C # abstract classes and interfaces

What is the difference between an abstract class and an interface? Why do you need an interface with an abstract class?

Interfaces and abstract classes of the same point is not instantiated, the difference is that the method in the interface has no method body, and abstract class is not, except the abstract method has no method body, other methods have method body.

The reason: In C #, a class can inherit only one class, but it can inherit multiple interfaces.

Abstract class:

1. Cannot be instantiated

2. The abstract method must be overridden by the quilt class

3. If the class contains an abstract method, the class must be defined as an abstract class

Abstract before class.

Abstract methods are added before the return value, with no method body, and a semicolon is added directly after the parentheses.

1. Classes containing abstract methods must be abstract classes

2. Abstract classes do not necessarily contain abstract methods

A virtual method is used to implement polymorphism, in order for an instance of a subclass to completely replace a member from a parent class, the parent class must declare the member as virtual, which is accomplished by adding the virtual keyword before the member's access type.

Subclasses can choose to use the Override keyword to replace the parent class implementation with its own implementation, which is the method override, and of course it can not be overridden.

classanimal{ Public Virtual voidShout () {Console.WriteLine ("Animal Bark! "); }}classcat:animal{ Public Override voidShout () {Console.WriteLine ("The cat barks! "); }}classdog:animal{ Public Override voidShout () {Console.WriteLine ("Dog Bark! "); }}classprogram{Static voidMain (string[] args) {animal[] Animals=Newanimal[2]; animals[0]=NewCat (); animals[1]=NewDog (); foreach(varAnimalinchanimals) {Animal.        Shout ();    } console.readline (); }}

C # abstract classes and interfaces