Web GUI design issue

I'm writing a page with several text fields and a drop down. The fields in the drop down affect the value of the text fields.

For example: the drop down options are "a" and "b". The text fields are "name" and "last name". When choosing "a", "name" is filled with "Joe". When choosing "b", "name" is filled with "Bob".

I've written a class which contains the drop down display name and the values for "name" and "last name".

The question: Design-wise, what's the correct solution - having the class change the text fields, or changing the text fields externally and only accessing the class' data?

Thanks.

P.S - I'm using ASP.Net and Javascript, but this is more of a design issue and not language dependent.

Why do you need to populate an input field with the results of a SELECT change? Can't you get your value directly from the SELECT? What do you do if the user changes the result in the input field? The rule I follow is, if the user is allowed to enter any input, use an input text field. If the user is limited to an array of choices, use a SELECT (or possibly a radio button group).

If it is a long list of choices (longer than your example by a couple orders of magnitude), you can include a filter input where the user can type a few letters and pare the options down to a manageable level, but that is the only case I can think of where you'd want to go the other way with it.

Of course, there may be additional information that's on your mind but haven't imparted here. If so, please elaborate.

Since the class contains all three controls, it is correct that it change the text fields, as it is internal behavior to the class. Now if the fields were all separate classes then it would make more sense to manipulate them externally.

If those select fields and text fields combined work as maybe a widget, then it makes much sense to package them as such in a Class like you have already done. Then as Justin said, operations on these controls should be managed by your class, including keeping all fields synchronized.

If there are enough such widgets to care about, then I'd consider separating the data part of it from the views. Maybe create an additional class that represents the data, and pass an object of that data class to the widget. But pragmatism always comes first.