private void showStaffInComboBoxScheduleSurgery() {
        scheduleSurgery_attnPhysicianComboBox.removeAllItems();
        scheduleSurgery_primPhysicianComboBox.removeAllItems();
        scheduleSurgery_nurseComboBox.removeAllItems();
        for(Person person : hospital.getAllStaff().values()) {
            if(person.getType() == 1) {
                // surgeon
                scheduleSurgery_attnPhysicianComboBox.addItem(person.getUserName());
            } else if (person.getType() == 2) {
                // doctor
                scheduleSurgery_primPhysicianComboBox.addItem(person.getUserName());
            } else if (person.getType() == 4) {
                // nurse
                scheduleSurgery_nurseComboBox.addItem(person.getUserName());
            }

        }
    }