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

The final keyword and when to invoke it.

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

Pre-requisites

• 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 or classes.

Slide 6

final variable is a variable whose value cannot be changed.

That is, it will be a constant.

Point to MyProject

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

Highlight variable name

We have made the variable name as final.

The final field Employee.name cannot be assigned

The final field Employee.name cannot be assigned

public final string name = “sneha”

We can initialize a final variable only once.

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

Employee class.

TestEmployee class and Employee class.

That is remove “sneha”.

Uncomment the method.

The final field Employee.name cannot be assigned

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 semicolon .

Comment the method

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We have made the final variable as static.

The final field Employee.name cannot be assigned

The final field Employee.name cannot be assigned

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.

Highlight 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.

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

We got the desired output,

We have successfully initialized static final variable.

We have made the parameter as final.

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Type newEmail="abc@gmail.com";

Inside the method we will type,

newEmail is equal to abc@gmail.com semicolon

We have modified the final variable newEmail.

The final local variable newEmail cannot be assigned.

The final local variable newEmail cannot be assigned.

So lets remove the variable modification.

We have made the method as final.

class Manager overrides final method getDetails.()

class Manager overrides final method getDetails.()

Manager class method getDetails overrides getDetails method in Employee class.

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.

remove final keyword>>

Remove static keyword

Remove static keyword before final variable name.

Type,

Employee()

For that we will again create a constructor.

So instead of static we will type, Employee parentheses.

Illegal modifier for the constructor in type Employee

Illegal modifier for the constructor in type Employee

We will remove the final keyword before the constructor.

The method setEmail is undefined for the type Manager

The method setEmail is undefined for the type Manager

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

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

The type Manager cannot subclass the final class Employee

The type manager cannot subclass the final class Employee.

Here Manager class extends Employee class.

Save the class.

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

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

Name: Sneha

Email: abc@gmail.com

Manager of: Accounts

Summary

In this tutorial we learnt:

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

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.

About Spoken Tutorial Project

About Spoken Tutorial workshops

• Conducts workshops
• Gives certificates for those who pass an online test
• For more details, please write to us

Acknowledgement

That's it for this tutorial.

This is Trupti Kini from IIT Bombay.

Thank you very much for watching.