import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
import javafx.scene.control.Button;
import javafx.scene.control.Label;

public class App extends Application {
    Stage primaryStage;

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

    @Override
    public void start(Stage primaryStage) {
        this.primaryStage = primaryStage;

        Label label1 = new Label("Első");
        Button button1 = new Button("Másik");
        VBox vbox1 = new VBox();
        vbox1.getChildren().addAll(label1, button1);
        Scene scene1 = new Scene(vbox1, 300, 250);

        Label label2 = new Label("Második");
        Button button2 = new Button("Vissza");
        VBox vbox2 = new VBox();
        vbox2.getChildren().addAll(label2, button2);
        Scene scene2 = new Scene(vbox2, 300, 250);

        button1.setOnAction(e -> primaryStage.setScene(scene2));
        button2.setOnAction(e -> primaryStage.setScene(scene1));

        primaryStage.setScene(scene1);
        primaryStage.show();
    }
}