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Practice Creating Classes in C#

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Instantiating Class Instances

3:58 with James Churchill

In this video, we'll review the solution to the first challenge and introduce our second challenge—instantiating instances of the classes that we created in the first challenge.

Instructions

2nd Challenge
  1. In the Program.cs file Main() method, use the new keyword to create at least one instance of each of your media type classes.
  2. For each of the objects that you create, set each field to an appropriate value.

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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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    Welcome back, how did it go? 0:00
    It's okay if you weren't unable to complete every part of the challenge. 0:02
    It's not unusual to struggle when you're learning something new. 0:05
    Let's walk through my solution. 0:09
    I started by adding a .cs file for each of my media types. 0:10
    Remember that it's a convention for the file name to match the class name. 0:15
    So File > New File then Album.cs. 0:20
    Then File > New File, Book.cs. 0:27
    And then File > New File, again, and Movie.cs. 0:34
    In the Album.cs file, I then added the Treehouse.MediaLibrary namespace. 0:41
    Then, within the namespace code block, I added the class definition. 0:53
    The class keyword, followed by the name of the class, Album, and 0:58
    a set of curly braces. 1:02
    To save a bit of typing, I copied and pasted this code into the other files, 1:07
    And changed the class name to the correct name for that file. 1:15
    Then I added the fields to each class. 1:24
    For the Album class, I added Title and Artist fields, both of type string. 1:29
    So public string Title, then public string Artist. 1:34
    Each of my media types has a Title field, so 1:41
    I'm going to copy this line of code to the clipboard. 1:45
    Then in Book, I'll paste that line of code, And 1:49
    add one more field, public string Author. 1:53
    Then in the Movie class, I'll paste from the clipboard again and 1:59
    add the second field, public string Director. 2:03
    Once I finished writing the code for the classes, I open the console and 2:09
    use the mcs command to compile my program, 2:13
    just to make sure that I didn't make any mistakes in my code. 2:16
    mcs, and then I'll use *.cs to include all of the .cs files in my project's folder. 2:20
    And I'll include -out:Program.exe, 2:27
    which is the name of the exe file that I want the compiler to create. 2:31
    All right, I didn't receive any compiler errors, so 2:43
    it looks like I didn't make any mistakes, at least so far. 2:46
    I did receive some warnings, but that's because we're not using the media type 2:49
    classes and setting any of the field values. 2:54
    Let's fix that now. 2:57
    Remember that a class is a template for 2:59
    making individual objects of a particular type. 3:01
    For example, using the Album class, I can create three objects, or 3:04
    instances, of the Album class. 3:09
    For the second challenge, use the new keyword in the Program.cs file Main 3:11
    method to create at least one instance of each of your media type classes. 3:15
    Then, for 3:21
    each of the objects that you create, set each field to an appropriate value. 3:22
    I created three media types, so I'll create or 3:27
    instantiate an instance of the Album, Book, and Movie classes. 3:30
    Then for the Album class instance, I'll set values on the Title and Artist fields. 3:36
    And for the Book class instance, I'll set values on the Title and Author fields. 3:42
    And for the Movie class instance, I'll set values on the Title and Director fields. 3:48
    And that's it for the second challenge. 3:53
    After the break, I'll show you my solution. 3:55

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