Difference between revisions of "Java/C3/Abstract-Classes/English-timed"

 

{| Border=1

| <center>'''Time'''</center>

| <center>'''Narration'''</center>

| 00:01

| Welcome to the Spoken Tutorial on''' Abstract Classes.'''

| 00:05

| In this tutorial we will learn about:  '''Abstract Methods '''and''' Concrete Methods'''

| '''Abstract Classes '''and''' Concrete Classes '''and

| 00:15

| How to use '''Abstract Classes'''

| 00:18

| For this tutorial, I am using

* '''Ubuntu 12.04'''

* '''JDK 1.7 '''and

* '''Eclipse''' '''4.3.1'''

| 00:28

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

| You should also have the knowledge of''' subclassing '''in''' Java.''' If not, for relevant''' Java '''tutorials, please visit the link shown.

| 00:46

| First we will see about '''Abstract Method'''.

| 00:50

| An '''Abstract method''' is a''' method''' that is declared without implementation.

| It is declared using''' abstract '''keyword. There should not be opening and closing parenthesis for this '''method'''.

| 01:04

| The''' method showDetails()''' illustrated here, is an example of''' abstract method'''.

| 01:10

| Note that this '''method''' is declared using the''' abstract '''keyword, with no current implementation.

| 01:18

| Next we will see about '''concrete method'''.

| 01:21

| A '''Concrete method''' is completely implemented within the curly brackets.

| 01:27

| This method''' showBasicDetails()''' illustrated here is an example of '''concrete method'''.

| 01:35

| Observe that this '''method''' is implemented completely.

| 01:39

| Now we will learn about '''abstract class''' with an example.

| 01:44

| An''' abstract class''' usually contains at least one''' abstract method'''.

| 01:49

|   '''Abstract methods '''can be added only to '''abstract classes.'''

| 01:54

| The '''class Person''' illustrated here is an''' abstract class.'''

| 01:59

| It contains an''' abstract method''' called''' showDetails()'''.

| 02:04

| It can also contain '''variables''' and other '''concrete methods.'''

| 02:09

| The figure here represents an '''inheritance relation'''. Here, the''' Person class''' is an''' abstract class.'''

| 02:18

| The''' Employee class''' and the '''Student class''' are '''subclasses''' of the''' Person class'''.

| 02:24

| These '''subclasses''' can provide their own different implementations.

| 02:29

| These are done by''' showDetails( ) method''' present in the''' Person class.'''

| 02:35

| For example: '''ShowDetails() Method''' in the''' Employee class''' prints the '''Employee ID''' and the''' Salary''', where as  '''ShowDetails() Method''' in the''' Student class''' prints the '''Student Reg No''' and the '''Grade.'''

| 02:49

| A '''class''' is said to be a''' concrete class,''' if all the '''methods''' in that '''class''' are''' concrete methods'''.  

| 02:57

| The '''class Employee''' illustrated here, is a''' concrete class'''.  All the '''methods''' inside this '''class''' including''' showDetails()''' are '''concrete'''.

| 03:07

| Let us understand the usage of '''Abstract class '''with a sample program.

| 03:12

| Now we will switch to''' Eclipse''' and create a new '''project''' called '''AbstractDemo'''.

| 03:19

| Inside this '''project''', we will create the necessary '''classes''' to demonstrate the usage of''' Abstract class.'''

| 03:27

| Now, right click on '''src''' folder and click '''new-'''> '''class'''.

| 03:33

| Type the name of the '''class''' as '''Person''' and press '''Enter'''.

| 03:38

| Now we will add the fields to represent the name and age of the''' Person'''.

| 03:44

| Type''' String name semicolon.''' Also type''' int age semicolon.'''

| 03:51

| Now click on''' source ->''' and select''' generate constructor using fields. '''

| 03:58

| Delete the '''super '''keyword from the generated code.

| 04:02

| The '''constructor''' can initialise the values of '''name''' and '''age '''fields.

| 04:08

| We will add a''' concrete method''' to this '''class''' to print the name and age.  

| 04:14

| So type '''public void showBasicDetails( )''' within '''brackets''' type, '''System.out.println''' within round brackets and within quotes type''' Name colon''' plus''' name semicolon'''

| 04:33

| Also type '''System.out.println''' within round brackets and within quotes''' Age colon''' plus''' age semicolon'''

| 04:46

| Now we will add an '''abstract method''' to this '''class'''. So type '''public void showDetails( ) semicolon'''

| 04:56

| An error comes up, since we have not yet added the''' abstract '''keyword.  

| 05:01

| So now, add the keyword '''abstract.'''

| 05:04

| Now we can see, another error comes up. This is because, '''abstract methods''' can be added only to '''abstract classes'''.

| 05:13

| So now, add the keyword''' abstract''' to the''' Person class '''to make it an''' abstract class.'''

| 05:20

| Then right click on the '''default package''' and create another''' class''' called''' Employee.'''

| 05:26

| Now to make this a '''subclass''' of '''Person class, '''type''' extends Person'''.

| 05:34

| Now we can see an error comes up in the '''Eclipse IDE.'''

| 05:38

| It indicates that, we should provide an implementation to the '''abstract method showDetails( )'''.

