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

|  Welcome to the '''spoken-tutorial''' on '''Using final keyword.'''  

|  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'''.

|  To record this tutorial, I am using:  '''Ubuntu Linux''' version 12.04 , '''JDK''' 1.7 , '''Eclipse''' 4.3.1  

|  To follow this tutorial, you must have basic knowledge of '''Java''' and '''Eclipse IDE.'''

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

|  '''final''' is a '''keyword''' or reserved word in '''Java'''.  

|  Now, let us learn what '''final''' variable is.  

|  So, we will directly go to the '''Employee class''' of the project.  

|  We will initialize the variable '''name '''with value "sneha".  

|  We get compilation error: '''The final field Employee.name cannot be assigned'''  

|  This is because here the '''final variable 'name'''' is already declared and initialized.  

|  We can initialize a '''final''' variable only once.  

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

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

|  Great!!! We got the output, '''Name: Sneha''' ,'''Email: abc@gmail.com''' '''Manager of: Accounts''' .

|  We got this output as we already initialized variables with these values in '''TestEmployee class''' and '''Employee class'''.  

|  Remove the initialization of '''final variable name.'''  That is, remove “'''sneha”.'''  

|  We get the error: '''The final field Employee.name cannot be assigned'''  

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

|  So, we will type: '''Employee, parentheses, open and close curly brackets''' and inside the curly brackets, let's initialize the variable '''name''' with value '''sneha''' semicolon.

|  We get error: '''The final field Employee.name cannot be assigned'''  

|  So, now we will create a '''static block.'''  

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

|  Here, instead of '''Employee''' parenthesis , we will type '''static'''.  We have created a '''static block'''.  

|  Come to the method '''setEmail''' in '''Employee''' class.  

|  Now, come to the method''' setEmail'''. Inside the '''method''', we will type: '''newEmail is equal to abc@gmail.com''' semicolon

|  We get error: '''The final local variable newEmail cannot be assigned.'''  

|  So, let's remove the variable modification.  

|  We get error: '''class Manager overrides final method getDetails()'''.

|  '''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.  

|  In '''Employee''' class, remove '''final''' keyword before method '''getDetails'''.  

|  Remove '''static''' keyword before '''final''' variable '''name'''.  

|  Now, we will learn whether '''constructor''' can be declared as''' final '''or not.  

|  For that, we will again create a '''constructor'''. So, instead of '''static''' we will type: '''Employee''' parentheses.  

|  We get error: '''Illegal modifier for the constructor in type Employee'''.

|  This is because, '''constructor''' cannot be '''final''' since '''constructors''' cannot be inherited.  

|  Add '''final''' keyword before the '''class Employee''' to make it '''final'''.  

|  We get  error: '''The method setEmail is undefined for the type Manager'''.

|  To know the actual error, let's come to '''TestEmployee '''class and comment the lines

|  '''Save''' the class and '''run''' the program.

|  Here, '''Manager class''' extends '''Employee class.'''  

|  So, let's come back to''' Employee''' class and remove the '''final '''keyword. Save the class.

|  Now let's summarize. In this tutorial, we learnt: When to invoke final keyword , What are '''final variables, final methods '''and '''final classes'''.

|  As an assignment, Repeat the steps of '''Using final keyword '''tutorial for the '''Bike''' and '''Vehicle''' class which we used in the previous tutorial.

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

|  The Spoken Tutorial Project Team: Conducts workshops ,Gives certificates to those who pass an online test. For more details, please write to us.

|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.