Managing Related Data: The Array Class

Have you ever had a bunch of variables that have a lot in common? For example, do you have variables such as name_1, name_2, name_3, name_4, and so on? These variables look like lists of common information, such as:

 var name_1:String = "Peng"; var name_2:String = "Django"; var name_3:String = "Jenn"; var name_4:String = "Frank"; 

In programming languages, an array is a list of values that can be addressed by their position in the list. An array is created by using the Array constructor:

 var visitors:Array = new Array(); 

The preceding code object simply creates the array container for data. You create an array with information already specified, such as:

 var visitors:Array = new Array("Peng"," Django"," Jenn"," Frank"); 

or

 var visitors:Array = ["Peng", "Django", "Jenn", "Frank"]; 

To access an item in visitors, you would use the array access operators with an array index number. To access the first position's data, you would use the following code:

 var message:String = "Hello "+ visitors[0] + ", and welcome."; 

Here, visitors[0] will return the value "Peng". If you traced the message variable, it would read:

 Hello Peng, and welcome. 

In most programming languages, the first index value (the starting position) is 0, not 1. In the following table, you'll see how the index number increases with the sample visitors array.

Index Position	0	1	2	3
Index Value	Peng	Django	Jenn	Frank

You can set and get the values within an array using the array access operators. You can replace existing array values by setting the index position to a new value, and you can add values to the array by increasing the index number, as in:

 var visitors:Array = new Array("Peng"," Django"," Jenn"," Frank"); visitors[3] = "Nicole"; visitors[4] = "Candice"; 

In the example, "Nicole" replaces "Frank", and "Candice" is added to the end of the array. You can also add elements to the array using the push() method of the Array class, as in:

 var visitors:Array = new Array("Peng"," Django"," Jenn"," Frank"); var nLength:Number = visitors.push("Nicole"," Candice"); 

This code will add "Nicole" and "Candice" after "Frank", and set the variable nLength equal to the length of the visitors array. length is an Array property that returns the number of elements in the array. In the preceding example, nLength is equal to 6 because there are now six names in the array.

Emulating Arrays in Flash Player 4 or Flash Lite 1.0/1.1 Movies

In Flash Player 4 or Flash Lite 1.0/1.1, you can only emulate arrays, using expressions for variable names. In the earlier array examples, you could create an array-like structure for a Flash Player 4 movie by using the following code:

 var name_1 = "John"; var name_2 = "Vanessa"; var name_3 = "Jennifer"; var name_4 = "Frank"; 

Then you could use another variable, i, to refer indirectly to different name_ variables, as in:

 var i = 2; var currentName = eval("name_" add i); message = "Hello " add currentName add ", and welcome!"; 

For Flash Player 4 compatibility, the add operator (instead of the + operator) and the eval() function are used to return the current value of the name_ variable you want to insert. If you traced the message variable, the Output window would display:

 Hello Vanessa, and welcome! 

We only mention array emulation in this section because many Flash developers may encounter clients who wish to have Flash movies (or sites) that will work with the Flash Player 4 plug-in, especially for Flash banner ads, or with newer mobile phones that feature Flash Lite 1.0 or 1.1.