Minimal JavaFx project without fxml, controller and launcher

Just for learning and testing purpose. First I create normally a javafx project with java and gradle with no additional libraries.

After creation of JavaFx, IntellJ normally created three classes, HelloApplication, HelloController and Launcher, there are also hello-view.fxml. First I run the project, open up Launcher class and debug or run it with following configuration and a little issue, why is there warning?

I want just to have only one class MainApp, so renamed HelloApplication to MainApp, delete hello-view.fxml, HelloController and Launcher classes, modify also build script from HelloApplication to MainApp. But i have issue with running or debugging.

There are now just only one class MainApp here.

 

Contant of MainApp is

package com.company.javafxgradlewrapperdemo;

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

public class MainApp extends Application {

    @Override
    public void start(Stage stage) {
        Label label = new Label("Hello JavaFX 👋 (Gradle Wrapper, minimal)");
        Button button = new Button("Click me");
        button.setOnAction(e -> label.setText("Clicked!"));

        VBox root = new VBox(10, label, button);
        Scene scene = new Scene(root, 320, 200);

        stage.setTitle("JavaFX Minimal with Wrapper");
        stage.setScene(scene);
        stage.show();
    }

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

content of build.gradle.kts

plugins {
    java
    application
    id("org.javamodularity.moduleplugin") version "1.8.15"
    id("org.openjfx.javafxplugin") version "0.0.13"
    id("org.beryx.jlink") version "2.25.0"
}

group = "com.company"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
}

val junitVersion = "5.12.1"

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(21)
    }
}

tasks.withType<JavaCompile> {
    options.encoding = "UTF-8"
}

application {
    mainModule.set("com.company.javafxgradlewrapperdemo")
    mainClass.set("com.company.javafxgradlewrapperdemo.MainApp")
}

javafx {
    version = "21.0.6"
    modules = listOf("javafx.controls")
}

dependencies {
    testImplementation("org.junit.jupiter:junit-jupiter-api:${junitVersion}")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:${junitVersion}")
}

tasks.withType<Test> {
    useJUnitPlatform()
}

jlink {
    imageZip.set(layout.buildDirectory.file("/distributions/app-${javafx.platform.classifier}.zip"))
    options.set(listOf("--strip-debug", "--compress", "2", "--no-header-files", "--no-man-pages"))
    launcher {
        name = "app"
    }
}
 

Only change the configuration from Launcher class to MainApp

After running I got this

How can I solve this problem, just only one class MainApp without Launcher, controller and fxml?