LLD:11-UI Render System

UI Render System - Factory Pattern Implementation

This is an implementation of the Factory design pattern for a cross-platform UI framework that renders OS-specific components without the client code needing to know which operating system it's running on.

Problem Statement

Building a UI framework that runs on both Windows and Mac operating systems. The challenge is to render platform-specific UI components while keeping the client code completely decoupled from the underlying OS-specific implementations.

Key Challenge:

Windows Button → [WINDOWS] Rendering a Windows style button.
Mac Button → [MAC] Rendering a Mac style button.
Client code must never use new WindowsButton() or new MacButton() directly
Adding new OS support should not require changes to client code

Class Diagram

                            +----------------------+
                            |      UIFactory       |
                            +----------------------+
                            | + createButton()     |
                            +----------+-----------+
                                       |
                                       | (Creates)
                                       v
                            +----------------------+
                            |        Button        |
                            |      (Interface)     |
                            +----------------------+
                            | + render()           |
                            +----------+-----------+
                                       ^
                                       | (Implements)
                      +----------------+----------------+
                      |                                 |
           +----------+----------+           +----------+----------+
           |    WindowsButton    |           |       MacButton     |
           +---------------------+           +---------------------+
           | + render()          |           | + render()          |
           +---------------------+           +---------------------+

Implementation

package factory.uirendersystem;

public class UIRenderSystem {

    /**
     * Enum to define supported operating systems.
     * Ensures type safety and prevents invalid string inputs.
     */
    enum OperatingSystem {
        WINDOWS,
        MAC
    }

    /**
     * Component Interface.
     * Defines the contract all platform-specific buttons must follow.
     */
    interface Button {
        void render();
    }

    /**
     * Concrete Product for Windows.
     * Renders a Windows-style button.
     */
    static class WindowsButton implements Button {
        @Override
        public void render() {
            System.out.println("[WINDOWS] Rendering a Windows style button.");
        }
    }

    /**
     * Concrete Product for Mac.
     * Renders a Mac-style button.
     */
    static class MacButton implements Button {
        @Override
        public void render() {
            System.out.println("[MAC] Rendering a Mac style button.");
        }
    }

    /**
     * The Factory Class.
     * This is the ONLY place where the new keyword is used to
     * instantiate concrete button classes.
     * The client remains completely ignorant of which class is created.
     */
    static class UIFactory {
        public Button createButton(OperatingSystem operatingSystem) {
            return switch (operatingSystem) {
                case WINDOWS -> new WindowsButton();
                case MAC -> new MacButton();
                default -> throw new IllegalArgumentException(
                    "Unsupported OS Type"
                );
            };
        }
    }

    /**
     * Main driver method.
     * The client only interacts with the Factory and the Button Interface.
     * It never references WindowsButton or MacButton directly.
     */
    public static void main(String[] args) {
        System.out.println("---- Cross-Platform UI Library ----");

        UIFactory uiFactory = new UIFactory();

        Button windowsBtn = uiFactory.createButton(OperatingSystem.WINDOWS);
        windowsBtn.render();

        Button macBtn = uiFactory.createButton(OperatingSystem.MAC);
        macBtn.render();
    }
}

Key Features

Factory Pattern: Centralizes platform-specific object creation in one place
Type Safety: Uses Enum for OS types instead of raw strings
Loose Coupling: Client only depends on the Button interface, never on concrete classes
Platform Independence: Client code works identically regardless of OS
Open/Closed Principle: Add new OS support without modifying existing code
Extensible: New platforms require only a new class and a new Enum value

How It Works

Interface (Button): Defines the render() contract all platform buttons must follow
Concrete Classes: Each class implements its own OS-specific rendering logic
Factory (UIFactory): Takes an OperatingSystem Enum and returns the right button object
Client (main): Only talks to the factory and the interface — never touches concrete classes directly

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