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In this video, we'll review the solution to the second challenge and introduce our third and final challenge—adding constructors to our classes.
Instructions
3rd Challenge
- Add a constructor to each of your media type classes.
- Define a constructor parameter for each of the media type's required fields and use those parameter values to initialize its fields.
- Update the Program.cs file
Main()method in order for your program to successfully compile.
Help
If you get stuck on any of the following topics or simply need a refresher, click on a topic in list below to view the associated video in the C# Objects course.
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How did you with the second challenge?
0:00
Let's walk through my solution.
0:02
In the program.cs file main method,
0:04
I used the new keyword to create an
instance of each of my media type classes.
0:07
First a variable, var album
0:13
= new Album with a capital
A followed by a set of parentheses.
0:16
Then var book = new Book.
0:21
Then var movie = new Movie.
0:29
Then I set each object field to a value.
0:34
First the album.
0:38
So album.Title = and
0:39
then how about Yellow Submarine?
0:43
Then album.artist = "The Beatles".
0:49
For the book, how about
0:57
book.title = Moby Dick and
1:02
book.author equals Herman Melville.
1:08
And for the movie,
1:23
movie.Title = Lawrence of Arabia and
1:26
movie.Director = David Lean and
1:33
lastly I compiled my program.
1:39
View, Show Console,
1:44
mcs *.cs-out:Program.exe.
1:48
Now let's try running the program.
1:57
So mono Program.exe and
1:58
nothing happened.
2:03
Let's take another look at our code.
2:07
So here's our static void main method.
2:10
That's the method that's getting called
when we ran our application, but notice
2:13
that I instantiated each of my media type
classes, and then I set field values.
2:16
But I didn't do anything,
I didn't write anything to the console.
2:22
Let's fix that.
2:25
For now, let's just write each
object's field values to the console.
2:28
So console.WriteLine, then for
2:33
the value I'll start
with a string literal,
2:38
album: " + plus album.title
2:45
+ " by " + album.Artist);
2:50
let's repeat that again for
2:55
both the book and the movie.
3:00
To save some typing I'll copy and paste.
3:04
Change Album to Book and
then Album here to book and
3:11
then instead of album.Artists
it's book.Author.
3:14
And then instead of album
3:18
it's Movie Movie.title by
3:24
movie.Director.
3:34
Now let's compile and
run the program again.
3:39
This time,
I'll run both commands at the same time.
3:47
So, ncs*.cs -out: Program.exe
3:49
&& mono Program.exe.
3:56
And this time, we got our media type
information written to the console.
4:01
Great work.
4:05
Let's review how we're
setting our field values.
4:07
Currently, we're creating a class
instance, then writing a line of code for
4:10
each field value that we want to set.
4:14
As we've seen, this works fine but
4:17
if we had a lot of fields,
this approach could become tedious.
4:19
Furthermore, when thinking about these
media types, setting a value for
4:23
each of these fields doesn't
really feel optional.
4:27
Though, with our current approach,
4:30
it's perfectly valid at least as far
as the C# compiler's concern to create
4:33
an instance of any of these media types,
and not set any of the field values.
4:38
To fix this, we can add a constructor
to each of our media type classes,
4:45
each constructor can
define a parameter for
4:50
each field that should have a value,
the required fields for that media type.
4:53
For example, here in my album class,
I'll add a constructor with title and
4:58
artist parameters and then use those
parameters to initialize these fields.
5:02
For the third and
last challenge in this practice session,
5:09
add a constructor to each
of your media type classes.
5:11
Define a parameter for
each of the required fields and
5:16
use those parameter values
to initialize the fields.
5:19
After adding your class constructors,
you'll need to update the code
5:24
in the Program.cs file
'Main()' method in order for
5:27
your program to successfully compile.
5:30
And that's it for the third challenge.
5:32
See you in a bit.
5:35
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