How to call a JAVA FX Class from another class many times

I want to rerun java FX application from another class. But error throws “Exception in thread “main” java.lang.IllegalStateException: Application launch must not be called more than once”. How to resolve this.

In my code I do console part and FX part. I do the console part in a single class and FX part in another class. So I just want to call the FX part to my console class(to the switch case). Means I just want to call FX part when I required it. it can be several times. When I select the FX option from the menu i t should call the FX part in different class.

Just simply I want to call the FX application from my menu many times. But when I do it throws an exception. How to avoid it and what is the way to do it

import javafx.application.Application;
import java.util.Scanner;

public class Test2{
    static  Scanner sc = new Scanner(System.in);

    public static void main(String[] args){
        System.out.print("ENTER THE CHOICE [OPTION NUMBER]: ");
        String option = sc.nextLine();

        switch (option){
            case ("1"):
               test();
                break;

            case("2"):
                Application.launch(Application1.class,args);// I WANT TO RE RUN THIS SEVERAL TIMES
                break ;

            default:
                System.out.println("invalid option. please re enter");
        }

    }

    private static void test() {
    }
}

import javafx.application.Application;
import javafx.stage.Stage;

public class Application1 extends Application{
    @Override
    public void start(Stage primaryStage){

        //SOMETHING FX

    }

}

Answer

As suggested in the comments, don’t use the predefined application lifecycle defined by the Application class. Just make the UI a regular Java class:

import javafx.scene.Parent;
import javafx.scene.control.Button;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;

public class Ui {

    private final Pane view ;
    
    public Ui() {
        view = new StackPane();
        Button button = new Button("Close");
        button.setOnAction(e -> button.getScene().getWindow().hide());
        view.getChildren().add(button);
    }
    
    public Parent getView() {
        return view ;
    }
}

and then start the JavaFX platform “by hand”, and show a window as needed. You just need to take a little care here to ensure that UI tasks are performed on the FX Application Thread.

You probably want to wait to prompt the user again until the window is closed. I use a CountDownLatch for this. If you want the prompt to appear again immediately (so the user can have multiple windows open at the same time), just omit that logic.

import java.util.Scanner;
import java.util.concurrent.CountDownLatch;

import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class App {

    public static void main(String[] args) {
        
        // Start the JavaFX Platform:
        Platform.startup(() -> {});
        
        // Don't exit JavaFX platform when the last window closes:
        Platform.setImplicitExit(false);
        
        try (Scanner scanner = new Scanner(System.in)) {
            while (true) {
                System.out.println("Enter choice (1=test, 2=Show UI, 3=Exit):");
                switch(scanner.nextLine()) {
                case "1": 
                    test();
                    break ;
                case "2":
                    showUI();
                    break ;
                case "3":
                    System.exit(0);
                default:
                    System.out.println("Invalid option");
                }
            }
        }
    }
    
    private static void test() {
        System.out.println("Test");
    }
    
    private static void showUI() {
        
        // latch to indicate window has closed:
        CountDownLatch latch = new CountDownLatch(1);
        
        // create and show new window on FX Application thread:
        Platform.runLater(() -> {
            Stage stage = new Stage();
            Ui ui = new Ui();
            Scene scene = new Scene(ui.getView(), 600, 600);
            stage.setScene(scene);
            
            // signal latch when window is closed:
            stage.setOnHidden(e -> latch.countDown());
            
            // show window:
            stage.show();
        });
        try {
            // Wait for latch (i.e. for window to close):
            latch.await();
        } catch (InterruptedException exc) {
            Thread.currentThread().interrupt();
        }
    }

}