Classes in ActionScript 3

In the previous page, you looked at our Name class and what it contains. In this page, you will learn how to use this class as part of an application.

Creating Objects from a Class
Creating a class and populating it with properties and functions is just one part of writing an application. An equally important part is to create objects out of those classes. You've already done that, and the code for doing that can be found in your FLA file where you pasted the following lines of code on a keyframe:

var author:Name = new Name();

author.SetFirstName("Charles");

author.SetLastName("Dickens");

 

trace(author.GetFullName());

Let's look at the above lines of code in greater detail:

var author:Name = new Name();

In the first line, we declare a variable whose name is author. Beyond just giving it a name, we specify its type to be Name as wel. In case you are wondering, the type Name is exactly the same Name class we looked at a few moments ago.

Creating a variable is only the first half of what the above line does. The second-half deals with creating your Name object. On the right-hand side of the equal sign, you set the variable to an actual Name object using the new keyword followed by the Name constructor that you saw earlier inside the name class.

This is where a constructor comes in handy. When you call a constructor, you are essentially constructing a new object, and this is commonly known also as instantiating an object. At the end of this first line, your author variable is now an instance - a real manifestation of the class Name.

When you have an instance of a type, which is what we have with our author variable, you have the ability to access the functions and any variables from your type easily such as what I do in the following two lines:

author.SetFirstName("Charles");

author.SetLastName("Dickens");

SetFirstName and SetLastName are both functions defined in your Name class, but because the author variable is an instance of the name class, you can call it directly from author itself.

Let's look at the final line of our code:

trace(author.GetFullName());

In this line, I am tracing the value returned by the GetFullName function from our author object. As you recall, the GetFullName function returns a value of type string, and this means that you can manipulate its output like you would any other string-based data.

I am keeping things simple by just tracing the values that you see. Next, let's look at this in a bit more complicated light by creating many objects and visualizing how they probably look.

Creating Many Objects
To help in explaining what is going on, the code you currently have only creates a single object. Let's make things a bit more interesting by creating many objects.

In the code you pasted in your Flash file's keyframe, replace your current code with the following:

//Book Author

var author:Name = new Name();

author.SetFirstName("Charles");

author.SetLastName("Dickens");

 

trace(author.GetFullName());

 

//Video Game Character

var game:Name = new Name();

game.SetFirstName("Marcus");

game.SetLastName("Fenix");

 

trace(game.GetFullName());

 

//TV Personality

var tv:Name = new Name();

tv.SetFirstName("Mike");

tv.SetLastName("Rowe");

 

trace(tv.GetFullName());

 

//Normal by day, Superhero by night

var superHero:Name = new Name();

superHero.SetFirstName("Bruce");

superHero.SetLastName("Wayne");

 

trace(superHero.GetFullName());

When you run your application now by pressing Ctrl + Enter, the following is what you will see displayed in your Output window:

In the first page of this article, I showed you the following diagram describing the relationship between classes and objects:

Let's reuse the idea from the above diagram and fill in some missing details by visualizing the Name class and the objects that it contains:

You have the four objects that we created based on the Name class, and notice that each object stores the values that are unique to it. In the above diagram, I have populated the firstName and lastName values.

Conclusion
Hopefully this article helped you to get a better understanding of classes and their place in modern applications. If you have done some minor ActionScript 3 programming in Flash already, you probably have used classes already. Any variable that you declare has a type associated with it, and that type is basically a class. For example, a common class you saw in this tutorial is String, and there are dozens more built-in types that the ActionScript language provides.

Fortunately, you are not limited to just using the built-in types. As you saw in this article, creating your own class is pretty straightforward. The Name class is probably on the simpler side of the classes that you can create, but even more complicated classes will follow a similar pattern.

A great follow-up tutorial to read is Classes and MovieClips where you learn how to associate movie clips on your stage to classes, but otherwise, that's it for this article!

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