Why SOLID violations and fixes in LLD? - Purpose & Use Cases

The Big Idea

What if your code could change as easily as swapping LEGO blocks without breaking everything?

The Scenario

Imagine building a big LEGO castle where every piece is glued together. If you want to change a tower or add a new room, you have to break the glue and risk damaging the whole castle.

The Problem

When code breaks SOLID principles, it becomes like that glued LEGO castle. Making changes is slow, risky, and causes unexpected bugs because parts are tightly connected and hard to fix or replace.

The Solution

SOLID principles guide us to build code like LEGO blocks that snap together but can be taken apart easily. This makes the system flexible, easier to understand, and safer to change without breaking other parts.

Before vs After

✗ Before

class OrderProcessor {
  void process(Order order) {
    // process payment
    // update inventory
    // send confirmation email
  }
}

✓ After

interface PaymentService { void pay(Order order); }
interface InventoryService { void update(Order order); }
interface NotificationService { void notify(Order order); }

class OrderProcessor {
  PaymentService payment;
  InventoryService inventory;
  NotificationService notification;

  void process(Order order) {
    payment.pay(order);
    inventory.update(order);
    notification.notify(order);
  }
}

What It Enables

It enables building software that adapts easily to new needs without breaking existing features.

Real Life Example

Think of a smartphone app where you can add new features like payment methods or notifications without rewriting the whole app.

Key Takeaways

SOLID helps keep code flexible and maintainable.

It reduces bugs when making changes.

It makes teamwork easier by separating responsibilities.