Design Pattern # Abstract Factory Design Pattern

 Here is a clear, real-world (LIVE) example of the Abstract Factory Design Pattern with Java implementation — exactly what is asked in interviews.

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⭐ Real-World Example: Cross-Platform UI Component Factory

Imagine you are building software that must run on:

• Windows

• Mac

• Linux

Each OS has its own style of:

• Buttons

• Checkboxes

• Menus

Your application should not contain if-else everywhere to check OS type.

👉 Abstract Factory solves this.

It gives you one factory per family of related objects, and the client never knows which OS it is using.

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🎯 LIVE EXAMPLE: Create UI for Windows & Mac

You want to create UI components (Button, Checkbox) but the style depends on OS.

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🧱 1️⃣ Product Interfaces (Common API)

interface Button {
    void paint();
}

interface Checkbox {
    void paint();
}

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🪟 2️⃣ Concrete Products for Windows

class WindowsButton implements Button {
    @Override
    public void paint() {
        System.out.println("Windows style Button");
    }
}

class WindowsCheckbox implements Checkbox {
    @Override
    public void paint() {
        System.out.println("Windows style Checkbox");
    }
}

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🍎 3️⃣ Concrete Products for Mac

class MacButton implements Button {
    @Override
    public void paint() {
        System.out.println("Mac style Button");
    }
}

class MacCheckbox implements Checkbox {
    @Override
    public void paint() {
        System.out.println("Mac style Checkbox");
    }
}

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🏭 4️⃣ Abstract Factory (interface)

interface GUIFactory {
    Button createButton();
    Checkbox createCheckbox();
}

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🏭 5️⃣ Concrete Factories

Windows Factory

class WindowsFactory implements GUIFactory {
    @Override
    public Button createButton() {
        return new WindowsButton();
    }

    @Override
    public Checkbox createCheckbox() {
        return new WindowsCheckbox();
    }
}

Mac Factory

class MacFactory implements GUIFactory {
    @Override
    public Button createButton() {
        return new MacButton();
    }

    @Override
    public Checkbox createCheckbox() {
        return new MacCheckbox();
    }
}

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🎮 6️⃣ Client Code (Application Layer)

The client never knows the OS. It only uses the factory.

class Application {
    private Button button;
    private Checkbox checkbox;

    public Application(GUIFactory factory) {
        button = factory.createButton();
        checkbox = factory.createCheckbox();
    }

    public void paint() {
        button.paint();
        checkbox.paint();
    }
}

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🚀 7️⃣ App Runner

public class Demo {
    public static void main(String[] args) {
        
        GUIFactory factory;
        String os = "WINDOWS"; // This could be detected dynamically
        
        if (os.equals("WINDOWS")) {
            factory = new WindowsFactory();
        } else {
            factory = new MacFactory();
        }

        Application app = new Application(factory);
        app.paint();
    }
}

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⭐ OUTPUT

Windows style Button
Windows style Checkbox

If OS = Mac:

Mac style Button
Mac style Checkbox

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📌 Where This is Used in Real Industry?

✔ 1. Spring Framework

Different beans for:

• AWS

• Azure

• GCP

Using different factory configurations.

✔ 2. JDBC DriverManager

Creates different connection objects:

• MySQLConnection

• OracleConnection

✔ 3. UI Libraries

React Native, Flutter, Swing → create widgets based on platform.

✔ 4. Car Manufacturing System

Factory for:

• Tesla components

• BMW components

• Audi components

Each family has:

• Engine

• Tyres

• Dashboard

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📝 Interview Summary (Best 2 Lines)

Abstract Factory creates families of related objects without specifying their concrete classes.
Example: A Cross-Platform UI library creates Windows Button + Windows Checkbox OR Mac Button + Mac Checkbox using a single factory.

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