I Would NOT Start Learning Low-Level Design With Design Patterns in 2026

If you are starting LLD from zero, this is the order I would follow — and why most beginners make it harder than it needs to be.

I Would NOT Start Learning Low-Level Design With Design Patterns in 2026

When I first started looking at Low-Level Design interview questions, they looked suprisingly simple.

  • “Design a Parking Lot.”
  • “Design an Elevator.”
  • “Design a Library Management System.”

At first, I thought:

“How difficult can it be? I just need to create a few classes.”

Then I opened someone else’s solution.

  • There were interfaces.
  • Abstract classes.
  • SOLID principles.
  • Strategy Pattern.
  • Factory Pattern.
  • Observer Pattern.
  • UML diagrams.

And suddenly a Parking Lot didn’t feel like a Parking Lot anymore.

It felt like I was designing the next version of Amazon.

If you have ever felt this way, you are not alone.

The biggest mistake beginners make with LLD is starting from the wrong place.

They start memorising design patterns.

  • Or they watch 20 hours of LLD videos.
  • Or they try to solve complicated machine-coding problems without understanding object-oriented programming properly.

A better approach is to build the knowledge step by step.

In this article, I’ll walk through the roadmap I would follow if I had to learn Low-Level Design from scratch in 2026.

First, What Exactly Is Low-Level Design?

Before learning LLD, let’s clear up one common confusion.

LLD is not the same thing as System Design.

Think about building a food delivery application.

At the high-level/system-design level, you might ask:

  • Do we need MySQL or MongoDB?
  • How will services communicate?
  • Do we need Kafka?
  • How will the system handle millions of users?
  • Where should caching happen?
  • How do we handle failures?

That’s the big picture.

LLD goes one level deeper.

Now we start asking:

  • What classes do we need?
  • What should each class be responsible for?
  • Which objects interact with each other?
  • What methods should each class expose?
  • Should this be an interface?
  • Should we use inheritance or composition?
  • How can we make the code easier to extend?

A simple way to remember it:

System Design
 ↓
Big picture
 ↓
Services
Databases
Caching
Queues
Scalability
 ↓
Low-Level Design
 ↓
Classes
Objects
Interfaces
Methods
Relationships
Code

So if System Design decides what major components exist, LLD gets closer to deciding how those components are actually structured in code.

Step 1: Understand What Kind of LLD Interview You Are Preparing For

This is something I would figure out before spending weeks preparing.

Not every company conducts LLD interviews in exactly the same way.

The three common formats:

  1. Object-Oriented Design
  2. Machine Coding
  3. Concurrency Design

And they require slightly different preparation.

1. Object-Oriented Design

You may get a problem like:

Design a Parking Lot.

You are generally expected to discuss:

  • classes
  • interfaces
  • attributes
  • methods
  • relationships
  • design decisions

You may write pseudocode or class skeletons instead of building a complete application.

For example:

class ParkingLot {
 private List<ParkingFloor> floors;
 public Ticket parkVehicle(Vehicle vehicle) {
 // Find suitable spot
 // Assign vehicle
 // Generate ticket
 }
}

The interviewer isn’t necessarily checking whether you can write 500 lines of code.

They are checking whether you can think about software structure.

2. Machine Coding

This is different.

Here, the interviewer may actually expect working code.

Your code should:

  • compile
  • run
  • handle important use cases
  • handle edge cases
  • have a reasonable structure
  • be readable and maintainable

Machine-coding rounds can also be longer, often around 90–120 minutes.

So ask yourself:

Can I design something AND turn that design into working code quickly?

That’s a different skill from simply drawing classes on a whiteboard.

3. Concurrency Design

This is where things get even more interesting.

Suppose you have:

Thread A → reads parking spots
Thread B → assigns parking spot

What happens if both threads try to reserve the same spot at exactly the same time?

Now you have to think about:

  • race conditions
  • locks
  • synchronization
  • deadlocks
  • shared state

Concurrency can also appear as an extension to a normal LLD question.

For example:

“You designed the Parking Lot. Now make it thread-safe.”

If your target interviews include concurrency-heavy LLD, prepare for it separately.

Step 2: Pick ONE Object-Oriented Programming Language

You don’t need to learn five languages for LLD.

Pick one language you are comfortable with.

The important part isn’t:

“Which language is best for LLD?”

The better question is:

“Which language lets me express my design clearly?”

For example, if you’re comfortable with Java:

interface PaymentStrategy {
 void pay(double amount);
}
class CardPayment implements PaymentStrategy {
 public void pay(double amount) {
 System.out.println("Paid using card");
 }
}
class UPIPayment implements PaymentStrategy {
 public void pay(double amount) {
 System.out.println("Paid using UPI");
 }
}

You should be comfortable reading and writing this kind of code before going deep into LLD.

