Button b = new Button();
Button front = new Button("Stop");
front.setPrefWidth(50);
front.setOnAction((e) -> {
    System.out.println("front click");
});
HBox h = new HBox();
h.getChildren().addAll(front);
b.setGraphic(h);

b.setOnAction((e) -> {
        System.out.println("back click");
});

front click
back click
front click
back click
front click
back click
front click
back click
front click
back click
front click
back click