将一个ChangeListener添加到ChoiceBox的selectionmodel和selectedIndexProperty：

Add a ChangeListener to the ChoiceBox's selectionmodel and selectedIndexProperty:

final ChoiceBox<String> box = new ChoiceBox<String>();

    box.getItems().add("1");
    box.getItems().add("2");
    box.getItems().add("3");

    box.getSelectionModel().selectedIndexProperty().addListener(new ChangeListener<Number>() {
      @Override
      public void changed(ObservableValue<? extends Number> observableValue, Number number, Number number2) {
        System.out.println(box.getItems().get((Integer) number2));
      }
    });