Explain the Decorator design pattern.

The Decorator design pattern is a structural design pattern that allows adding new functionality to an existing object dynamically without altering its structure. It involves creating a decorator class that wraps the original object and provides additional behavior by adding new methods or modifying existing ones.

The decorator class implements the same interface as the original object, allowing it to be used interchangeably. It maintains a reference to the original object and delegates the calls to it, while also adding its own functionality before or after the delegated calls.

This pattern promotes the principle of open-closed design, as it allows adding new features to an object without modifying its code. It provides a flexible and modular approach to extending the functionality of objects, as decorators can be stacked or combined to achieve different combinations of features.

Overall, the Decorator design pattern enhances the functionality of an object dynamically by wrapping it with additional behavior, while keeping the original object's interface intact.