Java Reference
In-Depth Information
Figure 3.2. Sequence diagram for action mapping
Benefits and Drawbacks
The Adapter offers greatly improved reuse, allowing two or more objects to interact that would otherwise be
incompatible. However, some planning and forethought are required in order to develop a framework flexible
enough to be conveniently adaptable. This problem has two aspects: functional call structure and parameter
translation.
If there is a functional mismatch between the call framework and the Adaptee, the Adapter needs to manage the
call requirements of the Adaptee, invoking any required setup methods before the framework's call can be
satisfied.
Another challenge for the Adapter is the transfer of parameters, since passed parameters are not always
compatible between the framework and the Adaptee. In these cases, the Adapter usually either creates appropriate
objects when there is no direct equivalent between the two environments, or wraps an object to make it usable by
the Adaptee.
The most generic of environments for the Adapter are typically built around the Command pattern, using some
form of messaging or introspection/reflection. In its most generic form, the Command pattern might eliminate the
Pattern Variants
Adapters are, by their very nature, dynamic and it's rare to see two that are exactly alike. Nevertheless, there are
some common variations. Three of these common variations are listed here:
Multi-Adaptee Adapters - Depending on the system design, it can be advantageous to make an Adapter part of
the calling framework. Such an Adapter often acts as an intermediary between the system and multiple Adaptees.
Non-Interface-based Adapters - Use of the interface in the Java programming language makes it possible to
develop even more flexible Adapters. But it may not always be possible to use interfaces. For instance, it's not
possible when you're given complete components that do not implement any interface. In those situations you will
see the Adapter pattern used without using interfaces. It goes without saying that these implementations are less
flexible.
An interface layer between the caller and Adapter, and another between the Adapter and Adaptee - An interface
layer between caller and Adapter allows new Adapters to be more easily added to the system during runtime. An
interface between Adapter and Adaptee allows the Adaptees to be dynamically loaded during runtime. In
combination, these interface layers make it possible to develop a truly pluggable Adapter design, where the
Adaptees can be changed as needed in a running system.
Related Patterns
Related patterns include the following:
