Essential ActionScript 3.0

Chapter 4. Static Variables and Static Methods

In Chapter 1, we learned how to define the characteristics and behavior of an object using instance variables and instance methods. In this chapter, we’ll learn how to manage information and create functionality that pertains to a class, itself, rather than its instances.

Static Variables

Over the past several chapters, we’ve had a fair bit of practice working with instance variables, which are variables associated with a particular instance of a class. Static variables, by contrast, are variables associated with a class itself, rather than a particular instance of that class. Static variables are used to keep track of information that relates logically to an entire class, as opposed to information that varies from instance to instance. For example, a class representing a dialog box might use a static variable to specify the default size for new dialog box instances, or a class representing a car in a racing game might use a static variable to specify the maximum speed of all car instances.

Like instance variables, static variables are created using variable definitions within class definitions, but static variable definitions must also include the static attribute, as shown in the following generalized code:

class SomeClass {
  static var identifier = value;
}

As with instance variables, access-control modifiers can be used to control the accessibility of static variables in a program. The access-control modifiers available for static-variable ...