The Facade pattern provides a simplified, unified interface to a set of complex subsystems. It hides internal complexities and makes the system easier to use for clients.   Purpose To reduce complexity for the client by exposing a single point of interaction with multiple dependent classes and operations behind the scenes.   Key Characteristics Provides a high-level API Internally coordinates multiple complex operations Does not restrict access to lower-level subsystems (optional)   Pros Simplifies usage of complex systems Promotes separation of concerns Makes code easier to read and maintain   Cons Can become a god class if too much is added May hide important details needed by advanced users   Use Cases Wrapping financial transactions involving multiple steps (validation, logging, processing) Providing a simplified API for investment operations ...

The Decorator pattern allows you to add new behavior to objects dynamically without modifying their structure. It wraps an object to enhance or alter its behavior at runtime.   Purpose To extend the functionality of objects in a flexible and reusable way without changing the original class code.   Key Characteristics Uses composition , not inheritance Decorators implement the same interface as the target object Can be stacked or chained to combine behaviors   Pros Adds behavior without modifying existing classes Supports open/closed principle Allows dynamic behavior composition   Cons Many small classes can increase complexity Can be harder to trace behavior flow when deeply nested   Use Cases Adding features like logging, security, or validation to financial operations Applying transaction fees, taxes, or discounts dynamically Decorating notifica...