In need of a pattern for a common problem - what to instantiate?

Question

I'm sure this is a common problem with a standard solution (in a form of well known pattern), but I am not aware of one nor do I have any idea how would I Google for it... So, here it goes (exemplified):
a user is presented with a combo box that enables him to choose what item he wishes to purchase. Depending on his choice, the application is supposed to instantiate an appropriate class that represents the purchased item. So, if the user chooses a book from the combo box, the class Book should be instantiated, if he chooses a comic book, the ComicBook class would be instantiated etc.
Apart from introducing a naming convention and instantiating the classes through Class.forName(), how would this problem be solved, in a way as generic as possible?
This is supposed to be used in a Web app, but I hardly believe that's relevant...

Answer 1

Hmmm... I'm using JSF but it's my first project so I don't really know it's powers.
I instantiated all classes that will eventually populate the combo box (through reflection) and now I'm trying to find one which of the objects did the user select.
Would it be a problem for you to give me at least a rough scatch of what I should do?
I tried it like this:
in my managed bean:
public HtmlSelectOneMenu getProductsMenu() {
        //instantiate and populate the list of products (prodlist)
        for (Product p : prodlist){
            optionlist.add(new SelectItem(p, p.getName()));
        final UISelectItems items = new UISelectItems();
        items.setValue(optionlist);
        productsMenu.getChildren().add(items);
        return productsMenu;
    }and in my JSP:
<h:selectOneMenu binding="#{managedBean.productsMenu}" />but then, in the bean, when I try:
((Product)productsMenu.getValue())I get a Class cast exception. it says it can't can't cast String to Product...
What am I doing wrong?
Thank you!