Step 3: Strengthen Your OOP Fundamentals

This is probably the most important step.

Because at its core, LLD is about taking a real-world problem and representing it using:

Classes + Objects + Interfaces + Relationships

I recommend starting with the basic building blocks of OOP before moving further.

Learn:

  • Classes
  • Objects
  • Constructors
  • Enums
  • Interfaces
  • Abstract classes
  • Access modifiers

Then understand the four core OOP concepts:

Encapsulation

Keep data and the operations on that data together.

class BankAccount {
private double balance;
 public void deposit(double amount) {
 balance += amount;
 }
 public double getBalance() {
 return balance;
 }
}

The caller doesn’t directly modify:

account.balance = -100000;

because balance is private.

Abstraction

Expose what someone needs to use without exposing unnecessary implementation details.

interface PaymentService {
 void pay(double amount);
}

The caller doesn’t need to know how the payment happens internally.

Inheritance

A class can reuse or extend behaviour from another class.

class Vehicle {
 String number;
}
class Car extends Vehicle {
}

But don’t start thinking:

“Inheritance = always good.”

It isn’t.

In real LLD, choosing composition vs inheritance is often an important design decision.

Polymorphism

The same interface can have different implementations.

PaymentStrategy payment = new CardPayment();
payment.pay(1000);

Later:

PaymentStrategy payment = new UPIPayment();
payment.pay(1000);

The calling code can remain the same.

That’s powerful.

Step 4: Understand Relationships Between Classes

Once you know classes, the next question is:

How do these classes relate to each other?

Some important relationships are:

  • Association
  • Aggregation
  • Composition
  • Dependency

For example:

ParkingLot
 |
 └── ParkingFloor
 |
 └── ParkingSpot

You need to understand what these relationships actually mean instead of simply memorising UML arrows.

The goal is to answer questions like:

Should ParkingLot create ParkingFloor?
Can ParkingFloor exist independently?
Should this class own that object?
Is this object merely using another object?

These questions become important when your design grows.

Step 5: Learn Design Principles Before Design Patterns

This is where I would deliberately slow down.

Don’t jump directly to:

“I need to learn all 23 design patterns.”

First learn how to write good code.

Start with principles such as:

  • DRY
  • KISS
  • YAGNI
  • Separation of concerns
  • Low coupling
  • High cohesion
  • Law of Demeter

Then learn SOLID.

Why?

Because design patterns are tools.

If you don’t understand the problem you’re trying to solve, a pattern becomes just another piece of syntax to memorise.

For example, imagine this class:

class OrderService {
public void placeOrder() {
 // validate order
 // calculate price
 // process payment
 // send email
 // update inventory
 // generate invoice
 }
}

It might work.

But now ask:

What happens when payment logic changes?
What happens when email is replaced with SMS?
What happens when we add another way of calculating discounts?

This is where design principles start becoming useful.

Step 6: Learn SOLID Through Problems, Not Definitions

You don’t need to memorise five textbook definitions and hope the interviewer asks you to repeat them.

Instead, understand the problem each principle tries to prevent.

For example:

Single Responsibility Principle

Ask:

“Does this class have one clear responsibility?”

Instead of:

class Invoice {
void calculateTotal() {}
 void saveToDatabase() {}
 void sendEmail() {}
 void printInvoice() {}
}

You might separate responsibilities.

Invoice
 ↓
InvoiceCalculator
InvoiceRepository
InvoiceEmailService
InvoicePrinter

Now each component has a clearer job.

That’s much more useful in an interview than simply saying:

“SRP means a class should have one reason to change.”

Know the definition, but more importantly, recognise the problem.

Step 7: Learn Just Enough UML

You don’t need to become a UML expert.

For LLD interviews, the most useful diagrams are:

Class Diagram

Shows:

Classes
Attributes
Methods
Relationships

This is probably the most directly useful one for LLD.

Use Case Diagram

Helps clarify:

Who uses the system?
What can they do?

Sequence Diagram

Shows how objects interact step by step.

For example:

Customer
 |
 | placeOrder()
 ↓
OrderService
 |
 | processPayment()
 ↓
PaymentService
 |
 | charge()
 ↓
PaymentGateway

You don’t need beautiful diagrams.

You need diagrams that help you explain your thinking.

Step 8: Now Learn Design Patterns

Only now.

Because now patterns will start making sense.

There are 23 classic Gang of Four patterns, but you don’t need to memorise all of them before your first LLD interview.

