Nancyvarkey at 05:37, 29 April 2015

2015-04-29T05:37:24Z

Nancyvarkey at 06:57, 27 April 2015

2015-04-27T06:57:44Z

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Trupti at 09:34, 30 March 2015

2015-03-30T09:34:24Z

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Trupti: Created page with "'''Title of script''':''' Polymorphism in Java''' '''Author: Trupti Rajesh Kini''' '''Keywords: Polymorphism, virtual method, run-time polymorphism, Compile-time polymorphis..."

2015-03-30T09:14:30Z

Created page with "'''Title of script''':''' Polymorphism in Java''' '''Author: Trupti Rajesh Kini''' '''Keywords: Polymorphism, virtual method, run-time polymorphism, Compile-time polymorphis..."

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'''Title of script''':''' Polymorphism in Java'''

'''Author: Trupti Rajesh Kini'''

'''Keywords: Polymorphism, virtual method, run-time polymorphism, Compile-time polymorphism, static binding, dynamic binding, video tutorial'''

{| style="border-spacing:0;"
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Visual Cue'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Narration'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Slide 1

| style="border:0.05pt solid #000000;padding:0.185cm;"| Welcome to the '''spoken-tutorial '''on '''Polymorphism in Java.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Slide 2

| style="border:0.05pt solid #000000;padding:0.185cm;"| In this tutorial we will learn :

* About '''Polymorphism''' in Java
* '''Run-time polymorphism'''
* '''Virtual Method Invocation'''
* '''Compile-time polymorphism'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Slide 3

'''Software Requirements'''

| style="border:0.05pt solid #000000;padding:0.185cm;"| Here we are using

* '''Ubuntu Linux Version 12.04'''
* '''JDK 1.7'''
* '''Eclipse 4.3.1'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Slide 4

'''Prerequisites'''

| style="border:0.05pt solid #000000;padding:0.185cm;"| To follow this tutorial, you must have basic knowledge of,

* '''Java and Eclipse IDE.'''
* '''Subclassing '''& '''method overriding and overloading'''

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

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Slide 5 and slide 6

What is '''polymorphism?'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Polymorphism''' is an ability of an object to take on many forms.

The major advantages of '''Polymorphism '''are:

1. Reduction of complexity &

2. Code re-usability

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Slide 7
| style="border:0.05pt solid #000000;padding:0.185cm;"| In '''Java''', there are two types of '''polymorphism''':

'''Compile-time''' and '''Run-time polymorphism.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Compile-time polymorphism''' is essentially referred as '''method overloading'''.

It is also called '''Static Binding'''.

'''Run-time polymorphism''' is essentially referred as '''method overriding'''.

It is also called '''Dynamic Binding.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| We have already learnt '''Run-time polymorphism''' i.e. '''method overriding'''.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Go to the '''Eclipse IDE '''
| style="border:0.05pt solid #000000;padding:0.106cm;"| Let us Switch to '''Eclipse IDE.'''

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

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"|
| style="border:0.05pt solid #000000;padding:0.106cm;"| Let us take the code files of '''Using final keyword '''tutorial'''.'''

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"|
| style="border:0.05pt solid #000000;padding:0.106cm;"| '''Employee '''class is the parent class.

'''Manager '''class is the subclass.

'''Manager''' class contains an additional variable department.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"|
| style="border:0.05pt solid #000000;padding:0.106cm;"|

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Highlight '''manager '''method '''getDetails()'''
| style="border:0.05pt solid #000000;padding:0.106cm;"| '''Manager '''class method '''getDetails()''' overrides the '''Employee '''class method '''getDetails().'''

We are calling the '''getDetails()''' method by '''Manager '''class object i.e. '''Manager.'''

In order to print details '''system.out.println''' type '''Details of Manager Class.'''

'''Save '''and run the program.

So we can see '''department''' variable value in the output.

Therefore subclass method is invoked at runtime.

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Slide 8
| style="border:0.05pt solid #000000;padding:0.185cm;"| Method invocation is determined by the '''JVM,''' not compiler.

