What is Low Level Design?

Imagine you're building a house. Before construction begins, you need two types of plans:

• High Level Design (HLD): The architect's blueprint - how many floors, where's the kitchen, how does water flow through the building
• Low Level Design (LLD): The detailed engineering - what type of joints for the pipes, how thick are the wires, how do the switches connect

In software, LLD is about designing the internal structure of your code - the classes, methods, and how they work together.

The Design Flow

A Real Example: Notification System

Let's say your team needs to build a notification system. Here's how HLD and LLD differ:

Why LLD Matters

Bad LLD leads to spaghetti code - code that's hard to understand, modify, or extend.

Good LLD makes your code:

Let's See It In Code

Here's what bad design looks like - everything crammed into one class:

# ❌ Bad: One giant class doing everything
class NotificationManager:
    def send(self, user, message, type):
        if type == "email":
            # 50 lines of email sending logic
            smtp = smtplib.SMTP('smtp.gmail.com')
            smtp.login(EMAIL, PASSWORD)
            # ... more email code
        elif type == "sms":
            # 50 lines of SMS logic
            twilio = TwilioClient(SID, TOKEN)
            # ... more SMS code
        elif type == "push":
            # 50 lines of push notification logic
            firebase = FirebaseApp()
            # ... more push code

Now here's good LLD - clear separation of concerns:

# ✓ Good: Each class has one job
class NotificationService:
    def __init__(self, sender):
        self.sender = sender

    def notify(self, user, message):
        self.sender.send(user, message)

class EmailSender:
    def send(self, user, message):
        # Only email logic here
        pass

class SMSSender:
    def send(self, user, message):
        # Only SMS logic here
        pass

# Easy to use, easy to extend
email_notifier = NotificationService(EmailSender())
email_notifier.notify(user, "Hello!")

What You'll Learn in This Course

By the end of this course, you'll be able to:

• Break down problems into well-designed classes
• Apply SOLID principles to write flexible code
• Use design patterns to solve common problems
• Design systems that are easy to maintain and extend

Key Takeaways

Next up: SOLID Principles - the foundation of good object-oriented design.