How to prevent JavaFX GUI to auto-close after closing the graph generated by JGraphX?

Question

There's a button btn in my JavaFX GUI interface. When clicking btn, a graph will be drawn.

But when I close the graph, my JavaFX GUI will auto-close as well, which is not desired.

How can I prevent the JavaFX GUI from auto-close?

If the solution involve embedding the generated graph inside the JavaFX GUI, I am also fine. Thanks!

import javax.swing.JFrame;
import com.mxgraph.swing.mxGraphComponent;
import com.mxgraph.view.mxGraph;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class MainFx extends Application {
    
    
    @Override
    public void start(Stage primaryStage) {
    Button btn = new Button();
    btn.setText("Draw Graph");
    btn.setOnAction(new EventHandler<ActionEvent>() {
        
        // draw graph when clicking the button
        @Override
        public void handle(ActionEvent event) {
                
        JGraphXLearning1 frame = new JGraphXLearning1();    
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 320);
        frame.setVisible(true);
        
        }
    });
    
    StackPane root = new StackPane();
    root.getChildren().add(btn);
    
    Scene scene = new Scene(root, 300, 250);
    
    primaryStage.setScene(scene);
    primaryStage.show();
    }
 
    public static void main(String[] args) {
    launch(args);
    }
 
    public class JGraphXLearning1 extends JFrame {
                 
          public JGraphXLearning1() {
            super("JGraphXLearning1");
            mxGraph graph = new mxGraph();
            Object defaultParent = graph.getDefaultParent();
            graph.getModel().beginUpdate();
            Object v1 = graph.insertVertex(defaultParent, null, "Hello", 20, 20, 80, 30);
            Object v2 = graph.insertVertex(defaultParent, null, "World", 240, 150, 80, 30);
            graph.insertEdge(defaultParent, null, "Edge", v1, v2);
            graph.getModel().endUpdate();
            mxGraphComponent graphComponent = new mxGraphComponent(graph);
            getContentPane().add(graphComponent);
          }

        }
}