The LLD Roadmap

Get the full map of this course — from OOP fundamentals to mock interviews — and learn exactly how to travel it.

The Journey at a Glance

Low-Level Design isn't one skill — it's a stack of skills, each building on the one below it. You can't reason about design patterns if you don't understand SOLID; you can't apply SOLID if you don't think in objects. This course is sequenced deliberately so that every layer rests on solid foundations.

Here is the seven-stage roadmap we'll follow:

1. OOP — Encapsulation, abstraction, inheritance, polymorphism. The vocabulary of design.
2. SOLID — Five principles that turn "code that works" into "code that survives change."
3. UML — A shared visual language to communicate a design before writing a line of code.
4. Design Patterns — Battle-tested solutions to recurring problems (Strategy, Factory, Observer…).
5. The 8-Step Framework — A repeatable method to attack any design prompt under time pressure.
6. Case Studies — Full end-to-end designs: parking lot, elevator, Splitwise, and more.
7. Mock Interviews — Timed dry runs that simulate the real thing and expose your blind spots.

Why this order?

Each stage is a prerequisite for the next. SOLID is impossible to discuss without OOP terms like abstraction and polymorphism. Design patterns are literally named applications of SOLID principles. And the 8-Step Framework is the glue that lets you deploy patterns, draw UML, and respect SOLID — all in real time. Skipping ahead is the single most common way learners stall.

What "good design" looks like in code

Let's make the roadmap concrete. Below is a tiny preview that touches three stages at once: OOP (an interface + enum), SOLID (open for extension via a new strategy), and a Design Pattern (Strategy). Don't worry about mastering it now — just notice how clean code reads.

// Stage 1 (OOP): model the domain with a clear abstraction.
public interface DiscountStrategy {
    double apply(double amount);
}

// Stage 4 (Pattern): each rule is its own small, focused class.
public final class NoDiscount implements DiscountStrategy {
    @Override public double apply(double amount) { return amount; }
}

public final class PercentageDiscount implements DiscountStrategy {
    private final double percent;
    public PercentageDiscount(double percent) { this.percent = percent; }
    @Override public double apply(double amount) {
        return amount - (amount * percent / 100.0);
    }
}

// Stage 2 (SOLID): Checkout depends on the abstraction, not a concrete rule.
// Adding a new discount NEVER forces us to edit this class (Open/Closed).
public final class Checkout {
    private final DiscountStrategy strategy;
    public Checkout(DiscountStrategy strategy) {
        this.strategy = strategy;
    }
    public double total(double subtotal) {
        return strategy.apply(subtotal);
    }
}

public class Demo {
    public static void main(String[] args) {
        Checkout sale = new Checkout(new PercentageDiscount(10));
        System.out.println(sale.total(200.0)); // 180.0
    }
}

Three roadmap stages, eight lines of logic, zero if/else sprawl. That is the destination — and the rest of the course teaches you how to arrive there on demand.

How to use this course

This is a text-first, Java-first, interview-focused course. To get maximum value:

• Read in order. The sequence is the curriculum. Resist the urge to skip to "Design Patterns" — the foundations make them click.
• Type the code. Every Java block is compiling-quality. Run it. Break it. Fix it. Reading code is not learning code.
• Do every exercise. The ✍️ Exercise callouts are where understanding hardens into skill.
• Mine the Interview callouts. The 🎤 sections expose the exact traps interviewers set. Treat them as a hit-list.
• Use the Recap. Each lesson ends with three takeaways — perfect for spaced review before an interview.