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field its Are they tightly coupled or loosely coupled? So, if you do not know which way your software is going to go, there is no way you can base your decision of interface or abstract class on these reasons. So if you are using an abstract class and need to add a new method to your abstract class, you can happily add that without breaking any code using that class. I personally do not believe that these give a complete picture. Whether I am going to need to inherit from multiple abstract classes or not, Whether there is going to be a default implementation of some contract or not, Whether I would add a new method to a contract or define a new contract entirely in order to implement a change.

:laugh: This Provide an answer or move on to the next question. But they are both not the same type of things, they are completely different. If you find that line of thinking difficult, then work out if it is a can-do relationship that you are trying to model or an is-a relationship. spelling and grammar. By semantics I mean, what definition of an interface fundamentally differentiates it from an abstract class?

Don't tell someone to read the manual.

The content must be between 30 and 50000 characters. How about coupling of classes in inheritance? By that I mean, they all depend on you knowing how your design is going to take shape in future.

If a question is poorly phrased then either ask for clarification, ignore it, or. Originally published at Cheers! As your software grows and new features start pouring in, old features keep changing, you would hit a point where you would say to yourself Oh God, I should not have used an abstract class here.

email is in use. Correct me if my understanding is wrong. You can find me on LinkedIn as well. Interfaces represent capabilities and abstract classes represent type, Implementing interfaces represents can-do relationship and inheriting from (abstract) class represents an is-a relationship, To elaborate this point, lets consider following two classes, Both Camera and Gun can Shoot, that is their capability. This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL), I think inheritance supports tight coupling.

To summarise the recommendations from there and few other articles I have come across, here are the reasons in favour of abstract classes, And these are the reasons in favour of interfaces.

+1 (416) 849-8900. Do you need your, CodeProject,

20 Bay Street, 11th Floor Toronto, Ontario, Canada M5J 2N8 This article on MSDN offers a good discussion on the topic.

Lately, I have been using below heuristic to determine when to use interfaces/abstract classes and I feel quite excited about it as it works most of the time. If you google this topic you would find a lot of interesting articles.

Also, to be notified about my new articles and stories, follow me on Medium and Twitter. It is because the child classes are exposed to the majority of the parent class.

Instead of trying to predict feature about who will reuse which code, focus on determining whether it is a capability that you are abstracting away or a common type.

Prefer abstract classes if your contract has a possibility of changing over time. Learn on the go with our new app. Java Programming Language: For-Each Loop Example, Convert Excel to CSV or CSV to Excel using Java, Java vs C sharp: Top 8 Important Differences To Know, Use abstract class if you have a default implementation of some behaviour that child classes do not have to implement. Same is not true for interfaces. use interfaces if you need multiple inheritance).

If there is no default or common behaviour among all the classes that are inheriting from abstract class then interface may be a better choice. Second, I feel the above criteria are too futuristic. All these answers have helped me make a great addition to my knowledge. I get to hear a lot of interesting answers from folks. At times, I may have some idea of how my design is going to take shape in future but most of the times I do not have enough clarity to know in advance. Chances are they have and don't get it. Think about it: inheritance from a single base class had no alternative but to be tightly coupled! Head of Innovation at Collinson Group, Learning something new every day, author of Learning NHibernate 4.0 If you like my article, please dont forget to click to recommend it to others. First, above recommendations are mostly around syntax a particular language supports and not around semantics (e.g. Rectangle and Circle inheriting from Shape makes perfect sense here becauseRectangle/Circle are a type of Shape. So an interface like below would make more sense here, If you have learned OO programming the same way I did, then you would remember the classic shape example as below.

I have been asking this question in interviews for some years now. Understand that English isn't everyone's first language so be lenient of bad

Thank you for answering first question.