Decorator 

The Decorator Pattern allows you to dynamically add new behavior or responsibilities to an object without modifying its original structure or code. It provides a flexible alternative to subclassing for extending functionality.

Understanding the Concept

Sometimes, you want to add features or behaviors to existing objects, but you either can’t or shouldn’t modify their source code. The Decorator Pattern solves this by wrapping the original object inside another object (called a “decorator”) that adds the desired features.

This pattern promotes composition over inheritance. Instead of creating many subclasses for every possible combination of behaviors, you can create a few simple decorators and combine them in different ways.

Real-World Analogy

Imagine you’re ordering a coffee at a café. You start with a basic coffee, and then you add extra features — like milk, sugar, whipped cream, or flavor shots. Each add-on wraps around the base coffee and enhances it.

• Basic Coffee → Add Milk → Add Sugar → Add Cream
  Each new layer adds a new behavior or cost — but the core coffee remains unchanged.

Key Characteristics of the Decorator Pattern

• Flexible extension – Add features to objects at runtime, not compile-time.
• No alteration of original code – The base component stays untouched.
• Multiple layers – You can stack multiple decorators to create complex behaviors.
• Interface consistency – Both the base object and decorators share the same interface.

Where Decorator Is Commonly Used

• UI frameworks – Adding scrollbars, borders, or shadows to windows.
• File I/O streams – Wrapping streams with compression, encryption, or buffering.
• Logging systems – Wrapping functionality with additional logging.
• Permission systems – Adding access control around methods dynamically.

Benefits of the Decorator Pattern

• Open/Closed Principle – Classes are open for extension but closed for modification.
• Runtime flexibility – Combine or remove behaviors on-the-fly.
• Avoids subclass explosion – Reduces the need for many subclasses to represent every feature combination.
• Reusable components – Each decorator is reusable and composable with others.

Potential Drawbacks

• Complex stacking – Multiple layers can make the call stack harder to trace.
• Overhead – Frequent wrapping and unwrapping can add some performance cost.
• Harder debugging – Behavior can be distributed across multiple decorators, making bugs less obvious.

Summary

The Decorator Pattern is ideal when you need to extend or modify the behavior of objects without altering their source code. It offers a powerful, flexible way to build features layer by layer — much like customizing a product or stacking enhancements. By favoring composition over inheritance, it helps keep systems modular, scalable, and easier to maintain.