Java/C3/Abstract-Classes/English-timed

Time	Narration
00:01	Welcome to the Spoken Tutorial on Abstract Classes.
00:05	In this tutorial we will learn about: Abstract Methods and Concrete Methods
00:12	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.
00:36	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.
00:55	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. John is passed as Employee name,
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	This brings us to the end of this tutorial. Let us summarize.
11:05	In this tutorial we have learnt about Abstract Methods and Concrete Methods 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 asubclass 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.
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12:26	This script has been contributed by: Dept. of Information Technology, Amal Jyothi College of Engineering. This is Priya from IIT Bombay signing off. Thank you for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14