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

We will also learn about -

• final variables,
• final methods,
• final classes

Software Requirements

• Ubuntu Linux version 12.04
• JDK 1.7
• Eclipse 4.3.1

Prerequisites

• Basic knowledge of Java and Eclipse IDE.
• and knowledge of Subclassing and Method overriding.

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

final keyword

fkeywords are case sensitive, it should be final.doneinal is a keyword or reserved word in Java.

It can be applied to variables, methods and classes.

Slide 6

final variable is a variable whose value cannot be changed.

That is, it will be a constant.

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

We have made the variable name as final.

cannot assign a value to final variable name

name=newName;

“Cannot assign value to final variable name in the method as name=newName.”

But where?

...within a program

...within a function

...within a method

where?Actually here we are trying to say that final variable cannot be modified so its initialised once.

Then, it can be initialised when we declare it or else in the constructor. This we have explained ahead.So, what I understand is it has to be initialised only once in a program.rightSo pls mention this clearly in the script.We can initialize a final variable only once.

Point to the method setName

Enclose the method inside /* */

In the Employee class, we will comment the method setName.

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

Go 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.

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We got the output as,

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Go to the final variable name.

So we will remove “sneha”.

Uncomment the method.

cannot assign a value to final variable name

name=newName;

It says that we cannot assign a value to final variable name.

Not anywhere else in the program.

We have already learnt what a constructor is earlier.

Employee() { name="Sneha";

}

Employee, parentheses, open and close curly brackets

Inside the curly brackets, we will initialize name as Sneha.

Enclose the method inside /* */

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

<<PAUSE>>

cannot assign a value to final variable name

name="Sneha";

“Cannot assign a value to static final variable name.”

Further slide 9.1 and 9.2 [i.e. 25,26] contains one extra word block in second bullet,doneSlide 7

They must be assigned a value with their declaration.

Or they must be declared in a static block.

Creating a new object would change the static variable.

This is not allowed if the static variable is Is this bold text appropriate for the word "final"?Yes we need to, because the "final" word should not be translated.I asked this because I myself made that text bold. It was not so before.Ok may be I missed out to boldfinal.

Delete Employee and type static.

For that, in the Employee class, go to the constructor.

Here instead of Employee(), type static.

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Go to Employee class

Go to the method setEmail

Go to the method setEmail.

Inside the method type,

newEmail="abcIt is not recommended to give out personal email-ids in demos.

Remember 10,000 students will watch this tutorial.

Pls create an id for demo purpose

OR

Use the spokentutorial official email-id.Done@gmail.com";

final parameter newEmail may not be assigned

“final parameter newEmail may not be assigned”

<<PAUSE>>

Go to the method setEmail

Go to the method setEmail.

remove newEmail="kinitrupti@gmail.com";

Cannot override the final method from Employee

“Cannot override the final method from Employee.”

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.

Come to the Employee class.

Employee() { name="Sneha";

}

Type

Employee, parentheses, open and close curly brackets

Inside the brackets, we will declare name as Sneha.

modifier final not allowed here

“modifier final not allowed here”

The type Manager cannot subclass the final class Employee

“The type Manager cannot subclass the final class Employee.”

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

<<PAUSE>>

Summary

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

Assignment

• • Are you sure about the name of the tutorial? Pls chkThe bike vehicle was given as an assignment in the previous tutorial.
    We need to frame it properly.Pls frame it properly.doneRepeat the steps of Using final keyword tutorial for the Bike and Vehicle class.
  • Write down the classes in java that are final classes.

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Acknowledgement

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

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

This is Trupti Kini from IIT Bombay signing off.

Thanks for joining.