addEventlistener, array, as linkage - actionscript-3

Question

I have added 10 movieclips with the AS linkage Box in this function. I've named the different instances layer1 to layer10
My question is, how can one add an eventlistener to, lets say, only layer4?
var NUM_BOXES:int = 10;
var BOX_SPACING:int = 1;
var _boxes:Array = [];
function Test()
{
for (var i:int = 0; i < NUM_BOXES; i++)
{
var box:Box = new Box( i + 1 );
box.y = (box.height + BOX_SPACING) * i;
box.name= "layer" +( i + 1);
box.buttonMode = true;
box.addEventListener( MouseEvent.MOUSE_DOWN, onBoxPress );
box.addEventListener( MouseEvent.MOUSE_UP, onBoxRelease );
addChild( box );
_boxes.push( box );
}
}

Answer 1

Building on bluebill1049's answer:
The if(number == 4) approach is not scalable, i.e. if you want a hundred layers to have listeners, you can not write an if statement for each layer. The simple solution would be:
var NUM_BOXES:int = 10;
var BOX_SPACING:int = 1;
var _boxes:Array = [];
//Any numbers in this array are assigned listeners
var layers_with_listeners:Array = [1, 4, 9];
function Test()
{
for (var i:int = 0; i < NUM_BOXES; i++)
{
var box:Box = new Box( i + 1 );
box.y = (box.height + BOX_SPACING) * i;
box.name= "layer" +( i + 1);
box.buttonMode = true;
if(layers_with_listeners.indexOf(i+1) != -1) {
box.addEventListener( MouseEvent.MOUSE_DOWN, onBoxPress );
box.addEventListener( MouseEvent.MOUSE_UP, onBoxRelease );
}
addChild( box );
_boxes.push( box );
}
}

Answer 2

var NUM_BOXES:int = 10;
var BOX_SPACING:int = 1;
var _boxes:Array = [];
var number:int;
function Test()
{
for (var i:int = 0; i < NUM_BOXES; i++)
{
number = i + 1;
var box:Box = new Box(number);
box.y = (box.height + BOX_SPACING) * i;
box.name= "layer" +(number);
box.buttonMode = true;
if(number == 4)
{
box.addEventListener( MouseEvent.MOUSE_DOWN, onBoxPress );
box.addEventListener( MouseEvent.MOUSE_UP, onBoxRelease );
}
addChild( box );
_boxes.push( box );
}
}