Sesssion 14:- Abstract Class

Introduction about Abstract class:-

• Abstract class is incomplete class which may have contained abstract method as well as concrete method 
• In a class at least one method is abstract than class must be define as abstract class. 
• Abstract method can’t have body or implementation. 
•   When a class inherits the abstract class than its mandatory for child class to override all the parent abstract method, otherwise child class also become abstract. 
•   We can’t create an object of abstract class but parent abstract class can refer any of its child objects in the entire inheritance hierarchy. 
•   In abstract class can have constructor (User define, as well as default) 
•   Constructor of abstract class required to instance variable of abstract class 
• We can’t call constructor of an abstract class by using keyword “new” but it can be called by its child class constructor. 
•  A class can still be called as an abstract even through it doesn’t have abstract method.

Ex :- HttpServelt 

•   Variable & constructor or can’t be abstract.

Advantage:-

• Can achieve abstraction.
• Lose coupling. 
• Zero dependency.
• Standardization in method definition.  

Example :- Abstract class

public abstract class Mobile {
public void call()
{
System.out.println ("call function....");
}
public abstract void middleButton();
}
public class NokiaMobile extends Mobile{

@Override
public void middleButton() {
System.out.println ("start music player...");
} }
public class SonyMobile extends Mobile {
@Override
public void middleButton() {
System.out.println("start camera...");
}
}
public class Run
{
public static void main(String[] args)
{
Mobile m=null;
System.out.println ("first call sony mobile methods");
m=new Sonymobile();//PRCO
m.call();
m.middleButton();


System.out.println ("now call Nokia mobile methods");
m=new NokiaMobile();//PRCO m.call();
m.middleButton ();
}
}


OUT PUT:-
first call sony mobile methods
call function....
start camera...
now call Nokia mobile methods
call function....
start music player...

 Give me ans of following question.

Think:-“what is meaning of System.out.Println(“”) ????????”
Think:-“why main() method is static?????????”