Java FlowPane(double hgap, double vgap) Constructor

public FlowPane(double hgap,
  double vgap)

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.FlowPane;
import javafx.stage.Stage;
// w w w .  j a  v a 2  s.c o m
public class Main extends Application {
  public static void main(String[] args) {
    Application.launch(args);
  }

  @Override
  public void start(Stage primaryStage) {
    FlowPane flowPane = new FlowPane(4,3);
    flowPane.setPrefWrapLength(210);                 
    Button btn = new Button();
         
    for(int i=0; i<8; i++){
      btn = new Button("Button");
      btn.setPrefSize(100, 50);
      flowPane.getChildren().add(btn);
    }           
    Scene scene = new Scene(flowPane);
    primaryStage.setScene(scene);
    primaryStage.show();
  }
}