private Line connectLines(Line line, Circle startNode, Circle endNode) {
        line.startXProperty().bind(startNode.centerXProperty().add(startNode.translateXProperty()));
        line.startYProperty().bind(startNode.centerYProperty().add(startNode.translateYProperty()));
        line.endXProperty().bind(endNode.centerXProperty().add(endNode.translateXProperty()));
        line.endYProperty().bind(endNode.centerYProperty().add(endNode.translateYProperty()));

    return line;
}
       //mouse pressed event
        EventHandler<MouseEvent> mousePressed = new EventHandler<MouseEvent>() {
        @Override
        public void handle(MouseEvent e) {
            System.out.println("pressed");
            sceneX = e.getSceneX();
            sceneY = e.getSceneY();
            translateCircleX = ((Circle)(e.getSource())).getTranslateX();
            translateCircleY = ((Circle)(e.getSource())).getTranslateY();
        }
    };


    //mouse dragged event
    EventHandler<MouseEvent> mouseDragged = new EventHandler<MouseEvent>() {
        @Override
            public void handle(MouseEvent e) {
            System.out.println("dragged");
                double offsetX = e.getSceneX() - sceneX;
                double offsetY = e.getSceneY() - sceneY;
                double newTranslateCircleX = translateCircleX + offsetX;
                double newTranslateCircleY = translateCircleY + offsetY;
            ((Circle)(e.getSource())).setTranslateX(newTranslateCircleX);
            ((Circle)(e.getSource())).setTranslateY(newTranslateCircleY);
        }
    };