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

final 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;

The final field Employee.name cannot be assigned

We can initialize a final variable only once.

So we will comment the method setName which modifies the variable name.

Save the class

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

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.

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We got the output,

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Now come to the final variable name. in Employee class.

That is remove “sneha”.

Uncomment the method.

cannot assign a value to final variable name

name=newName;

The final field Employee.name cannot be assigned

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

We have already learnt what a constructor is earlier.

Employee() { name="Sneha";

}

Employee, parentheses, open and close curly brackets

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

Enclose the method inside /* */

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We have made the final variable as static.

cannot assign a value to final variable name

name="Sneha";

The final field Employee.name cannot be assigned

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 final

Delete Employee and type static.

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

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

We have created a static block.

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We have successfully initialized static final variable.

We have made the parameter as final.

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Inside the method we will type,

newEmail is equal to inside double quotes abc@gmail.com semicolon.

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

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

This is Trupti Kini from IIT Bombay signing off.

Thanks for joining.