Final Project & Course Summary

Introduction

Congratulations on completing Low-Level Design on TechLearningPRO. This final lesson consolidates the course arc and outlines a capstone project: design a mini e-commerce order module end-to-end using everything you learned.

You should now move comfortably from requirements to class diagrams, sequence flows, Java 21 implementations, pattern selection, and interview communication — the full loop hiring managers assess.

Keep practicing one timed problem weekly until interviews land.

Understanding the topic

Key concepts

• Course arc: OOP → SOLID → UML → patterns → guidelines → classic problems → interview skills.
• Capstone: Product, Cart, Order, Payment, Inventory services.
• Apply SRP per service; DIP for payment and repository.
• Document with class + sequence diagram.
• Implement core checkout in Java with tests.
• Reflect: patterns used, trade-offs, future extensions.

flowchart LR
  Requirements --> UseCases
  UseCases --> ClassModel
  ClassModel --> Patterns
  Patterns --> Code

Step-by-step explanation

1. Capstone step 1: write requirements and use cases for checkout.
2. Step 2: class diagram with Cart, Order, LineItem, Product, PaymentGateway.
3. Step 3: sequence diagram for addToCart and checkout.
4. Step 4: Java implementation with in-memory repositories.
5. Step 5: extension — coupon discount strategy.
6. Step 6: self-review against SOLID checklist.

Informative example

Capstone starter — order module skeleton tying the course together:

public final class Cart {
    private final Map<String, Integer> skuQty = new HashMap<>();

    public void add(String sku, int qty) {
        skuQty.merge(sku, qty, Integer::sum);
    }

    public Map<String, Integer> items() { return Map.copyOf(skuQty); }
}

public final class OrderService {
    private final InventoryService inventory;
    private final PaymentGateway payments;
    private final PricingPolicy pricing;

    public OrderService(InventoryService inventory, PaymentGateway payments, PricingPolicy pricing) {
        this.inventory = inventory;
        this.payments = payments;
        this.pricing = pricing;
    }

    public OrderResult checkout(String userId, Cart cart) {
        if (!inventory.reserve(cart.items())) {
            return OrderResult.failed("stock");
        }
        Money total = pricing.total(cart.items());
        var pay = payments.charge(userId, total);
        if (pay instanceof PaymentResult.Failure f) {
            inventory.release(cart.items());
            return OrderResult.failed(f.reason());
        }
        return OrderResult.success(UUID.randomUUID().toString());
    }
}

Extend capstone with OrderRepository persistence, email Notifier, and CouponPricing strategy — your portfolio LLD sample.

Real-world use

Real-world applications

• Portfolio design document for job applications.
• Weekly retention practice schedule post-course.
• Teaching LLD to teammates using course structure.

Best practices

• Maintain personal diagram template library.
• Mock interview monthly with feedback partner.
• Revisit weak modules (UML, patterns) selectively.
• Read one real RFC or design doc per week.
• Contribute LLD section to team projects.
• Track company-specific question frequency.

Common mistakes

• Stopping practice after course completion.
• Capstone too large — scope to checkout module only.
• No written summary of design decisions.
• Skipping self-review against SOLID checklist.

Advanced interview questions

Summary

Course covered OOP, SOLID, UML, patterns, guidelines, and classic LLD problems. Capstone: e-commerce checkout module design and implementation. Interview success = structured process + clear communication. Keep weekly timed practice after course end. TechLearningPRO LLD track prepares you for OOD hiring loops. Apply SOLID checklist to every new design.