📅Week-3 (Day-3) - Decorator Pattern Explained | Real-world use case + Code | Design patterns in LLD

NOTE: - I started my 8-week system design journey with Coder Army. I will be journaling every day, recording what I learn, reflecting on it, and sharing it with my network to help newcomers to system design.

💠What is the Decorator Pattern?

The Decorator Pattern allows you to dynamically add behavior or responsibilities to objects without modifying their code.

🎯 It gives you a flexible alternative to subclassing, perfect when you want to extend functionalities at runtime.

Decorator Pattern ek aisa design hai jisme aap kisi object ke upar naye features ya behavior add kar sakte ho bina uske original code ko chhue.

(Hindi : Jaise ek aadmi ne jacket pehna, phir topi lagayi, phir sunglasses — ek ke baad ek cheezein add hoti gayi!)

💠Real-life Analogy: Mario Game

Imagine Mario, the classic video game character:

• Base Mario: Can just walk.

• Eats a Mushroom → Grows taller.

• Eats a Fire Flower → Can shoot fireballs.

• Gets a Star → Becomes invincible.

👉 Mario’s core abilities stay the same, but new powers are added on top, dynamically — just like decorators!

💠How Does It Work?

We use:

• Component Interface (IComponent): Base functionalities

• Concrete Component (ConcreteComponent): Real object

• Decorator Class: Abstract wrapper

• Concrete Decorators: Extra powers

💠Why & When to Use the Decorator Pattern?

✅ Use When:

• You want to add behavior to objects at runtime.

• You don’t want to modify original code.

• You need a flexible way to extend functionality.

❌ Don’t Use When:

• Too many layers might make debugging hard.

• Can lead to too many small classes.

💠 Difference Between Inheritance vs Decorator

// Component Interface: defines a common interface for Mario and all power-up decorators.
interface Character {
    String getAbilities();
}

// Concrete Component: Basic Mario character with no power-ups.
class Mario implements Character {
    public String getAbilities() {
        return "Mario";
    }
}

// Abstract Decorator: CharacterDecorator "is-a" Character and "has-a" Character.
abstract class CharacterDecorator implements Character {
    protected Character character;  // Wrapped component

    public CharacterDecorator(Character c) {
        this.character = c;
    }
}

// Concrete Decorator: Height-Increasing Power-Up.
class HeightUp extends CharacterDecorator {
    public HeightUp(Character c) {
        super(c);
    }

    public String getAbilities() {
        return character.getAbilities() + " with HeightUp";
    }
}

// Concrete Decorator: Gun Shooting Power-Up.
class GunPowerUp extends CharacterDecorator {
    public GunPowerUp(Character c) {
        super(c);
    }

    public String getAbilities() {
        return character.getAbilities() + " with Gun";
    }
}

// Concrete Decorator: Star Power-Up (temporary ability).
class StarPowerUp extends CharacterDecorator {
    public StarPowerUp(Character c) {
        super(c);
    }

    public String getAbilities() {
        return character.getAbilities() + " with Star Power (Limited Time)";
    }
}

public class DecoratorPattern {
    public static void main(String[] args) {
        // Create a basic Mario character.
        Character mario = new Mario();
        System.out.println("Basic Character: " + mario.getAbilities());

        // Decorate Mario with a HeightUp power-up.
        mario = new HeightUp(mario);
        System.out.println("After HeightUp: " + mario.getAbilities());

        // Decorate Mario further with a GunPowerUp.
        mario = new GunPowerUp(mario);
        System.out.println("After GunPowerUp: " + mario.getAbilities());

        // Finally, add a StarPowerUp decoration.
        mario = new StarPowerUp(mario);
        System.out.println("After StarPowerUp: " + mario.getAbilities());
    }
}

💠 Real-World Example

📍Gift Wrapping Analogy:

• Gift = Base object.

• Wrapper = Decorator.

• Add ribbon, cover, bow — all without changing the gift itself!

📍 Zomato Order:

• You order food (base).

• Add cutlery, sauces, extra cheese (decorators).

Week - 3 (Day 3) Completed ✅ System Design

NOTE : - A big thanks to my mentors Rohit Negi Sir and Aditya Sir for launching this amazing 8-week course absolutely free on YouTube via CoderArmy9 :- youtube.com/@CoderArmy9 . 🙌

👉 Share this blog with your connections! Let’s keep learning, growing, and supporting one another on this journey. 🚀

✍️ Payal Kumari 👩‍💻 Github

Jai Hind 🇮🇳 | #CoderArmy #LearningInPublic #SystemDesign #TechForAll #MentorshipMatters #8weeksLLdChallenge #LowLevelDesign #LLD 👩‍💻