📅Week-6 (Day-3) - Understanding the Builder Design Pattern

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.

💠The Problem Without Builder Pattern

Before we go into Builder solutions, here’s what can go wrong:

• Constructor Explosion

  • Every new optional parameter = new constructor overload

  • Hard to read, hard to maintain

• Inconsistent Object States

  • Partially-built objects used before validation

• Mutable Objects

  • Exposing too many setters = risk of invalid data

• Difficult Validation

  • No single place to enforce rules

(Hindi: Jab aap har cheez constructor mein bharne lagte ho, toh code unreadable ho jaata hai aur validation mushkil ho jaati hai.)

💠Solution — Builder Pattern

The Builder Pattern helps you construct objects step by step with clarity, immutability, and validations. Let’s explore 3 flavors:

1. Classic Builder (Nested Builder)

Example: HttpRequestBuilder

• Use a nested static class to collect fields

• At the end, call .build()

🧩 Benefits:

• Central validation

• No constructor overloads

• Immutable objects

(Hindi: Sab fields ko pehle collect karo, fir build() function se ek final object banao — clean and readable.)

2. Builder with Director

Use a Director class to construct predefined or frequently-used configurations.

Example:

Director d;
UserProfile p = d.buildDefaultIndianUser();

✅ Reusable builds ✅ Keeps main builder clean

(Hindi: Director ek helper ki tarah hota hai jo common types of object banana asaan karta hai.)

3. Step Builder Pattern

Perfect when:

• Some fields are mandatory, others are optional

• You want compile-time safety

🔒 Enforces build flow like:

1. Set name

2. Set age

3. Then set optional things like hobbies/photos

💡 Extremely IDE-friendly + prevents accidental skip of required fields

(Hindi: Step Builder har ek zaroori field pe rok lagata hai jab tak aap usko set nahi karte. Safe and clean!)

💠 UML Diagram

💠 Code

Here :- github

💠Summary from Notes:

✅ Normal Builder:

• Clear, centralized construction

• Immutable, readable objects

• One place for validation logic

✅ Director:

• Reusable build logic

✅ Step Builder:

• Compile-time enforcement of required fields

• Great for IDE autocomplete + safe builds

💠Real-World Examples:

• 🛒 E-commerce checkout object

• 🧾 Invoice generation with optional metadata

• 📡 Network request builder with timeouts, headers, payloads

Week - 6 (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 👩‍💻

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