Interfaces - Why we need them?

Question

why do we need interfaces ... Suppose we have two interfaces like interface I1 { void display(); } interface I2 { void show(); } Suppose we implement these interfaces in a class as shown ... class ImplementInterfaces : I1 I2 { public void display() { Console.WriteLine(Display method in I1); } public void show() { Console.WriteLine(show method in I2); } } Suppose we have our program in a class like this ... class interfaceDemo { static void Main() { ImplementInterfaces obj = new ImplementInterfaces(); obj.display(); obj.show(); } } ---------------------------------------------------------------------------------------- my question is if we are going to declare and define what the methods are going to do in our class only then why take the pain of declaring them in an interface? Why do we need an interface if we are going to declare and define our methods explicitly in our class? We might as well get rid of both the interfaces and declare and define the show() and display() method in the class itself. why we need interfaces in the first place. eagerly awaiting a reply for this. regards Sarav

Mykonine · Answer

Consider this problem: You have a string of text you want to encrypt using a variety of encryption methods some drastically different from each other. So you have AES RSA and all those different algorithms but their implementations are so different that the base class would be pretty much useless. By implementing an interface you say this class does everything required by the interface. In the example of the encryption algorithms you could have a class AESEncrypter and RSAEncrypter. Between the normal text and the cipher text they have nothing in common. How do you do it? The answer: through interfaces. If both the afforementioned classes implement IEncryptable you can kill two birds with one stone. You have an object of type IEncryptable and based on which algorithm you chose you can initiate that object using an instance of either of the two classes. Then you can call IEncryptable.Encrypt and get your finished cipher text. What you basically did by using and instance of IEncryptable you basically said I know whatever encryption algorithm I used will do IEncryptable.Encrypt correctly because they all implement IEncryptable When it comes down to bare bones concepts though here's the separation: Classes and inheritance are used when two classes share common attributes and/or functionality where these two objects more or less act the same way. Interfaces are used when two classes share common functionality but their functions' implementations could be completely different and the classes themselves could be completely different. For example I may have a class ParkVisitor and a class QuizScore. They are radically different classes but by implementing System.IComparable you can then use an IComparable array to sort an array of either ParkVisitor or QuizScore type without actually caring what the class actually is.

madinewala · Answer

One more thing is classes in C# do not support multiple inheritance. For this we need to go for the interfaces in C# which do support multiple inheritance.

james · Answer

Interfaces give us the flexability to have more robust and stable inheritance models. While you could define a base class and create other classes that inherit from it any one class can only inherit from one class while it can have many interfaces. That way we can use these templates to ensure functionality. You can probably design good code without using interfaces but they are just another tool in our arsenal. -James