JavaUI

Declarative, Flutter-inspired UI framework for Java desktop apps. Backed by Swing, packaged as a normal Gradle library.

new JavaUIApp.Builder()
        .title("Hello, JavaUI")
        .size(420, 320)
        .theme(ThemeData.light())
        .build()
        .run(
            Scaffold()
                .appBar(AppBar("Hello"))
                .body(Center(
                    Column(
                        Text("Welcome to JavaUI").bold().fontSize(20),
                        SizedBox(0, 12),
                        Button("Click me", () -> Snackbar.show("Hi!"))
                    ).gap(8)
                ))
        );

Highlights

• Declarative widget tree — describe the UI as nested function calls; the framework rebuilds Swing components for you.
• Reactive state — State<T> with multiple listeners; StatefulWidget#setState triggers a coalesced rebuild on the EDT.
• Flexible router — pattern segments (/users/:id), back/forward history, route guards.
• Theming — light/dark ThemeData, hot-swappable at runtime; Theme.toggleDark() updates the active tree.
• Material-flavored widgets — buttons (filled/outlined/text), cards with elevation, FAB, app bar, dialogs, snackbars, tabs, badges, chips, avatars, progress, sliders, switches, checkboxes, radios, dropdowns, date pickers, and more.
• Cross-platform fonts — picks the best installed sans-serif (Inter → SF Pro → Segoe UI → ...) so apps look consistent on macOS / Windows / Linux.
• Pluggable image loading — file system, classpath (classpath:foo.png) and HTTP(S) with timeouts; SVG via SVG Salamander.
• Maven-publishable — gradle publishToMavenLocal produces a clean io.github._3xhaust:javaUI:0.2.0 artifact with sources and Javadoc jars.

Getting started

Prerequisites

• JDK 17 or newer
• Gradle 8+ (the Gradle wrapper is bundled)

Build & test

./gradlew build      # compiles + runs JUnit 5 tests + builds the jar
./gradlew test       # tests only

Try the bundled examples

./gradlew runHello       # minimal Hello World
./gradlew runCounter     # classic counter, demonstrates auto-rebuild
./gradlew runTodo        # list state, checkboxes, snackbar
./gradlew runGallery     # widget catalog
./gradlew runSettings    # live theme switching (dark/light)
./gradlew runLogin       # PostgreSQL-backed login (needs DB; see below)

The login example reads PG_URL / PG_USER / PG_PASS env vars (defaults to jdbc:postgresql://localhost:5432/javaui, postgres, postgres).

Concepts

Stateful widgets

Subclass StatefulWidget and call setState(...) (or mutate a State you previously watch-ed) to rebuild:

class CounterPage extends StatefulWidget {
    final State<Integer> count = State.of(0);

    @Override public void initState() { watch(count); }

    @Override public View build() {
        return Center(
            Column(
                Text(String.valueOf(count.get())).fontSize(64).bold(),
                Button("+1", () -> count.update(v -> v + 1))
            )
        );
    }
}

watch(state) subscribes the widget so any future state.set(...) schedules a single rebuild on the next EDT frame — no manual repaint needed.

Routing

new JavaUIApp.Builder()
    .route("/", () -> new HomePage())
    .route("/users/:id", params -> new UserPage(params.getInt("id", 0)))
    .route("/*", () -> new NotFoundPage())
    .build()
    .run();

Navigator.to("/users/42");
Navigator.back();          // history is preserved

Theming

Theme.set(ThemeData.dark());
// or build a custom theme
ThemeData custom = ThemeData.light().toBuilder()
        .primary(ColorUtils.fromHex("#6750A4"))
        .radius(12)
        .build();
Theme.set(custom);

The framework rebuilds the active route automatically when the theme changes.

Async dialogs and toasts

DialogWidget.showAlert("Oops", "Something went wrong");
boolean ok = DialogWidget.showConfirm("Sure?", "This cannot be undone.");
SnackbarWidget.show("Saved!", SnackbarWidget.Type.SUCCESS);

Widget catalog (highlights)

Category	Widgets
Layout	Scaffold, AppBar, Row, Column, Stack, Center, Align, Padding, Wrap, Expanded, Flexible, Spacer, SizedBox, Container, Card, ListView, GridView, SingleChildScrollView, Divider, Tabs
Inputs	Button, IconButton, FloatingActionButton, Input, TextArea, Checkbox, Switch, Radio, Slider, Dropdown, DatePicker, FormField
Display	Text, Icon, Image, Avatar, Badge, Chip, Tooltip, ProgressBar, CircularProgress
Feedback	Dialog, Snackbar, ErrorBoundary
Animation	Animation.tween(...) with easing curves

Using JavaUI as a library

./gradlew publishToMavenLocal

Then in another Gradle project:

repositories { mavenLocal() }
dependencies { implementation 'io.github._3xhaust:javaUI:0.2.0' }

Caveats

• A whole-route rebuild is used for state changes — focus and scroll are not preserved across rebuilds. If that matters for a particular widget, manage focus explicitly.
• Swing is the only renderer for now; the Renderer interface is platform-neutral so a JavaFX or Compose-Multiplatform backend can be added later.

License

MIT.