Binding centerX property doesn't work - properties

Question

I'm learning new features of Java 8 with the book Java SE 8 for the Really Impatient
On the pages 76 and 77 the author says:
We always want the circle centered in the scene.
...
When the scene width changes, so does
that property. All that remains is to bind that computed property to
the circle’s centerX property:
circle.centerXProperty().bind(Bindings.divide(scene.widthProperty(),
2));
As there was no complete runnable sample I created my own. Here is it:
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.FlowPane;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
public class Exercise0404 extends Application {
#Override
public void start(Stage stage) throws Exception {
Circle circle = new Circle(50);
FlowPane pane = new FlowPane(circle);
Scene scene = new Scene(pane);
circle.centerXProperty().bind(scene.widthProperty().divide(2));
circle.centerYProperty().bind(scene.heightProperty().divide(2));
stage.setScene(scene);
stage.setTitle("Hello");
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}
But if I run the code and resize the scene the circle doesn't move to the center. Do I miss anything?

Answer 1

You are putting your circle in a FlowPane which in charge of the layout.
When you use absolute positioning, prefer the use of an adequate pane: javafx.scene.layout.Pane. From Pane javadoc:
This class may be used directly in cases where absolute positioning of children is required since it does not perform layout beyond resizing resizable children to their preferred sizes.
You just have to change the FlowPane to a Pane and it will work.
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
public class Exercise0404 extends Application {
#Override
public void start(Stage stage) throws Exception {
Circle circle = new Circle(50);
Pane pane = new Pane(circle);
Scene scene = new Scene(pane);
circle.centerXProperty().bind(scene.widthProperty().divide(2));
circle.centerYProperty().bind(scene.heightProperty().divide(2));
stage.setScene(scene);
stage.setTitle("Hello");
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}