I recommend these 10 as particularly useful:

  1. Strategy
  2. Observer
  3. State
  4. Facade
  5. Factory Method
  6. Composite
  7. Decorator
  8. Command
  9. Chain of Responsibility
  10. Template Method

Let’s make them less scary.

Strategy Pattern

Suppose your application supports:

Credit Card
UPI
Digital Wallet

Instead of putting everything inside one giant if-else:

if (type.equals("CARD")) {
 // card payment
} else if (type.equals("UPI")) {
 // UPI payment
} else if (type.equals("WALLET")) {
 // wallet payment
}

You can define:

interface PaymentStrategy {
 void pay(double amount);
}

And create:

CardPayment
UPIPayment
WalletPayment

Each strategy implements its own payment behaviour.

The benefit?

Adding another payment method doesn’t require rewriting the entire payment system.

Observer Pattern

Imagine an order status changes:

Order = SHIPPED

Multiple things may care about this:

Email Service
SMS Service
Notification Service
Analytics

Instead of tightly coupling the Order to all of them, the Observer pattern can allow interested objects to subscribe to changes.

State Pattern

An object behaves differently depending on its current state.

For example:

Order
 ↓
CREATED
 ↓
PAID
 ↓
SHIPPED
 ↓
DELIVERED

The behaviour of an order can depend on its current state.

Facade

Sometimes a subsystem is complicated.

Instead of exposing everything:

PaymentService
InventoryService
NotificationService
ShippingService

you can provide a simpler interface:

orderService.placeOrder();

The facade hides the complexity behind a simpler API.

Factory Method

Useful when object creation depends on some input.

For example:

VehicleFactory
 |
 ├── Car
 ├── Bike
 └── Truck

Instead of spreading object-creation logic everywhere, centralise it.

Composite

Useful when you have tree-like structures.

A classic example:

Folder
 ├── File
 ├── File
 └── Folder
 ├── File
 └── File

Files and folders can be treated through a common interface.

Decorator

Useful when you want to add behaviour without modifying the original class.

For example:

Coffee
 ↓
MilkCoffee
 ↓
SugarMilkCoffee

You can add behaviour dynamically instead of creating a separate class for every combination.

Command

Turns an action into an object.

This becomes useful for things like:

Undo
Redo
Queueing operations
Logging operations

For example:

Command
 |
 ├── AddTextCommand
 ├── DeleteTextCommand
 └── FormatTextCommand

Chain of Responsibility

A request passes through multiple handlers.

For example:

Request
 ↓
Manager
 ↓
Senior Manager
 ↓
Director
 ↓
VP

Each handler can either process the request or pass it forward.

Template Method

Useful when multiple workflows have the same overall structure but differ in a few steps.

Think:

prepare()
process()
finish()

The overall flow stays the same while individual implementations customise specific steps.

But Here Is the Most Important Rule About Design Patterns

Don’t force a design pattern into every problem.

This is one of the easiest ways to make LLD unnecessarily complicated.

If you have a simple problem and someone asks:

“Why are you using Factory + Strategy + Observer + Abstract Factory here?”

and your answer is:

“Because these are design patterns.”

That’s not a good answer.

A pattern should solve a real problem.

Ask:

Does this pattern make the code easier to understand?
Does it make the system easier to extend?
Does it reduce coupling?
Does it make a future requirement easier to handle?

If the answer is no, don’t use it.

A simpler design is often a better design.

Step 9: Start Solving Real LLD Problems

Now comes the part where actual learning begins.

Pick problems such as:

  • Parking Lot
  • Elevator
  • Library Management System
  • Payment System
  • Notification System
  • Movie Ticket Booking
  • Task Management System

But don’t immediately search for the solution.

This is important.

Take a problem and spend some time thinking.

For example:

Design a Parking Lot.

Don’t immediately write:

ParkingLot
ParkingFloor
ParkingSpot
Vehicle
Ticket
Payment

Instead ask questions.

Q. What are the requirements?

  • Can the parking lot have multiple floors?
  • What vehicle types exist?
  • Can a car park in a bike spot?
  • How do we find an available spot?
  • How is a ticket generated?
  • How is payment calculated?
  • What happens when the parking lot is full?

These questions help define the design.

A Simple LLD Problem-Solving Process

This is the process I would personally keep beside me while practising:

Problem
 ↓
 Clarify Requirements
 ↓
 Define Scope
 ↓
 Identify Entities
 ↓
 Define Responsibilities
 ↓
 Define Relationships
 ↓
 Identify Interfaces
 ↓
 Apply Principles/Patterns
 Only if needed
 ↓
 Write Code
 ↓
 Think About Edge Cases
 ↓
 Think About Extensions

Notice something?