We will do it a little later.

| 05:48

| Now create two fields to represent the '''employee id''' and '''employee salary'''.

| 05:54

| So type ''' String empid semicolon''' and''' int salary semicolon'''

| 06:01

| Now click on '''source'''-> and then select''' generate constructor using fields.'''

| 06:08

| This '''constructor''' can initialise the values of '''name, age, empid '''and''' salary'''.

| 06:15

| Let us now define the''' showDetails method'''. So type''' public void showDetails( )'''

| 06:23

| Inside this '''method''', we need to print the employee details.  

| 06:27

| So type '''System.out.println''' within quotes''' Emp id colon''' plus''' empid semicolon'''

| 06:38

| '''System.out.println''' within quotes''' Salary colon''' plus''' salary semicolon'''

| 06:47

| Note that the error disappears, once the '''showDetails() method''' is implemented.

| 06:54

| Next we will see a '''Student class''' of the '''project'''.

| 06:57

| I have already created a '''subclass''' called''' Student'''.

| 07:02

| There are two fields in the '''Student class, regno (register number) ''' and''' grade''' which represent '''student reg. no (register number)''' and '''grade'''.

| 07:11

| A '''constructor''' is also created inside this '''class'''. This '''constructor''' can be used to initialize the values for''' name, age, register number '''and''' grade.'''

| 07:24

| The''' showDetails method''' is also implemented in this '''class'''.  It prints the values of''' Student Reg. Number''' and''' grade'''

| 07:34

| Now note that the''' Employee class''' has its own implementation of''' showDetails().'''

| 07:42

| And the''' Student class''' has its own implementation of''' showDetails().'''

| 07:48

| Now right click on the '''default package.''' Click on '''new'''-> '''class''' and then type name as''' Demo.'''

| 07:57

| Inside this '''class''', we will have the '''main method''', So type '''main''' and then press '''Ctrl space''' to generate the''' main method.'''

| 08:08

| Now let us try to instantiate the''' Person class''' by typing '''Person p equals new Person.'''

| 08:16

| Within brackets and double quotes, type '''John''' and put a '''semicolon'''.

| 08:23

| Now we can see an error. This is because the''' Person class''' is '''abstract''' and it cannot be instantiated. Let's remove this line.

| 08:34

| Type the following code as displayed on the screen.

| 08:38

| Now let us instantiate the''' Person class''' using the''' Employee class''' as '''Person p1 equals new Employee.'''

| 08:48

| In the first line, we are passing the values of different '''arguments'''.

 

| 08:57

| '''40''' as the value of '''age. E267''' as the value of '''Employee ID''' and

| 09:04

| '''10000''' as the value of '''Employee salary.'''

| 09:07

| Now we can invoke the '''concrete method''' in the '''Person class''' as '''p1.showBasicDetails()'''

| 09:16

| We can also call the''' showDetails() method''' using the '''object p1''' as '''p1.showDetails()'''

| 09:24

| Similarly, instantiate the''' Person class''' using the''' Student class'''. This is represented as '''Person p2 equals new Student.'''

| 09:35

| Now we are passing the values of different '''arguments'''.

 

'''Hari''' is passed as the value of''' student name''',

| 09:44

| '''20''' as the value of '''age'''.

| 09:47

| '''12005''' as the value of''' student Reg No.''' and '''A''' as the value of '''grade'''.

| 09:55

| Now we can call the''' showBasicDetails() method '''using the '''object p2''' as '''p2.showBasicDetails()'''

| 10:04

| We can also invoke the''' showDetails() method''' using the '''object p2''' as '''p2.showDetails()'''

| 10:13

| Now let us run this '''Demo''' program. So right click on the '''class Demo''' and then select '''Run as''' ->''' Java Application'''

| 10:23

| We can see the output with the basic employee details like''' name '''and''' age.'''

| 10:29

| These are printed by '''showBasicDetails() method.'''  

| 10:33

| Other Employee details like''' employee ID '''and '''salary '''are printed by the''' showDetails() method'''.

| 10:41

| Similarly, the basic student details like '''name''' and '''age''' are printed by''' showBasicDetails() method.'''

| 10:50

| Other details of the student like '''Student register no '''and '''grade''' are printed by the''' showDetails() method'''.

| 10:59

| 11:05

| In this tutorial we have learnt about

* '''Abstract Classes '''and''' Concrete Classes '''and  

* How to create and use''' Abstract Classes'''

| 11:19

| As an assignment- Create an '''abstract class Vehicle''' which contains an '''abstract method run()'''

| 11:27

| Create a '''subclass Car''' which extends the '''Vehicle class''' and implements the '''run method''' that prints '''“Car is running on 4 wheels”'''

| 11:37

| Also create a'''subclass Bike''' which again extends the '''Vehicle class''' and implements the '''run method''' that prints '''“Bike is running on 2 wheels”'''

| 11:48

| Also create a '''Demo class '''containing the''' main method''' to verify the results.

| 11:54

| The video at the following link summarizes the''' '''Spoken Tutorial Project. Please download and watch it.

| 12:02

| The Spoken Tutorial Project Team

* Gives certificates on passing the online tests

| 12:11

| For more details, please write to us.

| 12:15

More information on this Mission is available at the link shown.

| 12:26

| This script has been contributed by: Dept. of Information Technology, Amal Jyothi College of Engineering.

 

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