Decorator

Decorator is a structural design pattern that consists of dynamically augmenting the behavior of an existing object. It’s different from classical inheritance because the behavior is not added to all the objects of the same class, but only to the instances that are explicitly decorated.

Implementation-wise, it is very similar to the Proxy pattern, but instead of enhancing or modifying the behavior of the existing interface of an object, it augments it with new functionalities, as depicted in Figure 8.2:

Figure 8.2: Decorator pattern schematic

In Figure 8.2, the Decorator object is extending the Component object by adding the methodC() operation. The existing methods are usually delegated to the decorated object without further processing, but in some cases, they might also be intercepted and augmented with extra behaviors.

Techniques for implementing decorators

Although Proxy and Decorator are conceptually two different patterns with different...