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....); } }