MultiPageDemo.java

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class MultiPageDemo extends Application {

    private List<String> fxmls = Arrays.asList(
            "page0.fxml",
            "page1.fxml"
    );

    private int index = -1;

    private StackPane root;

    @Override
    public void start(Stage stage) {
        root = new StackPane();
        root.setPrefSize(400, 400);
        
        forward();

        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }

    // ページを進める
    public void forward() {
        try {
            index++;
            if (index >= fxmls.size()) {
                index = 0;
            }
            
            // 次のページの読み込み
            FXMLLoader loader = new FXMLLoader(getClass().getResource(fxmls.get(index)));
            Node page = loader.load();

            // 現在ページが表示されていれば、それを削除
            if (!root.getChildren().isEmpty()) {
                root.getChildren().remove(0);
            }
            // 次のページを表示
            root.getChildren().add(page);

            // FXMLLoader からコントローラクラスを取得
            Pageable pageable = (Pageable) loader.getController();
            // コントローラクラスに自分自身を登録
            pageable.setMain(this);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    public static void main(String... args) {
        launch(args);
    }
}

page0.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<StackPane prefHeight="400.0" prefWidth="400.0" style="-fx-background-color: red;" xmlns:fx="http://javafx.com/fxml" fx:controller="PageController0">
  <children>
    <Button mnemonicParsing="false" onAction="#forward" text="Page 0" />
  </children>
</StackPane>

page1.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<StackPane id="AnchorPane" prefHeight="400.0" prefWidth="400.0" style="-fx-background-color: green;" xmlns:fx="http://javafx.com/fxml" fx:controller="PageController1">
  <children>
    <Button mnemonicParsing="false" onAction="#forward" text="Page 1" />
  </children>
</StackPane>

Pageable.java

public interface Pageable {
    public void setMain(MultiPageDemo main);
}

PageController0.java

import java.net.URL;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;

public class PageController0 implements Initializable, Pageable {
    private MultiPageDemo main;
    
    @FXML
    private void forward(ActionEvent evet) {
        main.forward();
    }
    
    @Override
    public void setMain(MultiPageDemo main) {
        this.main = main;
    }
    
    @Override
    public void initialize(URL url, ResourceBundle rb) {}    
    
}

PageController1.java

import java.net.URL;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;

public class PageController1 implements Initializable, Pageable {
    private MultiPageDemo main;
    
    @FXML
    private void forward(ActionEvent evet) {
        main.forward();
    }
    
    @Override
    public void setMain(MultiPageDemo main) {
        this.main = main;
    }
    
    @Override
    public void initialize(URL url, ResourceBundle rb) {}    
    
}