javafx-application-lifecycle

name	javafx-application-lifecycle
description	Manage the JavaFX Application lifecycle, primary stage setup, startup sequencing, and shutdown behavior.
triggers	["javafx application lifecycle","application start stage","application stop javafx","primary stage initialization"]
compatibility	{"java":"17+","javafx":"21+"}
category	project-setup
tags	["application","lifecycle","stage","startup","shutdown"]
metadata	{"scope":"repository","maturity":"starter"}
allowed-tools	["view","rg","apply_patch"]

JavaFX Application Lifecycle

Use this skill when the application already exists or the question is specifically about Application.init(), start(Stage), stop(), or primary-stage ownership rather than initial scaffolding.

Example

package com.example.app;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.stage.Stage;

public class MainApp extends Application {

    private ExecutorService executor;

    @Override
    public void init() {
        executor = Executors.newSingleThreadExecutor();
    }

    @Override
    public void start(Stage stage) {
        stage.setTitle("Lifecycle Demo");
        stage.setScene(new Scene(new Label("Ready"), 320, 160));
        stage.show();
    }

    @Override
    public void stop() {
        executor.shutdownNow();
    }
}

Setup notes

• Keep init() for non-UI initialization; no scene graph access belongs there.
• Treat the primary Stage as application-level infrastructure and pass navigation decisions through a shell or coordinator instead of random controllers.
• Close executors, subscriptions, file watchers, and native resources explicitly in stop().

Gotchas

• The Stage is only available in start(Stage), not in init().
• UI changes must run on the JavaFX Application Thread.
• javafx-project-starter is the right skill for generating a new app skeleton; this skill is for lifecycle semantics and ownership boundaries inside an app.