employee class of the project.
Point to the variable name Come to the variable name.
Type final keyword

Highlight variable name

Add final keyword before the variable name.

We have made the variable name as final.

Type sneha We will initialize the variable name with value sneha.
Save and Run the program. We will Save and Run the program.
Highlight the error

The final field Employee.name cannot be assigned

We get compilation error.

The final field Employee.name cannot be assigned

Highlight

public final string name = “sneha”

This is because here the final variable name is already declared and initialised.

We can initialize a final variable only once.

Comment the method setName So we will comment the method setName which modifies the variable name.
Save the class. Save the class.
Go to TestEmployee class->main method

Type // before manager.setName("Nikkita Dinesh");

Now, come to TestEmployee class.

Come to the main method and comment the line manager.setName("Nikkita Dinesh");

We commented this line as it was instance of method setName.

We have already commented setName method in Employee class.


Save and Run the program. Now let us Save the class and Run the program.
Highlight the output

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Great!!!

We got the output,

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Highlight the initialization in TestEmployee class and

Employee class.

We got this output as we already initialized variables with these values in

TestEmployee class and Employee class.

Go to Employee class->final variable name Now come to the final variable name. in Employee class.
Remove the initialization “sneha” Remove the initialization of final variable name.

That is remove “sneha”.

Go to the method setName

Uncomment the method.

Uncomment the method setName.


Save and run the program. Save and Run the program.
Highlight the error

The final field Employee.name cannot be assigned

We get the error,

The final field Employee.name cannot be assigned

This is because, if the final variable is not initialised, then only constructor can initialize it.

That is, it cannot be modified anywhere else in the program.

Go to Employee class For that, let’s create a constructor in the Employee class.

We have already learnt what a constructor is earlier.

We know that constructor has the same name as class name.
Type,

Employee() {

name="Sneha";

}

So we will type

Employee, parentheses, open and close curly brackets

and inside the curly brackets, lets initialize the variable name with value sneha semicolon .

Point to the method setName

Comment the method

Comment the method setName.
Save and Run the program. Save and Run the program.
Highlight the output

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We got the desired output.


final variable is successfully initialized in a constructor.
Now we will learn about final static variables.
Go to the Employee class Come to the final variable in Employee class.
Type static before final keyword Add static keyword before final keyword.

We have made the final variable as static.

Save & Run the program. Save and Run the program.
Highlight the error

The final field Employee.name cannot be assigned

We get error.

The final field Employee.name cannot be assigned

Slide 7 This is because static final variables cannot be initialized in the constructor.

They must be assigned a value with their declaration.

Or they must be declared in a static block.

Slide 8 static variables are shared among all the objects of a class.

Creating a new object would change the static variable.

This is not allowed if the static variable is final.

Go to Eclipse IDE Switch back to Eclipse IDE.
Go to the Employee class ->Employee()

Delete Employee() and type static.

Highlight static block

So now we will create a static block.

For that, in the Employee class, come to the constructor. we created.

Here instead of Employee(), we will type static.

We have created a static block.

Now we will Save and Run the program. Now we will Save and Run the program.
Highlight the output,

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We got the desired output,

We have successfully initialized static final variable.


Now let’s use final variable as a parameter to the method.
Go to the method setEmail Come to the method setEmail. in Employee class.
Type final before String newEmail Add final keyword before String newEmail

We have made the parameter as final.

Save and Run the program. Save and Run the program.
Highlight the output

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We got the desired output.
Come to the method setEmail

Type newEmail="abc@gmail.com";

Now, come to the method setEmail.

Inside the method we will type,

newEmail is equal to abc@gmail.com semicolon

We have modified the final variable newEmail.

Save & Run the program. Once again we will Save & Run the program.
Highlight the error,

The final local variable newEmail cannot be assigned.

We get error.

The final local variable newEmail cannot be assigned.

This is because final variable as parameter to a method cannot be modified by that method.

So lets remove the variable modification.

Now we will learn about final method.
Come to the method getDetails in employee class. Come to the method getDetails in employee class.
Type final keyword before getDetails. Add final keyword before method getDetails.

We have made the method as final.

Save and Run the program. Save and Run the program.
Point to the compilation error,

class Manager overrides final method getDetails.()

We get error,

class Manager overrides final method getDetails.()

Highlight method getDetails() in Manager class. Come to the method getDetails() in Manager class.
Highlight method getDetails() in Manager class. This is because if you make any method as final, you cannot override it.

Manager class method getDetails overrides getDetails method in Employee class.

Slide 9 What if final method is private?

private methods are not inherited by the child class.

So we can add a method getDetails() in the child class.

You can try this as an assignment.

Go to Eclipse IDE Switch back to Eclipse IDE.
Go to Employee class >>

remove final keyword>>

Remove static keyword

In Employee class, remove final keyword before method getDetails.

Remove static keyword before final variable name.

Instead of static

Type,

Employee()

Now, we will learn whether constructor can me declared as final or not.

For that we will again create a constructor.

So instead of static we will type, Employee parentheses.

Type final before the constructor Add final keyword before the constructor.
Save and run the program. Save and run the program.
Highlight compilation error,

Illegal modifier for the constructor in type Employee

We get error

Illegal modifier for the constructor in type Employee

Remove the final keyword before Employee() This is because, constructor cannot be final since constructors cannot not be inherited.

We will remove the final keyword before the constructor.

Now, we will learn about final class.
Type final keyword before the class Employee. Add final keyword before the class Employee. to make it final.
Save and Run the program. Save and Run the program.
Highlight the compilation error,

The method setEmail is undefined for the type Manager

We get an error,

The method setEmail is undefined for the type Manager

Come to TestEmployee class and comment the lines.

manager.setEmail("abc@gmail.com"); manager.setDepartment("Accounts");

To know the actual error, lets come to TestEmployee class and comment the lines.

manager.setEmail("abc@gmail.com"); manager.setDepartment("Accounts");

Save the class and run the program Save the class and run the program
Highlight the compilation error,

The type Manager cannot subclass the final class Employee

The actual error is

The type manager cannot subclass the final class Employee.

Here Manager class extends Employee class.

Come back to Employee class and remove the final keyword So let's come back to Employee class and remove the final keyword.

Save the class.

Come to the TestEmployee class

Uncomment the lines manager.setEmail("abc@gmail.com"); manager.setDepartment("Accounts");

Come to the TestEmployee class.

Uncomment the lines manager.setEmail("abc@gmail.com"); manager.setDepartment("Accounts");

Save the class and run the program. Save the class and run the program.
Highlight the output

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We got the desired output.
Slide 10

Summary

Now let's summarize.

In this tutorial we learnt:

  • When to invoke final keyword.
  • What are:
    • final variables,
    • final methods and
    • final classes
Slide 11

Assignment

As an assignment,

Repeat the steps of Using final keyword tutorial for the Bike and Vehicle class. which we used in the previous tutorial.

Write down the classes in Java that are final classes.

Slide 12

About Spoken Tutorial Project

Watch the video available at the following link. It summarizes the Spoken Tutorial project
Slide 13

About Spoken Tutorial workshops

The Spoken Tutorial Project Team
  • Conducts workshops
  • Gives certificates for those who pass an online test
  • For more details, please write to us
Slide 14

Acknowledgement


Spoken Tutorial Project is supported by the National Mission on Education through ICT, MHRD, Government of India.

That's it for this tutorial.

This is Trupti Kini from IIT Bombay.

Thank you very much for watching.

Contributors and Content Editors

Nancyvarkey, Trupti

Retrieved from "https://script.spoken-tutorial.org/index.php?title=Java/C3/Using-final-keyword/English&oldid=21568"