I am a novice to javafx. I created a simple javafx fxml application. I defined a treeView in my fxml file. It is as follows,
FXMLDocument.fxml
 <AnchorPane id="AnchorPane" prefHeight="200.0" prefWidth="320.0" xmlns:fx="http://javafx.com/fxml/1"      xmlns="http://javafx.com/javafx/2.2" fx:controller="scenebuilderfirst.FXMLDocumentController">
   <children>
     <TreeView id="" fx:id="tree" layoutX="60.0" layoutY="14.0" prefHeight="172.0" prefWidth="200.0" />
   </children>
 </AnchorPane>
and created the controller class as follows,
FXMLDocumentController.java
 public class FXMLDocumentController implements Initializable {
     @FXML
     private TreeView<?> tree;   
     @Override
     public void initialize(URL url, ResourceBundle rb) {
     }    
 }
my main java file is as follows,
MyApp.java
 public class SceneBuilderFirst extends Application {
     @Override
     public void start(Stage stage) throws Exception {
         AnchorPane root = FXMLLoader.load(getClass().getResource("FXMLDocument.fxml"));
         Scene scene = new Scene(root);
         stage.setScene(scene);
         stage.show();
     }
     public static void main(String[] args) {
         launch(args);
     }    
 }
Now I need to add tree items to the TreeView while running the program. So I thought of writing the following peace of code inside the initialize() method of my contorller class,
    // creating root item for the tree
    TreeItem<String> rootItem = new TreeItem<>("root");
    rootItem.setExpanded(true);
    //creating childern for the tree
    TreeItem<String>item1= new TreeItem<>("content1");
    rootItem.getChildren().add(item1);
    TreeItem<String>item2= new TreeItem<>("content2");
    rootItem.getChildren().add(item2);
    //attaching root item to tree
    tree = new TreeView<>(rootItem);
But it didn't work.
I need to set the TreeItems while running the program. Not through the fxml file. So I think I should do the coding in my main java file I need a way to access my TreeView after loading it via FXMLLoader in my main java file so i can make a TreeView on my own choice and attach it to this TreeView while running the program. Please guide me.