Improve company productivity with a Business Account.Sign Up


When to use abstract class and when to use interface?

Posted on 2006-07-23
Medium Priority
Last Modified: 2010-03-31
Hello Expert,
 what is abstract?
 what is interface?              
 Please tell me When to use abstract class and when to use interface?
 plz give sutable example and defination.

                                        Thanks you
Question by:Atkari
LVL 92

Accepted Solution

objects earned 500 total points
ID: 17165618

Author Comment

ID: 17165730
give the example
Upgrade your Question Security!

Your question, your audience. Choose who sees your identity—and your question—with question security.


Assisted Solution

kaliyugkaarjun earned 500 total points
ID: 17165979
WHat is abstract class?

What is interface?

DIfference between the two

An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.

Assisted Solution

colr__ earned 500 total points
ID: 17166052
By implementing an interface, you guarantee that the class can service the methods defined in that interface. For example, if you’ve got an interface with a method getX(), then any class that implements that interface MUST  implement the method getX().

This is useful when you don’t know for sure what class type you are going to be using. For example, imagine an object reference passed into a method. You might not be aware what the type of the class is, but you might only need its getX() method - you can set the type argument in the method to be of the type of the interface, so no matter what the type of the class that is passed in, you know you can definitely call getX().

Abstract classes are a similar concept, but can contain pieces of implementation. So, an abstract class may have one method that is implemented/defined, and another method that is declared as abstract and which requires the programmer to implement.

Abstract classes and interface cannot be instantiated - they can only be extended by other classes.
LVL 30

Assisted Solution

by:Mayank S
Mayank S earned 500 total points
ID: 17167768

Expert Comment

ID: 17176165
some more

 Neither Interface or Abstract classes can be instantiated. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.

Use interface as much as possible and only use an abstract class in the case where you want to provide some (but not all, of course) implementation. In practice, you want to prefer using, passing and returning interfaces, not abstract class references. I think even in the case where you have an abstract class to share some implementation, you still want to have an interface represent what will be used by the client (for an example look at the new Collections -- you often pass around Collection, List, Set or Map references, but not a AbstractList, AbstractSet or AbstractMap, references).

Featured Post

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Java had always been an easily readable and understandable language.  Some relatively recent changes in the language seem to be changing this pretty fast, and anyone that had not seen any Java code for the last 5 years will possibly have issues unde…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
Viewers will learn about basic arrays, how to declare them, and how to use them. Introduction and definition: Declare an array and cover the syntax of declaring them: Initialize every index in the created array: Example/Features of a basic arr…
Viewers will learn about the regular for loop in Java and how to use it. Definition: Break the for loop down into 3 parts: Syntax when using for loops: Example using a for loop:

589 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question