[help]as3 xml error

So I’m playing around with xml and as3.

Now I got this:

var fileList:XMLList = bookInput.Songs.file1;

And now I want that if you push a button, file1 changes in file2.

So I got this:

var j:uint=1;

But when I change the first snipped in this:

var fileList:XMLList = bookInput.Songs.file+j;

it gives this error:

TypeError: Error #1034: Type Coercion failed: cannot convert “1” to XMLList.

How to fix it?

var fileList:XMLList = bookInput.Songs[“file”+j]