when to use abstract class and interface

[vidhyasagar reddy]

can any body explain me when to use abstract class and when to use interface . i know the basic differences b/w them

[Casper Maxwell]

As far as i remember, we can write method bodies into abstract classes:

...
public void printHello() {
System.out.println("Hello");
}
...

But we can not do this in interfaces. So when i have some common code to use between all specialized versions of my classes but also have interface requirements (inherited classes are required to have their own implementation of some methods), i will prefer to use abstract classes.

If there is no common functionality, i will just use an interface.

[David O'Meara]

"Casper Casper",
Please see the warning about your display name here.

If you do not update your display name soon your account will be deleted

Dave
[Edit - ooops, wrong link]
[ August 10, 2005: Message edited by: David O'Meara ]

[Ilja Preuss]

http://faq.javaranch.com/view?InterfaceVsAbstractClass

[Steve Morrow]

Abstract classes vs. interfaces: When does it make sense to choose an abstract class over an interface?
Abstract classes and interfaces practicum: Move from theory to practice on when to employ abstract classes vs. interfaces
Tech Tips: ABSTRACT CLASSES VS. INTERFACES

[Mahesh x Bogadi]

Simple rule.

* Use interface if you don't want to implement any of the member functions.
This implies.
- The class implementing the interface must implement all of its functions.

* In abstract class you need not define/implement all the functions like interface. This can be used where you can to define/implement some method and allow user to implement the rest(if there any unimplemented funtions..since there an abstract class can define/implement all the functions).

Interface and abstract class can be used for multiple inhertence. (OOP concept)