JavaFX FXML controller - constructor vs initialize method

Question

My Application class looks like this   public class Test extends Application        private static Logger logger   LogManager getRootLogger          Override     public void start Stage primaryStage  throws Exception            String resourcePath     resources fxml MainView fxml           URL location   getClass   getResource resourcePath           FXMLLoader fxmlLoader   new FXMLLoader location            Scene scene   new Scene fxmlLoader load    500  500            primaryStage setScene scene           primaryStage show               public static void main String   args            launch args             The FXMLLoader creates an instance of the corresponding controller  given in the FXML file via fx controller  by invoking first the default constructor and then the initialize method   public class MainViewController        public MainViewController             System out println  first                FXML     public void initialize             System out println  second              The output is   first second   So  why does the initialize method exist  What is the difference between using a constructor or the initialize method to initialize the controller required things   Thanks for your suggestions

User · Answer

The initialize method is called after all  FXML annotated members have been injected  Suppose you have a table view you want to populate with data    class MyController         FXML     TableView lt MyModel gt  tableView        public MyController             tableView getItems   addAll getDataFromSource        results in NullPointerException  as tableView is null at this point               FXML     public void initialize             tableView getItems   addAll getDataFromSource        Perfectly Ok here  as FXMLLoader already populated all  FXML annotated members

User · Answer

In a few words  The constructor is called first  then any  FXML annotated fields are populated  then initialize   is called  This means the constructor does not have access to  FXML fields referring to components defined in the  fxml file  while initialize   does have access to them  Quoting from the Introduction to FXML          the controller can define an initialize   method  which will be called once on an implementing controller when the contents of its associated document have been completely loaded       This allows the implementing class to perform any necessary post-processing on the content

User · Answer

In Addition to the above answers  there probably should be noted that there is a legacy way to implement the initialization  There is an interface called Initializable from the fxml library   import javafx fxml Initializable   class MyController implements Initializable        FXML private TableView lt MyModel gt  tableView        Override     public void initialize URL location  ResourceBundle resources            tableView getItems   addAll getDataFromSource               Parameters   location - The location used to resolve relative paths for the root object  or null if the location is not known  resources - The resources used to localize the root object  or null if the root object was not localized     And the note of the docs why the simple way of using  FXML public void initialize   works   NOTE This interface has been superseded by automatic injection of location and resources properties into the controller  FXMLLoader will now automatically call any suitably annotated no-arg initialize   method defined by the controller  It is recommended that the injection approach be used whenever possible

[java] JavaFX FXML controller - constructor vs initialize method

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