Therefore it is known as '''Runtime''' polymorphism or '''method overriding.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| We learnt what is '''Run time polymorphism.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| Now let us learn '''Virtual Method Invocation.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| Come to '''Employee '''class.

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Remove the '''static '''and '''final''' keyword for variable '''name.'''

Remove the '''static '''block.
| style="border:0.05pt solid #000000;padding:0.185cm;"| Remove the '''static '''and '''final''' keyword for variable '''name.'''

Remove the '''static '''block.

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Uncomment '''setName '''method
| style="border:0.05pt solid #000000;padding:0.185cm;"| Uncomment '''setName '''method.

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Come to '''TestEmployee '''class

Uncomment the line '''manager.setName(“Nikkita Dinesh”);'''

| style="border:0.05pt solid #000000;padding:0.185cm;"| Come to '''TestEmployee '''class in IDE.

Uncomment the value instance,

'''manager.setName(“Nikkita Dinesh”);'''

We uncommented this instance as we have uncommented the method '''setName().'''

|-
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #20124d;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"| Type,

'''Employee emp1 = new Employee();'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| Now, lets instantiate '''Employee''' object emp1 for '''Employee '''class reference.

Type,

'''Employee emp1 = new Employee();'''

|-
| style="border-top:0.05pt solid #20124d;border-bottom:0.05pt solid #20124d;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"| Type,

'''emp1.setName("Jayesh");'''

'''emp1.setEmail("jayesh@gmail.com");'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| Lets initialize the value for '''setEmail '''and '''setName''' for '''Employee '''class.

Type,

'''emp1.setName("Jayesh");'''

'''emp1.setEmail("pqr@gmail.com");'''

|-
| style="border-top:0.05pt solid #20124d;border-bottom:0.05pt solid #20124d;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"| Type,

'''System.out.println("Details of Employee class:" + "\n" + emp1.getDetails());'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| In order to print the employee details type,

'''System.out.println("Details of Employee class:" + "\n" + emp1.getDetails());'''

|-
| style="border-top:0.05pt solid #20124d;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"| Type,

'''Employee emp2 = new Manager();'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| Let us instantiate '''Manager '''object '''emp2 '''for '''Employee '''class reference i.e.

'''Employee emp2 = new Manager();'''

We are able to do this because''','''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Slide 9'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| Any '''Java''' object that pass more than one '''IS-A '''test is polymorphic.

In '''Java''', all objects are polymorphic since any object will pass the '''IS-A '''test for their own type and for the class Object.

* A Manager '''IS-A''' Employee
* A Manager '''IS-A''' Manager
* A Manager '''IS-A''' Object

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Highlight '''manager, emp1 '''and '''emp2'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| Only possible way to access an object is through a reference variable.

Reference variables like '''emp1, emp2 '''and '''manager.'''

Here, we instantiated two '''Manager''' objects:

One which references '''Employee '''class.

Other references '''Manager '''class.

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Type,

'''emp.setName("Ankita");'''

'''emp.setEmail("ankita@gmail.com");'''

| style="border:0.05pt solid #000000;padding:0.185cm;"| Let’s initialize the values for '''setEmail, setName''' and '''setDepartment '''using '''emp''' object.

Type,

'''emp.setName("Ankita");'''

'''emp.setEmail(“xyz[mailto:ankita@gmail.com @gmail.com]”''');'''

'''emp.setDepartment(“IT”);'''

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Point to the red cross.

Highlight error,

'''The method setDepartment(String) is undefined for the type Employee'''

| style="border:0.05pt solid #000000;padding:0.106cm;"| We see that there is an error,

'''The method setDepartment(String) is undefined for the type Employee'''

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"|
| style="border:0.05pt solid #000000;padding:0.106cm;"| This is because, '''setDepartment '''method does not exist for '''Employee '''class.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Remove the line,

'''emp.setDepartment("IT");'''
| style="border:0.05pt solid #000000;padding:0.106cm;"| Remove the line,

'''emp.setDepartment("IT");'''

|-
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #20124d;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"| Type,

'''System.out.println("Details of Manager class:" + "\n" + emp.getDetails());'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| In order to print the employee details type,

