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

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

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

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

| For this tutorial, I am using

|You should also have the knowledge of''' subclassing '''in''' Java.'''

|It is declared using''' abstract keyword'''.

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

|Now, right click on '''src''' folder and click '''New-'''> '''Class'''.

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

|Also type''' int age semicolon.'''

|Now click on''' Source ->''' and select''' Generate constructor using fields. '''

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

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

|So type '''public void showDetails( )''' semicolon.

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

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

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

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

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

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

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

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

|Now click on '''Source'''-> and then select''' Generate constructor using fields.'''  

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

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

| There are two fields in the '''Student class – register number''' and''' grade''' which represent student egister number and grade.

|It prints the values of''' Student Register Number''' and''' grade'''

|Click on '''New'''-> '''Class''' and then type name as''' Demo. '''

|Inside this '''class''' we will have the '''main method''',

|So type '''main''' and then press ctrl+space to generate the''' main method.'''

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

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

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

|We can invoke the''' showBasicDetails() method '''and''' showDetails()''' '''method '''using the '''object''' as shown.

| Now let us run this '''Demo''' program.  

|So right click on the '''class Demo''' and then select '''Run as''' ->''' Java Application'''

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

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

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

|Other details of the student like '''Student register number '''and '''grade''' are printed by the''' showDetails() method'''.

| 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'''

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

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

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

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

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

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