Why do we need Interfaces?

Why do we need Interfaces?

• Jakob S

  Hi,

  Its difficult to explain the real-time benefits of interfaces, abstract cls etc in such a short span/space. So let me conclude few of the things..

  Interfaces
  - Allows multiple inheritance, extensibility, runtime polymorphism, abstraction/data hiding, easy maintainance/management etc ... long list of benefits but finally all depends on your application requirements....
  e.g if you wish that a Human will have some specific characteristics, some of then can be found in other species and some of them are specific to the human then you can have IHuman (for human specific), ISpecies (common to all species) etc and you can impl these in Human

  So Human implements IHuman, ISpecies

  Now ISpecies can be implemented in Animal class to so this class can be implemented from IAnimal, ISpecies

  In concrete class or abstract class this is not possible. you can inherit from only ONE class while multi interface can be allowed.

  So if you have such requirement then you must use interfaces to reduce repeating code, good maintainability.

  Also lets say if you have created ISpecies and you have derived Human class then its possible that ISpecies can be used in future for Animal class or something like that etc then fur extensibility point of view its good to have it.

  Its basically OOP design concepts why you need to use interfaces.

  If yo have a very small application which has not future extension requirement and straight forward impl then you dont worry about interfaces but in else can you should...

  Also there is another benefit which is already explained in some post for your reply... that if you have two diff objects consiting same method then you can use interface to call that method without worring that which actual object it is.
  e.g. Lets say,
  public void AssignColor (IShape objShape) {
  objShape.Color = "Blue";
  }
  here, lets say IShape has a property named Color and you have a common method to assign color then you dont need to worry that which object is being passed wheter its Square, Triangle or something else.[which impl IShape]
  so AssignColor(objSqare) and AssignColor(objTriangle) both can work without changing your code. Even in future if you add some more shapes using IShape then also this method will work for them also.

  This way LOTS of real-time uses are there but all depends on your application need.

  But this is what i have faced so far that if your project is even a small project, then also its always good to follow OOPs concepts which will give you lots of future benefits.

  May be if you are not much aware/experienced using OOPs designs then it will be difficult to visualize the benefits but the fact is, I always used to use OOPs even in a smallest application. It can give you benefits but if not then also it will never harm you...

  Please find on google about differences between "Interfaces vs. classes" and "Interfaces vs. Abstract classes" etc, and read just top 5-10 links, you will get enough information.

  HTH,

  
  
  

• RabinLin

  Hi

  this is a question i've heard before...
  

  one of the principles of object oriented programming is the abstraction or separation if you wish, of the interface and the implementation of classes.

  consider, for example the IDbCommand interface in the system.data namespace.
  Regardless if the object's instance is a SqlCommand or a OledbCommand
  you can use the IDbCommand interface to "command" the object.

  so there you have the reusability of the code...

  However, an interface is more..
  an interface is the public face of a class, even if you don't explicitly declare it.
  consider the following:
  
  public class Test{
  public void DoSomething()
  public void DoSomethingElse()
  private void DoSomethingPrivate()
  }

  the two public methods, and any public properties can be considered as the interface of the class,
  so, i guess you could say that anything that is accessible for outside the class is it's interface...

  now, declaring an interface explicitly, is adding a layer of abstraction,
  which can come in handy later, if you want to add a second class that needs to implement it (reuse of code)
  but generally it's saying, or rather commiting to a number of behaviours by your class (separation of code and interface)

  Hope this sheds some light ;)

  
  
  

• enric vives

  Thank you. Now I could think of the uses of Interface somewhat.

  I got one more doubt, How does it differ from an Abstract/Base class

  Is there any specific reason/requirement to use Abstract class/Interface

  When sohuld we go for an abstract class and for Interface

  Thanks and Regards,

  Benin.

  
  
  

• Can-Ann

  Hi,

  Suppose you have an application that has two types of people: Customer and Employee. Both Customer and Employee can subscribe to an event. The procedure of subscribing is different. Customers need to pay and subscbribe where as Employees only need to subscribe.

  When you have a list of objects (both Customers and Employees) that want to subscribe, you need to check for each object what type of person it is before knowing how it needs to subscribe to the event. If at a certain point you add a different person type, you need to add additional code in the calling class.

  With interfaces this can be a lot easier. First we create an interface named IPerson. This interface has a method named Subscribe. Than we make sure that all the person types implement this interface. The method Subscribe is implemented in the classes (Customer, Employee).
  
  If we need to have a list of persons we create the list as follow:
  List<IPerson> myList = new List<IPerson>();
  
  IPerson person1 = new Customer();
  myList.Add(person1);
  
  IPerson person2 = new Employee();
  myList.Add(person2);

  Now when we loop through the list, we can use IPerson.Subscribe() to subscribe a person. This will cause the .NET framework to call the Subscribe method from the objects class.

  Interfaces make it easier to extend this type of code. When a different person type is needed, you only need to add a class that implements the IPerson interface.

  Let me know if the above is not clear.

  Greetz,

  Geert

   

  Geert Verhoeven
  Consultant @ Ausy Belgium

  My Personal Blog

  
  
  

• TheQuietShadow

  Well if you know that you are dealing with only one type, and will never have a second type then no you don't need to use interfaces, but interfaces are useful when you want extensible code, you don't have to use them but if you do they make your life a lot easier.
  
  Say for example you want to create a sorting algorithm, and you want it to work with any type of object, an easy way to do this is to write you're sorting class to operate on objects that implement a certain interface, say sortable. Without interfaces you would have to write a new class or method for any new classes you wish to sort, but if you use interfaces you just have to write one class that has one method that takes in a sortable object as it's parameter, and it will just work.
  
  Like anything in programming they aren't something that you absolutly have to use but they are a tool that can be used to create elegant and powerful code.
  
  
  
  

• marco.ragogna

  http://www.codersource.net/csharp_tutorial_interface.html
  http://www.codeguru.com/csharp/csharp/cs_syntax/interfaces/article.php/c7563/
  http://msdn2.microsoft.com/en-us/library/ms173156.aspx

  I'm not saying that I truely understand the meaning of interfaces but I wanted to provide you some links.

  Hope this helps!

  Timo

  
  
  

• BetterTrades

  You can read my article about the difference here: http://blogs.microsoft.co.il/blogs/maordavid/archive/2007/05/09/Interface-vs-Abstract-Class.aspx

  Interface vs Abstract Class

  
  
  

• Pixelpands

  Hi

  an abstract base class differs have some similarities

  they both provide a number of methods, properties and so on that are common to it's children and implementors

  but... a base class can define a code body (which can or can not be overriden),

  while an Interface only defines method signatures

  also, for inheritance i try and look at the "is a" rule

  so base class company
  child class client is a company
  child class supplier is a company

  all these can implement the

  public interface IIdentifiable{
  int id {get set};
  DateTime LastSave{get;set;}
  }

  which is not to say that interfaces can only be used for "util" purposes...

  Hope this helps you out!

  
  
  

• kalai

  If I understood correctly,

  Irrespective of the object's type we can assign it to the Interface type and call the implemented funtion (without knowing the type of object).

  But what is the significance of Interface while I am dealing with only one Type (either a Customer or an Emploee) Does Interface matters there

  Still I couldn't understand the real Need for the interface :(.

  What are difficulties do we have to face if there are no Interfaces (Is that 'we have to find the type of object and call the appropriate funtion' the (only) problem But even this can be achived without interface)

  Is there any situation which can only be achived through Interfaces (please bear with me:-) )

  Thanks and Regards,

  Benin.

  
  
  
• Why do we need Interfaces?