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Coding 101 32

C# Abstract Classes and Interfaces

August 28 2014

Hosts: Fr. Robert Ballecer, SJ and Shannon Morse

Guest: Lou Maresca

The Code for today's show is available at our: Github

Snubs Compiled
No Viewer Submitted Code, however we did get some useful tips for C# from our community:

Cosmic Ray links us to a C# Fundamentals series that's super useful for newbies!

Nathan says learning the syntax of the languages is great, but you need to know how to problem solve!

Kelvin links us to Mono, for Mac users

Joe gives us info on how to get C# running via notepad!

Ivory Tower
Interfaces, Classes, & Abstract Classes

Remember from last week that "Classes" are blueprints
- They are a collection of Methods, variables, properties and events
- Classes DO NOT EXIST until they are created (i.e. the difference between having a blueprint and the building built from those blueprints)
- When an instance of a class is "created" -- and "object" is born

Declaring a Class
public class C101

{

//Fields, methods, properties, events
// everything in the "blue print" goes in here

}

Creating an OBJECT of a class:
C101 object1 = new C101();

** One of the topics that was covered towards the end of our "Code Warrior" section last week, was the idea of inheritance.
-- You can make new classes that inherit their members from another class, with derrivations from the original class.

Inheriting from a class
public class Module4 : C101

{

//Fields, methods, properties, events
//everything in the ""blue print"" goes in here

}

** However, there's another way to do that... another way that perhaps is MORE suited for inheritance and derrivation than a class... an ABSTRACT CLASS

Now let's talk about "Abstract Classes"
* If classes are blueprints --- things that are ready to create --- to turn into objects, then "ABSTRACT Classes" are architectural designs.
-- They have the right shape of the thing to be created
-- They have much of the information needed to create the thing being created
-- But they are not complete
-- They cannot be instantiated - (They cannot not be "created" into an object)

* The sole purpose of an abstract class is to act as a "base" for inheritance
-- They cannot be instantiated, but a derrivative class, which inherits the abstract members from the abstract class, can be.
-- That derrivative class must provide proper implementation for all the abstract members of the abstract class, then it CAN create an object. (It complete's the blueprints)

Declaring an abstract class
public abstract class C101

{

//Fields, methods, properties, events
//everything in the ""blue print goes in here

public abstract void menu()

{

}

}

Inheriting from an abstract class
public class Module4 : C101

{

public void menu()

{

Console.WriteLine("This is a Menu");

}

}

* The inherited class from C101 MUST provide implementation for any abstract members within that class.

A few things about Abstract Classes:
1. They are created with the keyword "abstract"
2. They are incomplete and therefore CANNOT be instantiated. (an object cannot be created from the class)
3. Abstract classes and incomplete, and therefore can only be used as a base class
4. Non-abstract classes that are derived from abstract classes MUST provide proper implementation for any abstract members that are inherited from the abstract class.

Why have an Abstract Class?
* Abstract classes ENFORCE a particular hierarchy - They FORCE those who are inheriting from the class to code in a particular way to complete implementation.
* Abstract classes give us "parent" classes from which we can derive objects with customized implementation
* Going back to the blueprint:
-- An abstract class can give us the overview of what an object should look like, but then each derrivative class can implement the pieces of the abstract class as then need to be to best suit function

Let's talk about an Interface
* An Interface is like an Abstract class in that it can be used to define hierarchies for any sub-classes
* Unlike an Abstract Class, an Interface has NO body.
-- It's just the definitions of methods, with no body whatsoever.

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