Decorator

Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extended functionality.

Applicability

• Need to add responsibilities to objects dynamically and transparently.
• Need to withdraw responsibilities
• Need to support large combinations of responsibilities without a class explosion.

Consequences

• More flexible than static inheritance
• Avoids feature-laden classes high up in the hierarchy
• A decorator and its comonent aren't identical
• Lots of little objects!