- Inheritance 3:35
- Inheritance in Code 5:27
- Inheritance 5 questions
- Inheritance 1 objective
- Catching Exceptions in C#
- Throwing Exceptions 4:49
- Throwing Exceptions 1 objective
- Catching Exceptions 1 objective
- Exception Messages 3:02
- Custom Exceptions 6:23
- Custom Exceptions 2 objectives
- Catching Exceptions 5:02
- Catching Exceptions 6 questions
Preview
Video Player
00:00
00:00
Inheritance in Code
5:27Let's use inheritance to make a subclass of the Point class.
Let's create a subclass of the point class
to do that we need to create a new class,
0:00
let's call it map location.
0:06
So we'll create a new file
called MapLocation.cs in here
0:08
we'll create a new class
called map location.
0:12
We specify that the map location class
is a subclass of the point class by
0:25
typing : Point after the name of
the class here, and there you go.
0:30
We've just subclassed the point class.
0:35
We need to do one more thing
to make this class usable.
0:38
When a map location object is created,
we're creating a point object too.
0:42
They aren't two distinct objects, it's
just that a map location is also a point.
0:47
In the same way that when a mammal
is born, a vertebrate and
0:52
an animal are also born because a mammal
is both a vertebrate and an animal.
0:56
Remember that the point object
requires that we pass in both x and
1:02
y coordinates to the constructor
in order for it to be created.
1:06
So we still have to
satisfy those requirements
1:10
because a map location is
just another type of point.
1:13
When a map location object is created
it first needs to call the point class
1:17
constructor and pass it what it needs.
1:21
So the map location class will also
need a constructor that takes the x and
1:24
y coordinates, so that it can pass
them to the point class constructor.
1:28
Again, we name the constructor
the same as the class name.
1:33
In this case,
1:39
it will take the same parameters as
the constructor of the point class.
1:40
Now that we have a map
location constructor,
1:48
we need to tell it to call the point class
constructor and pass these parameters.
1:50
We do that by typing : base here and
list the parameters.
1:55
We use the base keyword here because the
point class is MapLocation's base class.
1:59
You'll hear people refer to the base class
as the parent class or the super class and
2:05
you'll hear people refer to the sub class
as the child class or derived class.
2:10
We're calling the base classes constructor
here and passing it the values it needs.
2:17
So now, any map location objects we
create will also be point objects,
2:22
let's go to main to see what this means.
2:28
Instead of using the point class here,
2:30
let's change it to use
the map location class.
2:33
To avoid any confusion I'll
rename this variable to x.
2:44
Even though x is now a map location,
this line here will still work.
2:52
The map location class doesn't have
a distance to method directly but
2:58
it inherits it from the point class or
3:03
you could say that x is both a point and
a map location.
3:06
So it has all of the methods
of both classes.
3:10
We can even assign map
location to a point.
3:13
We can also assign it to a point
at the same time we create it.
3:19
We can even pass MapLocation objects
into methods that are expecting a point.
3:23
Remember the maps OnMapMethod,
that takes a point as a parameter?
3:29
Let's pass it a MapLocation instead.
3:33
Let's compile just to
make sure this works.
3:48
See, no compiler errors.
3:53
These all works because map
location is a subclass of point.
3:56
We can say that the point and map location
classes have an is a relationship,
4:01
in that map location is a point.
4:07
There's even a way in C# to see
if an object is a certain type.
4:10
The is operator returns true if
a variable is of a given type
4:14
this is called a type check.
4:20
Let's print out the result
of a few type checks.
4:22
Let's first check to see
if x is a map location.
4:26
Let's also check to see if x is a point.
4:35
Finally let's create a new point object
and see if it's of type map location.
4:44
What do you think the result
of this expression will be?
4:53
Let's run it and see.
5:03
As you can see,
x is both the map location and a point but
5:12
point is not a map location.
5:17
That would be like saying that
an animal is a vertebrate,
5:20
when the only thing we know
is that it's an animal.
5:24