Answer Posted / janardhan

abstract class:-- abstract class contains abstract methods
and concreat methods,abstract class may have Zero(0)
abstract methods also, for example HttpServlet class is
best example for abstract class, HttpServlet class contains
Zero abstract methods, The SUN People declared HttpServlet
as abstract,B'ecz out side people unable to create object
for HttpServlet(abstract class)and due to security reasons
HttpServlet declared as abstract class.

If you are declared abstract methods in a abstract class,
we should provide the implementation in child classes.

we can't create Object for abstract class, we can create
refrence for abstract class.

In real-time, we can use abstract classes depends on
requirement only.

Interface:---

By default all the methods in Interface are public abstract
methods.Variables are by default public static final.
All the methods are non-implemented in interface and we
need to provide the implemantation for abstract methods in
interface implemented class(child class)

For example Servlet is a interface, if MyServlet class
implements Servlet, then we should provide the
implementation for Servlet interface methods like init
(),service(), destroy(),servletConfig(),etc..

EX:-- MyServlet implements Servlet{

init(){
........
........

}
service(){

........
...........

}
destroy(){

........
........

}
//we have some of the methods of Servlet interface ,those
//methods we need to implement here
}

Mostly In real time we need to use Interfaces.

for example :--

All business methods we need to declare in interface and we
need to provide the implementation for those business
methods in implemented class.

Main purpose of interface is :--

Reusability
maintainability

Example:--

public interface DaoInterface{

public abstract getDetails();
public abstract getProductId();
public abstract getProductName();
public abstract searchProduct();
public abstract editProduct();
.........
............
}

public class DaoClass implements DaoInterface{
public abstract getDetails();{

// we need to write our business logic here depends on
requirement.
}
public abstract getProductId();{
// we need to write our business logic here depends on
requirement.
}
public abstract getProductName();{
// we need to write our business logic here depends on
requirement.
}
public abstract searchProduct();{
// we need to write our business logic here depends on
requirement.
}
public abstract editProduct(); {
// we need to write our business logic here depends on
requirement.
}
}

Note:-- The above DaoInterface business methods any body
can implement their own way and write business logic
depends requirement.

Thanks

Jana

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