setHgap（）方法设置垂直间隙而不是水平

Question

我刚刚开始学习JavaFX，我制作了一个程序，在GridPane中显示三个随机多米诺骨牌。我只是好奇为什么setHgap（）方法创建垂直线而不是水平线，反之亦然？

下面的代码示例和图片：

public class Chapter_14_E03_DisplayThreeTiles extends Application {

    public static void main(String[] args) {

        Application.launch(args);

    }

    public void start(Stage primaryStage) {

        // Create an arraylist to store number values
        ArrayList<Integer> tileNumbers = new ArrayList<>();
        for (int i = 1; i <= 36; i++)
            tileNumbers.add(i);
        java.util.Collections.shuffle(tileNumbers);

        // Create a pane to hold the images
        GridPane pane = new GridPane(); 
        pane.setHgap(2); // Creates horisontal lines ???

        // Add images to pane
        for (int i = 0; i <= 2; i++) {
            pane.add(new ImageView(new Image("file:image\\tiengow\\" + tileNumbers.get(i) + ".png")), i, 0);
        }

        // Create a scene and place it in the stage
        Scene scene = new Scene(pane);
        primaryStage.setTitle("Exercise_14_03");
        primaryStage.setScene(scene);
        primaryStage.show();

    }

}

产生以下输出：