'''System.out.println("Details of Manager class:" + "\n" + emp.getDetails());'''

|-
| style="border-top:0.05pt solid #20124d;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.106cm;"| '''Save '''and '''Run '''the program.
| style="border:0.05pt solid #000000;padding:0.106cm;"| '''Save '''and '''Run '''the program.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Highlight output,

'''Details of Employee class:'''

'''Name: Jayesh'''

'''Email: pqr@gmail.com'''

'''Details of Manager class:'''

'''Name: Ankita'''

'''Email: xyz@gmail.com'''

'''Manager of:'''

'''Name: Nikkita Dinesh'''

'''Email: abc@gmail.com'''

'''Manager of: Accounts'''

| style="border:0.05pt solid #000000;padding:0.106cm;"| We get the output,

'''Details of Employee class:'''

'''Name: Jayesh'''

'''Email: pqr@gmail.com'''

'''Details of Manager class:'''

'''Name: Ankita'''

'''Email: xyz@gmail.com'''

'''Manager of:'''

'''Name: Nikkita Dinesh'''

'''Email: abc@gmail.com'''

'''Manager of: Accounts'''

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"|
| style="border:0.05pt solid #000000;padding:0.106cm;"| Here in the output we get the '''Manager of: '''as blank.

This is because we have not initialized department in '''Manager '''class using emp2 object .

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Type,

'''public String department="IT";'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| For demo purpose let the default department be IT.

So, go to '''Manager '''class and initialize the value for '''department.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Save '''and '''run '''the program.
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Save''' and '''run''' the program.

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| Highlight output,

'''Details of Manager class :'''

'''Name: Ankita'''

'''Email: ankita@gmail.com'''

'''Manager of:'''

'''Details of Manager class:'''

'''Name: Jayesh'''

'''Email: jayesh@gmail.com'''

'''Details of Manager class:'''

'''Name: Nikkita Dinesh'''

'''Email: abc@gmail.com'''

'''Manager of: Accounts'''

| style="border:0.05pt solid #000000;padding:0.185cm;"| We get the output,

Employee object referring Employee class,

Manager object referring Employee class &

Manager object referring Manager class,

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| Here we see that the '''getDetails() '''method of Manager class is called by '''emp2'''.

But when '''emp2''' tried calling '''setDepartment''', we got an error.

The reason for that is as follows:

|-
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #20124d;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| The compiler sees the '''getDetails()''' method in the '''Employee''' class during '''emp2.getDetails()'''.

So, it does not throw an error and validates the code.

At run time, however, the '''JVM''' invokes '''''getDetails()''''' in the '''Manager''' class.

As '''getDetails() '''of '''Manager '''class overrides '''getDetails() '''of '''Employee '''class.

So we get the output as per '''getDetails() '''of '''Manager '''class.

But the compiler does not see the '''setDepartment''' method in the '''Employee '''class.

Therefore, it raises an error in case of '''setDepartment''' call by emp2.

|-
| style="border:0.05pt solid #20124d;padding:0.185cm;"| Highlight

'''System.out.println("Details of Employee class:" + "\n" + emp1.getDetails());'''
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #20124d;border-right:0.05pt solid #000000;padding:0.185cm;"| Here, '''Employee '''method '''getDetails()''' is invoked for '''Employee '''class.

The compiler references '''Employee''' class for '''getDetails()''' during '''emp1.getDetails().'''

At run time, the '''JVM''' invokes '''''getDetails()''''' in the '''Employee''' class.

So we get the output as per '''getDetails() '''of '''Employee '''class.

Thus JVM calls the appropriate method for the object that is referred to in each variable

This behavior is referred to as '''Virtual Method Invocation.'''

The methods are referred to as '''Virtual Methods'''.

|-
| style="border:0.05pt solid #20124d;padding:0.185cm;"|
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #20124d;border-right:0.05pt solid #000000;padding:0.185cm;"| All methods in Java behave in this manner.

|-
| style="border-top:0.05pt solid #20124d;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| *

|-
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #20124d;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| We successfully learnt what is '''Virtual Method Invocation.'''

|-
| style="border-top:0.05pt solid #20124d;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"| Slide 10
| style="border:0.05pt solid #000000;padding:0.185cm;"| We have already learnt '''Compile-time polymorphism '''i.e. method overloading.

