Difference between revisions of "Java/C3/Abstract-Classes/English-timed"
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| − | | In this tutorial, we will learn about: | + | | In this tutorial, we will learn about: '''Abstract Methods '''and''' Concrete Methods''' |
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| 00:12 | | 00:12 | ||
| − | | | + | | '''Abstract Classes '''and''' Concrete Classes '''and |
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| − | | | + | |How to use '''Abstract Classes'''. |
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| For this tutorial, I am using: | | For this tutorial, I am using: | ||
| − | + | '''Ubuntu 12.04''' | |
| − | + | '''JDK 1.7 '''and | |
| − | + | '''Eclipse''' '''4.3.1''' | |
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| − | | In this tutorial, we have learnt about: | + | | In this tutorial, we have learnt about: '''Abstract Methods '''and''' Concrete Methods''' |
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|09:14 | |09:14 | ||
| − | | | + | | '''Abstract Classes '''and''' Concrete Classes '''and How to create and use''' Abstract Classes'''. |
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| − | | The Spoken Tutorial Project Team: | + | | The Spoken Tutorial Project Team: Conducts workshops using spoken tutorials and |
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|10:09 | |10:09 | ||
| − | | | + | |Gives certificates on passing the online tests. |
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Latest revision as of 17:33, 24 April 2019
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| 00:00 | 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 |
| 00:16 | 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. |
| 00:40 | 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. |
| 00:59 | There should not be opening and closing parenthesis for this method. |
| 01:04 | Let us understand the usage of Abstract class with a sample program. |
| 01:09 | Now we will switch to Eclipse and create a new project called AbstractDemo. |
| 01:16 | Inside this project, we will create the necessary classes to demonstrate the usage of Abstract class. |
| 01:24 | Now, right-click on src folder and click New > Class. |
| 01:30 | Type the name of the class as Person and press Enter. |
| 01:35 | Now we will add the fields to represent the name and the age of the Person. Type: String name semicolon. |
| 01:44 | Also type: int age semicolon. |
| 01:48 | Now click on Source and select Generate constructor using fields. |
| 01:55 | Delete the super keyword from the generated code. |
| 01:59 | The constructor can initialise the values of name and age fields. |
| 02:05 | Next we will see about concrete method. |
| 02:08 | A Concrete method is completely implemented within the curly brackets. |
| 02:14 | We will add a concrete method to this class to print the name and age. |
| 02:21 | Type the following code as displayed on the screen. |
| 02:25 | This method showBasicDetails() illustrated here, is an example of concrete method. |
| 02:32 | Observe that this method is implemented completely. |
| 02:36 | Now we will add an abstract method to this class. |
| 02:41 | So, type: public void showDetails( ) semicolon. |
| 02:46 | An error comes up, since we have not yet added the abstract keyword. |
| 02:51 | So, now add the keyword abstract. |
| 02:55 | Now we can see another error comes up. |
| 02:58 | This is because, abstract methods can be added only to abstract classes. |
| 03:03 | So, now add the keyword abstract to the Person class to make it an abstract class. |
| 03:10 | The class Person illustrated here is an abstract class. |
| 03:15 | It contains an abstract method called showDetails(). |
| 03:20 | The figure here represents an inheritance relation. |
| 03:24 | Here, the Person class is an abstract class. |
| 03:29 | The Employee class and the Student class are subclasses of the Person class. |
| 03:35 | These subclasses can provide their own different implementations. |
| 03:40 | These are done by showDetails( ) method present in the Person class. |
| 03:45 | 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 Register Number and Grade. |
| 04:01 | Then right-click on the default package and create another class called Employee. |
| 04:07 | Now to make this a subclass of Person class, type: extends Person. |
| 04:14 | Now, we can see an error comes up in the Eclipse IDE. |
| 04:19 | It indicates that we should provide an implementation to the abstract method showDetails( ). |
| 04:26 | We will do it a little later. |
| 04:28 | Now create two fields to represent the employee id and employee salary. |
| 04:34 | So, type: String empid semicolon and int salary semicolon. |
