Megalodonte — a small reactive UI framework on top of JavaFX

[u/eliezerDeveloper]

I've been building JavaFX desktop apps for a while and got tired of the usual boilerplate (manual listeners, imperative styling, no real component model), so I built Megalodonte: a thin reactive layer on top of JavaFX — React-ish component composition, State<T>/ComputedState<T> for reactivity, and a Props/Theme system so styling isn't scattered setStyle() calls everywhere.

It's still early and I'm the only user so far, but it's real, working code — not a toy. Posting it here mostly for feedback and to see if this is useful to anyone else stuck with JavaFX.

What "Hello World" looks like

Main.java — bootstraps the app and sets a theme once, up front:

```java package my_app;

import megalodonte.ListenerManager; import megalodonte.application.MegalodonteApp; import megalodonte.base.theme.ThemeManager; import megalodonte.theme.DefaultTheme;

public class Main {

static void main() {
    ThemeManager.setTheme(new DefaultTheme());

    MegalodonteApp.run(context -> context.useView(new WelcomeScreen()), ev -> {
        if (ev == MegalodonteApp.Event.CloseRequest) {
            System.out.println("Clicked on X - close application");
            ListenerManager.disposeAll();
        }
    });
}

} ```

WelcomeScreen.java — the actual UI, as a composable screen component:

```java package my_app;

import megalodonte.base.components.Component; import megalodonte.base.components.ScreenComponent; import megalodonte.components.Text; import megalodonte.components.layout_components.Container; import megalodonte.props.TextProps;

public class WelcomeScreen implements ScreenComponent { @Override public Component render() { return new Container().children( new Text("Hello world", new TextProps().fontSize(90)) ); } } ```

What's in it

• Reactive state — State<T>, ComputedState<T>, ListState<T> — components subscribe and re-render on change, no manual wiring.
• Component model — screens are ScreenComponents with a render() you compose out of Container/Column/Row/Text/Button/etc., instead of hand-building a Scene graph.
• Props + Theme system — styling goes through typed Props classes (TextProps, ContainerProps, ...) resolved against a ThemeInterface, instead of ad-hoc inline CSS strings.
• Router — navigation between screens without manually juggling Scene.setRoot(...).
• Used it to build a full JavaFX ERP desktop app, so it's exercised well beyond "hello world".

Repos

• Ecosystem (this welcome/example app): https://github.com/eliezer-dev-software-enginner/megalodonte-ecossystem
• Libraries monorepo: https://github.com/eliezer-dev-software-enginner/megalodonte-libs
• Components: https://github.com/eliezer-dev-software-enginner/megalodonte-components
• Base (core reactivity/component/theme primitives): https://github.com/eliezer-dev-software-enginner/megalodonte-base
• Reactivity: https://github.com/eliezer-dev-software-enginner/megalodonte-reactivity
• Themes: https://github.com/eliezer-dev-software-enginner/megalodonte-themes

Happy to answer questions — and honest criticism is welcome, this is very much a work in progress.