How can I update my Choice box everytime other choice box changes?

Question

so I have this problem... I have 2 choice boxes, the first one contains guitar brands, and the second one the type of guitars that brand has. I am using an Item Listener and it works, the only problem is that it keeps adding. For example: I select 2 times the same brand, it will write 2 times the type of guitar, and I just want the types of guitars. How can I fix this? Here's my code of the listener:

private class ItemHandler implements ItemListener {
    @Override
    public void itemStateChanged(ItemEvent event) {
        try {
            if(event.getSource() == choice_GuitarBrand) {
                /*I have a guitar array that will fetch the associated ID of the selected
                item given the name */
                int id = cmd.fetchGuitarID(choice_GuitarBrand.getSelectedItem());
                for(Guitar g : cmd.getSpecificGuitar(id)) {
                    choice_TypeOfGuitar.add(g.getName());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
}

Answer 1

You need to remove the objects in the list before adding new ones:

private class ItemHandler implements ItemListener {
    @Override
    public void itemStateChanged(ItemEvent event) {
        try {
            if(event.getSource() == choice_GuitarBrand) {
                /*I have a guitar array that will fetch the associated ID of the selected
                item given the name */
                int id = cmd.fetchGuitarID(choice_GuitarBrand.getSelectedItem());
                choice_TypeOfGuitar.removeAll(); // see https://docs.oracle.com/javase/7/docs/api/java/awt/Choice.html#removeAll()
                for(Guitar g : cmd.getSpecificGuitar(id)) {
                    choice_TypeOfGuitar.add(g.getName());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
}