| 04:42 | Now click on Source and then select Generate constructor using fields. |
| 04:49 | This constructor can initialize the values of name, age, empid and salary. |
| 04:56 | Let us now define the showDetails method. So, type: public void showDetails( ). |
| 05:04 | Inside this method, we need to print the employee details. |
| 05:09 | Type the following code as displayed on the screen. |
| 05:13 | Note that the error disappears, once the showDetails() method is implemented. |
| 05:19 | Next we will see a Student class of the project. |
| 05:23 | I have already created a subclass called Student. |
| 05:28 | There are two fields in the Student class – register number and grade which represent student register number and grade. |
| 05:37 | A constructor is also created inside this class. |
| 05:42 | This constructor can be used to initialize the values for name, age, register number and grade. |
| 05:50 | The showDetails method is also implemented in this class. |
| 05:56 | It prints the values of Student Register Number and grade. |
| 06:00 | Now note that the Employee class has its own implementation of showDetails(). |
| 06:08 | And the Student class has its own implementation of showDetails(). |
| 06:14 | Now right-click on the default package. |
| 06:17 | Click on New > Class and then type name as Demo. |
| 06:23 | Inside this class, we will have the main method. |
| 06:27 | So, type main and then press ctrl+space to generate the main method. |
| 06:33 | Now let us try to instantiate the Person class by typing Person p equals new Person. |
| 06:42 | Within brackets and double quotes type John and put a semicolon. |
| 06:48 | Now we can see an error. This is because the Person class is abstract and it cannot be instantiated. |
| 06:58 | Let's remove this line. |
| 07:00 | Type the following code as displayed on the screen. |
| 07:04 | Now, let us instantiate the Person class using the Employee class as Person p1 equals new Employee. |
| 07:14 | In the first line, we are passing the values of different arguments. |
| 07:19 | John is passed as Employee name. |
| 07:22 | 40 as the value of age. |
| 07:25 | E267 as the value of Employee ID and 10000 as the value of Employee salary. |
| 07:33 | Now we can invoke the concrete method in the Person class as p1.showBasicDetails(). |
| 07:41 | We can also call the showDetails() method using the object p1 as p1.showDetails(). |
| 07:50 | Similarly instantiate the Person class using the Student class. |
| 07:55 | This is represented as Person p2 equals new Student. |
| 08:01 | Now we are passing the values of different arguments. |
| 08:06 | We can invoke the showBasicDetails() method and showDetails() method using the object as shown. |
| 08:15 | Now let us run this Demo program. |
| 08:18 | So, right-click on the class Demo and then select Run as > Java Application. |
| 08:25 | We can see the output with the basic employee details like name and age. |
| 08:31 | These are printed by showBasicDetails() method. |
| 08:35 | Other employee details like employee ID and salary are printed by the showDetails() method. |
| 08:43 | Similarly the basic student details like name and age are printed by showBasicDetails() method. |
| 08:52 | Other details of the student like Student register number and grade are printed by the showDetails() method. |
| 09:01 | This brings us to the end of this tutorial. Let us summarize. |
| 09:07 | In this tutorial, we have learnt about: Abstract Methods and Concrete Methods |
| 09:14 | Abstract Classes and Concrete Classes and How to create and use Abstract Classes. |
| 09:21 | As an assignment, create an abstract class Vehicle which contains an abstract method run(). |
| 09:29 | Create asubclass Car which extends the Vehicle class and implements the run method that prints “Car is running on 4 wheels”. |
| 09:39 | Also create asubclass Bike which again extends the Vehicle class and implements the run method that prints “Bike is running on 2 wheels”. |
| 09:50 | Also create a Demo class containing the main method to verify the results. |
| 09:56 | The video at the following link summarizes the Spoken Tutorial Project. Please download and watch it. |
| 10:03 | The Spoken Tutorial Project Team: Conducts workshops using spoken tutorials and |
| 10:09 | Gives certificates on passing the online tests. |
| 10:13 | For more details, please write to us. |
| 10:16 | Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India. |
| 10:23 | More information on this mission is available at the link shown. |
| 10:28 | This script has been contributed by Dept. of Information Technology, Amal Jyothi College of Engineering. |
| 10:35 | This is Priya from IIT Bombay, signing off. Thank you for joining. |
