Inheritance vs. interface in C# [duplicate]

Answer 1

Refering to Abstract Class versus Interface.

There are some similarities and differences between an interface and an abstract class:

A class may implement several interfaces.
A class may inherit only one abstract class.

An interface cannot provide any code, just the signature.
An abstract class can provide complete, default code and/or just the details that have to be overridden.

An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public
An abstract class can contain access modifiers for the subs, functions, properties

Interfaces are used to define the peripheral abilities of a class. In other words both Human and Vehicle can inherit from a IMovable interface.
An abstract class defines the core identity of a class and there it is used for objects of the same type.

If various implementations only share method signatures then it is better to use Interfaces.
If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.

If we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method.
If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly.

No fields can be defined in interfaces
An abstract class can have fields and constrants defined

Answer 2

Class inheritance represents an "is-a" relationship, e.g., a Tank is a Vehicle. If your situation doesn't at least meet this, choose interface over inheritance.

If the proposed base class doesn't provide default implementations for your methods, this would be another reason to choose interface over inheritance.

In C#, you can only inherit from one class but multiple interfaces. This would be yet another reason to choose interface over inheritance.

Get the idea?

Answer 3

An interface contains only the signatures of methods, delegates or events. The implementation of the methods is done in the class that implements the interface.

A class can implement multiple interfaces.

A class can have only one direct base class.

Answer 4

Interfaces allows to define the structure of common behaviors.

Inheritance is useful if you can extract a common implementation of one or more specific behaviors.

Basically if several classes scrape a date the same way, it make sense to put scrapeDate in a base class; otherwise use only an interface and define the specific scrapeDate in every class that implement your interface.

Answer 5

Honestly, do both.

public interface IScraper
{
  string ScrapeDate(string url);
}

public abstract class Scraper : IScraper
{
  public string ScrapeDate(string url)
  {
    // default implementation
  }
}

There's advantages either way, but those are difficult to quantify without knowing more about your requirements. However, there's no reason you can't do both. Having an interface for your class makes it mockable for testing purposes as well.

Something else to consider though; if the functionality for each of your derived classes are similar enough, it may be easier to simply have a single class that takes parameters to the constructor.

Answer 6

If you have common functionality, you should use inheritance - the functionality will then be available in all child classes, and each child class can extend or override the parent class code.

If you have something consuming your classes, you would use interfaces to ensure that all of the classes implement the same methods and properties, but not necessarily the same functionality.