Often
in programming you’ll need to work with a set of items rather than
a single object. For example, in a music player application, you
might want to have a list of songs waiting to be played. You wouldn’t
want to have to create a separate variable for each song on that
list. It would be preferable to have all the Song objects together
in a bundle, and be able to work with them as a group.
An array is a programming element that acts as a container for
a set of items, such as a list of songs. Most commonly all the items
in an array are instances of the same class, but that is not a requirement
in ActionScript. The individual items in an
array are known as the array’s
elements
. You can think of
an array as a file drawer for variables. Variables can be added
as elements in the array, which is like placing a folder into the
file drawer. You can work with the array as a single variable (like
carrying the whole drawer to a different location). You can work with
the variables as a group (like flipping through the folders one
by one searching for a piece of information). You can also access
them individually (like opening the drawer and selecting a single
folder).
For example, imagine you’re creating a music player application
where a user can select multiple songs and add them to a playlist.
In your ActionScript code, you have a method named
addSongsToPlaylist()
,
which accepts a single array as a parameter. No matter how many
songs you want to add to the list (a few, a lot, or even only one),
you call the
addSongsToPlaylist()
method only one time,
passing it the array containing the Song objects. Inside the
addSongsToPlaylist()
method,
you can use a loop to go through the array’s elements (the songs)
one by one and actually add them to the playlist.
The most common type of ActionScript array is an
indexed array
.
In an indexed array each item is stored in a numbered slot (known
as an
index
). Items are accessed using the number, like an
address. Indexed arrays work well for most programming needs. The
Array class is one common class that’s used to represent an indexed
array.
Often, an indexed array is used to store multiple items of the
same type (objects that are instances of the same class). The Array
class doesn’t have any means for restricting the type of items it
contains. The Vector class is a type of indexed array in which all
the items in a single array are the same type. Using a Vector instance instead
of an Array instance can also provide performance improvements and other
benefits. The Vector class is available starting with Flash Player
10 and Adobe AIR 1.5.
A special use of an indexed array is a
multidimensional array
.
A multidimensional array is an indexed array whose elements are
indexed arrays (which in turn contain other elements).
Another type of array is an
associative array
, which uses
a string
key
instead of a numeric index to identify individual
elements. Finally, ActionScript 3.0 also includes the Dictionary
class, which represents a
dictionary
. A dictionary is an array
that allows you to use any type of object as a key to distinguish
between elements.
Important concepts and terms
The following
reference list contains important terms that you will encounter when
programming array and vector handling routines:
-
Array
-
An object that serves as a container to group multiple objects.
-
Array access ([]) operator
-
A pair of square brackets surrounding an index or key that
uniquely identifies an array element. This syntax is used after
an array variable name to specify a single element of the array
rather than the entire array.
-
Associative array
-
An array that uses string keys to identify individual elements.
-
Base type
-
The data type of the objects that a Vector instance is allowed
to store.
-
Dictionary
-
An array whose items consist of pairs of objects, known as
the key and the value. The key is used instead of a numeric index
to identify a single element.
-
Element
-
A single item in an array.
-
Index
-
The numeric “address” used to identify a single element in
an indexed array.
-
Indexed array
-
The standard type of array that stores each element in a numbered
position, and uses the number (index) to identify individual elements.
-
Key
-
The string or object used to identify a single element in
an associative array or a dictionary.
-
Multidimensional array
-
An array containing items that are arrays rather than single
values.
-
T
-
The standard convention that’s used in this documentation
to represent the base type of a Vector instance, whatever that base
type happens to be. The T convention is used to represent a class
name, as shown in the Type parameter description. (“T” stands for
“type,” as in “data type.”).
-
Type parameter
-
The syntax that’s used with the Vector class name to specify the
Vector’s base type (the data type of the objects that it stores).
The syntax consists of a period (
.
), then the data
type name surrounded by angle brackets (
<>
).
Put together, it looks like this:
Vector.<T>
.
In this documentation, the class specified in the type parameter
is represented generically as
T
.
-
Vector
-
A type of array whose elements are all instances of the same
data type.
