Understanding AS3 super() statement

核心提示：One interesting statement that’s almost unexplained in the web is super().Before explaining super()’s features, let me talk about superclasses.From

One interesting statement that’s almost unexplained in the web is super().

Before explaining super()’s features, let me talk about superclasses.

From Wikipedia: In computer science, a superclass is a class from which other classes are derived. A superclass is also called a parent class’. The classes that are derived from a superclass are known as child classes, derived classes, or subclasses. We can also say that a class A extends class B when A is a subclass of the B superclass.

Ok, now we know a superclass provides data (instance variables) and functions (methdods) to be inherited by the subclass.

So what can you do with super() statement?

With this constructor you can call the superclass or methods of the superclass (superclass’ functions) by just using the super prefix as a reference.

Let’s take this class:

package　{
　import　flash.display.Sprite;
　public　class　real_class　extends　Sprite　{
　　public　function　real_class(s:String)　{
　　　trace("I　am　the　text　contained　in　the　real　class");
　　　trace(s);
　　}
　　public　function　another_function()　{
　　　trace("I　am　the　text　passed　in　another　function");
　　}
　}
}

This is our superclass, and it’s not the main class inside our Flash project.

The main class is this one:

package　{
　import　flash.display.Sprite;
　public　class　super_example　extends　real_class　{
　　public　function　super_example()　{
　　　trace("I　am　the　text　contained　in　the　main　class");
　　　super("I　am　the　text　passed　in　the　real　class");
　　　super.another_function();
　　}
　}
}

As you can see, at line 3 I am not extending the Sprite class as usual, but the real_class one.

So in this case I could remove the import flash.display.Sprite; line.

At line 5 I am tracing some text, then at line 6 I am calling the superclass passing another text and at line 7 I am calling a metod, that is a function in the real_class you can find at line 8 that outputs more text.

The result is this one:

I　am　the　text　contained　in　the　main　class
I　am　the　text　contained　in　the　real　class
I　am　the　text　passed　in　the　real　class
I　am　the　text　passed　in　another　function

Using superclasses will improve reusability, it means you are writing code that can be used again to add new functionalities with slight or no modification