ComboBox doesn't update

Hi, I have a Combobox which contains 3 items (id : 1,2,3). I can select them via the mouse. By default, my combobox is on blank field (no item selected). When I want to change its value via a button (setValue(1) ,for example), my ComboBox doesn't update !
I don't understand this behavior ! Someone can help me ? :)
 

Can you post a minimal code sample?

public void construireListeExecutions(List<Execution> executions) {
        //On remet le composant à zéro
        listeDeroulanteExecutions.removeAllItems();
        listeDeroulanteExecutions.setNullSelectionAllowed(false);

        //Pour chaque execution, creation d'un item dans la liste
        for (Execution execution : executions) {
            listeDeroulanteExecutions.addItem(execution.getId());
            listeDeroulanteExecutions.setItemCaption(execution.getId(), execution.getNom());
        }
        System.out.println("before "+listeDeroulanteExecutions.getValue());
        listeDeroulanteExecutions.setValue(2);
        System.out.println("after "+listeDeroulanteExecutions.getValue());
    }

Anyway, when I make a SetValue(), in reality, the value doesn't change..
Resultat :
before 1
after 1
 

Ok, what does execution.getId() return (Which type)? 
Because basically, this should work.

Thanks for quick answer !
But I resolved my problem. My Ids on my combobox are Long, not Integer.. So I replace 2 to 2L and it works correctly !
thanks Tom ;) have a good day