Let us quickly know '''Compile time polymorphism '''in brief.

'''Compile time polymorphism''' is nothing but '''method overloading''' in java.

Class can have more than one methods.

The methods have same name but with different number of arguments.

Compiler is able to figure out the method call at compile-time.

That’s the reason it is known as '''compile time polymorphism.'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"|
| style="border:0.05pt solid #000000;padding:0.185cm;"| So let us summarize.

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Slide 11'''

'''Summary'''

| style="border:0.05pt solid #000000;padding:0.185cm;"| In this tutorial we learnt:

* What is '''Polymorphism''' in Java?
* '''Run-time polymorphism'''
* '''Compile-time polymorphism'''
* '''Virtual Method Invocation'''

|-
| style="border:0.05pt solid #000000;padding:0.185cm;"| '''Slide 12'''

'''Assignment'''
| style="border:0.05pt solid #000000;padding:0.185cm;"| As an assignment,

Override methods for '''Vehicle''' and '''Bike class''' which we used in previous tutorials.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Slide 13

'''About Spoken Tutorial Project'''

| style="border:0.05pt solid #000000;padding:0.106cm;"| The video available at the following link summarizes the Spoken Tutorial project. Please watch it.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Slide 14

'''About Spoken Tutorial workshops'''

| style="border:0.05pt solid #000000;padding:0.106cm;"| The Spoken Tutorial Project Team conducts workshops and gives certificates to those who pass an online test.

For more details, please write to us.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"| Slide 15

'''Acknowledgement'''

| style="border:0.05pt solid #000000;padding:0.106cm;"| Spoken Tutorial Project is supported by the NMEICT, MHRD, Government of India.

More information on this Mission is available at this link.

|-
| style="border:0.05pt solid #000000;padding:0.106cm;"|
| style="border:0.05pt solid #000000;padding:0.106cm;"| This is Trupti Kini from IIT Bombay signing off. Thank you for joining.

|}

@@ Line 282: / Line 282: @@
 |-
-| style="border:0.05pt solid #000000;padding:0.106cm;"|
+| style="border:0.05pt solid #000000;padding:0.106cm;"| Switch to TestEmployee
 | style="border:0.05pt solid #000000;padding:0.106cm;"| This is because, '''setDepartment '''method does not exist for '''Employee '''class.
@@ Line 306: / Line 306: @@
 |-
-| style="border:0.05pt solid #000000;padding:0.106cm;"|
+| style="border:0.05pt solid #000000;padding:0.106cm;"| Highlight the output.
-| style="border:0.05pt solid #000000;padding:0.106cm;"| Here in the output we get the '''Manager of: '''as blank.
 This is because we have not initialized '''department''' in '''Manager '''class using '''emp2'''.
@@ Line 347: / Line 354: @@
 '''Manager of: Accounts'''
 '''Employee''' object referring '''Employee''' class,
@@ Line 364: / Line 372: @@
 But when '''emp2''' tried calling '''setDepartment''', we got an error.
 |-
 | style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #20124d;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.185cm;"| Highlight '''getDetails()'''
-| style="border:0.05pt solid #000000;padding:0.185cm;"| The compiler sees the '''getDetails()''' method in the '''Employee''' class during '''emp2.getDetails()'''.
+| style="border:0.05pt solid #000000;padding:0.185cm;"| The reason for that is as follows:
 So, it does not throw an error and validates the code.
@@ Line 398: / Line 406: @@
 So we get the output as per '''getDetails() '''of '''Employee '''class.
 This behavior is referred to as '''Virtual Method Invocation.'''
 The methods are referred to as '''Virtual Methods'''.

Java/C3/Polymorphism/English - Revision history

Nancyvarkey at 05:37, 29 April 2015

Nancyvarkey at 06:57, 27 April 2015

Trupti at 09:34, 30 March 2015

Trupti: Created page with "'''Title of script''':''' Polymorphism in Java''' '''Author: Trupti Rajesh Kini''' '''Keywords: Polymorphism, virtual method, run-time polymorphism, Compile-time polymorphis..."