Constructor Methods
A constructor method (or, constructor, for short) is a discrete set of instructions used
to initialize the instances of a class. To create a constructor method, we use a function
definition within a class block, as shown in the following generalized code:
class SomeClass {
function SomeClass ( ) {
}
}
In the preceding code, the keyword function begins the constructor method. Next
comes the constructor method name, which must exactly match the class name (case
sensitivity matters!). The constructor method name is followed by a pair of parentheses
that contain a list of constructor parameters, which we’ll study later. The curly
braces ({}) following the parameter list are a block statement, just like the block
statements in package and class definitions. A constructor method’s block statement
is known as the constructor body. The constructor body contains the directives that
initialize instances. Whenever a new instance of SomeClass is created, the directives in
the constructor body are executed (sequentially, from top to bottom). Executing the
directives in the constructor body is known as executing the constructor or, more
casually, running the constructor.
Constructor methods are created using the function keyword because
they are, technically speaking, a type of function. We’ll study functions
in Chapter 5.
When a class does not define a constructor function explicitly, ActionScript automatically
provides a default constructor that performs no initialization on new
instances of the class. Despite this convenience, as a best practice, always include a
constructor, even if it is just an empty one. The empty constructor serves as a formal