The  Composite pattern  allows you to treat  individual objects  and  groups of objects (composites)  in a  uniform way . It represents part-whole hierarchies so that client code can interact with both single and grouped items through a common interface.   Purpose To build complex tree-like structures where  leaf nodes (single elements)  and  composite nodes (groups)  can be treated the same way.   Key Characteristics Defines a  component interface  for both leaf and composite Leaf handles base operations Composite stores child components and delegates operations   Pros Simplifies  client code  by treating all components uniformly Supports  hierarchical  and  recursive  structures Easy to add new types of components   Cons Can make the system overly general Harder to  restrict certain operations  for leaf-only o...

The Proxy pattern provides a placeholder or surrogate for another object. It controls access to the real object and can add extra behavior like caching, logging, lazy initialization , or security .   Purpose To control access to another object. It can be used to defer resource-heavy operations, restrict access, or wrap remote calls and security logic.   Key Characteristics Implements the same interface as the real object Delegates requests to the actual object Can add extra logic (e.g., access control, logging)   Pros Adds control, performance optimizations, or protection Supports lazy loading or remote access Keeps real object usage transparent to the client   Cons Introduces additional layers Can increase complexity Misuse may lead to tight coupling   Use Cases Security proxies for sensitive financial operations Virtual proxies to delay ...

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 ...