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Abstract Classes vs Interfaces

4 replies on 1 page. Most recent reply: Aug 12, 2003 10:19 PM by Michael Geisler

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Michael Rosenthal

Posts: 1
Nickname: mike1111
Registered: Aug, 2003

Abstract Classes vs Interfaces

Posted: Aug 11, 2003 7:00 PM

I am looking for some help around why I would use an abstract class instead of an interface. Preferable list the answers as pro/con.

neelakkannan

Posts: 1
Nickname: snkannan
Registered: Aug, 2003

Re: Abstract Classes vs Interfaces

Posted: Aug 12, 2003 1:25 AM

in interface all the methods are abstracts..but in abstract
class not the case..

with regards
snk

Lakhdip Nagra

Posts: 3
Nickname: lakhdip
Registered: Aug, 2003

Re: Abstract Classes vs Interfaces

Posted: Aug 12, 2003 4:08 AM

I have sometimes wondered that too, but I usually stick to the rule where I use an abstract class as a bit of a class, in that I know what some of the implementation is going to be and put those bits in and the rest of the stuff leave to be added in by subclasses.

I use interfaces just where I want to define what set of operations will be available, so for example, if I'm working on a group project, I can agree the interface to say a Clock object with a friend and they can implement it while I can write the code that uses it and when we finish, it should work fine.

Hope that helps in some way,

David

Posts: 150
Nickname: archangel
Registered: Jul, 2003

Re: Abstract Classes vs Interfaces

Posted: Aug 12, 2003 4:29 AM

Abstract Classes:
- Can contain instance variables.
- Can contain methods with an implementation.
- Can contain private/protected methods.

Interfaces:
- Can only contain public static final variables.
- Can only contain public abstract methods (no implementation).

Michael Geisler

Posts: 2
Nickname: goosey
Registered: Jul, 2003

Re: Abstract Classes vs Interfaces

Posted: Aug 12, 2003 10:19 PM

Or you could use both.

Define an interface and partially implement it with an
abstract class - then you can give the users of your type
a choice - fully implement the interface themselves or extend the abstract class and only override the methods they need
to...Generally I think any type you define that you expect
to be sub-classed by other users should be defined as an interface first at the very least

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