Interfaces

Question

Hi, I'm new to C-Sharp and I would like to know what is the use of "interfaces" ? When should we use this "interfaces"

ssswamii · Answer

Here's an example of where you might want to use an interface. Let's say you have the following code: interface ISomeCollectionType { void AddObject(object obj); } public class CollectionTypeA : ISomeCollectionType { void AddObject(object obj) { Console.WriteLine("hey, you added an object to a CollectionTypeA instance! You passed object {0}", obj); } } public class CollectionTypeB : ISomeCollectionType { void AddObject(object obj) { Console.WriteLine("hey, you added an object to a CollectionTypeB instance! You passed object {0}", obj); } } public class CollectionTypeC : ISomeCollectionType { void AddObject(object obj) { Console.WriteLine("hey, you added an object to a CollectionTypeC instance! You passed object {0}", obj); } } Now here's where interfaces could come in handy. All the 3 classes above (CollectionTypeA, CollectionTypeB, CollectionTypeC) are all of type ISomeCollectionType. Which means you could do the following: CollectionTypeA collA = new CollectionTypeA(); CollectionTypeB collB = new CollectionTypeB(); CollectionTypeC collC = new CollectionTypeC(); // OOOOH special! Check this out, we can pass collA, collB, or collC and all of them will work and print out their respective messages. // Try accomplishing this without interfaces or inheritance and you'd be shit out of luck AddObjectToCollection(collA, "dummy parameter1"); AddObjectToCollection(collB, "dummy parameter2"); AddObjectToCollection(collC, "dummy parameter3"); private void AddObjectToCollection(ISomeCollectionType theColl, string theObject) { theColl.AddObject(theObject); }

peevee12 · Answer

So if it acts like a guide for forth-comming classes, why don't you just implement it directly to the class?Because it seems like you need to guess all the properties and methods of a interface and write it into the class and do some implementation when a class uses an interface. I'm new to C# and I want to appreciate interfaces.Can you please discuss me some more, coz I've read so many articles and I don't see anything that would justify why we should use an interface in an object oriented approach

send2manivannan · Answer

Interface, It is like Abstarct Class. But all the methods are Pure Virtual Function. Interface only have the Member Function. In C# By default all the Members have the Public Access specifier.(no need to give public Modifier to Interface members) Interface only supports , Functions. Properties. It is very usefull way to design the Classes. It give the common layout of the forth-comming classes. Interface are well-defined common structure/skeleton of the classes. In C# Interface only supports the Multiple Inheritance. (Exampel), public interface Book { long TotalPage { get; set; } void ShowSamplePages(); } public class ComputerBooks : Book { int tPg; public long TotalPage { get { return tPg; } set { tPg=value; } } public void ShowSamplePages(); { Console.Write("Computer Books, Sample Page...."); } } public class StoryBooks : Book { int tPg; public long TotalPage { get { return tPg; } set { tPg=value; } } public void ShowSamplePages(); { Console.Write("Story Books, Sample Page...."); } }