Simple Class and the Display List

Question

I have very simple code for a class:
package
    import flash.text.TextField;
    import flash.display.Sprite;
    public class Greeter extends Sprite
        public function Greeter()
            var txtHello:TextField = new TextField();
            txtHello.text = "Hello World";
            trace("hi");
            addChild(txtHello);
The above file is saved as Greeter.as in say folder  C:\test
I then create a Fla file named test_display.fla (saved in C:\test) and its contents are:
import Greeter;
var tt:Greeter = new Greeter();
Now the Output window shows hi due to the trace statement but the addChild method should show
Hello World in the Flash movie but it does not. The only way to get Hello World to the Flash Movie
is to change the test_display.fla to:
import Greeter;
var tt:Greeter = new Greeter();
addChild(tt);
In other words I have to use the addChild method twice ( once in Greeter.as and once in test_display.fla )
to get Hello World to display in the Flash movie. Does anyone know why this is so?

Answer 1

Thanks Andrei1,
I honestly am having trouble with your answer. I am sure it is correct, I just don't get it right now.
As a slight twist on the original code say for example you want to get Hello World to output
inside the output window NOT the Flash movie. I see the code snippet  inside the class it reads:
var txtHello:TextField = new TextField();
txtHello.text = "Hello World";
So now inside the FLA file ( not inside the class file )  I have tried various ways to get Hello World to print in output window:
I have tried trace(tt.text);  and I get an error.
So the question is I know tt is an instance of Greeter and inside Greeter I see
where Hello World is assigned via:
txtHello.text = "Hello World";
So the question is why can't I get Hello World to print in the output window ( using trace) via
the instance tt somehow?