Meet the problem when to display the message using TextArea!

I am use the code below to display the message :

//“str” is the message i recieved

//Outputwindow the instance of the TextArea

//Inputwindow the instance of the TextInput

Outputwindow.text += str;

Outputwindow.vPosition =Outputwindow.maxVPosition;

Inputwindow.setFocus();

as i know in two way the use of the CPU will grow more and more, some time goes to 50%,60% or more.

the first:[/b] when the message come high frequency ,for example:two messages in one second;

the socend:[/b]because i am display all the message recieved, so after a period of time the text in the Outputwindow will grow more and more .And the use CPU will goes to more;

And this is irrelative of the performance of my computer.

Is anyone meet the same proplem like me.And help me ,thanks a lot!

Use TextField is OK!