"C# Streams and Data Processing" was retired on July 14, 2025.
Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Well done!
You have completed C# Objects!
You have completed C# Objects!
Preview
Methods that are called directly on a class name are static methods. Don't confuse them with instance methods which are called on unique instances of the class (AKA objects).
This video doesn't have any notes.
Related Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign upRelated Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign up
Towers can only shoot so far.
0:00
So we need to know if an invader
is in range of a tower.
0:02
For that we need to calculate the distance
between two points on the map.
0:06
We should write a method to
perform this calculation and
0:11
return the distance between two points.
0:13
First we need to decide
where to put this method.
0:16
Take a moment to think about which of
these classes this method should go in.
0:20
We should think about which class has
the most in common with this method.
0:25
This method will only deal with points.
0:29
So the natural place to
put it is the point class.
0:32
That way we can ask any point how
far away it is from any other point.
0:35
This method will need to be public.
0:41
Since we're only working in whole
units it will return an integer.
0:43
We'll call our method DistanceTo.
0:47
And it will take x and y parameters.
0:49
So this method will need to calculate the
distance between the coordinates passed
0:54
in and those inside of the point object.
0:59
For that we can use
the Cartesian distance formula,
1:02
which tells us exactly how far
two points are from each other.
1:05
I'm having a little trouble remembering
how to do the Cartesian Distance Formula.
1:10
Let's search for it using Google.
1:15
So we'll go to Google and
type in Cartesian Distance Formula.
1:18
Here's a link that looks promising.
1:29
Now I remember,
1:33
it's the square root of the sum of
the squared differences of each component.
1:35
Let's code up this formula by
working from the inside out.
1:40
The innermost operation
involves subtracting
1:44
the x components from each other.
1:47
Let's do that and
assign the results to variables.
1:50
So we'll say int xDiff.
1:52
Difference is a long word so
I'll just shorten it to Diff.
1:57
Equals X- x and
I’ll do the same thing with y.
2:00
So this is subtracting the x and y that
was passed into this method from the x and
2:16
y that are in the point that
this method was called on.
2:21
Let's look at the formula again.
2:27
We need to square the differences.
2:30
Squaring a value is just
multiplying it by itself.
2:34
We can do that for both of these pieces
and then assign the results to a variable.
2:38
Let's call it xDiffSquared.
2:42
XDiffSquared will be xDiff * xDiff.
2:52
Will do the same thing
to get yDiffSquared.
3:01
Now the formula says that we need to add
them together and take the square root.
3:13
How do we take the square
root of a value in C#?
3:19
That sounds like a good question for
Google.
3:22
Let's go to Google and
type in C# square root.
3:26
The top result is from
the Microsoft Developer Network.
3:33
And says, return the square
root of a specified number.
3:36
That looks like what we want,
let's click on the link.
3:39
Looking at this we can tell that it
takes a parameter of type double and
3:43
returns a double.
3:49
We can also see that it's in the Math
class which is in the System namespace.
3:51
If you take a closer look at this method
definition here, you'll notice this static
3:56
keyword between the public access
modifier and the return type.
4:00
Math.Square root is what's
known as a static method.
4:04
Static methods are different than
the methods we've been creating.
4:09
They're different because they're
called directly on the class.
4:13
We don't need to construct
an object before we can use them.
4:17
This starts to make sense when
we look at how they're called.
4:21
Let's go down here and
look at an example of how it's used.
4:24
As you can see, they typed Math.Sqrt.
4:29
Math, with a capital m,
is the name of the Math class.
4:33
There's no Math object being used.
4:38
The square root method is being
called directly on the class.
4:40
This is what makes static methods special.
4:45
We've actually already called
a static method in our code.
4:48
Take a look at the Game.cs file.
4:52
We called a static method when
we called WriteLine here.
4:56
Console is the name of the class.
5:01
And we're calling WriteLine
directly on the Console class
5:04
without constructing a console object.
5:08
Contrast that to the way
we use the OnMap method.
5:11
The OnMap method is not static.
5:17
So we had to construct a map object here.
5:20
And then call OnMap.
5:24
In fact, the Main method, which is
the first method called in the program,
5:28
has to be a static method.
5:32
That's why it has the static keyword here.
5:36
This allows the Main method to be called
without first creating a game object.
5:40
The OnMap method and the DistanceTo
methods are known as instance methods,
5:46
because they're called on objects.
5:51
We learned earlier that objects
are also known as instances of a class.
5:54
Math.Sqrt and
Game.Main are static methods.
5:59
They're called directly
using their class name.
6:05
So whenever we see a method being
called directly on the name of a class
6:08
like Console.WriteLine is,
we know that the method is static.
6:12
Let's take a quick break.
6:18
When we come back, we'll go back
to the DistanceTo formula and
6:19
finish coding it up.
6:22
You need to sign up for Treehouse in order to download course files.
Sign upYou need to sign up for Treehouse in order to set up Workspace
Sign up