Dekorator

Dekorator is a design pattern used in software engineering. It allows behavior to be added to an individual object dynamically and transparently, without affecting the behavior of other objects that share the same class. This is achieved by creating a set of wrapper classes, each of which adds a specific piece of functionality.

The Dekorator pattern is a structural pattern that provides an alternative to subclassing for extending functionality. Instead of creating a new subclass for every possible combination of features, Dekorator uses composition. An object is wrapped by one or more Dekorator objects, each of which adds its own responsibilities. The client code interacts with the outermost Dekorator, which in turn delegates calls to the next Dekorator or the original object.

Key components of the Dekorator pattern include the Component interface, which defines the common interface for both the concrete objects and the Dekorators; the ConcreteComponent, which is the base class for objects that can be decorated; the Decorator, which maintains a reference to a Component object and defines an interface that conforms to Component's interface; and ConcreteDecorators, which add specific responsibilities to the Component.

This pattern is useful when you need to add responsibilities to individual objects, dynamically and without affecting other objects. It also helps to avoid a large and complex class hierarchy that would result from subclassing for every variation. Examples of its application can be found in graphical user interfaces, where different widgets might be decorated with scrollbars or borders, or in data stream processing, where different readers or writers might be combined to add buffering or compression.