Hey there, budding architects! ?♂️?♀️ Ready to dive into the nitty-gritty of low-level design? Think of it like this: low-level design is that magical blueprint for every detail of your software’s mansion! Without it, you’d have chaos, like putting a refrigerator in your bathroom. Let’s fix that!
Low-Level Design (LLD) focuses on the granular details of your system. If High-Level Design (HLD) is your map showing cities and highways, LLD is the GPS zooming in to show which street you turn on to reach your destination. It’s the perfect marriage of functionality and finesse! It’s about defining:
Now imagine building a project like a food delivery app. The LLD answers how your system is going to handle the nitty-gritty tasks. From which classes are responsible for the restaurant data, to how you structure the API calls to show a user’s order history.
Scenario: We’re designing a low-level system for an online food delivery service like Zomato or Uber Eats. The goal: handle orders, users, restaurants, and deliveries smoothly without creating spaghetti code ?.
At this level, you are the director. You need to cast the perfect "actors" (classes) and tell them what roles to play.
java Copy code class User { private String userId; private String name; private String email; private List<Order> orders; public User(String userId, String name, String email) { this.userId = userId; this.name = name; this.email = email; this.orders = new ArrayList<>(); } public void placeOrder(Order order) { orders.add(order); } // Getters and Setters } class Restaurant { private String restaurantId; private String name; private List<FoodItem> menu; public Restaurant(String restaurantId, String name, List<FoodItem> menu) { this.restaurantId = restaurantId; this.name = name; this.menu = menu; } public List<FoodItem> getMenu() { return menu; } } class Order { private String orderId; private User user; private Restaurant restaurant; private List<FoodItem> foodItems; private OrderStatus status; public Order(String orderId, User user, Restaurant restaurant, List<FoodItem> foodItems) { this.orderId = orderId; this.user = user; this.restaurant = restaurant; this.foodItems = foodItems; this.status = OrderStatus.PENDING; } public void updateOrderStatus(OrderStatus status) { this.status = status; } }
Why Classes? Think of them as Lego blocks ?. Without them, you’d have a giant mess of unstructured bricks. We define who (User, Restaurant) and what (Order) gets involved.
Now that you have your "actors," let's look at how they interact. What’s a play without dialogue, right?
When a User places an order, it creates a new instance of Order. But what if the user is still thinking about which pizza to get? That’s where OrderStatus helps us track whether the order is Pending, InProgress, or Delivered.
Restaurants have menus (duh!) which are lists of FoodItems. When the user places an order, they choose from these items.
java Copy code class FoodItem { private String itemId; private String name; private double price; public FoodItem(String itemId, String name, double price) { this.itemId = itemId; this.name = name; this.price = price; } }
Here’s a typical flow of events in your food delivery app:
A sequence diagram can help you visualize how objects interact across time. It shows you step-by-step how User, Order, Restaurant, and Delivery Partner come together.
sql Copy code +---------+ +------------+ +--------------+ +--------------+ | User | | Restaurant | | Delivery | | Order | +---------+ +------------+ +--------------+ +--------------+ | | | | | Browse Menu | | | |---------------------->| | | | | | | | Place Order | | | |---------------------->| | | | | Prepare Food | | | |------------------------>| | | | | Assign Delivery | | | |---------------------->| | | | | | | | Update Status: InProgress | | |---------------------->| | | | | | Get Delivered Order | | | |<------------------------------------------------| | | Update Status: Delivered | | |<-----------------------------------------------------------------------|
Handling errors is crucial because real systems aren’t sunshine and rainbows ?. Let’s say the delivery partner can’t reach the restaurant because of road closure. Do we just cry? Nope!
We add fallback mechanisms.
java Copy code class DeliveryPartner { public void pickOrder(Order order) throws DeliveryException { if (roadClosed()) { throw new DeliveryException("Road is closed!"); } order.updateOrderStatus(OrderStatus.IN_PROGRESS); } private boolean roadClosed() { // Dummy logic to simulate a road closure return true; } }
When the exception is thrown, your system might notify the user, reassign a new delivery partner, or ask the restaurant to prepare a fresh order if it got delayed.
Here comes the fun part. After getting the system running, you can start thinking about improvements like:
java Copy code // Example of caching the menu class MenuService { private Map<String, List<FoodItem>> cachedMenus = new HashMap<>(); public List<FoodItem> getMenu(String restaurantId) { if (!cachedMenus.containsKey(restaurantId)) { cachedMenus.put(restaurantId, fetchMenuFromDB(restaurantId)); } return cachedMenus.get(restaurantId); } private List<FoodItem> fetchMenuFromDB(String restaurantId) { // Fetch from DB return new ArrayList<>(); } }
Low-Level Design is your battle plan. It prepares your system to be scalable, efficient, and robust. In our food delivery example, we went through class design, interactions, error handling, and even touched on optimizations. If you get the LLD right, your system is like a well-oiled machine, ready to handle anything the world throws at it.
So next time you’re deep into coding, think like an architect. Know your actors, know their dialogues, and keep the show running smoothly.
Now, go ahead and start placing those orders… I mean, writing those classes! ??
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