Decorator Pattern

Decorator Pattern

Overview

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

Participants

Component

defines the interface for objects that can have responsibilities added to them dynamically.
this participant can not be read-only.

Component implementation

defines an object to which additional responsibilities can be attached.
this participant can not be read-only.

Decorator

maintains a reference to a Component object and defines an interface that conforms to Component's interface.
this participant can not be read-only.
this participant can not be an interface.

Decorator implementation

adds responsibilities to the component.
this participant can not be read-only.
this participant can not be an interface.

Parameters

Attribute

here you can specify the name of a Decorator's attribute where it keeps a reference to a Component object.

Decorator Initialization

the "Initialization variant" option defines the kind of initialization of that attribute.

Create Pattern Links

when selected, will create special JavaDoc links in the code between pattern participants, describing their relationships.

Applicability

Use Decorator

to add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects.
for responsibilities that can be withdrawn.
when extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for subclassing.