Design patterns come quite late.

They aren’t the starting point.

Ask Yourself These 5 Questions While Designing

Whenever you’re solving an LLD problem, keep asking:

1. Does every class have a clear responsibility?

If you see a class doing ten unrelated things, that’s a warning sign.

2. Can I easily add a new requirement?

Suppose today we support:

UPI
Card

Tomorrow:

Wallet
Net Banking
Crypto

Would you have to rewrite half your system?

If yes, reconsider the design.

3. Am I creating unnecessary complexity?

More classes don’t automatically mean better design.

4. Is my code easy to test?

If one small change requires starting the entire application, something may be too tightly coupled.

5. Can I explain why I made this decision?

This is huge in interviews.

Don’t just say:

“I used Strategy Pattern.”

Say:

“I used Strategy because the payment algorithm can vary independently, and I want to add new payment methods without changing the main order-processing logic.”

That explanation demonstrates understanding.

The Biggest Difference Between Beginners and Experienced Developers

A beginner often thinks:

“What code should I write?”

An experienced developer usually starts with:

“What exactly is the problem I’m trying to model?”

That’s the mindset shift LLD is trying to develop.

Suppose the requirement changes.

Initially:

Payment → Card

Later:

Payment → Card
 → UPI
 → Wallet

A beginner may modify the existing code.

An experienced developer starts asking:

“Why was my original design difficult to extend?”

That question is much more valuable.

You Don’t Need to Find the “Perfect” Design

This is another thing that makes LLD confusing.

There is rarely one perfect answer.

Two engineers can design the same system differently and both designs can be reasonable.

Why?

Because design depends on:

  • requirements
  • expected changes
  • complexity
  • maintainability
  • performance
  • team preferences
  • trade-offs

So instead of asking:

“Is my design exactly the same as the solution?”

Ask:

“Can I justify my design?”

That’s a much better benchmark.

A Practical 2026 LLD Roadmap

If I had to start from zero today, my learning order would look like this:

Week 1
│
├── Choose one OOP language
├── Classes & Objects
├── Interfaces
├── Abstract Classes
└── OOP fundamentals
↓
Week 2
│
├── Encapsulation
├── Abstraction
├── Inheritance
├── Polymorphism
└── Class relationships
 ↓
Week 3
│
├── DRY
├── KISS
├── YAGNI
├── Coupling
├── Cohesion
└── SOLID
 ↓
Week 4
│
├── Basic UML
├── Class diagrams
├── Sequence diagrams
└── Use-case diagrams
 ↓
Week 5
│
├── Strategy
├── Observer
├── Factory
├── State
├── Decorator
└── Other important patterns
 ↓
Week 6+
│
├── Parking Lot
├── Elevator
├── Library
├── Payment System
├── Notification System
└── Machine-coding problems

Don’t rush to design patterns before understanding OOP.

Don’t solve machine-coding problems before you can structure classes comfortably.

And don’t memorise solutions before learning how to identify responsibilities.

One More Thing: Practice Without Looking at Solutions

This sounds obvious.

Most people don’t actually do it.

They see:

“Design a Parking Lot.”

They think for two minutes.

Then they open YouTube.

Then they copy:

Vehicle
ParkingSpot
ParkingFloor
ParkingLot
Ticket
Payment

It feels like learning.

But when the interviewer gives:

“Design a Movie Ticket Booking System.”

the same structure doesn’t magically appear.

Instead, try this:

Step 1

Read the problem.

Step 2

Clarify requirements.

Step 3

Write down entities.

Step 4

Assign responsibilities.

Step 5

Draw relationships.

Step 6

Think about changing requirements.

Step 7

Only then look at a solution.

This forces your brain to actually practise design.

My Biggest Takeaway

If I had to reduce this entire roadmap to one sentence, it would be:

Don’t learn LLD as a collection of design patterns. Learn it as a way of thinking about code.
  • Start with OOP.
  • Then understand class relationships.
  • Then learn design principles.
  • Then learn SOLID.
  • Then learn enough UML to communicate your design.
  • Then learn commonly used design patterns.

And finally, solve real problems repeatedly.

Because the goal isn’t to look at a Parking Lot question and immediately think:

“Ah, Strategy Pattern!”

The goal is to look at it and think:

“What are the responsibilities here?
What can change?
What should depend on what?
And how can I design this so that the next requirement doesn’t force me to rewrite everything?”

That is when LLD starts becoming much easier.

And honestly, that’s also when it becomes useful beyond interviews.

From Tech By Neha Gupta

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