isAvailable.add(new AjaxFormChoiceComponentUpdatingBehavior() {

    private static final long serialVersionUID = -4154749887506180749L;

    @Override
    protected void onUpdate(AjaxRequestTarget target) {
        if(isAvailable.getModelObject().equals(YesOrNo.YES.getKey())) {
            number.setVisible(true);
            currency.setVisible(true);
        } else {
            number.setVisible(false);
            currency.setVisible(false);
        }
        target.add(number);
        target.add(currency);
    }

});