Abstract Factory Pattern

// ─── EXAMPLE 1 ──────────────────────────────────────────────────────────────
// WHAT WE ARE IMPLEMENTING:
// A cross-platform UI theme manager supporting Dark and Light skins
// consistently.
//
// WHERE THE PATTERN FITS IN:
// ThemeFactory acts as the Abstract Factory. DarkThemeFactory and
// LightThemeFactory are Concrete Factories creating matching Button and
// Checkbox products.
// ────────────────────────────────────────────────────────────────────────────
// --- Product interfaces ---
interface Button { void render(); }
interface Checkbox { void render(); }
interface ThemeFactory {
    Button createButton();
    Checkbox createCheckbox();
}

// --- Dark theme family ---
class DarkButton implements Button {
    public void render() { System.out.println("  [DarkButton] Rendered with dark bg"); }
}

class DarkCheckbox implements Checkbox {
    public void render() { System.out.println("  [DarkCheckbox] Rendered dark"); }
}

class DarkThemeFactory implements ThemeFactory {
    public Button createButton() { return new DarkButton(); }
    public Checkbox createCheckbox() { return new DarkCheckbox(); }
}

// --- Light theme family ---
class LightButton implements Button {
    public void render() { System.out.println("  [LightButton] Rendered with light bg"); }
}

class LightCheckbox implements Checkbox {
    public void render() { System.out.println("  [LightCheckbox] Rendered light"); }
}

class LightThemeFactory implements ThemeFactory {
    public Button createButton() { return new LightButton(); }
    public Checkbox createCheckbox() { return new LightCheckbox(); }
}

class Application {
    private final Button button;
    private final Checkbox checkbox;
    public Application(ThemeFactory factory) {
        button = factory.createButton();
        checkbox = factory.createCheckbox();
    }
    void render() {
        button.render();
        checkbox.render();
    }
}

public class Main {
    public static void main(String[] args) {
        // Choose family once — all products are consistent
        Application app = new Application(new DarkThemeFactory());
        app.render();
    }
}