Error en JavaFX

 package application; import javafx.application.Application; import javafx.stage.Stage; import javafx.scene.Group; import javafx.scene.Scene; import javafx.scene.shape.Rectangle; import javafx.scene.shape.Shape; public class Main extends Application { @Override public void start(Stage primaryStage) { try { Group root = new Group(); Scene scene = new Scene(root,800,800); Shape s = new Shape(); Rectangle r = new Rectangle(); r.setX(750); r.setY(100); r.setWidth(200); r.setHeight(100); r.setArcWidth(30); r.setArcHeight(20); root.getChildren().add(r); primaryStage.setScene(scene); primaryStage.setTitle("Hello world"); primaryStage.show(); } catch(Exception e) { e.printStackTrace(); } } public static void main(String[] args) { launch(args); } }