Decorator Pattern

The Decorator Pattern is a design pattern in software development used to extend the functionality of objects without modifying their classes. It belongs to the category of structural patterns and allows behavior to be added to an object dynamically.

The main goal of the Decorator Pattern is to enhance the functionality of an object by adding additional responsibilities or properties without altering the core logic of the object. This makes the pattern more flexible and reusable compared to a static subclass hierarchy.

The pattern uses a composition structure where decorators implement the same interface as the original object. Each decorator contains a reference to the object being decorated and can add additional functionality by calling the methods of the original object and performing its own operations if necessary.

Benefits of the Decorator Pattern:

1. Flexibility: Since decorators implement the same interface as the original object, they can be combined in various ways to create different combinations of functionalities.

2. No class explosion: Unlike static subclass hierarchies where separate classes would need to be created for each combination of functionalities, the Decorator Pattern allows dynamic extension without class explosion.

3. Open for extension, closed for modification: Functionality can be added at runtime without modifying existing code, supporting the open/closed principle.

A well-known example of the Decorator Pattern is the extension of streams in the Java Standard Library. Various decorators such as "BufferedInputStream," "DataInputStream," "GzipInputStream," etc., can be used to add additional features like buffering or data processing to a base stream class without modifying the base class itself.