Java HBox(double spacing) Constructor

public HBox(double spacing)

/*from  w  w  w. j a va  2s.c  o m*/
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Priority;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class Main extends Application {
  public static void main(String[] args) {
    Application.launch(args);
  }

  @Override
  public void start(Stage primaryStage) {
    Group root = new Group();
    Scene scene = new Scene(root, 300, 250, Color.WHITE);

    HBox hbox = new HBox(0.5);
    Button button1 = new Button("Add               ");
    Button button2 = new Button("Remove   ");
    HBox.setHgrow(button1, Priority.ALWAYS);
    HBox.setHgrow(button2, Priority.ALWAYS);
    button1.setMaxWidth(Double.MAX_VALUE);
    button2.setMaxWidth(Double.MAX_VALUE);
    hbox.getChildren().addAll(button1, button2);
    
    root.getChildren().add(hbox);
    primaryStage.setScene(scene);
    primaryStage.show();
  }
}