Eu simplesmente estava tentando entender por que o tamanho da janela (que eu defino em tela cheia) está mudando quando eu mudo de cena. Existe uma maneira (isto é, um comando) que pode ser emitida uma vez para que o Java FX saiba que não mudar o tamanho?

import javafx.application.Application;
import javafx.geometry.Pos;

import javafx.scene.Scene;

import javafx.scene.control.Button;
import javafx.scene.control.ContentDisplay;

import javafx.scene.image.Image;

import javafx.scene.image.ImageView;
import javafx.scene.layout.BorderPane;

import javafx.scene.layout.HBox;

import javafx.scene.layout.StackPane;

import javafx.stage.Stage;

public class Main extends Application {

    Scene scene,scene_2;

    public static void main(String[] args) {

        launch(args);

    }

    @Override

    public void start(Stage Win_primary) throws Exception {

        Win_primary.setTitle("AN-0");



        Button start,exit_pro,back_to_start;

        start= new Button();

        start.setText("Start");

        Image exit_door = new Image("file:C:\\Users\\MyPc\\Pictures\\FX\\vector-icons_05-128 (2).png");



        exit_pro= new Button ();
        exit_pro.setGraphic(new ImageView(exit_door));





          start.setStyle(

                "-fx-background-radius: 100em; " +

                "-fx-min-width: 200px; " +

                "-fx-min-height: 200px; " +

                "-fx-max-width: 200px; " +

                "-fx-max-height: 170px;" +

                "-fx-font-size: 20px"

        );


           exit_pro.setMaxSize(50, 50);
           exit_pro.setOnAction(e -> Win_primary.close());

        StackPane layout = new StackPane();
        layout.setStyle("-fx-background-color: #FFFFFF ;");
        layout.getChildren().add(start);
        layout.setAlignment(exit_pro, Pos.BOTTOM_CENTER);
         layout.getChildren().add(exit_pro);


        start.setOnAction(e -> {
             Win_primary.setScene(scene_2);

            });
        scene = new Scene(layout, 300, 250);


        //scene 2

        StackPane layout2 = new StackPane();
        back_to_start = new Button("Cancel");
        layout2.setStyle("-fx-background-color: #FFFFFF ;");
        layout2.getChildren().add(back_to_start);
        layout.setAlignment(back_to_start, Pos.BOTTOM_CENTER);
        scene_2 = new Scene (layout2,300,250);   
        back_to_start.setOnAction(e -> Win_primary.setScene(scene));


        Win_primary.setScene(scene);
        Win_primary.setMinHeight(700);
        Win_primary.setMinWidth(700);
        Win_primary.setMaximized(true);

        Win_primary.setFullScreen(true);

        Win_primary.show();

    }

}