JavaFX Use one Loader load two different nodes - javafx

Question

Everyone.I would like to ask, Can we use one loader to load two different FXMLs at one time? Actually, I want to know whether can I load two fxmls, so that these two fxmls can be displayed at the same time, at one screen.
public class NodeLink extends Application {
#Override
public void start(Stage stage) throws Exception {
FXMLLoader loader = new FXMLLoader();
AnchorPane root = (AnchorPane)loader.load(getClass().getResource("StartPanel.fxml"));
Group centralNode = (Group)loader.load(this.getClass().getResource("CentralNode.fxm."));
root.getChildren().setAll(centralNode);
//Group centralNode = FXMLLoader.load(getClass().getResource("CentralNode.fxml"));
Scene scene = new Scene(root);
stage.setScene(scene);
stage.show();
}
As above, Group centralNode = ... this statement will cause error, as follows:
Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:367)...
So, why this will cause errors? Can we use several fxmls once to make up a screen?
Thank you so much!