Is it possible to create UI elements purely in Actionscript 3?

I am familiar with the method of embedding a SWF file in Actionscript and then creating a variable and assigning a corresponding UI element from the SWF.

My question is this:
Is it possible to create and place UI elements like TextFields and SimpleButtons purely with Actionscript without first creating them in a SWF and embedding it?

Thanks in advance.