About creating and using classes

As discussed previously, a class consists of two parts: the declaration and the body. The class declaration consists minimally of the class statement, followed by an identifier for the class name, then left and right curly braces. Everything inside the braces is the class body.

class className {
  // class body
}

You can define classes only in ActionScript (AS) files. For example, you can't define a class on a frame script in a FLA file. Also, the specified class name must match the name of the AS file that contains it. For example, if you create a class called Shape, the AS file that contains the class definition must be named Shape.as.

// In file Shape.as
class Shape {
  // Shape class body
}

All AS class files that you create must be saved in one of the designated classpath directories—directories where Flash looks for class definitions when compiling scripts. (See Understanding the classpath.)

Class names must be identifiers; that is the first character must be a letter, underscore (_), or dollar sign ($), and each subsequent character must be a letter, number, underscore, or dollar sign. Also, the class name must be fully qualified within the file in which it is declared; that is, it must reflect the directory in which it is stored. For example, to create a class named RequiredClass that is stored in the myClasses/education/curriculum directory, you must declare the class in the RequiredClass.as file like this:

class myClasses.education.curriculum.RequiredClass {
}

For this reason, it's good practice to plan your directory structure before you begin creating classes. Otherwise, if you decide to move class files after you create them, you will have to modify the class declaration statements to reflect their new location.