code: public static void prepareComboBox(ComboBox box, Map<?, String> options) {
  
          IndexedContainer container = new IndexedContainer();
          container.addContainerProperty(PROPERTY_VALUE, Object.class, null);
          container.addContainerProperty(PROPERTY_LABEL, String.class, "");
          for (Entry<?, String> entry : options.entrySet()) {
              Item item = container.addItem(entry.getKey());
              item.getItemProperty(PROPERTY_VALUE).setValue(entry.getKey());
              item.getItemProperty(PROPERTY_LABEL).setValue(entry.getValue());
          }
          box.setContainerDataSource(container);
          box.setItemCaptionPropertyId(PROPERTY_LABEL);
      }
docs: Generates the options items for the combo box using the map entry keys as values and the values as labels.<p>
  
  @param box the combo box to prepare
  @param options the box options