Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll

C# Objects

Well done!

You have completed C# Objects!

Sign up for Treehouse Back to Library
Preview
Video Player
00:00
00:00
00:00
  1. 2x 2x
  2. 1.75x 1.75x
  3. 1.5x 1.5x
  4. 1.25x 1.25x
  5. 1.1x 1.1x
  6. 1x 1x
  7. 0.75x 0.75x
  8. 0.5x 0.5x
Use Up/Down Arrow keys to increase or decrease volume.

Inheritance

3:35 with Jeremy McLain

We can create new types that inherit the attributes and behaviors of existing types.

[MUSIC] 0:00
In the first part of this course we wrote a class that models a point. 0:04
It has x and y fields and 0:08
even has a method that calculates how far it is from another point. 0:11
The Treehouse defense game uses this class to identify locations on the map. 0:16
But it could be used for a lot more than that. 0:21
Lots of software applications use x and y coordinates to identify a location. 0:24
Perhaps the next game we write will also need a point class. 0:29
Software that displays charts and graphs also needs points. 0:32
If we keep our implementation of the point class as general purpose as possible, 0:36
we can reuse it in all those different applications. 0:41
What if we need to add something to the point class that's specific 0:45
to Treehouse defense? 0:48
For example what if we wanted to make it impossible to create a point that 0:50
isn't on the map? 0:54
Making a change like that to the point class would make it unusable to 0:55
all other applications that don't have maps. 0:59
We don't want to add code to a general purpose class that we're 1:02
fairly certain won't be useful to other users of the class. 1:05
We also don't want to create a new class that's specific to Treehouse defense and 1:09
rewrite everything we wrote for the point class. 1:14
What we want is to create a new class that has our new functionality, but 1:17
also reuses the point class. 1:21
The principles of object-oriented programming 1:24
provide lots of ways to reuse and extend existing classes. 1:26
One of them is called inheritance. 1:31
There are four core principles of object-oriented programming. 1:34
Encapsulation, inheritance, polymorphism and abstraction. 1:38
By saying that C# is an object-oriented programming language, we're really saying 1:43
that C# has features built into the language to support these four principles. 1:48
As you can see, inheritance is one of the four core principles. 1:54
Don't worry about these other three principles right now. 1:59
We'll discuss them later. 2:02
The principle we want to focus on right now is inheritance. 2:04
You see, 2:08
many objects in the real world often share many of the same attributes and behaviors. 2:09
A classic example is an animal, all animals have similar characteristics. 2:15
For example, a defining characteristic of all animals is the ability to move. 2:20
There are two types of animals, vertebrates and invertebrates. 2:25
Vertebrates have backbones and invertebrates don't. 2:30
But they're both still animals, so they can both move. 2:34
Mammals and birds are types of vertebrates. 2:37
By saying that a creature is a mammal we're 2:40
also saying that it has a backbone and it can move. 2:43
You might say, 2:46
that it inherits these characteristics from the larger categories, 2:47
or classifications, of vertebrates and animals of which it's a member. 2:51
You can see now that the C# key word class is short for classification. 2:56
C# classes define what it means to be in a particular classification. 3:02
As we saw with the animal example, classes of animals 3:07
can have more refined classifications within them, we call these subclasses. 3:11
Subclasses inherit the attributes and behaviors of the more general classes. 3:16
So if we wanted a new type of point that inherited 3:22
all of the features of the point class, but 3:25
was more specific to our application, we just need to create a subclass of point. 3:28
Let's look at how we do that in code. 3:33