Interface (Java and C# Cross Reference Guide)

An element of coding where you define a common set of properties and methods for use with the design of two or more classes.

Both interfaces and abstract classes are types of abstraction. With interfaces, like abstract classes, you cannot provide any implementation. However, unlike abstract classes, interfaces are not based on inheritance. You can apply an Interface to any class in your class tree. In a real sense, interfaces are a technique for designing horizontally in a class hierarchy (as opposed to inheritance where you design vertically). Using interfaces in your class design allows your system to evolve without breaking existing code.

Java:  "Interfaces" Yes  Java Interfaces (Yes)

C#:  "Interfaces" interface Classes and structs can inherit from interfaces in a manner similar to how classes can inherit a base class or struct, but a class or struct can inherit more than one interface and it inherits only the method names and signatures, because the interface itself contains no implementations. class MyClass: IMyInterface {   public object Clone() { return null; } // IMyInterface implemented here... } Syntax Example: interface IMyInterface {   bool IsValid(); }  C# Interfaces (interface)